U.S. patent application number 11/980980 was filed with the patent office on 2009-05-21 for preparation of stable nanotube dispersions in liquids.
Invention is credited to Frances E. Lockwood, Zhiqiang Zhang.
Application Number | 20090131289 11/980980 |
Document ID | / |
Family ID | 32911595 |
Filed Date | 2009-05-21 |
United States Patent
Application |
20090131289 |
Kind Code |
A1 |
Zhang; Zhiqiang ; et
al. |
May 21, 2009 |
Preparation of stable nanotube dispersions in liquids
Abstract
The introduction of nanotubes in a liquid provides a means for
changing the physical and/or chemical properties of the liquid.
Improvements in heat transfer, electrical properties, viscosity,
and lubricity can be realized upon dispersion of nanotubes in
liquids; however, nanotubes behave like hydrophobic particles and
tend to clump together in liquids. Methods of preparing stable
dispersions of nanotubes are described and surfactants/dispersants
are identified which can disperse carbon nanotubes in aqueous and
petroleum liquid medium. The appropriate dispersant is chosen for
the carbon nanotube and the water or oil based medium and the
dispersant is dissolved into the liquid medium to form a solution.
The carbon nanotube is added to the dispersant containing the
solution with agitation, ultrasonication, and/or combinations
thereof.
Inventors: |
Zhang; Zhiqiang; (Lexington,
KY) ; Lockwood; Frances E.; (Georgetown, KY) |
Correspondence
Address: |
WOOD, HERRON & EVANS, LLP
2700 CAREW TOWER, 441 VINE STREET
CINCINNATI
OH
45202
US
|
Family ID: |
32911595 |
Appl. No.: |
11/980980 |
Filed: |
October 31, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10929636 |
Aug 30, 2004 |
|
|
|
11980980 |
|
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Current U.S.
Class: |
508/113 ;
977/750; 977/752; 977/902 |
Current CPC
Class: |
D01F 9/127 20130101;
Y10S 977/787 20130101; Y10S 977/842 20130101; B82Y 30/00
20130101 |
Class at
Publication: |
508/113 ;
977/750; 977/752; 977/902 |
International
Class: |
C10M 125/02 20060101
C10M125/02 |
Claims
1. A method of preparing the stable dispersion of the carbon
nanotube in a liquid medium with the combined use of dispersants
and physical agitation (e.g. ultrasonication).
2. The method of claim 1 wherein said carbon nanotube is either
single-walled, or multi-walled, with typical aspect ratio of
500-5000.
3. The method of claim 1 wherein said carbon nanotube is not
required, but may optionally be surface treated to be hydrophilic
at surface for ease of dispersing into the aqueous medium.
4. The method of claim 1 wherein the said dispersant is soluble in
the said liquid medium.
5. The method of claim 1 includes the two-step approach: dissolving
the said dispersant into the said liquid medium first, and then
adding the said carbon nanotube into the above mixture while being
strongly agitated or ultrasonicated.
6. The method of claim 5 where the carbon nanotube is added into
the liquid while being agitated or ultrasonicated, and then the
surfactant is added.
7. The method of claim 1 wherein said liquid medium can be a
petroleum distillate or a synthetic petroleum oil.
8. The dispersant for the said liquid medium of claim 6 is of the
type used in the lubricant industry, or it is a surfactant or a
mixture of surfactants with low HLB (<8), preferably nonionic or
mixture of nonionic and ionic surfactant. More typically, the said
dispersant can be the ashless polymeric dispersant used in the
lubricant industry.
9. The dispersant of claim 7 is included in a dispersant-detergent
(DI) additive package typical sold in the lubricant industry.
10. The method of claim 1 wherein said liquid medium can be water
or any water based solution.
11. The dispersant for the said liquid medium of claim 8 is high
HLB (>10), preferably nonylphenoxypoly-(ethyleneoxy)ethanol-type
surfactants.
12. The uniform dispersion with designed viscosity obtained from
the method of claim 1 of nanotube in petroleum liquid medium.
13. The uniform dispersion in a form as a gel or paste obtained
from the method of claim 1 of nanotube in petroleum liquid medium
or aqueous medium.
14. The uniform dispersion in a form as a grease obtained from the
method of claim 1 of nanotube in petroleum liquid medium or aqueous
medium.
15. The uniform and stable dispersion in a form containing
dissolved non-dispersing, "other" compounds in the liquid medium of
claim 6.
16. The uniform and stable dispersion in a form containing
dissolved non-dispersing, "other" compounds in the liquid medium of
claim 8.
Description
BACKGROUND OF THE INVENTION
[0001] This application is a Continuation application of Ser. No.
10/929,636 filed on Aug. 30, 2004 claiming priority from
Provisional application 60/254,959 filed on Dec. 12, 2000 both of
which are incorporated by reference herein in their entirety.
TECHNICAL FIELD
[0002] Methods are described and surfactants are identified which
can disperse carbon nanotubes in aqueous and petroleum liquid
medium utilizing selected dispersants and mixing methods to form
stable carbon nanotube dispersions.
DESCRIPTION OF THE PRIOR ART
[0003] Carbon nanotubes are a new form of the material formed by
elemental carbon, which possess different properties than the other
forms of the carbon materials. They have unique atomic structure,
very high aspect ratio, and extraordinary mechanical properties
(strength and flexibility), making them ideal reinforcing fibers in
composites and other structural materials.
[0004] Carbon nanotubes are characterized as generally to rigid
porous carbon three dimensional structures comprising carbon
nanofibers and having high surface area and porosity, low bulk
density, low amount of micropores and increased crush strength. The
instant process is applicable to nanotubes with or without
amorphous carbon.
[0005] The term "nanotube" refers to elongated structures having a
cross section (e.g., angular fibers having edges) or diameter
(e.g., rounded) less than 1 micron. The structure may be either
hollow or solid. Accordingly, the term includes "nanofibrils" and
"bucky tubes". Such structures provide significant surface area
when incorporated into a structure because of their size and shape.
Moreover, such fibers can be made with high purity and
uniformity.
