U.S. patent application number 17/486152 was filed with the patent office on 2022-06-09 for aerogel composites including phase change materials.
This patent application is currently assigned to Aspen Aerogels, Inc.. The applicant listed for this patent is Aspen Aerogels, Inc.. Invention is credited to Redouane Begag, George Gould, Roxana Trifu, Shannon White.
Application Number | 20220177765 17/486152 |
Document ID | / |
Family ID | |
Filed Date | 2022-06-09 |
United States Patent
Application |
20220177765 |
Kind Code |
A1 |
Trifu; Roxana ; et
al. |
June 9, 2022 |
AEROGEL COMPOSITES INCLUDING PHASE CHANGE MATERIALS
Abstract
The present disclosure can provide aerogel compositions which
have a thermal storage capacity, and which are durable and easy to
handle. The present disclosure can provide aerogel compositions
which include PCM coatings, particle mixtures, or PCM materials
confined within the porous network of an aerogel composition. The
present disclosure can provide methods for producing aerogel
compositions by coating an aerogel composition with PCM materials,
by forming particle mixtures with PCM materials, or by confining
PCM materials within the porous network of an aerogel
composition.
Inventors: |
Trifu; Roxana; (Worcester,
US) ; Begag; Redouane; (Hudson, US) ; Gould;
George; (Mendon, US) ; White; Shannon;
(Bolton, US) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Aspen Aerogels, Inc. |
Northborough |
MA |
US |
|
|
Assignee: |
Aspen Aerogels, Inc.
Northborough
MA
|
Appl. No.: |
17/486152 |
Filed: |
September 27, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15270759 |
Sep 20, 2016 |
11130895 |
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17486152 |
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International
Class: |
C09K 5/06 20060101
C09K005/06; C08J 9/28 20060101 C08J009/28; C08J 9/36 20060101
C08J009/36; C08K 5/01 20060101 C08K005/01; C08K 5/053 20060101
C08K005/053; C08K 3/16 20060101 C08K003/16; C08J 9/00 20060101
C08J009/00; C01B 33/158 20060101 C01B033/158; B32B 5/18 20060101
B32B005/18 |
Goverment Interests
STATEMENT OF GOVERNMENT SUPPORT
[0001] This invention was made with Government support under
Contract W9132T-11-C-0003 awarded by the U.S. Army Corps of
Engineers Engineer Research and Development Center. The Government
has certain rights in this invention.
Claims
1. An aerogel composition comprising aerogel material and phase
change material.
2. The aerogel composition of claim 1, wherein the aerogel material
is coated with a coating material, and wherein the coating material
comprises a phase change material.
3. The aerogel composition of claim 1, further comprising at least
one layer of reflective material.
4. The aerogel composition of claim 1, wherein the aerogel
comprises a particulate aerogel material.
5. The aerogel composition of claim 1, further comprising a
reinforcing material, wherein the reinforcing material comprises a
fibrous reinforcing material or a foam reinforcing material.
6. The aerogel composition of claim 1, wherein the phase change
material is an unencapsulated phase change material.
7. The aerogel composition of claim 1, wherein the aerogel material
comprises a gel framework and a corresponding network of pores
within the gel framework, wherein the phase change material is
confined within the network of pores within the aerogel
material.
9. The aerogel composition of claim 7, wherein the phase change
material is nanoconfined within the network of pores within the
aerogel material.
10. The aerogel composition of claim 1, wherein the aerogel
composition has a thermal conductivity of 25 mW/m-K or less at
37.5.degree. C. and ambient pressure.
11. The aerogel composition of claim 1, wherein the phase change
material in the aerogel composite comprises 50 wt % or less of the
total solids.
12. The aerogel composition of claim 1, wherein the phase change
material in the aerogel composite comprises 30 wt % or less of the
total solids; and wherein aerogel composition has a thermal
conductivity of 25 mW/m-K or less at 37.5.degree. C. and ambient
pressure.
13. The aerogel composition of claim 1, wherein the aerogel
composite comprises 50 wt % or less of the total solids; and
wherein aerogel composition has a weight loss of less than 10% when
heated at 40.degree. C. for 150 hours.
14. The aerogel composition of claim 1, wherein the phase change
material is selected from the group consisting of: paraffins;
petroleum waxes; fatty acids; fatty acid esters; organic acids;
polyethylene glycol; polyethylenes; carbohydrates; Naphthalenes;
glycerin; metals, inorganic salts; inorganic hydrated salts; and
combinations thereof.
15. The aerogel composition of claim 1, wherein the aerogel
composition has a resilience of more than 25%.
16. The aerogel composition of claim 1, further comprising one or
more layers of a barrier material.
17. The aerogel composition of claim 16, wherein the barrier
material is impermeable to the phase change material in a fluid
state.
18. The aerogel composition of claim 16, wherein the barrier
material comprises a foil.
19. The aerogel composition of claim 1, wherein the aerogel
composition is encased within a pouch.
20. The aerogel composition of claim 19, wherein pouch comprises a
foil.
21. A gel precursor solution comprising gel precursor materials and
phase change materials.
22. The gel precursor solution of claim 21, wherein the phase
change material is an unencapsulated phase change material.
23. The gel precursor solution of claim 21, wherein the phase
change materials are solubilized or emulsified within the precursor
solution.
24. The gel precursor solution of claim 21, wherein the phase
change material is selected from the group consisting of:
paraffins; petroleum waxes; fatty acids; fatty acid esters; organic
acids; polyethylene glycol; polyethylenes; carbohydrates;
Naphthalenes; glycerin; metals, inorganic salts; inorganic hydrated
salts; and combinations thereof.
25. A method of preparing an aerogel composition, comprising the
steps of: a) providing a precursor solution comprising gel
precursor materials and a solvent; b) incorporating a phase change
material into the precursor solution; c) allowing the gel precursor
materials in the precursor solution to transition into a gel
composition comprising a gel framework and a corresponding network
of pores within the gel framework, such that the phase change
material is confined within the network of pores within the gel
composition; d) extracting at least a portion of the solvent from
the gel composition to obtain an aerogel composition.
26. The method of claim 25, wherein the phase change material is an
unencapsulated phase change material.
27. The method of claim 25, wherein the method further comprises:
incorporating a reinforcement material into the aerogel composition
by combining the reinforcement material with the precursor solution
either before or during the transition of the gel precursor
materials in the precursor solution into the gel composition.
28. The method of claim 25, wherein the method further comprises
processing the phase change material before, during, or after
incorporation into the gel precursor solution, to produce a phase
change material which can be dispersed within the gel precursor
solution or within the gel composition.
29. The method of claim 25, wherein processing the phase change
material comprises heating, mixing, emulsification with a
surfactant, surface functionalization, pH modification, molecular
charge modification, hydration or dehydration.
30. The method of claim 25, wherein the phase change material is
selected from the group consisting of: paraffins; petroleum waxes;
fatty acids; fatty acid esters; organic acids; polyethylene glycol;
polyethylenes; carbohydrates; Naphthalenes; glycerin; metals,
inorganic salts; inorganic hydrated salts; and combinations
thereof.
Description
BACKGROUND
[0002] Low-density aerogel materials are widely considered to be
the best solid insulators available. Aerogels function as
insulators primarily by minimizing conduction (low structural
density results in tortuous path for energy transfer through the
solid framework), convection (large pore volumes and very small
pore sizes result in minimal convection), and radiation (IR
absorbing or scattering dopants are readily dispersed throughout
the aerogel matrix). Aerogels can be used in a broad range of
applications, including: heating and cooling insulation, acoustics
insulation, electronic dielectrics, aerospace, energy storage and
production, and filtration. Furthermore, aerogel materials display
many other interesting acoustic, optical, mechanical, and chemical
properties that make them abundantly useful in various insulation
and non-insulation applications.
SUMMARY OF THE INVENTION
[0003] In one general aspect, the present disclosure can provide
aerogel compositions which have a thermal storage capacity, and
which are durable and easy to handle. In certain embodiments, the
aerogel compositions incorporate the thermal energy storage
properties of PCMs.
[0004] In another general aspect, the present disclosure can
provide aerogel compositions which incorporate the thermal energy
storage properties of PCMs without significantly detracting from
the superior insulating properties of aerogels. In certain
embodiments, the thermal energy storage properties of PCMs are
incorporated into aerogel compositions by forming composite
compositions comprising aerogel and PCM materials. In certain
embodiments, a coating composition comprising PCM materials is
applied to at least one side of an aerogel composition. The PCM
coating is coated onto one side of the aerogel composition, onto
both sides of the aerogel composition, or sandwiched between
multiple layers of aerogel material. In certain embodiments,
aerogel particles are mixed with particles of PCM materials to
produce an aerogel composite mixture. The aerogel/PCM composite
particle mixture optionally includes a binder material. In certain
embodiments, an aerogel/PCM composition is produced by confining
the PCM materials within the porous network of an aerogel
composition. The PCM material in the aerogel composite comprises 50
wt % or less of the total solids, 30 wt % or less of the total
solids, 25 wt % or less of the total solids, 20 wt % or less of the
total solids, or 15 wt % or less of the total solids. In certain
embodiments, the aerogel composition comprises PCM materials
confined within the porous network of an aerogel material, and the
aerogel composition has a thermal conductivity of about 50 mW/m-K
or less, about 40 mW/m-K or less, about 30 mW/m-K or less, about 25
mW/m-K or less, about 20 mW/m-K or less, about 18 mW/m-K or less,
about 16 mW/m-K or less, about 14 mW/m-K or less or about 12 mW/m-K
or less.
[0005] In another general aspect, the present disclosure can
provide an aerogel composition which mitigates the complications
related to the use of PCMs without significantly detracting from
the superior thermal energy storage properties of PCMs. In certain
embodiments, the complications related to the use of PCMs are
mitigated by confining the PCM materials within the porous network
of an aerogel material. In certain embodiments, the PCM materials
are confined within the pores of a gel material by incorporating a
PCM material into the sol-gel solution prior to gelation of the gel
material. The present disclosure can provide a sol-gel solution
comprising PCM materials which are dispersed, solubilized, or
emulsified within the sol-gel solution. In certain embodiments, the
sol-gel solution comprises silica gel precursor materials.
