Note: Descriptions are shown in the official language in which they were submitted.
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2598R/B
Title: ELECTRORHEOLOGICAL FLUIDS CONTAINING CELLULOSE
AND FUNCTIONALIZED POLYSILOXANES
Field of the Invention
This invention relates to elecuorheological fluids. More particular-
- Iy, this invention relates to electrorheological flulds coQtsining cellulosic
particles as the dispersed particulate phase.
Backeround of the Invention
Electrorheological (ER) fluids are dispersions which can rapidly and
reversibly vary their apparent viscosity in the presence of an applied electric
fleld. The electrorheological fluids are dlspersions of finely divided solids inhydrophobic, electrically non-conducting oils and such fluids have the ability to
change their flow characteristics, even to the point of becoming solid, when
subjected to a sufflciently strong elecuical field. When the field is removed, the
fluids revert to their normal liquld state. Electrical DC fields and also AC fields
may be used to effect this change. The current passing through the electrorheo-
logical fluid is extremely low. Thus, ER fluids are used in applications in which
it is desired to control the transmission of forces by low elecuic power levels
such as, for example, clutches, hydraulic valves, shock absorbers, vibrators or
systems used for positioning and holding work pieces in position.
U.S. Patent 2,417,508 (issued in 1947 to Willis M. Winslow) disclosed
that certain dispersions composed of finely divided solids such as starch, carbon,
limestone, gypsum, flour, etc., dispersed in a non-conducting liquld such as a
lightweight transformer oil, olive oil or mineral oil, etc., would undergo an
increase in flow resistance when an electrical potential difference was applied
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to.the dispersion. This observation has been referred to as the Winslow Effect.
Subsequently, investlgators demonstrated that the increase in the flow resistance
was due not only to an increase in the viscosity, in the Newtonian sense, but also
to rheological changes in which the fluid displays a positive yield stress in the
presence of an electric field. This relationship is often described using the
Bingham plastic model. Yield stress is the amount of stress which must be
exceeded before the system moves or yields. The yield stress is a function of
electric field and has been reported to be llnear or quadratic, depending on fluid
composition and the experimental techniques. Measurement of yield stress can
be achieved by extrapolatlon of stress vs. strain curves, sliding plate, controlled
stress, or caplllary rheometers.
Electrorheological fluids which have been described in the
literature can be classlfied into two general categories: water containlng; and
those which do not require water. Although fluids were known to function
without water, for many years, It was believed that ER fluids had to contain
small quantities of water which were believed to be prlncipally associated with
the dispersed phase to exhiblt slgnificant ER properties. However, from an
application standpoint, the presence of water generally Is undesirable since it
may result in corrosJon, operating temperature limitations (loss of water at
higher temperatures), and significant electrlcal power consumption.
The present invention is concerned primarily with the preparation
of ER fluids which do not contain significant amounts of water and these are
hereinafter termed non-aqueous or substantially anhydrous ER fluids. U.S.
Patent 3,984,339 describes hydraullc oil compositions having a large Winslow
effect containing an electrical insulatlng oil, a water-soluble electrolyte, a liquid
having a high dielectric constant, and microcrystalline cellulose particles. While
water is a preferred liquid with a high dielectric constant, other liquids may be
used including formamide, methyl alcohol, ethyl alcohol, etc. Examples of
water-soluble electrolytes which are included in the hydraulic oil compositions
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in~lude all salts which are dissoclable into cations and anions such as, for
example, sodlum chloride, ammonium chloride, sodium hydroxide, etc.
U.S. Patent 4,645,614 describes electroviscous liquids based on a
mixture of an aqueous silica gel with silicone oil as a liquid phase to which a
dispersant is added. The dispersant consists of amino-functional, hydroxy-
functional, acetoxy-functional or alkoxy-functional polysiloxanes having a
molecular weight above 800. The concentration of the dispersant is from 1 to
30% by weight based on the weight of the silica gel particles. The electroviscous
suspensions described are reported to be hlghly compatible with elastomeric
materials.
- U.S. Patent 4,702,855 describes electroviscous fluids whlch are
composed of aluminum silicate particles in an electrically non-conductive liquidand a suitable dlspersing agent. The atomic ratio of aluminum to silicon on the
surface of the aluminum silicate is within the range of 0.15 to 0.80. In a
preferred embodiment, the dispersing agent is an amino-functional, hydroxy-
functional, acetoxy-functional or an alkoxy-functional polysiloxane havlng a
molecular weight above 800. The functional polysiloxanes are included in the
fluid at a concentration of I to 30% based on the weight of aluminum silicate
partlcles.
