U.S. patent application number 11/463964 was filed with the patent office on 2008-12-04 for composite, nanostructured, super-hydrophobic material.
This patent application is currently assigned to UT-BATTELLE, LLC. Invention is credited to Brian R. D'Urso, John T. Simpson.
Application Number | 20080296252 11/463964 |
Document ID | / |
Family ID | 35732613 |
Filed Date | 2008-12-04 |
United States Patent
Application |
20080296252 |
Kind Code |
A1 |
D'Urso; Brian R. ; et
al. |
December 4, 2008 |
COMPOSITE, NANOSTRUCTURED, SUPER-HYDROPHOBIC MATERIAL
Abstract
A method of making a hydrophobic, disordered composite material
having protrusive surface features includes the following steps:
making a disordered composite body comprised of a recessive phase
and a protrusive phase, the recessive phase having a higher
susceptibility to a preselected etchant than the protrusive phase;
treating a surface of the composite body with the preselected
etchant so that the protrusive phase protrudes from the surface to
form a plurality of protrusive surface features and the recessive
phase defines a recessive surface between the surface features; and
applying a hydrophobic coating to the protrusive surface
features.
Inventors: |
D'Urso; Brian R.; (Clinton,
TN) ; Simpson; John T.; (Clinton, TN) |
Correspondence
Address: |
UT-Battelle, LLC;Office of Intellectual Property
One Bethal Valley Road, 4500N, MS-6258
Oak Ridge
TN
37831
US
|
Assignee: |
UT-BATTELLE, LLC
Oak Ridge
TN
|
Family ID: |
35732613 |
Appl. No.: |
11/463964 |
Filed: |
August 11, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10900249 |
Jul 27, 2004 |
7258731 |
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11463964 |
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Current U.S.
Class: |
216/11 ; 106/2;
427/307; 427/444; 427/534; 428/142; 428/144; 428/306.6; 428/309.9;
428/323; 428/410 |
Current CPC
Class: |
C23F 1/02 20130101; B05D
5/083 20130101; B08B 17/065 20130101; Y10T 428/315 20150115; C03C
17/30 20130101; F05D 2230/90 20130101; F05D 2300/512 20130101; Y10T
428/249955 20150401; Y10T 428/24996 20150401; Y02T 50/60 20130101;
Y10T 428/24479 20150115; C03C 15/00 20130101; B05D 2350/35
20130101; Y02T 50/672 20130101; F01D 5/288 20130101; B08B 17/06
20130101; C03C 2217/77 20130101; Y10T 428/2438 20150115; B82Y 30/00
20130101; C03C 11/005 20130101; Y10T 428/24364 20150115; Y10T
428/25 20150115; F01D 5/286 20130101 |
Class at
Publication: |
216/11 ; 106/2;
427/307; 427/444; 427/534; 428/142; 428/144; 428/306.6; 428/323;
428/410; 428/309.9 |
International
Class: |
B44C 1/22 20060101
B44C001/22; B32B 5/16 20060101 B32B005/16 |
Goverment Interests
[0001] The United States Government has rights in this invention
pursuant to contract no. DE-AC05-00OR22725 between the United
States Department of Energy and UT-Battelle, LLC.
Claims
1. A method of making a hydrophobic, disordered composite material
having protrusive surface features comprising: a. making a
disordered composite body comprised of a recessive phase and a
protrusive phase, said recessive phase being contiguous and said
protrusive phase being contiguous, said recessive and protrusive
phases forming an interpenetrating structure, said recessive phase
having a higher susceptibility to a preselected etchant than said
protrusive phase; b. treating a surface of said composite body with
said preselected etchant so that said protrusive phase protrudes
from said surface to form a plurality of protrusive surface
features and said recessive phase defines a recessive surface
between said surface features; and c. applying a hydrophobic
coating to said protrusive surface feature.