[0006] In another general aspect, the present disclosure can
provide an aerogel compositions comprising aerogel and PCM
materials which are coated with or confined within one or more
layers of a barrier material which is impermeable to PCMs in fluid
state, such as a foil or impermeable wrap material. In certain
embodiments, an aerogel composition coated with PCM materials is
covered on at least one side with a barrier material, such as a
foil. In certain embodiments, an aerogel composition coated with
PCM materials is encased within multiple layers of barrier
material, such as a foil pouch. In certain embodiments, an aerogel
composition comprising PCM materials confined within the porous
network of the aerogel is covered on at least one side with a
barrier material, such as a foil. In certain embodiments, an
aerogel composition comprising PCM materials confined within the
porous network of the aerogel is encased within multiple layers of
barrier material, such as a foil pouch.
[0007] In another general aspect, the present disclosure can
provide aerogel compositions comprising aerogel and PCM materials,
and which also include a reflective coating or layer. In certain
embodiments, an aerogel composition comprising PCM materials is
coated with or confined within one or more layers of a reflective
material, such as a foil. Inventors have discovered that reflective
foils or coatings can significantly reduce the thermal conductivity
of an aerogel/PCM composite within confined air gaps. The present
disclosure can provide aerogel compositions comprising PCM and
reflective elements which have thermal conductivities of about 15
mW/m-K or less, about 10 mW/m-K or less, or about 7 mW/m-K or less
in the presence of air spacings of 4 inches or less, 2 inches or
less, or 0.8 inches or less.
[0008] In another general aspect, the present disclosure can
provide composite materials comprising aerogel and PCM material
which are thermally stable for long durations of time. In certain
embodiments, the aerogel/PCM composite material, when heated at
40.degree. C. for 150 hours, has a weight loss of less than 10%,
less than 5%, less than 2%, or less than 1%. In certain
embodiments, the aerogel/PCM composite material loaded at 50 wt %
PCM, when heated at 40.degree. C. for 150 hours, has a weight loss
of less than 10%, less than 5%, less than 2%, or less than 1%. In
certain embodiments, the aerogel/PCM composite material loaded at
30 wt % PCM, when heated at 40.degree. C. for 150 hours, has a
weight loss of less than 10%, less than 5%, less than 2%, or less
than 1%.
[0009] In another general aspect, the present disclosure can
provide a method for producing aerogel compositions which have a
thermal storage capacity, such as composite materials comprising
aerogel and PCM material. In certain embodiments, a method for
producing aerogel compositions which have a thermal storage
capacity comprising: a) providing an aerogel composition, b)
providing a coating material comprising a PCM material, and c)
applying the coating material onto at least one surface of the
aerogel composition. In certain embodiments, the aerogel
composition is a reinforced aerogel composition. In certain
embodiments, the aerogel composition is a reinforced aerogel
composition which is reinforced by a fibrous reinforcement sheet or
a foam reinforcement sheet. In certain embodiments, the method
includes covering the PCM-coated aerogel composition with at least
one layer of a barrier material, such as foil. In certain
embodiments, the method includes covering the PCM-coated aerogel
composition with at least one layer of a reflective material, such
as foil.
[0010] In another general aspect, the present disclosure can
provide a method for producing aerogel compositions which have a
thermal storage capacity comprising: a) providing an aerogel
composition comprising aerogel particles, b) providing a PCM
material comprising particles of PCM materials, and c) mixing the
aerogel particles with the particles of PCM materials to produce an
aerogel composite mixture. In certain embodiments, the aerogel
composite mixture further comprises a binder material. In certain
embodiments, the method includes covering the aerogel/PCM composite
material with at least one layer of a barrier material, such as
foil. In certain embodiments, the method includes covering the
aerogel/PCM composite material with at least one layer of a
reflective material, such as foil.
[0011] In another general aspect, the present disclosure can
provide a method for producing aerogel compositions which have a
thermal storage capacity comprising: a) providing a sol-gel
solution comprising gel precursor material and a solvent, b)
incorporating PCM material into the sol-gel solution, c) allowing
the gel precursor materials in the sol-gel solution to transition
into a gel composition, and d) extracting at least a portion of the
solvent from the gel composition to obtain an aerogel composition.
In certain embodiments, the method includes heating or processing
the PCM material before incorporation into the sol-gel solution to
produce a PCM material which can be controllably dispersed,
solubilized, or emulsified within the sol-gel solution. In certain
embodiments, the method includes subjecting the PCM/sol-gel mixture
to heat and/or mixing conditions after incorporation of the PCM
material into the sol-gel solution to produce a solution of PCM
material within the sol-gel solution. In certain embodiments, the
method includes using a surfactant to emulsify the PCM material
into the sol-gel solution. The emulsified PCM is subsequently
confined within the porous network of the aerogel as an
unencapsulated PCM, or as a PCM encapsulated by the surfactant
material. In certain embodiments, the method includes covering the
aerogel/PCM composite material with at least one layer of a barrier
material, such as foil. In certain embodiments, the method includes
covering the aerogel/PCM composite material with at least one layer
of a reflective material, such as foil.
[0012] In another general aspect, the present disclosure can
provide a method for producing aerogel compositions which have a
thermal storage capacity comprises: a) providing a sol-gel solution
comprising gel precursor material and a solvent, b) incorporating
PCM material into the sol-gel solution, c) combining the precursor
solution with a reinforcement material, d) allowing the gel
precursor materials in the sol-gel solution to transition into a
gel composition, and e) extracting at least a portion of the
solvent from the gel composition to obtain an aerogel composition.
In certain embodiments, the reinforcement material is a fibrous
reinforcement sheet or a foam reinforcement sheet. In certain
embodiments, the method includes covering the aerogel/PCM composite
material with at least one layer of a barrier material, such as
foil. In certain embodiments, the method includes covering the
aerogel/PCM composite material with at least one layer of a
reflective material, such as foil.
[0013] In another general aspect, the present disclosure can
provide aerogel compositions produced by the methods described
herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a graph depicting the thermal conductivity
measurements for examples of aerogel compositions of the present
invention.
DETAILED DESCRIPTION
[0015] Thermal energy storage using the latent heat of materials,
such as Phase Change Materials (PCMs), can delay or regulate
temperature fluctuations in materials. This temperature regulation
is achieved by the latent heat of material absorbing or releasing
large amounts of heat during physical transformations, such as
solid-liquid, liquid-gas, or solid-solid phase transitions. A need
exists for the development of aerogel compositions which
incorporate the thermal energy storage properties of PCMs into
aerogels compositions without detracting from the superior
insulating properties of aerogels.
[0016] There are a variety of complications related to the broad
commercial use of PCMs, including flammability, low thermal
conductivity, loss of phase-change capability, corrosion,
degradation, and PCM leakage. A need therefore exists for the
development of compositions which mitigate the complications
related to the use of PCMs without detracting from the superior
thermal energy storage properties of PCMs.
[0017] Aerogels can be difficult to produce due to the sensitive
nature of their gel frameworks and pore networks, with a range of
processing variables and conditions that must be carefully
optimized and controlled to produce a functional aerogel material.
Aerogels can also be extremely brittle, and difficult to handle and
maintain. A need therefore exists for the development of reinforced
aerogel compositions which are flexible, durable and easy to
handle; which incorporate the thermal energy storage properties of
PCMs into aerogels compositions without detracting from the
superior insulating properties of aerogels; and which mitigate the
complications related to the use of PCMs without detracting from
the superior thermal energy storage properties of PCMs. A need also
exists for methods which allow the favorable properties of PCMs to
be incorporated into aerogels without interfering with the delicate
conditions required to produce and maintain a functional aerogel
material.
[0018] Aerogels are a class of porous materials with open-cells
comprising a framework of interconnected structures, with a
corresponding network of pores integrated within the framework, and
an interstitial phase within the network of pores which is
primarily comprised of gases such as air. Aerogels are typically
characterized by a low density, a high porosity, a large surface
area, and small pore sizes. Aerogels can be distinguished from
other porous materials by their physical and structural
properties.
[0019] Within the context of the present disclosure, the term
"aerogel" or "aerogel material" refers to a gel comprising a
framework of interconnected structures, with a corresponding
network of interconnected pores integrated within the framework,
and containing gases such as air as a dispersed interstitial
medium; and which is characterized by the following physical and
structural properties (according to Nitrogen Porosimetry Testing)
attributable to aerogels: (a) an average pore diameter ranging from
about 2 nm to about 100 nm, (b) a porosity of at least 80% or more,
and (c) a surface area of about 20 m.sup.2/g or more.
[0020] Aerogel materials of the present disclosure thus include any
aerogels or other open-celled compounds which satisfy the defining
elements set forth in previous paragraphs; including compounds
which can be otherwise categorized as xerogels, cryogels, ambigels,
microporous materials, and the like.
[0021] Aerogel materials may also be further characterized by
additional physical properties, including: (d) a pore volume of
about 2.0 mL/g or more, preferably about 3.0 mL/g or more; (e) a
density of about 0.50 g/cc or less, preferably about 0.25 g/cc or
less; and (f) at least 50% of the total pore volume comprising
pores having a pore diameter of between 2 and 50 nm; though
satisfaction of these additional properties is not required for the
characterization of a compound as an aerogel material.
[0022] Within the context of the present disclosure, the term
"innovative processing and extraction techniques" refers to methods
of replacing a liquid interstitial phase in a wet-gel material with
a gas such as air, in a manner which causes low pore collapse and
low shrinkage to the framework structure of the gel. Drying
techniques, such as ambient pressure evaporation, often introduce
strong capillary pressures and other mass transfer limitations at
the liquid-vapor interface of the interstitial phase being
evaporated or removed. The strong capillary forces generated by
liquid evaporation or removal can cause significant pore shrinkage
and framework collapse within the gel material. The use of
innovative processing and extraction techniques during the
extraction of a liquid interstitial phase reduces the negative
effects of capillary forces on the pores and the framework of a gel
during liquid phase extraction.