U.S. Patent 4,772,407 (European Patent Application 319,201)
describes an electrorheological fluid exhibiting desirable properties at low
current densitles and at hlgh temperatures In the complete absence of adsorbed
water or water of hydration. In one embodiment, the fluid comprises llthlum
hydrazJnium sulfate dJspersed in silicone oil and containlng an appropriate
suspenslon stablllzlng agent. Among the suspension stabilizers described are theamino-, hydroxy-, acetoxy-, or alkoxy-functlonalized polydimethyl siloxanes.
Block and graft copolymers are described which are also useful as stabilizing
agents.
Japan Published Application Hel-1-197595 describes electroviscous
fluids composed of silicone oil, an amino denatured sillcone oil or alcohol
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~~ denatured silicone oil, crystal cellulose, and a hydrophilic that may be either
water or alcohol. The silicone oils are polydimethyl silicone oils, and the
denatured sillcone oils are functionalized polydimethyl silicones where the
functional groups are amino or alcohol functional groups. All of the examples
S of the invention found in the published patent application comprise 100 parts of
straight silicone oil and 40 parts of the amino or alcohol denatured silicone oils.
In addition, the fluids contain from 50 to 200 parts of the crystal cellulose per
100 parts of the silicone mixture, and from 5 to 15 parts of water or alcohol per
100 parts of the silicone mixture. Examples of the alcohol include methanol and
ethylene glycol. Formic acid and formamide are also listed as examples of the
hydrophilic. In comparative Examples 21-24 the invention is compared to fluids
containing a mixture of 100 parts of the straight sllicone wlth 40 parts of either
epoxy functionallzed, carboxy functionallzed, polyether functlonallzed or
mercapto functionalized slllcones.
Japanese Published Application Hel-1-207396 describes electrovls-
cous fluids composed of a mlxture of sillcone oil and an amlno denatured or
alcohol denatured sillcone oil, a crystal cellulose and a muitl-functional alcohol
such as ethylene glycol, propylene glycol or butanedlol. The mlxtures of straJght
silicone and functlonallzed sllicones used in the inventlon comprise 100 parts of
the straight sillcone and 40 parts of the arnlno or alcohol functlonallzed sllicones.
lapan Publlshed Appllcation Hei-2-26633 descrlbes electrorheolog-
lcal flulds whlch are composed of a dlspersold that consists of hydrous sllicate,
a liquld phase that consists of non-conducting hydrophobic llquid, and disperslng
agent. Polyether denatured silicone oil or epoxy polyether denatured silicone oil
is utilized as a dlsperslng agent. The use of these denatured sllicone oils ls
reported to improve the stablllty of the electrorheological fluids. The dispersoid
content of the fluld Is generally 20 to 50%, the content of the dispersing agentis from 1 to 20%, and the remainder is a liquid phase.
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Summarv of the Invention
Electrorheological fluids are described which comprise a hydropho-
bic liquid phase, cellulosic particles as a dispersed phase and from about 0.1 up
to about 25% by weight, based on the weight of the hydrophobic liquid phase of
at least one functionalized polysiloxane containing at least one functional group
whlch Is capable of being absorbed or adsorbed on the surface of the cellulosic
particles. The electrorheological fluids of the invention are useful in a variety
of applications including flotational coupling devices such as clutches for
automobiles or industrial motors, transmissions, brakes or tension control
devlces; and linear damping devices such as shock absorbers, engine mounts and
- hydraulic actuators.
Detailed DescriDtion of the Invention
Unless otherwise specified in the disclosure and claims, the
following definitions are applicable. The term hydrocarbyr denotes a group or
substituent having a carbon atom directly attached to the remainder to the
molecule and having predominantly hydrocarbon character.