2. A method of making a hydrophobic, disordered composite material
in accordance with claim 1 wherein step (a) further comprises: 1.
providing a precursor that separates into differentially etchable
phases; and 2. treating said precursor to separate said precursor
into differentially etchable phases.
3. A method of making a hydrophobic, disordered composite material
in accordance with claim 2 wherein said step of treating said
precursor to separate said precursor into differentially etchable
phases involves spinodal decomposition.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0002] This patent application is related to another patent
application by D'Urso and Simpson entitled "Composite, Ordered
Material Having Sharp Surface Features" and filed on even date
herewith, the entire disclosure of which is incorporated herein by
reference.
FIELD OF THE INVENTION
[0003] The present invention relates to composite super-hydrophobic
materials, and more particularly to differentially etched,
super-hydrophobic materials
BACKGROUND OF THE INVENTION
[0004] Hydrophobic surfaces bind very weakly with water, which
makes drops of water "bead up" on the surface. A hydrophobic
surface is generally defined and defined herein as that which has a
contact angle greater than 90.degree. with a drop of water.
Hydrophobic materials include many well known, commercially
available polymers.
[0005] A super-hydrophobic surface is generally defined and defined
herein as that which has a contact angle greater than 150.degree.
with a drop of water. The lotus leaf surface is known to be
naturally super-hydrophobic due to the texture of its waxy
surface.
[0006] New materials are and methods are being sought that provide
capability for making protrusive-featured surfaces that are
especially suitable for super-hydrophobic applications.
OBJECTS OF THE INVENTION
[0007] Accordingly, objects of the present invention include: the
provision of a composite, differentially etched, super-hydrophobic
material. Further and other objects of the present invention will
become apparent from the description contained herein.
SUMMARY OF THE INVENTION
[0008] In accordance with one aspect of the present invention, the
foregoing and other objects are achieved by a hydrophobic
disordered composite material having a protrusive surface feature
including a recessive phase and a protrusive phase, the recessive
phase having a higher susceptibility to a preselected etchant than
the protrusive phase, the composite material having an etched
surface wherein the protrusive phase protrudes from the surface to
form a protrusive surface feature, the protrusive feature being
hydrophobic.
[0009] In accordance with another aspect of the present invention,
a composite material having sharp surface features includes a
recessive phase and a protrusive phase, the recessive phase having
a higher susceptibility to a preselected etchant than the
protrusive phase, the composite material having an etched surface
wherein the protrusive phase protrudes from the surface to form a
sharp surface feature, at least one of the protrusive phase and the
recessive phase further including a disordered composite material
having a protrusive surface sub-feature including a sub-recessive
phase and a sub-protrusive phase, the sub-recessive phase having a
higher susceptibility to a preselected etchant than the
sub-protrusive phase, the composite material having an etched
surface wherein the sub-protrusive phase protrudes from the surface
to form a protrusive surface sub-feature.
[0010] In accordance with a further aspect of the present
invention, a hydrophobic disordered composite material having a
protrusive surface feature includes a recessive phase and a
protrusive phase, the recessive phase having a higher
susceptibility to a preselected etchant than the protrusive phase,
the recessive phase and the protrusive phase being contiguous and
interpenetrating, the composite material having an etched surface
wherein the protrusive phase protrudes from the surface to form a
protrusive surface feature, the protrusive feature being
hydrophobic.
[0011] In accordance with another aspect of the present invention,
a composite material having sharp surface features includes a
recessive phase and a protrusive phase, the recessive phase having
a higher susceptibility to a preselected etchant than the
protrusive phase, the composite material having an etched surface
wherein the protrusive phase protrudes from the surface to form a
sharp surface feature, at least one of the protrusive phase and the
recessive phase further including a disordered composite material
having a protrusive surface sub-feature including a sub-recessive
phase and a sub-protrusive phase, the sub-recessive phase having a
higher susceptibility to a preselected etchant than the
sub-protrusive phase, the sub-recessive phase and the
sub-protrusive phase being contiguous and interpenetrating, the
composite material having an etched surface wherein the
sub-protrusive phase protrudes from the surface to form a
protrusive surface sub-feature.