[0023] In certain embodiments, an innovative processing and
extraction technique uses near critical or super critical fluids,
or near critical or super critical conditions, to extract the
liquid interstitial phase from a wet-gel material. This can be
accomplished by removing the liquid interstitial phase from the gel
near or above the critical point of the liquid or mixture of
liquids. Co-solvents and solvent exchanges can be used to optimize
the near critical or super critical fluid extraction process.
[0024] In certain embodiments, an innovative processing and
extraction technique includes the modification of the gel framework
to reduce the irreversible effects of capillary pressures and other
mass transfer limitations at the liquid-vapor interface. This
embodiment can include the treatment of a gel framework with a
hydrophobizing agent, or other functionalizing agents, which allow
a gel framework to withstand or recover from any collapsing forces
during liquid phase extraction conducted below the critical point
of the liquid interstitial phase. This embodiment can also include
the incorporation of functional groups or framework elements which
provide a framework modulus which is sufficiently high to withstand
or recover from collapsing forces during liquid phase extraction
conducted below the critical point of the liquid interstitial
phase.
[0025] Within the context of the present disclosure, the terms
"framework" or "framework structure" refer to the network of
interconnected oligomers, polymers or colloidal particles that form
the solid structure of a gel or an aerogel. The polymers or
particles that make up the framework structures typically have a
diameter of about 100 angstroms. However, framework structures of
the present disclosure can also include networks of interconnected
oligomers, polymers or colloidal particles of all diameter sizes
that form the solid structure within in a gel or aerogel.
Furthermore, the terms "silica-based aerogel" or "silica-based
framework" refer to an aerogel framework in which silica comprises
at least 50% (by weight) of the oligomers, polymers or colloidal
particles that form the solid framework structure within in the gel
or aerogel.
[0026] Within the context of the present disclosure, the term
"aerogel composition" refers to any composite material which
includes aerogel material as a component of the composite. Examples
of aerogel compositions include, but are not limited to:
fiber-reinforced aerogel composites; aerogel composites which
include additive elements such as opacifiers; aerogel-foam
composites; aerogel-polymer composites; and composite materials
which incorporate aerogel particulates, particles, granules, beads,
or powders into a solid or semi-solid material, such as binders,
resins, cements, foams, polymers, or similar solid materials.
[0027] Within the context of the present invention, the term
"monolithic" refers to aerogel materials in which a majority (by
weight) of the aerogel included in the aerogel material or
composition is in the form of a unitary interconnected aerogel
nanostructure. Monolithic aerogel materials include aerogel
materials which are initially formed to have a unitary
interconnected gel or aerogel nanostructure, but which are
subsequently cracked, fractured or segmented into non-unitary
aerogel nanostructures. Monolithic aerogel materials are
differentiated from particulate aerogel materials. The term
"particulate aerogel material" refers to aerogel materials in which
a majority (by weight) of the aerogel included in the aerogel
material is in the form of particulates, particles, granules,
beads, or powders, which can be combined or compressed together but
which lack an interconnected aerogel nanostructure between
individual particles.
[0028] Within the context of the present disclosure, the term
"reinforced aerogel composition" refers to aerogel compositions
which comprise a reinforcing phase within the aerogel material
which is not part of the aerogel framework. The reinforcing phase
can be any material which provides increased flexibility,
resilience, conformability or structural stability to the aerogel
material. Examples of well-known reinforcing materials include, but
are not limited to: open-cell foam reinforcement materials,
closed-cell foam reinforcement materials, open-cell membranes,
honeycomb reinforcement materials, polymeric reinforcement
materials, and fiber reinforcement materials such as discrete
fibers, woven materials, non-woven materials, battings, webs, mats,
and felts. Additionally, fiber based reinforcements may be combined
with one or more of the other reinforcing materials, and can be
oriented continuously throughout or in limited preferred parts of
the composition.
[0029] Within the context of the present disclosure, the term
"fiber-reinforced aerogel composition" refers to a reinforced
aerogel composition which comprises a fiber reinforcement material
as a reinforcing phase. Examples of fiber reinforcement materials
include, but are not limited to, discrete fibers, woven materials,
non-woven materials, battings, webs, mats, felts, or combinations
thereof. Fiber reinforcement materials can comprise a range of
materials, including, but not limited to: Polyesters, polyolefin
terephthalates, poly(ethylene) naphthalate, polycarbonates
(examples Rayon, Nylon), cotton, (e.g. lycra manufactured by
DuPont), carbon (e.g. graphite), polyacrylonitriles (PAN), oxidized
PAN, uncarbonized heat treated PANs (such as those manufactured by
SGL carbon), fiberglass based material (like S-glass, 901 glass,
902 glass, 475 glass, E-glass,) silica based fibers like quartz,
(e.g. Quartzel manufactured by Saint-Gobain), Q-felt (manufactured
by Johns Manville), Saffil (manufactured by Saffil), Durablanket
(manufactured by Unifrax) and other silica fibers, Duraback
(manufactured by Carborundum), Polyaramid fibers like Kevlar,
Nomex, Sontera (all manufactured by DuPont), Conex (manufactured by
Taijin), polyolefins like Tyvek (manufactured by DuPont), Dyneema
(manufactured by DSM), Spectra (manufactured by Honeywell), other
polypropylene fibers like Typar, Xavan (both manufactured by
DuPont), fluoropolymers like PTFE with trade names as Teflon
(manufactured by DuPont), Goretex (manufactured by W.L. GORE),
Silicon carbide fibers like Nicalon (manufactured by COI Ceramics),
ceramic fibers like Nextel (manufactured by 3M), Acrylic polymers,
fibers of wool, silk, hemp, leather, suede, TUBO Zylon fibers
(manufactured by Tyobo). Liquid crystal material like Vectan
(manufactured by Hoechst), Cambrelle fiber (manufactured by
DuPont), Polyurethanes, polyamaides, Wood fibers, Boron, Aluminum,
Iron, Stainless Steel fibers and other thermoplastics like PEEK,
PES, PEI, PEK, PPS.
[0030] Within the context of the present invention, the terms
"aerogel blanket" or "aerogel blanket composition" refer to aerogel
compositions reinforced with a continuous sheet of fiber
reinforcement material. Aerogel blanket compositions can be
differentiated from other fiber-reinforced aerogel composition
which are reinforced with a non-continuous fiber network, such as
separated agglomerates or clumps of fiber materials. Aerogel
blanket compositions are particularly useful for applications
requiring flexibility, since they are highly conformable and can be
used like a blanket to cover surfaces of simple or complex
geometry, while also retaining the excellent thermal insulation
properties of aerogels. Aerogel blanket compositions and similar
fiber-reinforced aerogel compositions are described in Published US
patent application 2002/0094426 (paragraphs 12-16, 25-27, 38-58,
60-88), which is hereby incorporated by reference according to the
individually cited sections and paragraphs.
[0031] Within the context of the present invention, the term "wet
gel" refers to a gel in which the mobile interstitial phase within
the network of interconnected pores is primarily comprised of a
liquid phase such as a conventional solvent, liquefied gases such
as liquid carbon dioxide, or a combination thereof. Aerogels
typically require the initial production of a wet gel, followed by
innovative processing and extraction to replace the mobile
interstitial liquid phase in the gel with air. Examples of wet gels
include, but are not limited to: alcogels, hydrogels, ketogels,
carbonogels, and any other wet gels known to those in the art.
[0032] Within the context of the present invention, the terms
"additive" or "additive element" refer to materials which can be
added to an aerogel composition before, during, or after the
production of the aerogel. Additives can be added to alter or
improve desirable properties in an aerogel, or to counteract
undesirable properties in an aerogel. Additives are typically added
to an aerogel material either prior or during gelation. Examples of
additives include, but are not limited to: microfibers, fillers,
reinforcing agents, stabilizers, thickeners, elastic compounds,
opacifiers, coloring or pigmentation compounds, radiation absorbing
compounds, radiation reflecting compounds, corrosion inhibitors,
thermally conductive components, phase change materials, pH
adjustors, redox adjustors, HCN mitigators, off-gas mitigators,
electrically conductive compounds, electrically dielectric
compounds, magnetic compounds, radar blocking components,
hardeners, anti-shrinking agents, and other aerogel additives known
to those in the art. Other examples of additives include smoke
suppressants and fire suppressants. Published US Pat. App.
20070272902 A1 (Paragraphs [0008] and [0010]-[0039]) includes
teachings of smoke suppressants and fire suppressants, and is
hereby incorporated by reference according to the individually
cited paragraphs.
[0033] Within the context of the present invention, the terms
"flexible" and "flexibility" refer to the ability of an aerogel
material or composition to be bent or flexed without
macrostructural failure. Preferably, aerogel materials or
compositions of the present invention are capable of bending at
least 5.degree., at least 25.degree., at least 45.degree., at least
65.degree., or at least 85.degree. without macroscopic failure;
and/or have a bending radius of less than 4 feet, less than 2 feet,
less than 1 foot, less than 6 inches, less than 3 inches, less than
2 inches, less than 1 inch, or less than 1/2 inch without
macroscopic failure. Likewise, the terms "highly flexible" or "high
flexibility" refer to aerogel materials or compositions capable of
bending to at least 90.degree. and/or have a bending radius of less
than 1/2 inch without macroscopic failure. Furthermore, the terms
"classified flexible" and "classified as flexible" refer to aerogel
materials or compositions which can be classified as flexible
according to ASTM classification standard C1101 (ASTM
International, West Conshohocken, Pa.).
[0034] Aerogel materials or compositions of the present invention
can be flexible, highly flexible, and/or classified flexible.