Examples of hydrocarbyl groups or substituents which can be useful
in connection wlth the present invention include the following: -
(1) hydrocarbon groups or substituents, that is allphatic (e.g.,
alkyl or alkenyl), allcyclic (e.g., cycloalkyl, or cycloalkenyl) substituents,
aromatic, aliphatic and alicyclic-substituted aromatic nuclei and the like, as well
as cyclic substituents wherein the ring is completed through another portion of
the molecule (that Is, for example, any two indicated substituents may together
form an allcyclic group);
(2) substituted hydrocarbon groups or substituents, that is, those
contalnlng nonhydrocarbon substituents which, in the context of thls invention,
do not alter the predominantly hydrocarbon character of the substituted group
or substituent and which do not interfere with the reaction of a component or donot adversely affect the performance of a material when It Is uset in an
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application within the context of this invention; those skilled in the art will be
aware of such groups (e.g., alkoxy, carbalkoxy, alkylthio, sulfoxy, etc.);
(3) hetero groups or substituents, that is, groups or substituents
which will, while having predominantly hydrocarbon character, contain atoms
other than carbon present in a ring or chain otherwise composed of carbon atoms.Suitable heteroatoms will be apparent to those of ordinary sklll in the art and
include, for example, sulfur, oxygen, and nitrogen. Moieties such as pyridyl,
furanyl, thiophenyl, imldazolyl, and the like, are exemplary of hetero groups orsubstituents. Up to two heteroatoms, and preferably no more than one, can be
present for each 10 carbon atoms in the hydrocarbon-based groups or substitu-
- ents.
Typically, the hydrocarbon-based groups or substltuents In this
invention are essentially free of atoms other than carbon and hydrogen and are,
therefore, purely hydrocarbon.
The HvdroDhobic Liauid Phase
The electrorheological fluids of the present invention comprise a
hydrophobic liquid phase whlch is a non-conducting, electric insulating liquid or
liquid mixture. Examples of Insulating liquids include silicone oils, transformer
oils, mineral oils, vegetable oils, aromatic oils, paraffin hydrocarbons, naphtha-
lene hydrocarbons, olefin hydrocarbons, chlorlnated paraffins, synthetic esters,hydrogenated olefin oligomers, and mixtures thereof. The hydrophobic llquid
phase selected for a particular ER fluid should be compatlble wlth the other
components, and the other components are preferably soluble In the hydrophoblc
llquld phase whlch may comprise mixtures of two or more of the above-ldentlfled
flulds. The cholce of the hydrophobic liquid phase also wlll depend In part uponthe Intended utlllty of the ER fluid. For example, the hydrophobic llquid shouldbe compatible wlth the environment in which it will be used. lf the ER fluid Is
to be In contact with elastomeric materials, the hydrophobic llquld phase shouldnot contaln oils or solvents which attack or swell, or, In some cases even dlssolve
elastomeric materlals. Additlonally, if the ER fluid is to be sub~ect to a wide
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,
~~ temperature range of, for example, from about -50C to about 150C, thehydrophobic liquid phase should be selected to provide a llquid and chemically
stable ER fluid over this temperature range and should exhibit an adequate
electrorheological effect over this temperature range. Suitable hydrophobic
liquids include those which are characterized as having a viscosity at room
temperature of from about 2 to about 300 or 500 centistokes. In another
embodiment, low viscosity liquids such as those having a viscosity at room
temperature of from 2 to about 20 or even 50 centistokes are preferred.
Mixtures of two or more different non-conducting electrically insulating liquidsmay be used for the hydrophobic liquid phase. Mixtures may be selected to
provide the desired viscosity, pour point, chemical and thermal stability,
component solubility, etc. For example, mixtures of hydrocarbons with
polysiloxanes may be used to dissolve hydrocarbon components such as the
viscosity modifiers discussed below.
Llquids useful as the hydrophobic continuous liquid phase generally
are characterized as having as many of the following properties as possible: (a)high bolling point and low freezing point; (b) low viscosity so the ER fluid has a
low no-field vlscoslty and greater proportions of the solid dispersed phase can be
Included in the fluid; (c) high electrical resistance and high dielectric breakdown
potential so that the fluid will draw little current and can be used over a widerange of applled electric field strengths; and (d) chemlcal and thermal stability
to prevent degradation on storage and service.
Slllcon-based oils such as the polyalkyl-, polyaryl-, polyalkoxy-, or
polyaryloxysiloxane oils and silicate oils comprise a particularly useful class of
synthetic hydrophobic liguids. Examples of silicate oils include tetraethyl
silicate, tetraisopropyl silicate, tetra-(2-ethylhexyl) silicate and tetra-(4-methyl-
2-ethylhexyl) silicate, tetra-(p-terbutylphenyl) silicate. The silicone or siloxane
oils are useful particularly in ER fluids which are to be in contact with
elastomers.
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In one embodiment, the silicone-based oils are polysilicones such
as alkyl phenyl sillcones or siloxanes. The alkyl phenyl sillcones can be prepared
by the hydrolysis and condensatlon reactions as described in the art such as, for
example, in An Introduction to the Chemistrv of the Silicones, by Eugene G.
Rochow, John Wiley & Sons, Inc., New York, Second Edltion (1951).