[0012] In accordance with a further aspect of the present
invention, a method of making a hydrophobic, disordered composite
material having protrusive surface features includes the following
steps: making a disordered composite body comprised of a recessive
phase and a protrusive phase, the recessive phase having a higher
susceptibility to a preselected etchant than the protrusive phase;
treating a surface of the composite body with the preselected
etchant so that the protrusive phase protrudes from the surface to
form a plurality of protrusive surface features and the recessive
phase defines a recessive surface between the surface features; and
applying a hydrophobic coating to the protrusive surface
features.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a photomicrograph of a composite glass having a
differentially etched surface in accordance with the present
invention.
[0014] FIG. 2 is a representation of a composite glass having an
elongated and differentially etched surface in accordance with the
present invention.
[0015] FIG. 3 is a representation of a spiked surface with
roughened spikes in accordance with the present invention.
[0016] FIG. 4 is a representation of a spiked surface with a
roughened base material in accordance with the present
invention.
[0017] FIG. 5 is a representation of a spiked surface with
roughened spikes and base material in accordance with the present
invention.
[0018] For a better understanding of the present invention,
together with other and further objects, advantages and
capabilities thereof, reference is made to the following disclosure
and appended claims in connection with the above-described
drawings.
DETAILED DESCRIPTION OF THE INVENTION
[0019] The present invention is based upon a composite structure
including a recessive phase material and a protrusive phase
material. The respective phases provide differential
etchability/solubility, the recessive phase having a greater
etchability/solubility than the protrusive phase. By subjecting the
surface of the composite structure to an etchant/solvent that
removes more of the recessive phase than the protrusive phase, some
of the protrusive phase forms a nanostructured surface comprised of
a protrusive surface feature such as, for example, spikes and/or
ridges and/or roughness.
[0020] The protrusive phase is often sharpened because even the
protrusive phase is etched in the process, just more slowly than
the recessive phase. The phrase "sharp surface feature" is defined
herein to mean a generally tapered, protrusive structure that
preferably terminates in a sharp terminus, ideally an atomically
sharp point or ridge.
[0021] The use of any differentially etchable/soluble recessive and
protrusive materials in any combination to produce the desired
effect is considered to fall within the scope of the present
invention. Moreover, there are no limits to the variations of sizes
and shapes of the nanostructured surface. The composite base
material may be made from any materials differentially etchable by
any known etching method or methods.
[0022] The composite base material may be made from any materials
which have suitable etching characteristics and phase separation
characteristics as described hereinabove. Suitable materials
include, for example, glasses, metals (including alloys), ceramics,
polymers, resins, and the like. Choices of materials can have an
effect on properties of the product, such as, for example, chemical
resistance, ease and/or need of coating, strength, toughness,
flexibility, elasticity, plasticity, etc.
[0023] One method for producing the composite base material starts
with a "precursor" material comprised of at least two phases which
are more miscible at a first temperature but less immiscible at a
second temperature. In this case, the precursor material can be
produced at an elevated temperature (where the phases are miscible)
as a homogenous material (typically molten). Next, the precursor
material is separated into two or more phases, at least one phase
of which is recessive and at least one other phase of which is
protrusive upon etching. The phase separation may take place while
cooling the precursor material or by heat treating the precursor
material to a temperature where the material is softer but the
phases are immiscible. Phase separation via spinodal decomposition,
which results in two contiguous phases, is one available mechanism,
and nucleated decomposition is another mechanism for achieving
phase separation. Following phase separation, the recessive phase
and protrusive phase are often contiguous and interpenetrating.
[0024] The composite base material may also be produced by
sintering or fusing at least two particulate, differentially
etchable materials together. The materials must be differentially
etchable, so that one material comprises the protrusive phase and
another other material comprises the recessive phase.