[0006] Preferably, the nanotube used in the present invention has a
diameter less than 1 micron, preferably less than about 0.5 micron,
and even more preferably less than 0.1 micron and most preferably
less than 0.05 micron.
[0007] The term "internal structure" refers to the internal
structure of an assemblage including the relative orientation of
the fibers, the diversity of and overall average of fiber
orientations, the proximity of the fibers to one another, the void
space or pores created by the interstices and spaces between the
fibers and size, shape, number and orientation of the flow channels
or paths formed by the connection of the void spaces and/or pores.
The structure may also include characteristics relating to the
size, spacing and orientation of aggregate particles that form the
assemblage. The term "relative orientation" refers to the
orientation of an individual fiber or aggregate with respect to the
others (i.e., aligned versus non-aligned). The "diversity of" and
"overall average" of fiber or aggregate orientations refers to the
range of fiber orientations within the structure (alignment and
orientation with respect to the external surface of the
structure).
[0008] Carbon nanotubes can be used to form a rigid assemblage or
be made having diameters in the range of 3.5 to 70 nanometers. The
nanotubes, fibrils, bucky tubes and whiskers that are referred to
in this application are distinguishable from continuous carbon
fibers commercially available as reinforcement materials. In
contrast to nanotubes, which have desirably large, but unavoidably
finite aspect ratios, continuous carbon fibers have aspect ratios
(L/D) of at least 10.sup.4 and often 10.sup.6 or more. The diameter
of continuous fibers is also far larger than that of nanotubes,
being always >1.0 micron and typically 5 to 7 microns.
Continuous carbon fibers are made by the pyrolysis of organic
precursor fibers, usually rayon, polyacrylonitrile (PAN) and pitch.
Thus, they may include heteroatoms within their structure. The
graphitic nature of "as made" continuous carbon fibers varies, but
they may be subjected to a subsequent graphitization step.
Differences in degree of graphitization, orientation and
crystallinity of graphite planes, if they are present, the
potential presence of heteroatoms and even the absolute difference
in substrate diameter make experience with continuous fibers poor
predictors of nanofiber chemistry.
[0009] Carbon nanotubes are typically hollow graphite tubules
having a diameter of generally several to several tens nanometers.
Carbon nanotubes exist in many forms. The nanofibers can be in the
form of discrete fibers or aggregate particles of nanofibers. The
former results in a structure having fairly uniform properties. The
latter results in a structure having two-tiered architecture
comprising an overall macrostructure comprising aggregate particles
of nanofibers bonded together to form the porous mass and a
microstructure of intertwined nanofibers within the individual
aggregate particles. For instance, one form of carbon fibrils are
characterized by a substantially constant diameter, length greater
than about 5 times the diameter, an ordered outer region of
catalytically grown, multiple, substantially continuous layers of
ordered carbon atoms having an outside diameter between about 3.5
and 70 nanometers, and a distinct inner core region. Each of the
layers and the core are disposed substantially concentrically about
the cylindrical axis of the fibril. The fibrils are substantially
free of pyrolytically deposited thermal carbon with the diameter of
the fibrils being equal to the outside diameter of the ordered
outer region.
[0010] Moreover, a carbon nanotube suitable for use with the
instant process defines a cylindrical carbon fibril characterized
by a substantially constant diameter between 3.5 and about 70
nanometers, a length greater than about 5 times the diameter and
less than about 5000 times the diameter, an outer region of
multiple layers of ordered carbon atoms and a distinct inner core
region, each of the layers and the core being disposed
concentrically about the cylindrical axis of the fibril. Preferably
the entire carbon nanotube is substantially free of thermal carbon
overcoat. The term "cylindrical" is used herein in the broad
geometrical sense, i.e., the surface traced by a straight line
moving parallel to a fixed straight line and intersecting a curve.
A circle or an ellipse are but two of the many possible curves of
the cylinder. The inner core region of the nanotube may be hollow,
or may comprise carbon atoms which are less ordered than the atoms
of the outer region. "Ordered carbon atoms," as the phrase is used
herein means graphitic domains having their c-axes substantially
perpendicular to the cylindrical axis of the nanotube. In one
embodiment, the length of the nanotube is greater than about 20
times the diameter of the nanotube. In another embodiment, the
nanotube diameter is between about 7 and about 25 nanometers. In
another embodiment the inner core region has a diameter greater
than about 2 nanometers.
[0011] Dispersing the nanotubes into organic and aqueous medium has
been a serious challenge. The nanotubes tend to aggregate, form
agglomerates, and separate from the dispersion.
[0012] Some industrial applications require a method of preparing a
stable dispersion of a selected carbon nanotube in a liquid
medium.
[0013] For instance, U.S. Pat. No. 5,523,006 by Strumban teaches
the user of a surfactant and an oil medium; however, the particles
are Cu--Ni--Sn--Zn alloy particles with the size from 0.01 micron
and the suspension is stable for a limited period of time of
approximately 30 days. Moreover, the surfactants don't include the
dispersants typically utilized in the lubricant industry.
[0014] U.S. Pat. No. 5,560,898 by Uchida et al. teaches that a
liquid medium is an aqueous medium containing a surfactant;
however, the stability of the suspension is of little consequence
in that the liquid is centrifuged upon suspension.
[0015] U.S. Pat. No. 5,853,877 by Shibuta teaches dispersing
disentangled nanotubes in a polar solvent and forming a coating
composition with additives such as dispersing agents; however, a
method of obtaining a stable dispersion is not taught.
[0016] U.S. Pat. No. 6,099,965 by Tennent et al. utilizes a kneader
teaching mixing a dispersant with other reactants in a liquid
medium using a high-torque dispersing tool, yet sustaining the
stability of the dispersion does not appear to be taught nor
suggested.
[0017] None of the conventional methods taught provide a process
for dispersing and maintaining nanotubes in suspension as described
and claimed in the instant invention as follows.
SUMMARY OF THE INVENTION
[0018] In this invention physical and chemical treatments are
combined to derive a method of obtaining a stable nanotube
dispersion.