The silicone-containing fluids may be polysiloxanes having units of
the general formula
Rnsi4-n/2
- wherein n has a ~rslue from about 1.1 to about 2.9 and each R is independently
an organyl group. Some examples of such organyl groups are hydrocarbons
including allphatlc groups, e.g., methyl, propyl, pentyl, hexyl, decyl, etc.,
alicyclic groups, e.g., cyclohexyl, cyclopentyl, etc., aryl groups, e.g., phenyl,
naphthyl, etc., aralkyl groups, e.g., benzyl, etc., and alkaryl groups, e.g., tolyl,
xylyl, etc.; the halogenated, oxygen-containing, and nitrogen-containing organylgroups including halogenated aryl groups, alkyl and aryl ether groups, aliphaticester groups, organic acid groups, cyanoalkyl groups, etc. The organyl groups,
In general, contain from I to about 30 carbon atoms.
Of particular interest are polysiloxane fluids containing organo-
siloxane units of the above formula wherein R is selected from the group of (a)
alkyl groups, e.g., methyl, (b) mixed alkyl and aryl, e.g., methyl and phenyl
groups"n a mole ratio of alkyl to aryl from about 0.5 to about 25, (c) mixed
alkyl and halogenated aryl groups, e.g., chlorinated, brominated phenyl, in a mole
ratio of alkyl to halogenated aryl of from 0.5 to about 25 and mlxed alkyl, aryland halogenated aryl groups in a mole ratio of alkyl to total aryl and halogenated
aryl from about 0.5 to about 25. The halogenated aryl groups ln all cases contain
from 1-5 halogen atoms each. These sillcone fluids may, of course, also be
physical mixtures of one or more of the polysiloxanes in which R Is as deflned
above.
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g
~~ In one preferred embodiment, the hydrophobic liquid phase
comprises non-functionalized polysiloxanes. The polysiloxanes may contain vinyl,alkyl, alkaryl, cycloalkyl or aryl groups, or mixtures of such groups, attached to
the silicon atoms. The alkyl and alkaryl groups may contain from I to about 20
carbon atoms; the cycloalkyl groups may contain from 5 to about 9 carbon atoms;
and the aryl groups may contain from 6 to about 8 carbon atoms. Examples of
such alkyl groups include methyl, ethyl, propyl, butyl, hexyl, octyl, dodecyl,
octadecyl, 2-phenyl propyl, etc. Examples of cycloalkyl groups include
cyclopentyl, cyclohexyl, cyclooctyl, etc. Examples of aryl groùps include phenyl,
benzyl, styryl, tolyl, etc.
Speciflc examples of alkyl siloxanes useful as the hydrophobic liquid
phase incJude: polydimethylsiloxane; polymethylethylslloxane; poly-
vinylmethylsiloxane; polydiethylsiloxane; polymethylhexylsiloxane;
polymethyloctylsiloxane; polymethyloctadecylsiloxane; polymethyl-
tetradecylsiloxane; polymethylhexadecylsiloxane; polymethylcyclohexylsil-
oxane.
Preferred silicone oils generally have a viscosity at 25C of from
about 1 up to about 300 or 500 or about 100 centlstokes. In another embodlment,
low viscosity oils (e.g., about 2 to about 20 or even 50 centistokes) are used
because an ER fluid with a lower zero field viscosity is obtained so that
substantial changes In viscosity can be obtained by means of the ER effect.
The alkyl phenyl silicon base oils useful in the present invention
may be represented as containing repeating units represented by the general
formula
~ Rl
si-o J
~R2
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~- wherein Rl is an alkyl group containing from I to about 6 carbon atoms and R2
is a hydrogen atom, halogen, or an alkyl group containing from I to 3 carbon
atoms.
Specific examples of the alkyl phenyl polysiloxanes of the type
containing the repeating structure (Il) include methyl phenyl silicone, methyl
tolyl silicone, methyl ethyl phenyl silicone, ethyl phenyl silicone, propyl phenyl
silicone, butyl phenyl s;licone and hexyl propyl phenyl sillcone.
The alkyl phenyl silicones of the type described above generally are
characterized as having molecular weights within the range of about 500 to 4000.Generally, however, the slze of the molecule is not expressed with reference to
the molecular weight, but, rather, by reference to a viscosity range. For
example, the alkyl phenyl silicones useful in the present Invention may have
kinematic viscosities ranging from about 10 to about 2000 centistokes at 25C.