[0025] The composite surface is etched to create a protrusive
nanostructure of the protrusive phase at the surface. The composite
surface is contacted with an etchant that etches the recessive
phase faster than the protrusive phase. The etching continues until
the recessive phase is etched back to the desired depth, leaving
some of the protrusive phase protruding from the surface. The
protrusive phase may also be etched in the process to form
sharpened and/or rough features. The aspect ratio of the sharpened
features or roughness is dependent on the ratio of the protrusive
and recessive phase etching rates.
[0026] The etchant can be a "mixed etchant system" which is
comprised of a mixture of a plurality of etchants that give
different etch contrast ratios when applied to the composite
surface. For example, one etchant can preferentially etch one phase
while the other etchant can preferentially etch the other phase. A
mixed etchant system can be particularly useful because the
contrast ratio of the etching process can be modified by changing
the composition and/or relative concentrations of the etchants. An
example of a mixed etchant system is a mixture of HF and HCl. The
possible compositions of suitable mixed etchant systems are
virtually without limits.
[0027] Moreover, a plurality of etchants can be used in a series of
two or more sequential etching steps. For example, HF is applied to
the composite surface in a first etching step, rinsed away, and
then HCl is applied to the composite surface in a second etching
step. The possible combinations of suitable etchants and etching
steps are virtually without limits.
[0028] The method by which the etching is carried out is not
critical to the invention, as long as the desired surface feature
is achieved. For example, other, non-solution etching techniques
may be used, such as plasma etching or other isotropic etch
techniques.
EXAMPLE I
[0029] In accordance with the present invention, sodium
borosilicate glass comprising 65 molecular % SiO.sub.2, 25
molecular % B.sub.2O.sub.3, and 10 molecular % Na.sub.2O was heat
treated at 700.degree. C. for 6 hours, resulting in phase
separation via spinodal decomposition. The surface of the material
was subsequently etched with an aqueous solution of HF, etching
back the recessive phase and revealing the protrusive phase. The
surface was then coated with a hydrophobic self-assembled monolayer
by immersing the material in a solution of (tridecafluoro-1,1,2,2
tetrahydrooctyl) trichlorosilane in hexanes. The result was a
super-hydrophobic, nanostructured composite, shown in FIG. 1.
[0030] At least the protrusive phase can be hydrophobic or treated
to make the surface thereof hydrophobic, for example by coating. It
is often advantageous but not necessary to make the recessive phase
hydrophobic as well. It is the combination of the structure and
hydrophobic material which can make the surface
super-hydrophobic.
[0031] Coating may not be necessary if the protrusive phase or both
phases are intrinsically hydrophobic. It can be particularly
advantageous for a super-hydrophobic surface if the protrusive
phase or both phases are fluorinated polymers, which are highly
hydrophobic and do not generally require any hydrophobic
coating.
[0032] To create a super-hydrophobic surface, the nanostructured
surface may be coated with a hydrophobic material such as a
fluorocarbon, for example. The hydrophobic coating may comprise,
for example, a coating of PTFE or similar polymer; polymers having
CF.sub.3 terminal groups are especially suitable. The coating may
be spin-coated (applied as a liquid while spinning the material) to
obtain a uniform thickness (e.g. Dupont Teflon.COPYRGT. AF may be
applied in solution). It may also be deposited via a vacuum
deposition process. For example, PTFE or other fluorocarbon may be
applied by sputtering or hot filament chemical vapor deposition
(HFCVD). A self-assembled monolayer is an especially simple and
effective hydrophobic coating for various materials, including
glass, as it can be applied by simply immersing the material in an
appropriate solution, or by pouring or spraying it onto the
surface, for example. The surface of a polymer may be fluorinated
to make the surface more hydrophobic. Other coatings may be used to
make the material hydrophobic and may depend on the materials used
in the composite. The result is a nanostructured, coated,
super-hydrophobic surface that repels water (including a variety of
aqueous fluids).
