Note: Descriptions are shown in the official language in which they were submitted.
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PREPARATION OF STABLE NANOTUBE DISPERSIONS IN LIQUIDS
BACKGROUND OF THE INVENTION
This application claims priority from United States Nonprovisional application
Serial No. 10/021,767 filed on December 12, 2001 entitled "Preparation of
stable carbon
Nanotube Dispersions in Liquids".
Technical Field
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
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.
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.
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
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structure because of their size and shape. Moreover, such fibers can be made
with high
purity and uniformity.
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.
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).
Carbon nanotubes can be used to form a rigid assemblage or be made having
diameters in the range of 3.5 to 70 manometers. The nanotubes, fibrils, bucky
tubes and
whiskers that are referred to inthis 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 104 and often 106 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
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present, the potential presence of heteroatoms and even the absolute
difference in
substrate diameter make experience with continuous fibers poor predictors of
nanofiber
chemistry.
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.
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
ab out the cylindrical axis of the fibril. Preferably the entire carbon
nanotube is sub stantially
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.
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"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 ofthe 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 manometers. In another embodiment the inner core region has a diameter
greater than
about 2 manometers.
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.
Some industrial applications require a method of preparing a stable dispersion
of
a selected carbon nanotube in a liquid medium.
For instance, U. S. Patent S, 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.
U. S. Patent 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.
U.S. Patent 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.
U.S. Patent 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.
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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.
SITMMARY OF THE INVENTION
Inthis invention physical and chemical treatments are combined to derive a
metho d
of obtaining a stable nanotube dispersion.
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.
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 Iong 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
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"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.
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 Lady
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
stabilizationby electrolytes, and steric stabilizationbypolymeric surfactants
(dispersants).
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
(HI.,B) 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 Tonics. A preferred
dispersant for the
aqueous liquid medium is of high HLB value (HLB > 10), preferably a
nonylphenoxypoly(ethyleneoxy)ethanol-type surfactant. Of course, other alcohol
based
glycols having a high HLB value can be used as well. 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.
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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.
It is an object of the present invention to provide a method of preparing a
stable
dispersion ofthe carbonnanotube in a liquid mediumwiththe combined use of
dispersants
and physical agitation.
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.
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.
It is another object of the present invention to utilize a dispersant that is
soluble
for a selected liquid medium.
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.
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.
It is another object of the present invention to utilize a petroleum
distillate or a .
synthetic petroleum oil as the liquid medium.
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 HL,~
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(<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.
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.
It is another object of the present invention to utilize a liquid medium
consisting
of water or any water based solution.
It is another object of the present invention to utilize a dispersant having a
high
HLB (>10), preferably nonylphenoxypoly-(ethyleneoxy)ethanol-type surfactants.
It is another object of the present invention to utilize a uniform dispersion
with a
designed viscosity having a nanotube in petroleum liquid medium.
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.
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.
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.
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.
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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
The present invention provides a method a dispersing carbon nanotubes into a
liquid medium.
As set forth above, the nanotubes can be either single-walled, or mufti-
walled,
having a typical nanoscale diameter of 1-500 manometers. More typically the
diameter is
around 10-30 manometers. The length of the tube can be in submicron and micron
scale,
usually from 500 manometers to 500 microns. More typical length is 1 micron to
100
microns. The aspect ratio ofthe tube can be from hundreds to thousands, more
typical 500
to 5000. the carbon nanotubes, fibers, particles or combination thereof can be
utilized as
is from the production. The carbon nano particles comprising carbon nanotubes,
carbon
fibers, carbon particles or combinations thereof can be utilized as a
substrate in the present
invention' as is' as a commercial product straight from a commercial
production process.
A preferred embodiment of the instant invention was obtained using a nano
particle
product having the surface treated chemically to achieve certain level of
hydrophilicity by
an activated carbon treatment. Moreover, a certain level of hydrophilicity can
be
achieved by utilizing avapor disposition process using chemicals such as
hydrogen sulfide;
and/or by treatment with a strong acid or base.
A preferred embodiment utilized a carbon nanotube product obtained from
Carbolex at the University of Kentucky which contains amorphous carbon
particles and
which is believed to utilize an activated carbon treatment to improve the
level of
hydrophilicity. 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.
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Petroleum Basestocks Liquid Medium
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.
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.
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.
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, malefic
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
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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.
Esters usefizl as synthetic oils also include those made from CS to Clz
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.
Preferred polyalphaoleflns (PAO), include those sold byMobil Chemical company
as SHF fluids, and those sold by Ethyl Corporation under the name ETHYLFLO, or
ALBERMAFvLE. 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.
Mobil SHF-42 from Mobil Chemical Company, Emery 3004 and 3006, and
Quantum Chemical Company provide additional polyalphaolefins basestocks. For
instance, Emery 3004 polyalphaolefln has a viscosity of 3.86 centistokes (cSt)
at 212 °F.
(100 °C) and 16.75 cSt at 104 °F (40 °C). It has a
viscosity index of 125 and a pour point
of -98 °F and it also has a flash point of 432 °F and a fire
point of 478 °F. Moreover,
Emery 3006 polyalphaolefln has a viscosity of 5.88 cSt at +212 °F and
31.22 cSt at +104
°F. It has a viscosity index of 135 and a pour point of -87 °F.
It also has a flash point of
+464 °F and a fire point of +514 °F.