Alkyl phenyl silicones of the type useful in the present invention
are commercially available from Dow Corning Corporation, the General Electric
Company and others. Specific examples of methyl phenyl silicones which may
be employed in the present invention include SF-1153 from General Electric
Company having a viscosity at 25C of 100 centistokes. Another synthetic
silicone is a methyl phenyl polysiloxane sold by General Electric Company under
the tradename SF-1038. The viscosity of thls material at 25C ranges from
about 50 to about 500 centistokes. Other methyl phenyl polyslloxanes are those
marketed by Dow Corning as Dow Corning 550 Fluid which has a viscosity at
25C of about 100 to 150 centistokes, and Dow Corning 710 Fluid having a
viscosity at 25C of about 500 centistokes. Alkyl phenyl silicones also are
available from the Toray Company Ltd., under such designations as silicone
SH500 (30 centistokes), and silicone SH203 (150 centistokes), and these are
reported to be meti y1 phenyl silicone and hexyl 4-propylphenyl silicone,
respectively.
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Various natural and synthetic liquids can also be used alone as the
hydrophobic liquid phase or in combination with any of the silicones described
above.
Oleaginous liquids such as petroleum derived hydrocarbon fractions
may be utilized as the hydrophobic liquid phase in the ER fluids of the invention.
Natural oils are usefùl and these include animal oils and vegetable oils (e.g.,
castor, lard oil, sunflower oil) liquid petroleum oils and hydrorefined, solvent-
treated or acid-treated mineral lubricating oils of the paraffinic, naphthenic and
mixed paraffinic-naphthenic types. Oils deri~ed from coal or shale are also
useful oils.
- Alkylene oxide polymers and interpolymers and derivatives thereofwhere the termlnal hydroxyl groups have been modified by esterification,
etherification, etc., constitute another class of known synthetic lubricating oils.
These are exemplified by polyoxyalkylene polymers prepared by polymerization
of ethylene oxide or propylene oxide, the alkyl and aryl ethers of these
polyoxyalkylene polymers (e.g., methyl-poly isopropylene glycol ether having an
average molecular weight of 1000, diphenyl ether of poly-ethylene glycol having
a molecular weight of 500-1000, diethyl ether of polypropylene glycol having a
molecular weight of 1000-1500); and mono- and polycarboxyllc esters thereof, forexample, the acetic acid esters, mixed C3-C8 fatty acld esters and C13 Oxo acid
diester of tetraethylene glycol.
Another suitable class of synthetic lubrlcating llquids comprises the
esters of dlcarboxylic acids (e.g., phthalic acid, succinic acid, alkyl succinic acids
and alkenyl succinic acids, maleic acid, azelaic acid, suberic acid, sebasic acid,
fumaric acid, adipic acid, linoleic acid dimer, malonic acid, alkylmalonic acids,
alkenyl malonic acids) with a variety of alcohols and polyols (e.g., butyl alcohol,
hexyl alcohol, dodecyl alcohol, 2-ethylhexyl alcohol, ethylene glycol, diethylene
glycol, monoether, propylene glycol). Specific examples of these esters include
dibutyl adipate, di(2-ethylhexyl) sebacate, di-n-hexyl furnarate, dioctyl sebacate,
diisooctyl azelate, diisodecyl azelate, dioctyl phthalate, dldecyl phthalate,
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-12-
dieicosyl sebacate, the 2-ethylhexyl diester of linoleic acid dimer, and the
complex ester formed by reacting one mole of sebacic acid with two moles of
tetraethylene glycol and two moles of 2-ethylhexanoic acid.
Esters useful as the hydrophobic liquid phase also include those
made from C5 to C12 monocarboxylic acids and polyols and polyol ethers such
as neopentyl glycol, trimethylolpropane, pentaerythritol, dipentaerythritol and
tripentaerythritol.
Polyalpha olefins and hydrogenated polyalpha olefins (referred to
in the art as PAO) are useful in the ER fluids of the invention. PAOs are derived
from alpha oleflns containing from 2 to about 24 or more carbon atoms such as
ethylene, propylene, I-butene, isobutene, I-decene, etc. Speciflc examples
include polyisobutylene having a number average molecular welght of 650; a
hydrogenated oligomer of l-decene having a viscosity at 100~C of 8 cst;
ethylene-propylene copolymers; etc. An example of a commercially available
hydrogenated polyalpha olefin is Emery 3004.
Other synthetic llquids include liquid esters of phosphorus-
containing acids such as tricresyl phosphate, trioctyl phosphate and the diethylester of decylphosphonic acid.