[0033] The microstructure of the composite base material may be
elongated by drawing or extruding during or after the separation or
fusing of the two phases. This is preferably done such that the
material is unidirectionally plastically deformed while maintaining
the phase separation. The material is then cut perpendicular to the
drawing direction and the cut surface is etched and coated as
before. Elongation may improve the super-hydrophobic properties by
increasing the sharpness of the surface features or by giving
larger aspect ratio features. A computer-generated representation
of the material in cross section is shown in FIG. 2. The choice of
composite materials is particularly important if the material is to
be elongated. If the two phases are excessively miscible, they may
mix together during elongation and form a homogeneous mix. If the
phases are insufficiently miscible, one may tend to break up into
small spheres within the other (like oil in water). A suitable
material system is sodium lithium borosilicate glasses, where the
sodium to lithium ratio can be adjusted to tune the miscibility of
the two phases.
[0034] Multi-stage heat treating can produce subsequent, smaller
size phase separations in one or more of the phases of the
material, resulting in a more complex nanostructure with smaller
features.
[0035] The material can be reduced to particles (by crushing, for
example) for coating and/or laminating a surface. Etching and/or
application of a hydrophobic coating can be carried out either
before or after application of the particles to a surface such as a
watercraft hull or hydrofoil, for example.
[0036] The composite base material of the present invention may be
used in combination as part of another, generally larger structure,
particularly when the composite base material is made by spinodal
decomposition. For example, a precursor composite can be used as at
least one of the phases in an ordered system such as a spiked
composite in accordance with the related invention referenced
above. Phase separation is generally carried out before or after
drawing, but before etching, resulting in a double-scaled structure
where the recessive phase and/or the protrusive phase has a
sub-structure comprising a sub-recessive phase and a sub-protrusive
phase.
[0037] These double-scaled structures are characterized by surface
sub-features comprising the nanostructure of the present invention,
in combination with sharp surface features in accordance with the
related invention referenced above. Such a combination can provide
an even more highly super-hydrophobic material. The roughness of
the features may be particularly helpful in preventing wetting of
the super-hydrophobic material under elevated water pressure.
[0038] Referring to FIG. 3, a double-scaled structure can be used
as the protrusive phase in an ordered system, resulting in a sharp
surface feature (spike) 32 having a protrusive surface sub-feature
(roughness of the spike) and a generally smooth recessive phase
34.
[0039] Moreover, a double-scaled structure can be used as the
recessive phase in an ordered system. Referring to FIG. 4, the
result is smooth sharp surface feature (spike) 42 and a recessive
phase 44 having a protrusive surface sub-feature (roughness).
[0040] Moreover, differentially etchable, double-scaled structures
can be used as both the protrusive phase and recessive phase in an
ordered system. Referring to FIG. 5, the result is rough sharp
surface feature (spike) 52 having a protrusive surface sub-feature
(roughness of the spike), and a recessive phase 54 also having a
protrusive surface sub-feature (roughness).
EXAMPLE II
[0041] In accordance with the present invention, glass rods having
a core glass composite comprising phase A and phase B as the
protrusive phase and phase C and phase D cladding as the recessive
phase are bundled, heated to a temperature sufficient to soften the
rods, and drawn to reduce the diameter thereof. The resulting rod
is cut into sections that are re-bundled and redrawn. The above
process is repeated until the diameter of the core glass is reduced
to 5 .mu.m and spaced apart about 7 .mu.m. The rod is cut into
sections, bundled, and fused to form a shorter, thicker rod having
a diameter of about 1.5 cm. The rod is heat treated at 700.degree.
C. for 6 hours, resulting in phase separation of phase A and phase
B, and of phase C and phase D via spinodal decomposition. A thin
plate is cut transversely from the end of the rod, polished, and
subject to etching with HF at room temperature for a period of 20
min. to produce a double-scaled, nano-spiked, roughened surface on
the disk as shown in FIG. 5. The nano-spikes are about 12 .mu.m
tall.