Aerogel materials or compositions of the present invention can also
be drapable. Within the context of the present invention, the terms
"drapable" and "drapability" refer to the ability of an aerogel
material or composition to be bent or flexed to 90.degree. or more
with a radius of curvature of about 4 inches or less, without
macroscopic failure. An aerogel material or composition of the
present invention is preferably flexible such that the composition
is non-rigid and may be applied and conformed to three-dimensional
surfaces or objects, or pre-formed into a variety of shapes and
configurations to simplify installation or application.
[0035] Within the context of the present invention, the terms
"resilient" and "resilience" refer to the ability of an aerogel
material or composition to at least partially return to an original
form or dimension following deformation through compression,
flexing, or bending. Resilience may be complete or partial, and it
may be expressed in terms of percentage return. An aerogel material
or composition of the present invention preferably has a resilience
of more than 25%, more than 50%, more than 60%, more than 70%, more
than 75%, more than 80%, more than 85%, more than 90%, or more than
95% return to an original form or dimension following a
deformation. Likewise, the terms "classified resilient" and
"classified as resilient" refer to aerogel materials or
compositions which can be classified as resilient flexible
according to ASTM classification standard C1101 (ASTM
International, West Conshohocken, Pa.).
[0036] Within the context of the present invention, the term
"self-supporting" refers to the ability of an aerogel material or
composition to be flexible and/or resilient based primarily on the
physical properties of the aerogel and any reinforcing phase in the
aerogel composition. Self-supporting aerogel materials or
compositions can be differentiated from other aerogel materials,
such as coatings, which rely on an underlying substrate to provide
flexibility and/or resilience to the material.
[0037] Within the context of the present invention, the term
"shrinkage" refers to the ratio of: 1) the difference between the
measured final density of the dried aerogel material or
composition, or aerogel-like material or composition, and the
target density calculated from solid content in the sol-gel
precursor solution, relative to 2) the target density calculated
from solid content in the sol-gel precursor solution. Shrinkage can
be calculated by the following equation: Shrinkage=[Final Density
(g/cm.sup.3)-Target Density (g/cm.sup.3)]/[Target Density
(g/cm.sup.3)]. Preferably, shrinkage of an aerogel material of the
present invention is preferably 50% or less, 25% or less, 10% or
less, 8% or less, 6% or less, 5% or less, 4% or less, 3% or less,
2% or less, 1% or less, 0.1% or less, about 0.01% or less, or in a
range between any two of these values.
[0038] Within the context of the present disclosure, the terms
"thermal conductivity" and "TC" refer to a measurement of the
ability of a material or composition to transfer heat between two
surfaces on either side of the material or composition, with a
temperature difference between the two surfaces. Thermal
conductivity is specifically measured as the heat energy
transferred per unit time and per unit surface area, divided by the
temperature difference. It is typically recorded in SI units as
mW/m*K (milliwatts per meter*Kelvin). The thermal conductivity of a
material may be determined by methods known in the art, including,
but not limited to: Test Method for Steady-State Thermal
Transmission Properties by Means of the Heat Flow Meter Apparatus
(ASTM C518, ASTM International, West Conshohocken, Pa.); a Test
Method for Steady-State Heat Flux Measurements and Thermal
Transmission Properties by Means of the Guarded-Hot-Plate Apparatus
(ASTM C177, ASTM International, West Conshohocken, Pa.); a Test
Method for Steady-State Heat Transfer Properties of Pipe Insulation
(ASTM C335, ASTM International, West Conshohocken, Pa.); a Thin
Heater Thermal Conductivity Test (ASTM C1114, ASTM International,
West Conshohocken, Pa.); Determination of thermal resistance by
means of guarded hot plate and heat flow meter methods (EN 12667,
British Standards Institution, United Kingdom); or Determination of
steady-state thermal resistance and related properties--Guarded hot
plate apparatus (ISO 8203, International Organization for
Standardization, Switzerland). Within the context of the present
disclosure, thermal conductivity measurements are acquired
according to ASTM C177 standards, at a temperature of about
37.5.degree. C. at atmospheric pressure, and a compression of about
2 psi, unless otherwise stated. Preferably, aerogel materials or
compositions of the present disclosure have a thermal conductivity
of about 50 mW/mK or less, about 40 mW/mK or less, about 30 mW/mK
or less, about 25 mW/mK or less, about 20 mW/mK or less, about 18
mW/mK or less, about 16 mW/mK or less, about 14 mW/mK or less,
about 12 mW/mK or less, about 10 mW/mK or less, about 5 mW/mK or
less, or in a range between any two of these values.
[0039] Within the context of the present invention, the term
"density" refers to a measurement of the mass per unit volume of an
aerogel material or composition. The term "density" generally
refers to the true density of an aerogel material, as well as the
bulk density of an aerogel composition. Density is typically
recorded as kg/m.sup.3 or g/cc. The density of an aerogel material
or composition may be determined by methods known in the art,
including, but not limited to: Standard Test Method for Dimensions
and Density of Preformed Block and Board-Type Thermal Insulation
(ASTM C303, ASTM International, West Conshohocken, Pa.); Standard
Test Methods for Thickness and Density of Blanket or Batt Thermal
Insulations (ASTM C167, ASTM International, West Conshohocken,
Pa.); or Determination of the apparent density of preformed pipe
insulation (ISO 18098, International Organization for
Standardization, Switzerland). Within the context of the present
invention, density measurements are acquired according to ASTM C167
standards, unless otherwise stated. Preferably, aerogel materials
or compositions of the present invention have a density of about
0.60 g/cc or less, about 0.50 g/cc or less, about 0.40 g/cc or
less, about 0.30 g/cc or less, about 0.25 g/cc or less, about 0.20
g/cc or less, about 0.18 g/cc or less, about 0.16 g/cc or less,
about 0.14 g/cc or less, about 0.12 g/cc or less, about 0.10 g/cc
or less, about 0.05 g/cc or less, about 0.01 g/cc or less, or in a
range between any two of these values.
[0040] Within the context of the present disclosure, the term
"hydrophobicity" refers to a measurement of the ability of an
aerogel material or composition to repel water.
[0041] Hydrophobicity of an aerogel material or composition can be
expressed in terms of the liquid water uptake. Within the context
of the present disclosure, the term "liquid water uptake" refers to
a measurement of the potential of an aerogel material or
composition to absorb or otherwise retain liquid water. Liquid
water uptake can be expressed as a percent (by weight or by volume)
of water which is absorbed or otherwise retained by an aerogel
material or composition when exposed to liquid water under certain
measurement conditions. The liquid water uptake of an aerogel
material or composition may be determined by methods known in the
art, including, but not limited to: Standard Test Method for
Determining the Water Retention (Repellency) Characteristics of
Fibrous Glass Insulation (ASTM C1511, ASTM International, West
Conshohocken, Pa.); Standard Test Method for Water Absorption by
Immersion of Thermal Insulation Materials (ASTM C1763, ASTM
International, West Conshohocken, Pa.); Thermal insulating products
for building applications: Determination of short term water
absorption by partial immersion (EN 1609, British Standards
Institution, United Kingdom). Within the context of the present
disclosure, measurements of liquid water uptake are acquired
according to ASTM C1511 standards, under ambient pressure and
temperature, unless otherwise stated. Preferably, aerogel materials
or compositions of the present disclosure can have a liquid water
uptake of according to ASTM C1511 of about 100 wt % or less, about
80 wt % or less, about 60 wt % or less, about 50 wt % or less,
about 40 wt % or less, about 30 wt % or less, about 20 wt % or
less, about 15 wt % or less, about 10 wt % or less, about 8 wt % or
less, about 3 wt % or less, about 2 wt % or less, about 1 wt % or
less, about 0.1 wt % or less, or in a range between any two of
these values. Aerogel materials or compositions of the present
disclosure can have a liquid water uptake of according to ASTM
C1763 of about 100 vol wt % or less, about 80 wt % or less, about
60 wt % or less, about 50 wt % or less, about 40 wt % or less,
about 30 wt % or less, about 20 wt % or less, about 15 wt % or
less, about 10 wt % or less, about 8 wt % or less, about 3 wt % or
less, about 2 wt % or less, about 1 wt % or less, about 0.1 wt % or
less, or in a range between any two of these values. An aerogel
material or composition which has improved liquid water uptake
relative to another aerogel material or composition will have a
lower percentage of liquid water uptake/retention relative to the
reference aerogel materials or compositions.
[0042] Hydrophobicity of an aerogel material or composition can be
expressed in terms of the water vapor uptake. Within the context of
the present disclosure, the term "water vapor uptake" refers to a
measurement of the potential of an aerogel material or composition
to absorb water vapor. Water vapor uptake can be expressed as a
percent (by weight) of water which is absorbed or otherwise
retained by an aerogel material or composition when exposed to
water vapor under certain measurement conditions. The water vapor
uptake of an aerogel material or composition may be determined by
methods known in the art, including, but not limited to: Standard
Test Method for Determining the Water Vapor Sorption of Unfaced
Mineral Fiber Insulation (ASTM C1104, ASTM International, West
Conshohocken, Pa.). Within the context of the present disclosure,
measurements of water vapor uptake are acquired according to ASTM
C1104 standards, under ambient pressure and temperature, unless
otherwise stated. Preferably, aerogel materials or compositions of
the present disclosure can have a water vapor uptake of about 50 wt
% or less, about 40 wt % or less, about 30 wt % or less, about 20
wt % or less, about 15 wt % or less, about 10 wt % or less, about 8
wt % or less, about 3 wt % or less, about 2 wt % or less, about 1
wt % or less, about 0.1 wt % or less, or in a range between any two
of these values. An aerogel material or composition which has
improved water vapor uptake relative to another aerogel material or
composition will have a lower percentage of water vapor
uptake/retention relative to the reference aerogel materials or
compositions.