Other specific examples of hydrophobic liquids which may be
utilized in the ER fluids of the present invention include, for example, mineraloil, di-(2-ethylhexyl) adipate; di-(2-ethylhexyl) maleate; dibenzylether,
dibuty1carbitol; di-2-ethylhexyl phthalate; I,1 -diphenylethane; tripropylene glycol
methyl ether; butyl cyclohexyl phthalate; di-2-ethylhexyl azelate; tricresyl
phosphate; trlbutyl phosphate; tri(2-ethylhexyl) phosphate; penta-chlorophenyl
phenyl ether; brominated dlphenyl methanes; olive oil; xylene; toluene, etc.
Commerclally avallable oils whlch may be used in the ER fluids of the Invention
include: Trisun 80 oil, a high oleic sunflower oil from The Lubrizol Corporatlon;
Emery 3004, a hydrogenated polyalpha olefin; Emery 2960, a synthetic
hydrocarbon ester; and Hatco HXL 427, believed to be a synthetic ester of a
monocarboxylic acid and a polyol.
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The amount of hydrophobic liquid phase in the ER fluids of the
present invention may range from about 20% to about 90 or 95% by weight.
Generslly, the ER fluids will contain a major amount of the hydrophobic liquid,
i.e., at least 51% by weight. More often, the hydrophobic liquid phase will
S comprise from about 60 to about 80 or 85% by weight of the ER fluid.As noted above, the hydrophobic liquid phase may be prepared from
mixtures of two or more of the above-described liquids and oils. For example,
the hydrophobic liquid phase may comprise from about 10 to 90 parts of one
liquid such as a polyol ester and 10 to 90 parts of a second llquid such as a
silicone fluid. Other useful welght ratios may be from 20:80 to 50:50.
The Cellulosic DlsDersed Particulate Phase
The electrorheological fluids of the present invention contain
cellulosic partlcles as a dispersed phase. The term "cellulosic particles" as used
throughout this application includes cellulose as well as derivatives of cellulose
as are described more fully below. The amount of the cellulosic particles
included in the ER fluids of the present inventlon may vary over a wide range
such as from about 5, 10 or 20% up to about 40, 49, 60 or even 80% by weight
based on the weight of the ER fluid. More often, the ER fluids will contain lessthan about 60% by weight of the dispersed phase, and In another embodiment, the
ER fluids contain a minor amount (i.e., up to about 49%) of the dispersed phase.The cellulosic particles utilized In the ER fluids of the present
invention may be in the form of powders, flbers, spheres, rods, etc. In one
embodiment, the cellulosic particles utilized In the present Inventior. are
microcrystalline cellulose particles. Mlcrocrystalline cellulose as used herein,is the insoluble residue obtained from the chemical decompositlon of natural or
regenerated cellulose. Crystalllte zones appear in regenerated, mercerlzed and
alkallzed celluloses, differlng from those found Jn natlve cellulose. By applying
a controlled chemical pretreatment to destroy molecular bonds holding these
crysta111tes, followed by mechanlcal treatment to dlsperse the crystallltes in
aqueous phase, smooth colloidal microcrystalllne cellulose gels with commercial-
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--14--
Iy important functional and rheological properties can be produced. More
particularly, in the hydrolysis of cellulose, the amorphous portlons of the original
cellulose chains are dlssolved, and the undissolved portions are in a particulate,
non-fibrous or crystalline form as a result of the disruption of the continuity of
the fine structures between crystalline and amorphous regions of the original
cellulose. Microcrystalline cellulose or cellulose crystallite aggregates resulting
from the hydrolysis and washlng steps are subjected to a mechanical dlsintegra-
tion to produce a material havlng particle sizes In the range of less than I up to
about 250 or 300 microns. Within this range, the particle size and size
distributlon are varlable, It being understood that the size and slze dlstrlbutlon
can be selected to sult a particular end use.
Mlcrocrystalline cellulose prepared in this manner is characterlzed
by its extremely low content of ash whlch is attributed to the fact thst
microcrystalline cellulose has almost no amorphous region, and, accordingly,
inorganic ash contained chiefly in the amorphous regions has been dissolved and
removed. The water content of the cellulose used in the ER flulds of the presentinvention may be reduced by drylng the cellulose for an extended period at
temperatures from about 50C to about 150C, generally under vacuum.