[0042] In Example II, the etchability of the composite of phase A
and phase B is less than the etchability of the composite of phase
C and phase D, the etchability of phase A is less than the
etchability of phase B, and the etchability of phase C is less than
the etchability of phase D.
[0043] In some embodiments of the present invention, the material
is preferably produced in tiles for coating a surface. Tiles may be
produced as thin slices of the composite material. Tiles can be
bonded to various surfaces, for example, watercraft hulls. In order
to apply the tiles to irregularly shaped surfaces, unetched tiles
can be cut very thin and/or heated to make the tiles became
flexible enough to mold to the irregular shape. Once the tiles
acquired the proper shape they can then be bonded thereto, and
processed (etched and optionally coated). Alternatively, the tiles
may be processed first and then bonded to the desired surface.
[0044] The composite material may be used to coat a surface before
decomposing into differentially etchable phases. The material may
be evaporated, sputtered, melted on from a powder, plasma sprayed,
attached as a powder with adhesive, etc. In some embodiments it may
be preferable to coat a surface with the separated components of
the composite simultaneously, forming the composite as a film. In
either case, the material is then heat treated, etched, and coated
to form a super-hydrophobic surface.
[0045] In some cases it is advantageous to etch away most or all of
the recessive phase to produce a porous structure that can be used,
for example, as a filter, for removal of dissolved gases from
various aqueous fluids, and for pressurization of a surface gas
layer in various aqueous fluids.
[0046] The nanostructured surface can be easily regenerated if it
has been damaged. Generally, all that is required is stripping off
of the old hydrophobic coating (if necessary), re-etching of the
surface to regenerate the sharp or rough features, and
reapplication of the hydrophobic coating (if necessary). The base
material (composite) contains the composite pattern through its
thickness, and does not need to be replaced unless it is completely
etched away. This is a great advantage since the tiny sharp or
rough features may be damaged by scraping.
[0047] Some advantages of the above described embodiments of the
invention include:
[0048] 1. Materials used in the construction of the surface can be
mostly inert or at least non-reactive.
[0049] 2. Simple acids and/or solvents can be used for the etching
step.
[0050] 3. Scaled-up production to large quantities of material is
simple and straightforward in most cases.
[0051] 4. Nanostructured surface features can be regenerated
in-situ quickly and inexpensively if needed.
[0052] Applications of the present invention, particularly the
super-hydrophobic embodiments thereof, include, but are not limited
to the following
[0053] By using a super-hydrophobic, porous structure as described
above, the present invention can be used as a dissolved gas
extractor/monitor. The material has a strong resistance to water
penetration or even wetting. As pressure or vacuum is used to force
water against the material (generally at ambient temperature), the
increased energy applied to the liquid becomes sufficient to effect
localized, microscopic boiling (vaporization) of the liquid. Any
dissolved gases can easily pass through the structure, but not
water. The present invention thus provides means of removing and/or
sampling for dissolved hazardous gasses (for example, poisonous
chemical and/or biological agents) from the water, acting as a
filter that is permeable to dissolved gases but impermeable to
water. This particular application of the present invention is
especially applicable to Homeland Security and the ongoing effort
to counter terrorism.
[0054] Use of the present invention on watercraft hulls,
hydrofoils, and the like significantly reduces frictional drag
through water, allowing higher speeds and/or longer range of travel
using the same amount of power. The coating/laminate can also be
used to reduce the disturbance or wake (i.e. signature) left in the
water by the craft. The coating/laminate may be used to reduce or
eliminate fouling of hulls by barnacles, dirt, and the like. The
coating/laminate can also be used to greatly reduce the corrosive
effects of salt water. Thus, the coating/laminate will be
advantageous for virtually any water vehicle or device including
small water craft, surface ships, submarines, torpedoes, unmanned
surface or underwater craft and ocean gliders.