[0019] The present invention provides a method of preparing a
stable dispersion of a selected carbon nanotube in a liquid medium,
such as water or any water based solution, or oil, with the
combined use of surfactants and agitation (e.g. ultrasonication) or
other means of agitation. The carbon nanotube can be either
single-walled, or multi-walled, with typical aspect ratio of
500-5000; however, it is contemplated that nanotubes of other
configurations can also be utilized with the instant invention. It
is contemplated that a mixture containing carbon nanotubes having a
length of 1 micron or more and a diameter of 50 nm or less. The raw
material may contain carbon nanotubes having a size outside of the
above ranges. The carbon nanotube is not required to be surface
treated providing a hydrophilic surface for dispersion into the
aqueous medium, but optionally may be treated. The selected
surfactant is soluble or dispersible in the liquid medium.
[0020] The term "surfactant" in the instant invention refers to any
chemical compound that reduces surface tension of a liquid when
dissolved into it, or reduces interfacial tension between two
liquids, or between a liquid and a solid. It is usually, but not
exclusively, a long chain molecule comprised of two moieties: a
hydrophilic moiety and a lipophilic moiety. The "hydrophilic" and
"lipophilic" moieties refer to the segment in the molecule with
affinity for water, and that with affinity for oil, respectively.
It is a broad term that covers all materials that have surface
activity, including wetting agents, dispersants, emulsifiers,
detergents and foaming agents, etc. The term "dispersant" in the
instant invention refers to a surfactant added to a medium to
promote uniform suspension of extremely fine solid particles, often
of colloidal size. In the lubricant industry the term "dispersant"
is general accepted to describe the long chain oil soluble or
dispersible compounds which function to disperse the "cold sludge"
formed in engines. These two terms are mostly interchangeable in
the instant invention; however, in some cases the term "dispersant"
is used with the tendency to emphasize, but not restrict to, the
ones commonly used in the lubricant industry.
[0021] The method of making a stable particle-containing
dispersions includes physical agitation in combination with
chemical treatments. The physical mixing includes high shear
mixing, such as with a high speed mixer, homogenizers,
microfluidizers, a Kady mill, a colloid mill, etc., high impact
mixing, such as attritor, ball and pebble mill, etc., and
ultrasonication methods. The mixing methods are further aided by
electrostatic stabilization by electrolytes, and steric
stabilization by polymeric surfactants (dispersants).
[0022] The chemical treatment and the use of the claimed
surfactants/dispersants are critical to long term stability of the
nanotube fluid mixtures. The treatment involves dissolving a
selected dispersant into a selected liquid medium. The chemical
method includes a two-step approach: dissolving the dispersant into
the liquid medium, and then adding the selected carbon nanotube
into the dispersant liquid medium mixture with mechanical agitation
and/or ultrasonication. These steps can be reversed but may not
produce as satisfactory a result. The liquid medium can be water or
any water solution, a petroleum distillate, a petroleum oil,
synthetic oil, or vegetable oil. The dispersant for the oily liquid
medium is a surfactant with low hydrophile-lipophile balance (HLB)
value (HLB<8) or a polymeric dispersant of the type used in the
lubricant industry. It is preferably nonionic, or a mixture of
nonionics and ionics. A preferred dispersant for the aqueous liquid
medium is of high HLB value (HLB>10), preferably a
nonylphenoxypoly(ethyleneoxy)ethanol-type surfactant. The uniform
dispersion of nanotubes is obtained with a designed viscosity in
the liquid medium. The dispersion of nanotubes may be obtained in
the form of a paste, gel or grease, in either a petroleum liquid
medium or an aqueous medium.
[0023] This dispersion may also contain a large amount of one or
more other chemical compounds, preferably polymers, not for the
purpose of dispersing, but to achieve thickening or other desired
fluid characteristics.
[0024] It is an object of the present invention to provide a method
of preparing a stable dispersion of the carbon nanotube in a liquid
medium with the combined use of dispersants and physical
agitation.
[0025] It is another object of the present invention to utilize a
carbon nanotube that is either single-walled, or multi-walled, with
typical aspect ratio of 500-5000.
[0026] It is another object of the present invention to utilize
carbon nanotubes which may optionally be surface treated to be
hydrophilic at surface for ease of dispersing into the aqueous
medium.
[0027] It is another object of the present invention to utilize a
dispersant that is soluble for a selected liquid medium.
[0028] It is another object of the present invention to utilize a
method of preparation dissolving the dispersant into the liquid
medium first, and then adding the carbon nanotube into the mixture
while being strongly agitated or ultrasonicated.
[0029] It is another object of the present invention to add the
carbon nanotube into the liquid while being agitated or
ultrasonicated, and then adding the surfactant.
[0030] It is another object of the present invention to utilize a
petroleum distillate or a synthetic petroleum oil as the liquid
medium.
[0031] It is another object of the present invention to utilize a
liquid medium of the type used in the lubricant industry, or a
surfactant, or a mixture of surfactants with a low HLB (<8),
preferably nonionic or mixture of nonionic and ionic surfactant.
More typically, the dispersant can be the ashless polymeric
dispersant used in the lubricant industry.
[0032] It is another object of the present invention to utilize a
dispersant-detergent (DI) additive package typical sold in the
lubricant industry as the surfactant/dispersant.
[0033] It is another object of the present invention to utilize a
liquid medium consisting of water or any water based solution.
[0034] It is another object of the present invention to utilize a
dispersant having a high HLB (>10), preferably
nonylphenoxypoly-(ethyleneoxy)ethanol-type surfactants.
[0035] It is another object of the present invention to utilize a
uniform dispersion with a designed viscosity having a nanotube in
petroleum liquid medium.
[0036] It is another object of the present invention to obtain a
uniform dispersion in a form as a gel or paste containing nanotubes
in petroleum liquid medium or aqueous medium.
[0037] It is another object of the present invention to obtain a
uniform dispersion of nanotubes in a form as a grease obtained from
dispersing carbon nanotube in petroleum liquid medium or aqueous
medium.
[0038] It is another object of the present invention to form a
uniform and stable dispersion of carbon nanotubes containing
dissolved non-dispersing, "other" compounds in the liquid oil based
medium.
[0039] It is yet another object of the present invention to form a
uniform and stable dispersion in a form containing carbon nanotubes
with dissolved non-dispersing, "other" compounds in the liquid
water medium.