Amorphous cellulose is also- useful, and examples of useful
'20 arnorphous cellulose particles, are CFl, CFIl and CC31 avallable from Whatman
Speclalty Products Divislon of Whatman Paper Limited, Maldstone Kent, ME
142LE. CFI is Identlfled as a long flber powder cellulose wlth a fiber length of100-400 micron and a mean dlameter of 20-25 ,um. CFII ls a medlum fiber
amorphous powder cellulose with a flber length range of from 50 to 250 micron
and a mean dlameter of 20 to 25 ~m. CC31 is Identifled as a very pure
microgranular powder cellulose. The ash content of these three cellulose
materlais Is about 0.015%. Useful cellulose particles are aiso avallable from the
James RlYer Corporatlon, Cellulose Floc Division, Hackensack; New Jersey 07601
under the general deslgnatlon Solka-Floc. Examples of varlous'grades of Solka-
Floc avallable Include AS-1040 (average fiber length 160 mlcrons and ash content
2~9~126
,5
of 0.05%); SW-40 (average fiber length 120 microns and ash content of 0.15%);
BW-100 (average fiber length 40 microns and an ash content of 0.2196); BW-300
(average fiber length 22 microns and 0.22% ash). An example of useful the
microcrystalline celluloses are those available from FMC Corporation, Food and
Pharmaceutical Products Division, Philadelphia, PA under the designation
LATTlCElM NT-103 having an average particle size of 25 microns.
Cellulose derivatives may also be utilized as the dispersed phase
in the ER fluids of the present invention. Among the useful derivatives are the
ethers and esters of cellulose. Specific examples of cellulose ethers include
methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose,
- and sodium carboxymethyl ce11ulose. Examples of cellulose esters include
cellulose proplonate, cellulose butyrate, cellulose valerate, cellulose triacetate,
etc. These cellulose ethers and esters are available commercially in a variety
of molecular welghts, and the particular molecular weight chosen for use in the
ER fluids of the present inventlon may be varied over a wide rsnge depending on
the particular derlvative utilized. Examples of such derivatives useful in the ER
fluids of the present invention include METHOCEL A (methylcellulose), and
METHOCEL E ~hydroxypropyl methyl cellulose) from Dow Chemical,
hydroxyethyl cellulose having a molecular weight of 90,000 to 105,000, sodium
carboxymethyl cellulose having a molecular weight of about 700,000, etc.
Naturally occurring celluloslcs also can be used in the ER fluids.
These include chltan, chitosan and chondrointon sulfate. Viscose or cellulose
xanthate obtained by reacting cellulose with an alkali and thereafter with carbon
disulflde can also be used as a celluloslc derlvatlve in this invention.
Other cellulose derivatives which may be utlllzed as the cellulosic
particles in the ER fluids of the present invention include cellulose phosphatesand cellulose reacted with various amine compounds eplchlorohydrin triethanol-
amine reaction products; etc. Examples of commercially available amine
contalnlng derivatives of cellulose Include ECTOLA cellulose (epichlorohydrin
trlethanolamlne); DEAE cellulose ~dlethylaminoethyl cellulose); PEI cellulose
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(polyethyleneamine cellulose); QAE cellulose (diethyl-12-hydroxypropyll
aminoethyl cellulose); and TEAE cellulose (triethylaminoethyl cellulose).
Cellulose phosphate is another useful derivative and is available from Sigma
Chemical Company.
Cellulose derivatlves also include cellulose rescted with or coated
with various slllcon compounds Including, for example: dlmethyl silicone in the
presence of a catalyst such as dl-t-butyl peroxide; epoxy slllcone such as GP-167
in the presence of a catalyst such as a base (e.g., NaOH); and tetramethyl or
tetraethyl orthosilicate in the presence of water, methanol and phosphoric acld
as a cata1yst.
The cellulose derivatives which may be utilized as cellulosic
particles in the ER fluids of the present invention also may be copolyrners of
cellulose obtained by grafting of various polymers to cellulose. For example,
cellulose may be grafted with polymerizable monomers such as acrylamides,
acrylonitriles, acrylic acids, esters or salts, methacrylic aclds, esters or salts,
and
(a) a sulfo acid monomer such as represented by the formula
(Rl)2C=c(Rl)Qazb (A)
wherein each Rl is Independently hydrogen or a hydrocarbyl group;
a Is 0 or 1; b is I or 2, provided that when a is 0, then b is 1;
Q is a dlvalent or trivalent hydrocarbyl group or C(X)NR2Q;
each R2 '5 independently hydrogen or a hydrocarbyl group;
Q is a dlvalent or trlvalent hydrocarbyl group;
X is oxygen or sulfur; and
Z is S(O)OH, or S(O)2OH; or
(b) a polymer of at least one of said monomers.