[0043] Hydrophobicity of an aerogel material or composition can be
expressed by measuring the equilibrium contact angle of a water
droplet at the interface with the surface of the material. Aerogel
materials or compositions of the present disclosure can have a
water contact angle of about 90.degree. or more, about 120.degree.
or more, about 130.degree. or more, about 140.degree. or more,
about 150.degree. or more, about 160.degree. or more, about
170.degree. or more, about 175.degree. or more, or in a range
between any two of these values.
[0044] Within the context of the present invention, the terms
"latent heat" or "latent energy" refer to energy released or
absorbed by a body or a thermodynamic system during a process while
maintaining a substantially constant temperature. Within the
context of the present invention, the terms "latent thermal storage
capacity", "latent heat storage capacity", "latent thermal
capacity", or "latent heat capacity" refer to the ability of a body
or a thermodynamic system to absorb or release latent heat or
latent energy while maintaining a substantially constant
temperature.
[0045] Within the context of the present invention, the terms
"Phase Change Material" or "PCM" refer to a material that can
maintain a substantially constant temperature while absorbing or
releasing energy in the form of latent heat through changes in
phase (such as liquid-to-solid, solid-to-liquid, or solid-solid),
hydration state, or crystalline structure (amorphous-to-crystal
transitions). PCMs of the present invention can comprise organic
materials, inorganic materials, eutectics, or mixtures thereof.
PCMs of the present invention can comprise organic materials such
as: paraffin/petroleum waxes; fatty acids and fatty acid esters
(Palmitic acid, Capric acid, Caprylic acid, lauric acid, myristic
acid, stearic acid); organic acids (lauric acid, myristic acid,
palmitic acid, stearic acid); crystalline polymers (polyethylene
glycol, PEG600, polyethylenes); carbohydrates (ribose, erythritol,
mannitol, dulcitol, pentaerythritol); Naphthalenes; and mixtures
thereof. PCMs of the present invention can comprise inorganic
materials such as metals, inorganic salts, inorganic hydrated salts
(MgCl.sub.2-6H.sub.2O, Mg(NO.sub.3).sub.2-6H.sub.2O,
Ba(OH).sub.2-8H.sub.2O, CaCl.sub.2-6H.sub.2O), and mixtures
thereof. SavENRG.TM. PCM is one example of a commercially available
PCM mixture comprising inorganic hydrated salts. PCMs of the
present invention can be selected, mixed or optimized based on a
range of desirable properties, including thermal conductivity,
transition temperature range, latent heat absorption capacity,
hygroscopic properties, and solvent solubility.
[0046] PCMs of the present invention can be in the form of
particles, droplets, crystals, or pore coatings. PCM particles,
droplets or crystals can be microencapsulated PCMs (3-100 .mu.m),
macroencapsulated PCMs (1-3 mm), or unencapsulated. In certain
embodiments, the PCM material comprises particles, droplets or
crystals which are microencapsulated or macroencapsulated. Examples
of commercially-available micro-encapsulated PCMs include WIPCM28
Microencapsulated Phase Change Material (paraffin based) sold by
Microtek Laboratories, Inc., and PureTemp.RTM.24 Microcapsules sold
by Entropy Solutions, Inc. Examples of commercially-available
macro-encapsulated PCMs include Synpar.TM. macrocapsules sold by
Syntroleum. Though microencapsulated phase change materials provide
an effective way to contain and protect a PCM during phase changes,
the process of microencapsulating the PCM can significantly
increase the cost and complexity of producing the final aerogel
composite. The encapsulation of the PCM can also complicate the gel
formation and drying process, and significantly decrease the
thermal conductivity and thermal storage performance of the
PCM.
[0047] In a preferred embodiment of the present invention, the PCM
material is unencapsulated. The unencapsulated PCM material can be
in the form of pore coatings of PCM material, or can be in the form
of particles, droplets or crystals which are confined within the
pores of the gel or aerogel material. Preferred unencapsulated PCM
material for use in the present invention include:
paraffin/petroleum waxes; fatty acids such as palmitic acid, capric
acid, caprylic acid, lauric acid, myristic acid, and stearic acid;
organic acids such as lauric acid, myristic acid, palmitic acid,
and stearic acid; glycerin; polyethylene glycols such as PEG600;
and mixtures of inorganic hydrated salts which include calcium
chloride.
[0048] Unencapsulated PCM materials can be conditioned or processed
before incorporation into the gel material. The PCM materials can
be exposed to heating, pressurization, solvation or other
processing conditions to produce a PCM material which can be
controllably dispersed, solubilized, or emulsified within a sol-gel
solution. Unencapsulated PCM materials can also be subjected to
heating, mixing, or other processing conditions after incorporation
into a sol-gel solution to controllably disperse, solubilize, or
emulsify the PCM materials within the solution. Processing the
phase change materials can comprise heating, mixing, emulsification
with a surfactant, surface functionalization, pH modification,
molecular charge modification, hydration or dehydration.
[0049] Aerogels are described as a framework of interconnected
structures which are most commonly comprised of interconnected
oligomers, polymers or colloidal particles. An aerogel framework
can be made from a range of precursor materials, including:
inorganic precursor materials (such as precursors used in producing
silica-based aerogels); organic precursor materials (such
precursors used in producing carbon-based aerogels); hybrid
inorganic/organic precursor materials; and combinations thereof.
Within the context of the present invention, the term "amalgam
aerogel" refers to an aerogel produced from a combination of two or
more different gel precursors.
[0050] Inorganic aerogels are generally formed from metal oxide or
metal alkoxide materials. The metal oxide or metal alkoxide
materials can be based on oxides or alkoxides of any metal that can
form oxides. Such metals include, but are not limited to: silicon,
aluminum, titanium, zirconium, hafnium, yttrium, vanadium, cerium,
and the like. Inorganic silica aerogels are traditionally made via
the hydrolysis and condensation of silica-based alkoxides (such as
tetraethoxylsilane), or via gelation of silicic acid or water
glass. Other relevant inorganic precursor materials for silica
based aerogel synthesis include, but are not limited to: metal
silicates such as sodium silicate or potassium silicate,
alkoxysilanes, partially hydrolyzed alkoxysilanes,
tetraethoxylsilane (TEOS), partially hydrolyzed TEOS, condensed
polymers of TEOS, tetramethoxylsilane (TMOS), partially hydrolyzed
TMOS, condensed polymers of TMOS, tetra-n-propoxysilane, partially
hydrolyzed and/or condensed polymers of tetra-n-propoxysilane,
polyethyl silicates, partially hydrolyzed polyethysilicates,
monomeric alkylalkoxy silanes, bis-trialkoxy alkyl or aryl silanes,
polyhedral silsesquioxanes, or combinations thereof.
[0051] In certain embodiments of the present invention,
pre-hydrolyzed TEOS, such as Silbond H-5 (SBH5, Silbond Corp),
which is hydrolyzed with a water/silica ratio of about 1.9-2, may
be used as commercially available or may be further hydrolyzed
prior to incorporation into the gelling process. Partially
hydrolyzed TEOS or TMOS, such as polyethysilicate (Silbond 40) or
polymethylsilicate may also be used as commercially available or
may be further hydrolyzed prior to incorporation into the gelling
process.
[0052] Inorganic aerogels can also include gel precursors which
comprise at least one hydrophobic group, such as alkyl metal
alkoxides, cycloalkyl metal alkoxides, and aryl metal alkoxides,
which can impart or improve certain properties in the gel such as
stability and hydrophobicity. Inorganic silica aerogels can
specifically include hydrophobic precursors such as alkylsilanes or
arylsilanes. Hydrophobic gel precursors can be used as primary
precursor materials to form the framework of a gel material.
However, hydrophobic gel precursors are more commonly used as
co-precursors in combination with simple metal alkoxides in the
formation of amalgam aerogels. Hydrophobic inorganic precursor
materials for silica based aerogel synthesis include, but are not
limited to: trimethyl methoxysilane [TMS], dimethyl dimethoxysilane
[DMS], methyl trimethoxysilane [MTMS], trimethyl ethoxysilane,
dimethyl diethoxysilane [DMDS], methyl triethoxysilane [MTES],
ethyl triethoxysilane [ETES], diethyl diethoxysilane, ethyl
triethoxysilane, propyl trimethoxysilane, propyl triethoxysilane,
phenyl trimethoxysilane, phenyl triethoxysilane [PhTES],
hexamethyldisilazane and hexaethyldisilazane, and the like.
[0053] Aerogels may also be treated to impart or improve
hydrophobicity. Hydrophobic treatment can be applied to a sol-gel
solution, a wet-gel prior to liquid phase extraction, or to an
aerogel subsequent to liquid phase extraction. Hydrophobic
treatment is especially common in the production of metal oxide
aerogels, such as silica aerogels. An example of a hydrophobic
treatment of a gel is discussed below in greater detail,
specifically in the context of treating a silica wet-gel. However,
the specific examples and illustrations provided herein are not
intended to limit the scope of the present invention to any
specific type of hydrophobic treatment procedure or aerogel
substrate. The present invention can include any gel or aerogel
known to those in the art, as well as associated methods of
hydrophobic treatment of the aerogels, in either wet-gel form or
dried aerogel form.
[0054] Hydrophobic treatment is carried out by reacting a hydroxy
moiety on a gel, such as a silanol group (Si--OH) present on a
framework of a silica gel, with a functional group of a
hydrophobizing agent. The resulting reaction converts the silanol
group and the hydrophobizing agent into a hydrophobic group on the
framework of the silica gel. The hydrophobizing agent compound can
react with hydroxyl groups on the gel according the following
reaction: RNMX.sub.4-N (hydrophobizing agent)+MOH
(silanol).fwdarw.MOMR.sub.N (hydrophobic group)+HX. Hydrophobic
treatment can take place both on the outer macro-surface of a
silica gel, as well as on the inner-pore surfaces within the porous
network of a gel.