[0040] The foregoing and other objects and advantages of the
invention will be set forth in or apparent from the following
description.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0041] The present invention provides a method a dispersing carbon
nanotubes into a liquid medium.
[0042] As set forth above, the nanotubes can be either
single-walled, or multi-walled, having a typical nanoscale diameter
of 1-500 nanometers. More typically the diameter is around 10-30
nanometers. The length of the tube can be in submicron and micron
scale, usually from 500 nanometers to 500 microns. More typical
length is 1 micron to 100 microns. The aspect ratio of the tube can
be from hundreds to thousands, more typical 500 to 5000. The
surface of the nanotube can be treated chemically to achieve
certain level of hydrophilicity by activated carbon treatment,
vapor disposition of chemicals, and/or treatment with a strong acid
or base, or the carbon nanotubes, fibers, particles or combination
thereof can be utilized as is from the production.
[0043] A preferred embodiment utilized a carbon nanotube product
obtained from Carbolex at the University of Kentucky which contains
amorphous carbon particles. The Carbolex carbon nanotubes comprise
single walled nanotubes, multi-wall nanotubes, and combinations
thereof. Moreover, the combination can include small fractions of
the carboneous materials made up of partially disordered spherical
particles and/or short carbon nanotubes.
Petroleum Basestocks Liquid Medium
[0044] The petroleum liquid medium can be any petroleum distillates
or synthetic petroleum oils, greases, gels, or oil-soluble polymer
composition. More typically, it is the mineral basestocks or
synthetic basestocks used in the lube industry, e.g., Group I
(solvent refined mineral oils), Group II (hydrocracked mineral
oils), Group III (severely hydrocracked oils, sometimes described
as synthetic or semi-synthetic oils), Group IV (polyalphaolefins),
and Group VI (esters, naphthenes, and others). One preferred group
includes the polyalphaolefins, synthetic esters, and
polyalkylglycols.
[0045] Synthetic lubricating oils include hydrocarbon oils and
halo-substituted hydrocarbon oils such as polymerized and
interpolymerized olefins (e.g., polybutylenes, polypropylenes,
propylene-isobutylene copolymers, chlorinated polybutylenes,
poly(1-octenes), poly(1-decenes), etc., and mixtures thereof;
alkylbenzenes (e.g., dodecylbenzenes, tetradecylbenzenes,
dinonylbenzenes, di-(2-ethylhexyl) benzenes, etc.); polyphenyls
(e.g., biphenyls, terphenyls, alkylated polyphenyls, etc.),
alkylated diphenyl, ethers and alkylated diphenyl sulfides and the
derivatives, analogs and homologs thereof and the like.
[0046] Alkylene oxide polymers and interpolymers and derivatives
thereof where the terminal hydroxyl groups have been modified by
esterification, etherification, etc. constitute another class of
known synthetic oils.
[0047] Another suitable class of synthetic oils comprises the
esters of dicarboxylic acids (e.g., phtalic acid, succinic acid,
alkyl succinic acids and alkenyl succinic acids, maleic acid,
azelaic acid, suberic acid, sebacic acid, fumaric acid, adipic
acid, alkenyl malonic acids, etc.) with a variety of alcohols
(e.g., butyl alcohol, hexyl alcohol, dodecyl alcohol, 2-ethylhexyl
alcohol, ethylene glycol diethylene glycol monoether, propylene
glycol, etc.). Specific examples of these esters include dibutyl
adipate, di(2-ethylhexyl) sebacate, di-hexyl fumarate, dioctyl
sebacate, diisooctyl azelate, diisodecyl azealate, dioctyl
phthalate, didecyl phthalate, dicicosyl sebacate, the 2-ethylhexyl
diester of linoleic acid dimer, the complex ester formed by
reacting one mole of sebacic acid with two moles of tetraethylene
glycol and two moles of 2-ethylhexanoic acid, and the like.
[0048] Esters useful as synthetic oils also include those made from
C.sub.5 to C.sub.12 monocarboxylic acids and polyols and polyol
ethers such as neopentyl glycol, trimethylolpropane,
pentaerythritol, dipentaerythritol, tripentaerythritol, etc. Other
synthetic oils include liquid esters of phosphorus-containing acids
(e.g., tricresyl phosphate, trioctyl phosphate, diethyl ester of
decylphosphonic acid, etc.), polymeric tetrahydrofurans and the
like.
[0049] Preferred polyalphaolefins (PAO), include those sold by
Mobil Chemical company as SHF fluids, and those sold by Ethyl
Corporation under the name ETHYLFLO, or ALBERMARLE. PAO's include
the Ethyl-flow series by Ethyl Corporation, "Albermarle
Corporation," including Ethyl-flow 162, 164, 166, 168, and 174,
having varying viscosity from about 2 to about 460 centistokes.
[0050] Mobil SHF-42 from Mobil Chemical Company, Emery 3004 and
3006, and Quantum Chemical Company provide additional
polyalphaolefins basestocks. For instance, Emery 3004
polyalphaolefin has a viscosity of 3.86 centistokes (cSt) at
212.degree. F. (100.degree. C.) and 16.75 cSt at 104.degree. F.
(40.degree. C.). It has a viscosity index of 125 and a pour point
of -98.degree. F. and it also has a flash point of 432.degree. F.
and a fire point of 478.degree. F. Moreover, Emery 3006
polyalphaolefin has a viscosity of 5.88 cSt at +212.degree. F. and
31.22 cSt at +104.degree. F. It has a viscosity index of 135 and a
pour point of -87.degree. F. It also has a flash point of
+464.degree. F. and a fire point of +514.degree. F.
[0051] Additional satisfactory polyalphaolefins are those sold by
Uniroyal Inc. under the brand Synton PAO-40, which is a 40
centistoke polyalphaolefin. Also useful are the Oronite brand
polyalphaolefins manufactured by Chevron Chemical Company.
[0052] It is contemplated that Gulf Synfluid 4 cSt PAO,
commercially available from Gulf Oil Chemicals Company, a
subsidiary of Chevron Corporation, which is similar in many
respects to Emery 3004 may also be utilized herein. Mobil SHF-41
PAO, commercially available from Mobil Chemical Corporation, is
also similar in many respects to Emery 3004.