[0055] The present invention can be used on moving parts and
stators of propellers, turbines, rudders, steering planes, and the
like to reduce drag and cavitations, improving the efficiency
thereof.
[0056] The present invention can be used to make glassware for
hazardous and/or precious liquid manipulation. When poured out of
glassware made of or coated with the material water and other water
based solutions leave no residue and are completed removed from the
glassware. An advantage is the elimination of contamination between
experiments.
[0057] The present invention can be used to make self cleaning
glassware, windows, lenses, and the like. The super-hydrophobic
material does not leave any residue, but as water and many aqueous
solutions roll off the surface, most dust or dirt encountered may
be wetted and swept away, thus making the material self
cleaning.
[0058] The present invention can be used as an anti-condensation
appliance. When water vapor condenses on the surface the droplets
move to the tips of the nanostructures and roll off the surface
very easily. This rolling off generally occurs at the micron to
sub-micron level, before any visible appearance of surface fog or
frost. Buildup of moisture or ice is eliminated. Applications
include, but are not limited to transparent appliances such as, for
example, eye glasses, safety goggles, masks, windshields, windows,
and the like. The ability of the structured material to be
transparent is governed by the laws of optical diffraction. Simply
put, when the nanostructure size is much less than an optical
wavelength, the structure will appear transparent. Moreover,
applications include, but are not limited to heat exchangers such
as, for example, refrigerators, heat pumps, dehumidifier cooling
coils, and the like, thus increasing their energy efficiencies and
decreasing or even eliminating the need for a defrost cycle.
[0059] The present invention can be used to coat airplane wings,
propellers, and the like to keep freezing rain from sticking or
accumulating. Such a coating is anti-icing because before water
droplets can form ice they drop off the surface.
[0060] The present invention can be used as a medium for
crystallization. When a water based solution resides on the surface
it forms a spherical droplet. When the droplet is allowed to
evaporate it will uniformly shrink without pinning to the surface
(pinning causes a "coffee stain" ring on most other surfaces). This
may be particularly useful for crystallizing ultra-pure proteins,
similar to what has been carried out in a micro-gravity
environment.
[0061] The present invention can be used as a coating for conduits
such as pipes, tubing, hoses, and the like, for example. The
reduction in viscous drag greatly reduces or eliminates the
shearing forces normally associated with laminar flow and
turbulence through the conduit. This will cause the entire volume
of water to move as a unit with little or no turbulence and thus
greatly reduce the amount of energy required to force the fluid
therethrough. This is especially true for convection circulation
systems where the driving force is weak. The surface properties may
also change the conditions under which the flow is turbulent. Since
water is in minimal contact with the surface, thermal contact is
also decreased, reducing thermal losses of heated and cooled
aqueous fluids, and enabling management thereof by strategically
locating the coating in the pipes.
[0062] The present invention can be used to separate liquids which
are immiscible, for example water and oil. The super-hydrophobic
material attracts oil and other organic liquids.
[0063] With selection of a suitable sharp surface feature and
surface properties, the present invention can be used as an
anti-clotting surface for blood, which generally will not stick to
the surface. Thus, the material prevents blood from clotting
thereon, and can be used as a coating for synthetic implants, such
as stents, heart valves, artificial heart surfaces, surgical
instruments, and for external machines used to circulate blood. The
decreased viscous drag on the surface may reduce the shear force on
the blood, reducing damage to the blood.
[0064] An electrically conductive substrate can be coated with
super-hydrophobic material of the present invention. The
super-hydrophobic properties can be electrically switched on and
off, for example by electro-wetting on dielectric (EWOD) or with an
electrically switchable surface coating.
[0065] While there has been shown and described what are at present
considered the preferred embodiments of the invention, it will be
obvious to those skilled in the art that various changes and
modifications can be prepared therein without departing from the
scope of the inventions defined by the appended claims.
* * * * *