[0055] A gel can be immersed in a mixture of a hydrophobizing agent
and an optional hydrophobic-treatment solvent in which the
hydrophobizing agent is soluble, and which is also miscible with
the gel solvent in the wet-gel. A wide range of
hydrophobic-treatment solvents can be used, including solvents such
as methanol, ethanol, isopropanol, xylene, toluene, benzene,
dimethylformamide, and hexane. Hydrophobizing agents in liquid or
gaseous form may also be directly contacted with the gel to impart
hydrophobicity.
[0056] The hydrophobic treatment process can include mixing or
agitation to help the hydrophobizing agent to permeate the wet-gel.
The hydrophobic treatment process can also include varying other
conditions such as temperature and pH to further enhance and
optimize the treatment reactions. After the reaction is completed,
the wet-gel is washed to remove unreacted compounds and reaction
by-products.
[0057] Hydrophobizing agents for hydrophobic treatment of an
aerogel are generally compounds of the formula: R.sub.NMX.sub.4-N;
where M is the metal; R is a hydrophobic group such as CH.sub.3,
CH.sub.2CH.sub.3, C.sub.6H.sub.6, or similar hydrophobic alkyl,
cycloalkyl, or aryl moieties; and X is a halogen, usually Cl.
Specific examples of hydrophobizing agents include, but are not
limited to: trimethylchlorosilane [TMCS], triethylchlorosilane
[TECS], triphenylchlorosilane [TPCS], dimethylchlorosilane [DMCS],
dimethyldichlorosilane [DMDCS], and the like. Hydrophobizing agents
can also be of the formula: Y(R.sub.3M).sub.2; where M is a metal;
Y is bridging group such as NH or O; and R is a hydrophobic group
such as CH.sub.3, CH.sub.2CH.sub.3, C.sub.6H.sub.6, or similar
hydrophobic alkyl, cycloalkyl, or aryl moieties. Specific examples
of such hydrophobizing agents include, but are not limited to:
hexamethyldisilazane [HMDZ] and hexamethyldisiloxane [HMDSO].
Hydrophobizing agents can further include compounds of the formula:
RNMV.sub.4-N, wherein V is a reactive or leaving group other than a
halogen. Specific examples of such hydrophobizing agents include,
but are not limited to: vinyltriethoxysilane and
vinyltrimethoxysilane.
[0058] Organic aerogels are generally formed from carbon-based
polymeric precursors. Such polymeric materials include, but are not
limited to: resorcinol formaldehydes (RF), polyimide, polyacrylate,
polymethyl methacrylate, acrylate oligomers, polyoxyalkylene,
polyurethane, polyphenol, polybutadiane, trialkoxysilyl-terminated
polydimethylsiloxane, polystyrene, polyacrylonitrile, polyfurfural,
melamine-formaldehyde, cresol formaldehyde, phenol-furfural,
polyether, polyol, polyisocyanate, polyhydroxybenze, polyvinyl
alcohol dialdehyde, polycyanurates, polyacrylamides, various
epoxies, agar, agarose, chitosan, and combinations thereof. As one
example, organic RF aerogels are typically made from the sol-gel
polymerization of resorcinol or melamine with formaldehyde under
alkaline conditions.
[0059] Organic/inorganic hybrid aerogels are mainly comprised of
ormosil (organically modified silica) aerogels. These ormosil
materials include organic components which are covalently bonded to
a silica network. Ormosils are typically formed through the
hydrolysis and condensation of organically modified silanes,
R--Si(OX).sub.3, with traditional alkoxide precursors, Y(OX).sub.4.
In these formulas: X may represent, for example, CH.sub.3,
C.sub.2H.sub.5, C.sub.3H.sub.7, C.sub.4H.sub.9; Y may represent,
for example, Si, Ti, Zr, or Al; and R may be any organic fragment
such as methyl, ethyl, propyl, butyl, isopropyl, methacrylate,
acrylate, vinyl, epoxide, and the like. The organic components in
ormosil aerogel may also be dispersed throughout or chemically
bonded to the silica network.
[0060] Within the context of the present invention, the term
"ormosil" encompasses the foregoing materials as well as other
organically modified ceramics, sometimes referred to as "ormocers."
Ormosils are often used as coatings where an ormosil film is cast
over a substrate material through, for example, the sol-gel
process. Examples of other organic-inorganic hybrid aerogels of the
invention include, but are not limited to, silica-polyether,
silica-PMMA, silica-chitosan, carbides, nitrides, and other
combinations of the aforementioned organic and inorganic aerogel
forming compounds. Published US Pat. App. 20050192367 (Paragraphs
[0022]-[0038] and [0044]-[0058]) includes teachings of such hybrid
organic-inorganic materials, and is hereby incorporated by
reference according to the individually cited sections and
paragraphs.
[0061] Aerogels of the present invention are preferably inorganic
silica aerogels formed primarily from alcohol solutions of
hydrolyzed silicate esters formed from silicon alkoxides. However,
the invention as a whole may be practiced with any other aerogel
compositions known to those in the art, and is not limited to any
one precursor material or amalgam mixture of precursor
materials.
[0062] Production of an aerogel generally includes the following
steps: i) formation of a sol-gel solution; ii) formation of a gel
from the sol-gel solution; and iii) extracting the solvent from the
gel materials through innovative processing and extraction, to
obtain a dried aerogel material. This process is discussed below in
greater detail, specifically in the context of forming inorganic
aerogels such as silica aerogels. However, the specific examples
and illustrations provided herein are not intended to limit the
present invention to any specific type of aerogel and/or method of
preparation. The present invention can include any aerogel formed
by any associated method of preparation known to those in the
art.
[0063] The first step in forming an inorganic aerogel is generally
the formation of a sol-gel solution through hydrolysis and
condensation of metal alkoxide precursors in an alcohol-based
solvent. Major variables in the formation of inorganic aerogels
include the type of alkoxide precursors included in the sol-gel
solution, the nature of the solvent, the processing temperature and
pH of the sol-gel solution (which may be altered by addition of an
acid or a base), and precursor/solvent/water ratio within the
sol-gel solution. Control of these variables in forming a sol-gel
solution can permit control of the growth and aggregation of the
gel framework during the subsequent transition of the gel material
from the "sol" state to the "gel" state. While properties of the
resulting aerogels are affected by the pH of the precursor solution
and the molar ratio of the reactants, any pH and any molar ratios
that permit the formation of gels may be used in the present
disclosure.
[0064] A sol-gel solution is formed by combining at least one
gelling precursor with a solvent. Suitable solvents for use in
forming a sol-gel solution include lower alcohols with 1 to 6
carbon atoms, preferably 2 to 4, although other solvents can be
used as known to those with skill in the art. Examples of useful
solvents include, but are not limited to: methanol, ethanol,
isopropanol, ethyl acetate, ethyl acetoacetate, acetone,
dichloromethane, tetrahydrofuran, and the like. Multiple solvents
can also be combined to achieve a desired level of dispersion or to
optimize properties of the gel material. Selection of optimal
solvents for the sol-gel and gel formation steps thus depends on
the specific precursors, fillers and additives being incorporated
into the sol-gel solution; as well as the target processing
conditions for gelling and liquid phase extraction, and the desired
properties of the final aerogel materials.
[0065] Water can also be present in the precursor-solvent solution.
The water acts to hydrolyze the metal alkoxide precursors into
metal hydroxide precursors. The hydrolysis reaction can be (using
TEOS in ethanol solvent as an example):
Si(OC.sub.2H.sub.5).sub.4+4H.sub.2O.fwdarw.Si(OH).sub.4+4(C.sub.2H.sub.5O-
H). The resulting hydrolyzed metal hydroxide precursors remain
suspended in the solvent solution in a "sol" state, either as
individual molecules or as small polymerized (or oligomarized)
colloidal clusters of molecules. For example,
polymerization/condensation of the Si(OH).sub.4 precursors can
occur as follows: 2
Si(OH).sub.4=(OH).sub.3Si--O--Si(OH).sub.3+H.sub.2O. This
polymerization can continue until colloidal clusters of polymerized
(or oligomarized) SiO.sub.2 (silica) molecules are formed.
[0066] Acids and bases can be incorporated into the sol-gel
solution to control the pH of the solution, and to catalyze the
hydrolysis and condensation reactions of the precursor materials.
While any acid may be used to catalyze precursor reactions and to
obtain a lower pH solution, preferable acids include: HCl,
H.sub.2SO.sub.4, H.sub.3PO.sub.4, oxalic acid and acetic acid. Any
base may likewise be used to catalyze precursor reactions and to
obtain a higher pH solution, with a preferable base comprising
NH.sub.4OH.
[0067] The sol-gel solution can include additional co-gelling
precursors, as well as filler materials and other additives. Filler
materials and other additives may be dispensed in the sol-gel
solution at any point before or during the formation of a gel.
Filler materials and other additives may also be incorporated into
the gel material after gelation through various techniques known to
those in the art. Preferably, the sol-gel solution comprising the
gelling precursors, solvents, catalysts, water, filler materials
and other additives is a homogenous solution which is capable of
effective gel formation under suitable conditions.
[0068] The gel composition can include a phase change material. The
phase change material can be externally bonded to the gel
composition. In certain embodiments, the phase change material can
be incorporated into the gel composition as a coating on the
surface of the composition before or after drying. In certain
embodiments, particles of PCM material can be mixed with particles
of gel material. The particle mixture can include a binder
material.
[0069] The phase change material can also be confined in the porous
network within the gel framework of the gel composition. In certain
embodiments, the PCM material is infiltrated into the framework of
the gel material after the gel-forming materials are transitioned
into the gel material (post-gelation infiltration). Post-gelation
infiltration can be conducted by using vacuum or high pressures to
infiltrate and spread the PCM materials through the porous network
of the gel. Post-gelation infiltration can also be completed by
solvent exchange, in which solvents are used to spread the PCM
materials through the porous network of the gel. Post-gelation
infiltration of the PCM material can often result in damage to the
framework and pore network of the gel material due to the
pressurized forces required to confine PCM material into the pores
of the gel material. Post-gelation infiltration can also provide
poor homogenous dispersal of the PCM materials throughout the gel
material, leading to inconsistent and unpredictable performance.