[0053] Preferably the polyalphaolefins will have a viscosity in the
range of about 2-40 centistoke at 100.degree. C., with viscosity of
4 and 10 centistoke being particularly preferred.
[0054] The most preferred synthetic based oil ester additives are
polyolesters and diesters such as di-aliphatic diesters of alkyl
carboxylic acids such as di-2-ethylhexylazelate,
di-isodecyladipate, and di-tridecyladipate, commercially available
under the brand name Emery 2960 by Emery Chemicals, described in
U.S. Pat. No. 4,859,352 to Waynick. Other suitable polyolesters are
manufactured by Mobil Oil. Mobil polyolester P-43, M-045 containing
two alcohols, and Hatco Corp. 2939 are particularly preferred.
[0055] Diesters and other synthetic oils have been used as
replacements of mineral oil in fluid lubricants. Diesters have
outstanding extreme low temperature flow properties and good
residence to oxidative breakdown.
[0056] The diester oil may include an aliphatic diester of a
dicarboxylic acid, or the diester oil can comprise a dialkyl
aliphatic diester of an alkyl dicarboxylic acid, such as di-2-ethyl
hexyl azelate, di-isodecyl azelate, di-tridecyl azelate,
di-isodecyl adipate, di-tridecyl adipate. For instance,
Di-2-ethylhexyl azelate is commercially available under the brand
name of Emery 2958 by Emery Chemicals.
[0057] Also useful are polyol esters such as Emery 2935, 2936, and
2939 from Emery Group of Henkel Corporation and Hatco 2352, 2962,
2925, 2938, 2939, 2970, 3178, and 4322 polyol esters from Hatco
Corporation, described in U.S. Pat. No. 5,344,579 to Ohtani et al.
and Mobil ester P 24 from Mobil Chemical Company. Mobil esters such
as made by reacting dicarboxylic acids, glycols, and either
monobasic acids or monohydric alcohols like Emery 2936
synthetic-lubricant basestocks from Quantum Chemical Corporation
and Mobil P 24 from Mobil Chemical Company can be used. Polyol
esters have good oxidation and hydrolytic stability. The polyol
ester for use herein preferably has a pour point of about
-100.degree. C. or lower to -40.degree. C. and a viscosity of about
2-460. centistoke at 100.degree. C.
[0058] Group III oils are often referred to as hydrogenated oil to
be used as the sole base oil component of the instant invention
providing superior performance to conventional motor oils with no
other synthetic oil base or mineral oil base.
[0059] A hydrogenated oil is a mineral oil subjected to
hydrogenation or hydrocracking under special conditions to remove
undesirable chemical compositions and impurities resulting in a
mineral oil based oil having synthetic oil components and
properties. Typically the hydrogenated oil is defined as a Group
III petroleum based stock with a sulfur level less than 0.03,
severely hydrotreatd and isodewaxed with saturates greater than or
equal to 90 and a viscosity index of greater than or equal to 120
may optionally be utilized in amounts up to 90 percent by volume,
more preferably from 5.0 to 50 percent by volume and more
preferably from 20 to 40 percent by volume when used in combination
with a synthetic or mineral oil.
[0060] The hydrogenated oil my be used as the sole base oil
component of the instant invention providing superior performance
to conventional motor oils with no other synthetic oil base or
mineral oil base. When used in combination with another
conventional synthetic oil such as those containing
polyalphaolefins or esters, or when used in combination with a
mineral oil, the hydrogenated oil may be present in an amount of up
to 95 percent by volume, more preferably from about 10 to 80
percent by volume, more preferably from 20 to 60 percent by volume
and most preferably from 10 to 30 percent by volume of the base oil
composition.
[0061] A Group I or II mineral oil basestock may be incorporated in
the present invention as a portion of the concentrate or a
basestock to which the concentrate may be added. Preferred as
mineral oil basestocks are the ASHLAND 325 Neutral defined as a
solvent refined neutral having a SABOLT UNIVERSAL viscosity of 325
SUS @ 100.degree. F. and ASHLAND 100 Neutral defined as a solvent
refined neutral having a SABOLT UNIVERSAL viscosity of 100 SUS @
100.degree. F., manufactured by the Marathon Ashland Petroleum.
[0062] Other acceptable petroleum-base fluid compositions include
white mineral, paraffinic and MVI naphthenic oils having the
viscosity range of about 20-400 centistokes. Preferred white
mineral oils include those available from Witco Corporation, Arco
Chemical Company, PSI and Penreco. Preferred paraffinic oils
include solvent neutral oils available from Exxon Chemical Company,
HVI neutral oils available from Shell Chemical Company, and solvent
treated neutral oils available from Arco Chemical Company.
Preferred MVI naphthenic oils include solvent extracted coastal
pale oils available from Exxon Chemical Company, MVI extracted/acid
treated oils available from Shell Chemical Company, and naphthenic
oils sold under the names HydroCal and Calsol by Calumet, and
described in U.S. Pat. No. 5,348,668 to Oldiges.
[0063] Finally, vegetable oils may also be utilizes as the liquid
medium in the instant invention.
Aqueous Medium
[0064] The selected aqueous medium is water, or it can be any
water-based solution including alcohol and its derivatives, such as
glycols or any water-soluble inorganic salt or organic
compound.
Surfactants/Dispersants
Dispersants Used in Lubricant Industry
[0065] Dispersants used in the lubricant industry are typically
used to disperse the "cold sludge" formed in gasoline and diesel
engines, which can be either "ashless dispersants", or containing
metal atoms. They can be used in the instant invention since they
have been found to be an excellent dispersing agent for soot, an
amorphous form of carbon particles generated in the engine
crankcase and incorporated with dirt and grease.