Additional satisfactory polyalphaolefins are those sold by Uniroyal Inc. under
the
brand Synton PAO-40, which is a 40 centistoke polyalphaolefln. Also useful are
the
Oronite brand polyalphaoleflns manufactured by Chevron Chemical Company.
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
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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.
Preferably the polyalphaolefins will have a viscosity in the range of about 2-
40
centistoke at 100°C, with viscosity of 4 and 10 centistoke being
particularly preferred.
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. Patent 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.
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.
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.
Also useful are polyol esters such as Emery 2935, 2936, and 2939 from Emery
Group ofHenkel Corporation andHatco 2352, 2962, 2925, 2938, 2939, 2970, 3178,
and
4322 polyol esters from Hatco Corporation, described in U.S. 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
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oxidation and hydrolytic stability. The polyol ester for use herein preferably
has a pour
point of about -100°C or lower to -40°C and a viscosity of about
2-460 centistoke at
100°C.
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.
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.
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.
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 U1VIVERSAL viscosity of 325 SUS @ 100°F
and
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ASHLAND 100 Neutral defined as a solvent refined neutral having a SABOLT
UNIVERSAL viscosity of 100 SUS @ 100°F, manufactured by the Marathon
Ashland
Petroleum.
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, P SI 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. Patent 5,348,668 to Oldiges.
Finally, vegetable oils may also be utilizes as the liquid medium in the
instant
invention.
Aqueous Medium
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
D~'~ persants used in Lubricant Industry
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
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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.
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 nitrite.
The lipophilic
group can be oligomeric or polymeric in nature, usually from 70 to 200 Gabon
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 malefic anhydride, or phosphorus sulfide or chloride, or by thermal
treatment, and
then with reagents such as polyamine, amine, ethylene oxide, etc.
Of these ashless dispersants the ones typically used in the petroleum industry
includeN-substitued polyisobutenyl succinimides and succinates,
allkylmethacrylate-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 9802A, and
the
whole DI package can be used as dispersing agent for the nanotube suspension.
For instance, LUBRIZOL 9802A is described in the technical brochure
(MATERIAL SAFETY DATA SHEET No. 1922959-1232446-3384064) by The
Lubrizol Corporation in Wickliffe, OH 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.
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LUBRIZOL 4999 is described in its Technical Brochure (MATERIAL SAFETY
DATA SHEET No. 1272553-1192556-3310026) by the Lubrizol Corporation in
Wickliffe, OH 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.
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.
IGEPAL CO-630 is described in Technical Brochure "MATERIAL SAFETY
DATA SHEET" from Rhodia Inc. and is hereby incorporated by reference. IGEPAL
CO-63 0 is described as a nonylphenoxy poly(ethyleneoxy) ethanol, branched
compound.
Other Types of Dispersants
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
Tonics, may be used in the instant invention.
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.
In both the water and oil based cases, the dispersants selected should be
soluble
or dispersible in the liquid medium.
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
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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.
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
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.
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
malefic
anhydride and then esterifying the intermediate using a mixture of alcohols.
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~
WSR
from Union Carbide, cellulose compounds such as carboxymethylcellulose,
polyvinyl
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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 resinpolymers such as polyvinyl
butyral resins,
polyurethane resins, acrylic resins and epoxy resins.
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
hydrolyzedkeratin, PPG-12/PEG-65 lanolin oil, dialkyl adipate,
alkylarylphosphate, 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.
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Physical Agitation
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.
LTltrasonication is the most preferred physical method inthe instant invention
since
it is less destructive to the carbon nanotube structure than the other methods
described.
LTltrasonication 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.
One dismembrator useful for preparing the instant invention is a Model 550
Sonic
dismembrator manufactured by Fisher Scientific Company, located in Pittsburgh
Pennsylvania. 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
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competing ultrasonic mixing devices could be utilized in accordance with the
present
invention.
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.
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 carbonnanotubeinto the dispersant containing
solutionwhile
strongly agitating, ball milling, or ultrasonication of the solution.
The present invention is further described and illustrated in the following
examples:
EXAMPLES
Example 1
Com onents ~ ~ Descri tion ~ ~Wei ht ercenta a
p______________________ I? _____________. .g_.d? ____~_.
Carbon nanotube Surface untreated, aspect ratio 2000, diameter 0.1
25 nm, length 50 ~m
Dispersant Lubrizol 9802A q..g
Liquid Poly(a-olefin), 6 cSt 95.1
Sonication Fisher Scientific 550 Sonic Dismembrator,
15 minutes
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Example 2
Components Description Weight percentage
Carbon nanotube Surface untreated, aspect ratio 2000, diameter 0.1
25 nm, length 50 ~,m
Dispersant Lubrizol 4999 4.8
Liquid Poly(a-olefin), 6 cSt 95.1
Sonication Fisher Scientific 550 Sonic Dismembrator,
15 minutes
Example 3
Com onents Descri tion ~ Wei ht ercenta a
_____P______________________1~______________.____~_.P_____~_.
Carbon nanotube Surface untreated, aspect ratio 2000, diameter 0.1
25 nm, length 50 ~,m
Dispersant OLOA 9061 4.8
Liquid Poly(a-olefin), 6 cSt 95.1
Sonication Fisher Scientific 550 Sonic Dismembrator,
15 minutes
Example 4
Components Description Weight percentage
Carbon nanotube Surface treated 0.1
Dispersant Igepal~ CO-630 5.0
Liquid Water 94.9
Sonication Fisher Scientific 550 Sonic Dismembrator,
15 minutes
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.
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
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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 .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 .Ol 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.
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 axt
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
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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.