Correspondingly, post-gelation infiltration can be subject to
oversaturation of PCM materials within the gel network because
large amounts of PCM are often required to provide homogenous
dispersal of the PCM materials throughout the gel material.
Post-gelation infiltration can also result in interporous
agglomerates of PCM materials within the porous network of the gel,
thus producing thermal bridges which can significantly reduce the
thermal performance of the gel material. Post-gelation infiltration
can also have limited effectiveness at nanoconfinement PCM
materials into extremely small pores within the gel material, due
to capillary and diffusion limitations related to materials flowing
in and out of extremely small pores.
[0070] In a preferred embodiment, the PCM material is confined into
the framework of the gel material as the gel-forming materials are
transitioned into the gel material (in situ confinement). This
method comprises adding a PCM material into the sol-gel solution
either before or during the gel-forming stage of the gelation.
[0071] The PCM material can be heated or processed into a
dispersible form before being incorporated into the sol-gel
solution, thereby facilitating homogenous dispersal of the PCM
within the sol-gel solution. This can include heating or processing
the PCM material into a form which is soluble with the sol-gel
solution. This can also include using a surfactant which
facilitates emulsification of the PCM material into the sol-gel
solution. The PCM/sol-gel mixture can also be subjected to heat or
mixing after incorporation of the PCM material to produce a
homogenous solution of PCM material within the sol-gel solution.
The PCM/sol-gel mixture can also be subjected to heating or mixing
conditions which produce a heterogeneous dispersal of PCM material
within the gel material, such as a concentration of PCM materials
near a gel surface.
[0072] Without being bound by theory, it is believed that the PCM
particles/droplets/crystals which are dispersed, solubilized, or
emulsified within the sol-gel solution are confined into the pores
of the gel material as the gel framework is formed. This in situ
confinement process can preclude the need for external PCM
coatings, and can also preclude the need for post-gelation
infiltration of PCMs into the gel material.
[0073] In situ confinement of the PCM material also provides for an
easy method of nanoconfining PCM materials into extremely small
pores within the aerogel. Within the context of the present
invention, the terms "nanoconfinement" or "nanoconfining" refer to
the confinement of a material within pores that have a diameter of
50 nm or less.
[0074] Once a sol-gel solution has been formed and optimized, the
gel-forming components in the sol-gel can be transitioned into a
gel material. The process of transitioning gel-forming components
into a gel material comprises an initial gel formation step wherein
the gel solidifies up to the gel point of the gel material. The gel
point of a gel material may be viewed as the point where the
gelling solution exhibits resistance to flow and/or forms a
substantially continuous polymeric framework throughout its volume.
A range of gel-forming techniques are known to those in the art.
Examples include, but are not limited to: maintaining the mixture
in a quiescent state for a sufficient period of time; adjusting the
pH of the solution; adjusting the temperature of the solution;
directing a form of energy onto the mixture (ultraviolet, visible,
infrared, microwave, ultrasound, particle radiation,
electromagnetic); or a combination thereof.
[0075] The process of transitioning gel-forming components into a
gel material can also include an aging step (also referred to as
curing) prior to liquid phase extraction. Aging a gel material
after it reaches its gel point can further strengthen the gel
framework by increasing the number of cross-linkages within the
network. The duration of gel aging can be adjusted to control
various properties within the resulting aerogel material. This
aging procedure can be useful in preventing potential volume loss
and shrinkage during liquid phase extraction. Aging can involve:
maintaining the gel (prior to extraction) at a quiescent state for
an extended period; maintaining the gel at elevated temperatures;
adding cross-linkage promoting compounds; or any combination
thereof. The preferred temperatures for aging are usually between
about 10.degree. C. and about 100.degree. C. The aging of a gel
material typically continues up to the liquid phase extraction of
the wet-gel material.
[0076] The time period for transitioning gel-forming materials into
a gel material includes both the duration of the initial gel
formation (from initiation of gelation up to the gel point), as
well as the duration of any subsequent curing and aging of the gel
material prior to liquid phase extraction (from the gel point up to
the initiation of liquid phase extraction). The total time period
for transitioning gel-forming materials into a gel material is
typically between about 1 minute and several days, preferably about
30 hours or less, about 24 hours or less, about 15 hours or less,
about 10 hours or less, about 6 hours or less, about 4 hours or
less, about 2 hours or less, about 1 hour or less, about 30 minutes
or less, or about 15 minutes or less.
[0077] The resulting gel material may be washed in a suitable
secondary solvent to replace the primary reaction solvent present
in the wet-gel. Such secondary solvents may be linear monohydric
alcohols with 1 or more aliphatic carbon atoms, dihydric alcohols
with 2 or more carbon atoms, branched alcohols, cyclic alcohols,
alicyclic alcohols, aromatic alcohols, polyhydric alcohols, ethers,
ketones, cyclic ethers or their derivative.
[0078] Once a gel material has been formed and processed, the
liquid phase of the gel can then be at least partially extracted
from the wet-gel using many extraction methods, including
innovative processing and extraction techniques, to form an aerogel
material. Liquid phase extraction, among other factors, plays an
important role in engineering the characteristics of aerogels, such
as porosity and density, as well as related properties such as
thermal conductivity. Generally, aerogels are obtained when a
liquid phase is extracted from a gel in a manner that causes low
shrinkage to the porous network and framework of the wet gel.
[0079] Aerogels are commonly formed by removing the liquid mobile
phase from the gel material at a temperature and pressure near or
above the critical point of the liquid mobile phase. Once the
critical point is reached (near critical) or surpassed
(supercritical) (i.e pressure and temperature of the system is at
or higher than the critical pressure and critical temperature
respectively) a new supercritical phase appears in the fluid that
is distinct from the liquid or vapor phase. The solvent can then be
removed without introducing a liquid-vapor interface, capillary
pressure, or any associated mass transfer limitations typically
associated with liquid-vapor boundaries. Additionally, the
supercritical phase is more miscible with organic solvents in
general, thus having the capacity for better extraction.
Co-solvents and solvent exchanges are also commonly used to
optimize the supercritical fluid drying process.
[0080] If evaporation or extraction occurs below the supercritical
point, strong capillary forces generated by liquid evaporation can
cause shrinkage and pore collapse within the gel material.
Maintaining the mobile phase near or above the critical pressure
and temperature during the solvent extraction process reduces the
negative effects of such capillary forces. In some embodiments of
the present invention, the use of near-critical conditions just
below the critical point of the solvent system may allow production
of aerogel materials or compositions with sufficiently low
shrinkage, thus producing a commercially viable end-product.
[0081] Several additional aerogel extraction techniques are known
in the art, including a range of different approaches in the use of
supercritical fluids in drying aerogels. For example, Kistler (J.
Phys. Chem. (1932) 36: 52-64) describes a simple supercritical
extraction process where the gel solvent is maintained above its
critical pressure and temperature, thereby reducing evaporative
capillary forces and maintaining the structural integrity of the
gel network. U.S. Pat. No. 4,610,863 describes an extraction
process where the gel solvent is exchanged with liquid carbon
dioxide and subsequently extracted at conditions where carbon
dioxide is in a supercritical state. U.S. Pat. No. 6,670,402
teaches extracting a liquid phase from a gel via rapid solvent
exchange by injecting supercritical (rather than liquid) carbon
dioxide into an extractor that has been pre-heated and
pre-pressurized to substantially supercritical conditions or above,
thereby producing aerogels. U.S. Pat. No. 5,962,539 describes a
process for obtaining an aerogel from a polymeric material that is
in the form a sol-gel in an organic solvent, by exchanging the
organic solvent for a fluid having a critical temperature below a
temperature of polymer decomposition, and supercritically
extracting the fluid/sol-gel. U.S. Pat. No. 6,315,971 discloses a
process for producing gel compositions comprising: drying a wet gel
comprising gel solids and a drying agent to remove the drying agent
under drying conditions sufficient to reduce shrinkage of the gel
during drying. U.S. Pat. No. 5,420,168 describes a process whereby
Resorcinol/Formaldehyde aerogels can be manufactured using a simple
air drying procedure. U.S. Pat. No. 5,565,142 describes drying
techniques in which the gel surface is modified to be stronger and
more hydrophobic, such that the gel framework and pores can resist
collapse during ambient drying or subcritical extraction. Other
examples of extracting a liquid phase from aerogel materials can be
found in U.S. Pat. Nos. 5,275,796 and 5,395,805.
[0082] One preferred embodiment of extracting a liquid phase from
the wet-gel uses supercritical conditions of carbon dioxide,
including, for example: first substantially exchanging the primary
solvent present in the pore network of the gel with liquid carbon
dioxide; and then heating the wet gel (typically in an autoclave)
beyond the critical temperature of carbon dioxide (about
31.06.degree. C.) and increasing the pressure of the system to a
pressure greater than the critical pressure of carbon dioxide
(about 1070 psig). The pressure around the gel material can be
slightly fluctuated to facilitate removal of the supercritical
carbon dioxide fluid from the gel. Carbon dioxide can be
recirculated through the extraction system to facilitate the
continual removal of the primary solvent from the wet gel. Finally,
the temperature and pressure are slowly returned to ambient
conditions to produce a dry aerogel material. Carbon dioxide can
also be pre-processed into a supercritical state prior to being
injected into an extraction chamber.
[0083] One example of an alternative method of forming an aerogel
includes the acidification of basic metal oxide precursors (such as
sodium silicate) in water to make a hydrogel. Salt by-products may
be removed from the silicic acid precursor by ion-exchange and/or
by washing subsequently formed gels with water. Removing the water
from the pores of the gel can be performed via exchange with a
polar organic solvent such as ethanol, methanol, or acetone. The
liquid phase in the gel is then at least partially extracted using
innovative processing and extraction techniques.