[0066] The ashless dispersants commonly used in the automotive
industry contain an lipophilic hydrocarbon group and a polar
functional hydrophilic group. The polar functional group can be of
the class of carboxylate, ester, amine, amide, imine, imide,
hydroxyl, ether, epoxide, phosphorus, ester carboxyl, anhydride, or
nitrile. The lipophilic group can be oligomeric or polymeric in
nature, usually from 70 to 200 cabon atoms to ensure oil
solubility. Hydrocarbon polymers treated with various reagents to
introduce polar functions include products prepared by treating
polyolefins such as polyisobutene first with maleic anhydride, or
phosphorus sulfide or chloride, or by thermal treatment, and then
with reagents such as polyamine, amine, ethylene oxide, etc.
[0067] Of these ashless dispersants the ones typically used in the
petroleum industry include N-substitued polyisobutenyl succinimides
and succinates, allkyl methacrylate-vinyl pyrrolidinone copolymers,
alkyl methacrylate-dialkylaminoethyl methacrylate copolymers,
alkylmethacrylate-polyethylene glycol methacrylate copolymers, and
polystearamides. Preferred oil-based dispersants that are most
important in the instant application include dispersants from the
chemical classes of alkylsuccinimide, succinate esters, high
molecular weight amines, Mannich base and phosphoric acid
derivatives. Some specific examples are polyisobutenyl
succinimide-polyethylenepolyamine, polyisobutenyl succinic ester,
polyisobutenyl hydroxybenzyl-polyethylenepolyamine,
bis-hydroxypropyl phosphorate. The dispersant may be combined with
other additives used in the lubricant industry to form a
"dispersant-detergent (DI)" additive package, e.g., Lubrizol.TM.
9802A, and the whole DI package can be used as dispersing agent for
the nanotube suspension.
[0068] For instance, LUBRIZOL 9802A is described in the technical
brochure (MATERIAL SAFETY DATA SHEET No. 1922959-1232446-3384064)
by The Lubrizol Corporation in Wickliffe, Ohio and is hereby
incorporated by reference. LUBRIZOL 9802A is described as a motor
oil additive is believed to contain as an active ingredient a zinc
dithiophosphate and/or zinc alkyldithiophosphate.
[0069] LUBRIZOL 4999 is described in its Technical Brochure
(MATERIAL SAFETY DATA SHEET No. 1272553-1192556-3310026) by the
Lubrizol Corporation in Wickliffe, Ohio and is hereby incorporated
by reference. LUBRIZOL 9802A is described as a engine oil additive
and contains as an active ingredient from 5 to 9.9 percent of a
zinc alkyldithiophosphate.
[0070] OLOA 9061 is described in Technical Brochure "MATERIAL
SAFETY DATA SHEET No. 006703" by Chevron Chemical Company LLC and
is hereby incorporated by reference. OLOA 9061 is described as zinc
alkyl dithiophosphate compound.
[0071] IGEPAL CO-630 is described in Technical Brochure "MATERIAL
SAFETY DATA SHEET" from Rhodia Inc. and is hereby incorporated by
reference. IGEPAL CO-630 is described as a nonylphenoxy
poly(ethyleneoxy) ethanol, branched compound.
Other Types of Dispersants
[0072] Alternatively a surfactant or a mixture of surfactants with
low HLB value (typically less than or equal to 8), preferably
nonionic, or a mixture of nonionics and ionics, may be used in the
instant invention.
[0073] The dispersant for the water based carbon nanotube
dispersion should be of high HLB value (typically less than or
equal to 10), preferable nonylphenoxypoly (ethyleneoxy)
ethanol-type surfactants are utilized.
[0074] In both the water and oil based cases, the dispersants
selected should be soluble or dispersible in the liquid medium.
[0075] The dispersant can be in a range of up from 0.001 to 30
percent, more preferably in a range of from between 0.5 percent to
20 percent, more preferably in a range of from between 1.0 to 8.0
percent, and most preferably in a range of from between 2 to 6
percent. The carbon nanotube can be of any desired weight
percentage in a range of from 0.0001 up to 50 percent. For
practical application it is usually in a range of from between 0.01
percent to 2 percent, and most preferably in a range of from
between 0.05 percent to 0.5 percent. The remainder of the formula
is the selected oil or water medium.
[0076] It is believed that in the instant invention the dispersant
functions by adsorbing onto the surface of the carbon nanotube. The
dispersant contains a hydrophilic segment and a hydrophobic segment
which surrounds the carbon particles thereby providing a means for
isolating and dispersing the carbon particles. The selection of a
dispersant having a particular HLB value is important to determine
the dispersant characteristics such as rate and the degree of
stabilization over time.
Other Chemical Compound Additives
[0077] This dispersion may also contain a large amount of one or
more other chemical compounds, preferably polymers, not for the
purpose of dispersing, but to achieve thickening or other desired
fluid characteristics.
[0078] The viscosity improvers used in the lubricant industry can
be used in the instant invention for the oil medium, which include
olefin copolymers (OCP), polymethacrylates (PMA), hydrogenated
styrene-diene (STD), and styrene-polyester (STPE) polymers. Olefin
copolymers are rubber-like materials prepared from ethylene and
propylene mixtures through vanadium-based Ziegler-Natta catalysis.
Styrene-diene polymers are produced by anionic polymerization of
styrene and butadiene or isoprene. Polymethacrylates are produced
by free radical polymerization of alkyl methacrylates.
Styrene-polyester polymers are prepared by first co-polymerizing
styrene and maleic anhydride and then esterifying the intermediate
using a mixture of alcohols.
[0079] Other compounds which can be used in the instant invention
in either the aqueous medium or the oil medium include: acrylic
polymers such as polyacrylic acid and sodium polyacrylate,
high-molecular-weight polymers of ethylene oxide such as
Polyox.RTM. WSR from Union Carbide, cellulose compounds such as
carboxymethylcellulose, polyvinyl alcohol (PVA), polyvinyl
pyrrolidone (PVP), xanthan gums and guar gums, polysaccharides,
alkanolamides, amine salts of polyamide such as Disparlon AQ series
from King Industries, hydrophobically modified ethylene oxide
urethane (e.g., Acrysol series from Rohmax), silicates, and fillers
such as mica, silicas, cellulose, wood flour, clays (including
organoclays) and nanoclays, and resin polymers such as polyvinyl
butyral resins, polyurethane resins, acrylic resins and epoxy
resins.
[0080] Chemical compounds such as plasticizers can also be used in
the instant invention and may be selected from the group including
phthalate, adipates, sebacate esters, and more particularly:
glyceryl tri(acetoxystearate), epoxidized soybean oil, epoxidized
linseed oil, N,n-butyl benzene sulfonamide, aliphatic polyurethane,
epoxidized soy oil, polyester glutarate, polyester glutarate,
triethylene glycol
[0081] In both the water and oil based cases, the dispersants
selected should be soluble or dispersible in the liquid medium.
[0082] The dispersant can be in a range of up from 0.001 to 30
percent, more preferably in a range of from between 0.5 percent to
20 percent, more preferably in a range of from between 1.0 to 8.0
percent, and most preferably in a range of from between 2 to 6
percent. The carbon nanotube can be of any desired weight
percentage in a range of from 0.0001 up to 50 percent. For
practical application it is usually in a range of from between 0.01
percent to 2 percent, and most preferably in a range of from
between 0.05 percent to 0.5 percent. The remainder of the formula
is the selected oil or water medium.
[0083] It is believed that in the instant invention the dispersant
functions by adsorbing onto the surf ace of the carbon nanotube.
The dispersant contains a hydrophilic segment and a hydrophobic
segment which surrounds the carbon particles thereby providing a
means for isolating and dispersing the carbon particles. The
selection of a dispersant having a particular HLB value is
important to determine the dispersant characteristics such as rate
and the degree of stabilization over time.
Other Chemical Compound Additives
[0084] This dispersion may also contain a large amount of one or
more other chemical compounds, preferably polymers, not for the
purpose of dispersing, but to achieve thickening or other desired
fluid characteristics.
[0085] The viscosity improvers used in the lubricant industry can
be used in the instant invention for the oil medium, which include
olefin copolymers (OCP), polymethacrylates (PMA), hydrogenated
styrene-diene (STD), and styrene-polyester (STPE) polymers. Olefin
copolymers are rubber-like materials prepared from ethylene and
propylene mixtures through vanadium-based Ziegler-Natta catalysis.
Styrene-diene polymers are produced by anionic polymerization of
styrene and butadiene or isoprene. Polymethacrylates are produced
by free radical polymerization of alkyl methacrylates.
Styrene-polyester polymers are prepared by first co-polymerizing
styrene and maleic anhydride and then esterifying the intermediate
using a mixture of alcohols.
[0086] Other compounds which can be used in the instant invention
in either the aqueous medium or the oil medium include: acrylic
polymers such as polyacrylic acid and sodium polyacrylate,
high-molecular-weight polymers of ethylene oxide such as
Polyox.RTM. WSR from Union Carbide, cellulose compounds such as
carboxymethylcellulose, polyvinyl alcohol (PVA), polyvinyl
pyrrolidone (PVP), xanthan gums and guar gums, polysaccharides,
alkanolamides, amine salts of polyamide such as Disparlon AQ series
from King Industries, hydrophobically modified ethylene oxide
urethane (e.g., Acrysol series from Rohmax), silicates, and fillers
such as mica, silicas, cellulose, wood flour, clays (including
organoclays) and nanoclays, and resin polymers such as polyvinyl
butyral resins, polyurethane resins, acrylic resins and epoxy
resins.
[0087] Chemical compounds such as plasticizers can also be used in
the instant invention and may be selected from the group including
phthalate, adipates, sebacate esters, and more particularly:
glyceryl tri(acetoxystearate), epoxidized soybean oil, epoxidized
linseed oil, N,n-butyl benzene sulfonamide, aliphatic polyurethane,
epoxidized soy oil, polyester glutarate, polyester glutarate,
triethylene glycol caprate/caprylate, long chain alkyl ether,
dialkyl diester glutarate, monomeric, polymer, and epoxy
plasticizers, polyester based on adipic acid, hydrogenated dimer
acid, distilled dimer acid, polymerized fatty acid trimer, ethyl
ester of hydrolyzed collagen, isostearic acid and sorbian oleate
and cocoyl hydrolyzed keratin, PPG-12/PEG-65 lanolin oil, dialkyl
adipate, alkylaryl phosphate, alkyl diaryl phosphate, modified
triaryl phosphate, triaryl phosphate, butyl benzyl phthalate, octyl
benzyl phthalate, alkyl benzyl phthalate, dibutoxy ethoxy ethyl
adipate, 2-ethylhexyldiphenyl phosphate, dibutoxy ethoxy ethyl
formyl, diisopropyl adipate, diisopropyl sebacate, isodecyl oleate,
neopentyl glycol dicaprate, neopenty glycol diotanoate, isohexyl
neopentanoate, ethoxylated lanolins, polyoxyethylene cholesterol,
propoxylated (2 moles) lanolin alcohols, propoxylated lanoline
alcohols, acetylated polyoxyethylene derivatives of lanoline, and
dimethylpolysiloxane. Other plasticizers which may be substituted
for and/or used with the above plasticizers including glycerine,
polyethylene glycol, dibutyl phthalate, and
2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, and diisononyl
phthalate all of which are soluble in a solvent carrier.
Physical Agitation
[0088] The physical mixing includes high shear mixing, such as with
a high speed mixer, homogenizers, microfluidizers, a Kady mill, a
colloid mill, etc., high impact mixing, such as attritor, ball and
pebble. mill, etc., and ultrasonication methods.
[0089] Ultrasonication is the most preferred physical method in the
instant invention since it is less destructive to the carbon
nanotube structure than the other methods described.
Ultrasonication can be done either in the bath-type ultrasonicator,
or by the tip-type ultrasonicator. More typically, tip-type
ultrasonication is applied for higher energy output. Sonication at
the medium-high instrumental intensity for up to 30 minutes, and
usually in a range of from 10 to 20 minutes is desired to achieve
better homogeneity.