[0084] Another example of an alternative method of forming aerogels
includes reducing the damaging capillary pressure forces at the
solvent/pore interface by chemical modification of the matrix
materials in their wet gel state via conversion of surface hydroxyl
groups to hydrophobic trimethylsilylethers, thereby allowing for
liquid phase extraction from the gel materials at temperatures and
pressures below the critical point of the solvent.
[0085] Large-scale production of aerogel materials or compositions
can be complicated by difficulties related to the continuous
formation of gel materials on a large scale; as well as the
difficulties related to liquid phase extraction from gel materials
in large volumes using innovative processing and extraction
techniques. Aerogel materials or compositions of the present
disclosure are preferably accommodating to production on a large
scale. In certain embodiments, gel materials of the present
disclosure can be produced in large scale through a continuous
casting and gelation process. In certain embodiments, aerogel
materials or compositions of the present disclosure are produced in
a large scale which requires the use of large scale extraction
vessels. Large scale extraction vessels of the present disclosure
can include extraction vessels which have a volume of about 0.1
m.sup.3 or more, about 0.25 m.sup.3 or more, about 0.5 m.sup.3 or
more, or about 0.75 m.sup.3 or more.
[0086] Aerogel compositions of the present disclosure can have a
thickness of 15 mm or less, 10 mm or less, 5 mm or less, 3 mm or
less, 2 mm or less, or 1 mm or less.
[0087] The embodiments of the present invention can be practiced
using any of the processing, extraction and treatment techniques
discussed herein, as well as other processing, extraction and
treatment techniques known to those in the art for producing
aerogels, aerogel-like materials, and aerogel compositions as
defined herein.
[0088] Aerogel compositions may be fiber-reinforced with various
fiber reinforcement materials to achieve a more flexible, resilient
and conformable composite product. The fiber reinforcement
materials can be added to the gels at any point in the gelling
process to produce a wet, fibrous gel composition. The wet gel
composition may then be dried to produce a fiber-reinforced aerogel
composition. Fiber reinforcement materials may be in the form of
discrete fibers, woven materials, non-woven materials, battings,
webs, mats, and felts. Fiber reinforcements can be made from
organic fibrous materials, inorganic fibrous materials, or
combinations thereof.
[0089] In a preferred embodiment, non-woven fiber reinforcement
materials are incorporated into the aerogel composition as
continuous sheet of interconnected or interlaced fiber
reinforcement materials. The process comprises initially producing
a continuous sheet of fiber reinforced gel by casting or
impregnating a gel precursor solution into a continuous sheet of
interconnected or interlaced fiber reinforcement materials. The
liquid phase may then be at least partially extracted from the
fiber-reinforced gel sheets to produce a sheet-like, fiber
reinforced aerogel composition.
[0090] Aerogel composition can also include an opacifier to reduce
the radiative component of heat transfer. At any point prior to gel
formation, opacifying compounds or precursors thereof may be
dispersed into the mixture comprising gel precursors. Examples of
opacifying compounds include, but are not limited to: Boron Carbide
[B.sub.4C], Diatomite, Manganese ferrite, MnO, NiO, SnO, Ag.sub.2O,
Bi.sub.2O.sub.3, carbon black, titanium oxide, iron titanium oxide,
zirconium silicate, zirconium oxide, iron (I) oxide, iron (III)
oxide, manganese dioxide, iron titanium oxide (ilmenite), chromium
oxide, carbides (such as SiC, TiC or WC), or mixtures thereof.
Examples of opacifying compound precursors include, but are not
limited to: TiOSO.sub.4 or TiOCl.sub.2.
[0091] Aerogel compositions of the present invention can be coated
with or confined within one or more layers of a barrier material
which is impermeable to PCMs in fluid state, such as a foil or
impermeable wrap material. These can include aerogel compositions
coated with PCM materials which are covered on at least one side
with a barrier material (such as a foil), or which are encased
within multiple layers of barrier material (such as a foil pouch).
These can also include aerogel composition comprising PCM materials
confined within the porous network of the aerogel which are covered
on at least one side with a barrier material (such as a foil), or
which are encased within multiple layers of barrier material (such
as a foil pouch)
[0092] Aerogel compositions of the present invention can be coated
with or confined within one or more layers of a reflective coating
or layer. Inventors have discovered that reflective foils or
coatings can significantly reduce the thermal conductivity of an
aerogel/PCM composite within confined air gaps. Aerogel
compositions comprising PCM and reflective elements have thermal
conductivities of about 15 mW/m-K or less, about 10 mW/m-K or less,
or about 7 mW/m-K or less in the presence of air spacings of 4
inches or less, 2 inches or less, or 0.8 inches or less.
[0093] The aerogel materials and compositions of the present
invention have been shown to be highly effective as insulation
materials. However, application of the methods and materials of the
present invention are not intended to be limited to applications
related to insulation. The methods and materials of the present
invention can be applied to any system or application which would
benefit from the unique combination of properties or procedures
provided by the materials and methods of the present invention.
[0094] The following examples provide various non-limiting
embodiments and properties of the present invention.
Example 1
[0095] A sheet of Spaceloft.RTM. aerogel insulation fabricated at
Aspen Aerogels, Inc. was provided as the base aerogel composition
for the coating. Formaldehyde-free encapsulated organic PCMs with a
phase transition temperatures of 22-28.degree. C. were mixed with
flame retardant binders comprising fire retardant additives. The
PCM/binder mixture was applied evenly over one surface of the
Spaceloft.RTM. aerogel insulation sheet, and allowed to cure at
room temperature. The resulting coated aerogel composite sheet had
good coating adherence and flame resistance. The resulting material
was designed to have a latent heat storage capacity of 34
Btu/ft.sup.2.
Example 2
[0096] MPCM28 Microencapsulated Phase Change Materials (paraffin
based) were acquired from Microtek Laboratories, Inc. A
silica-based sol-gel solution in ethanol was produced, and MPCM28
microcapsules were dispersed into the sol-gel solution by
sonication at PCM loadings percentages between 10-75 wt %. The
PCM/sol-gel mixtures were infiltrated into fiber batting coupons.
The resulting materials were base-catalyzed with ammonia, allowed
to gel at room temperature, and then surface functionalized with
hexamethyldisilazane, a hydrophobizing agent. The gels were dried
using supercritical carbon dioxide extraction.
Example 3
[0097] Polymeric diisocyanate precursors such as poly-MDI were
reacted with polyoxyethylene triamine in acetone solvent to form a
polyurea-based organic sol-gel. Individual samples of the organic
sol-gel were independently doped with the following unencapsulated
PCM materials: a) organic glycerol; b) polyethylene glycol of
molecular weight 600 (PEG600); and c) inorganic savENRG.TM. PCM 24P
based on calcium chloride hexahydrate. Each PCM/sol-gel mixture was
infiltrated into a fiber batting coupon. The resulting materials
were catalyzed with tertiary amines and allowed to gel at room
temperature. The materials were then aged in acetone solvent for
several days. The aged gel was dried using supercritical carbon
dioxide extraction at 1600 psi.
Example 4
[0098] Hydrolyzed silica and alkylated silica precursors in ethanol
solvent were mixed with the unencapsulated PEG600 in liquid phase.
Two samples were prepared: a) target aerogel density of 0.18 g/cc,
with PCM loading of 30% of total solids; and b) target aerogel
density of 0.25 g/cc, with PCM loading of 50% of total solids. The
PCM/sol-gel solutions were infiltrated into polyester fiber batting
coupons. The fiber reinforced gel coupons were catalyzed with
ammonia, gelled, aged in ethanol at 60.degree. C., and then the
solvent was removed by ambient pressure drying to produce
hydrophobic aerogel composite materials.
Example 5
[0099] Materials produced in Example 4 were tested for thermal
stability of the PCM material. Sampled were tested by monitoring
the weight of the coupons as the materials were heated at
40.degree. C. for up to 160 hours over 10 heating/cooling cycles.
Aerogel/PCM composites produced in example 4 showed a variable
weight loss of less than 1% for up to 160 hours of hot/cold
cycling.
Example 6
[0100] Materials produced in Example 2 and Example 4 were tested
for thermal conductivity performance relative to PCM target
concentration. The materials were tested according to ASTMC-518 at
37.5.degree. C. FIG. 1 shows thermal conductivity measurements for
the selected samples from Examples 2 and 4.
[0101] The thermal conductivity results presented in FIG. 1 show
thermal conductivity values between 17 and 20 mW/m-K for aerogel
composites containing non-encapsulated PCM materials. FIG. 1 also
shows a noticeable decline in thermal conductivity performance for
aerogel materials with non-encapsulated PCM concentrations above
30%.
[0102] As used herein, the conjunction "and" is intended to be
inclusive and the conjunction "or" is not intended to be exclusive
unless otherwise indicated. For example, the phrase "or,
alternatively" is intended to be exclusive.
[0103] The use of the terms "a", "an", "the", or similar referents
in the context of describing the invention (especially in the
context of the claims) are to be construed to cover both the
singular and the plural, unless otherwise indicated herein or
clearly contradicted by context.
[0104] The terms "comprising," "having," "including," and
"containing" are to be construed as open-ended terms (i.e., meaning
"including, but not limited to,") unless otherwise noted.
[0105] As used herein, the term "about" refers to a degree of
deviation typical for a particular property, composition, amount,
value or parameter as identified; such as deviations based on
experimental errors, measurement errors, approximation errors,
calculation errors, standard deviations from a mean value, routine
minor adjustments, and so forth.
[0106] Recitation of ranges of values herein are merely intended to
serve as a shorthand method of referring individually to each
separate value falling within the range, unless otherwise indicated
herein, and each separate value is incorporated into the
specification as if it were individually recited herein.
[0107] All methods described herein can be performed in any
suitable order unless otherwise indicated herein or otherwise
clearly contradicted by context. The use of any and all examples,
or exemplary language (e.g., "such as", "for example") provided
herein, is intended merely to better illuminate the invention and
does not pose a limitation on the scope of the invention unless
otherwise claimed.
* * * * *