[0090] One dismembrator useful for preparing the instant invention
is a Model 550 Sonic dismembrator manufactured by Fisher Scientific
Company, located in Pittsburgh Pa. The instruction manual
Publication No. FS-IM-2 published in November of 1996 describing
the use of the Fisher Scientific Model 550 Sonic Dismembrator is
hereby incorporated by reference. The generator power supply
converst conventional 50/60 Hz AC line power to 20 kHZ electrical
energy which is fed to the converter where it is transformed to
mechanical vibration. The heart of the convertor is a lead
zirconate titanate (Piezoelectric) crystal which, when subjected to
an alternating voltage, expands and contracts. The convertor
vibrates in the longitudinal direction and transmits this motion to
the horn tip immersed in the liquid solution. Cavitation results,
in which microscopic vapor bubbles are formed momentarily and
implode, causing powerful shock waves to radiate throughout the
sample from the tip face. Horns and probes amplify the longitudinal
vibration of the convertor; higher amplification (or gain) results
in more intense cavitational action and greater disruption. The
larger the tip of the probe, the larger the volume that can be
processed but at lesser intensity. The convertor is tuned to
vibrate at a fixed frequency of 20 kHZ. All horns and probes are
resonant bodies, and are also tuned to vibrate at 20 kHZ. Of course
it is contemplated that other models and competing ultrasonic
mixing devices could be utilized in accordance with the present
invention.
[0091] The raw material mixture may be pulverized by any suitable
known dry or wet grinding method. One grinding method includes
pulverizing the raw material mixture in the fluid mixture of the
instant invention to obtain the concentrate, and the pulverized
product may then be dispersed further in a liquid medium with the
aid of the dispersants described above. However, pulverization or
milling reduces the carbon nanotube average aspect ratio.
[0092] The instant method of forming a stable suspension of
nanotubes in a solution consist of two primary steps. First select
the appropriate dispersant for the carbon nanotube and the medium,
and dissolve the dispersant into the liquid medium to form a
solution, and second add the carbon nanotube into the dispersant
containing solution while strongly agitating, ball milling, or
ultrasonication of the solution.
[0093] The present invention is further described and illustrated
in the following examples:
EXAMPLES
Example 1
TABLE-US-00001 [0094] Weight Components Description percentage
Carbon Surface untreated, aspect ratio 0.1 nanotube 2000, diameter
25 nm, length 50 .mu.m Dispersant Lubrizol .TM. 9802A 4.8 Liquid
Poly(a-olefin), 6 cSt 95.1 Sonication Fisher Scientific 550 Sonic
Dismembrator, 15 minutes
Example 2
TABLE-US-00002 [0095] Weight Components Description percentage
Carbon Surface untreated, aspect ratio 0.1 nanotube 2000, diameter
25 nm, length 50 .mu.m Dispersant Lubrizol .TM. 4999 4.8 Liquid
Poly (a-olefin), 6 cSt 95.1 Sonication Fisher Scientific 550 Sonic
Dismembrator, 15 minutes
Example 3
TABLE-US-00003 [0096] Weight Components Description percentage
Carbon Surface untreated, aspect ratio 0.1 nanotube 2000, diameter
25 nm, length 50 .mu.m Dispersant OLOA 9061 4.8 Liquid Poly
(a-olefin), 6 cSt 95.1 Sonication Fisher Scientific 550 Sonic
Dismembrator, 15 minutes
Example 4
TABLE-US-00004 [0097] Weight Components Description percentage
Carbon Surface treated 0.1 nanotube Dispersant Igepal .TM. CO-630
5.0 Liquid Water 94.9 Sonication Fisher Scientific 550 Sonic
Dismembrator, 15 minutes
[0098] The dispersions in Examples 1-4 are very uniform, and will
remain in a stable dispersion without any sign of separation or
aggregation for at least a year.
[0099] It is contemplated that substitute dispersants could be
utilized in the examples set forth in Examples 1-4 and yield yield
similar results. For instance, in Example 1 up to 4.8 weight
percent of a zinc dithiophosphate could be substituted for the
LUBRIZOL 9802A since it is the primary active ingredient of the
product. In Example 2, up to 4.8 weight percent of a zinc
alkyldithiophosphate could be substituted for the LUBRIZOL 4999
product and be expected to yield similar results since a zinc
alkyldithiophosphate is the active ingredient in the LUBRIZOL 4999
product. In Example 3, up to 4.8 weight percent a zinc alkyl
dithiophosphate compound could be substituted for the OLOA 9061
since the alkyl dithiophosphate compound is the active ingredient
in the OLOA 9061 product. Finally, in Example 4, up to 5.0 weight
percent of a nonylphenoxy poly(ethyleneoxy) ethanol, branched
compound could be substituted fro the IGEPAL CO-630 product since
the nonylphenoxy poly(ethyleneoxy) ethanol, branched compound is
the primary active ingredient in the IGEPAL CO-630 product.
Moreover, the weight percent of the carbon nanotube can be up to 10
weight percent, and more preferably up to 1 weight percent and most
preferably from 0.01 to 1 weight percent in the formulations
depending upon the preferred viscosity and chemical and physical
properties of the resulting products. Accordingly the weight
percent of the liquid medium can be reduced and the weight percent
of the dispersant can be increased up to 20 weight percent, more
preferably from 0.01 to 10 weight percent and most preferably from
3 to 6 weight percent. The amount of nanotubes, dispersant, and
liquid medium can be varied as long as the desired HBL value is
maintained to produce compounds having a gel, grease, or wax type
consistency.
[0100] Specific compositions, methods, or embodiments discussed are
intended to be only illustrative of the invention disclosed by this
specification. Variation on these compositions, methods, or
embodiments are readily apparent to a person of skill in the art
based upon the teachings of this specification and are therefore
intended to be included as part of the inventions disclosed herein.
Reference to documents made in the specification is intended to
result in such patents or literature cited are expressly
incorporated herein by reference, including any patents or other
literature references cited within such documents as if fully set
forth in this specification. The foregoing detailed description is
given primarily for clearness of understanding and no unnecessary
limitations are to be understood therefrom, for modification will
become obvious to those skilled in the art upon reading this
disclosure and may be made upon departing from the spirit of the
invention and scope of the appended claims. Accordingly, this
invention is not intended to be limited by the specific
exemplification presented herein above. Rather, what is intended to
be covered is within the spirit and scope of the appended
claims.
* * * * *