In Formula A, Rl and R2 are each Independently hydrogen or
hydrocarbyl. In a preferred embodlment, Rl and R2 are eich independently
hydrogen or an alkyl group havlng from I to 12 carbon atoms, preferably to about
2099126
-17-
6, more preferably to about 4. In a preferred embodiment, Rl and R2 are each
independently hydrogen or methyl, preferably hydrogen.
Q is a divalent or trivalent hydrocarbyl group or C(X)NR2Q'. Q'
is a dit~alent or trivalent hydrocarbyl group. The divalent or trivalent hydrocar-
byl groups Q and Q' include alkanediyl (alkylene), alkanetriyl, arenylene (arylene)
and arenetriyl groups. Preferably, Q is an alkylene group, an arylene group or
C~H)(NR2)Q'. The hydrocarbyl groups each ir,dependently contain from 1,
preferably from about 3 to about 18 carbon atoms, preferably up to about 12,
more preferably to about 6, except when Q or Q' are aromatlc where they
contain from 6 to about 18 carbon atoms, preferably 6 to about 12. Examples
of di- or trivalent hydrocarbyl groups include di- or trivalent methyl, ethyl,
propyl, butyl, cyclopentyl, cyclohexyl, hexyl, octyl, 2-ethylhexyl, decyl, benzyl,
tolyl, naphthyl, dimethylethyl, dlethylethyl, and butylpropylethy} groups,
preferably a dimethylethyl group.
In one embodiment, Q is C(X)NR2Q' and Q' is an alkylene having
from about 4 to about 8 carbon atoms, such as dimethylethylene.
Specific ex-amples of useful sulfo acid monomers include vinyl
sulfonic acid, ethane sulfonic acid, vinyl naphthalene sulfonic acid, vinyl benzene
sulfonic acid, vlnyl anthracene sulfonic acid, vlnyl toluene sulfonic acid, methalyl
sulfonic acid, 2-methyl-2-propene-1-sulfonic acid and acrylamido hydrocarbyl
sulfonic acld. A particularb useful acrylamido hydrocarbyl sulfo monomer is 2-
acrylamido-2-methyl propane sulfonic acid. This compound is available from The
Lubrizol Corporation, Wickliffe, Ohio U.S.A. under the trademark AMPS
Monomer. Other useful acrylamido hydrocarbyl sulfo monomers Include 2-
acrylamldo methane sulfonic acid, 2-acrylamido propane sulfonic acid, 3-
methylacrylamldo propane sulfonic acid and I, I -bis(acrylamldo)-2-methyl
propane-2-sulfonic acid.
Specific examples of other monomers whlch can be copolymerlzed
with cellulose include acrylamide, methacrylamide, methylenebis(acrylamide),
hydroxymethylacrylamide, acrylic acid, methacrylic acid, methyl acrylate, ethyl
2099126
--18--
acrylate, butyl acrylate, 2-ethylhexyl acrylate, hydroxyethyl acrylate, hydroxy
butyl acrylate, crotonic acid, methylcrotonate, butylcrotonate,
hydroxyethylcrotonate, etc. Alkali or alkaline earth metal salts (preferably
sodium, potassium, calcium or magnesium) of acrylic, methacrylic or crotonic
acids may also be used. Substituted and unsubstituted vinyl pyrrolidones and
vinyl lactams such as vinyl caprolactam may also be used as monomers. The
amount of the comonomer reacted with cellulose may range from about 1% up
to about 25 or 50% and even up to about 75% by weight based on the weight of
the cellulose.
The cellulosic derivatlves useful in the ER fluids of the present
- invention also may be block or random polymers obtained by reactlng cellulose
with other polymers such as styrene-maleic anhydride copolymers In the presence
of catalysts. For example, cellulose can be reacted wlth a styrene maleic
anhydride copolymer in varying ratios in the presence of a catalyst such as 4-
N,N-dimethylaminopyridine.
The preparation of cellulosic derivatives which comprise the
reaction products of cellulose with polymerizable monomers and polymers is
illustrated in the following examples.
Exam~le A-l
A reaction vessel is charged with 40 parts (0.247 mole) of Solka
Floc BW-I00 cellulose and 500 parts of water. The mixture is stirred and purged
with nitrogen, and 20.7 parts (0.1 mole) of AMPS monomer are added. Ceric
ammonium nitrate (12 parts of a 0.1 molar solutlon in 1 Normal of nitric acid)
is added, and after about 6 hours, the mixture is allowed to stand overnight
without stirring. An additional 2 ml. of the ceric ammonium nitrate solution areadded with stirring and the mixture was then allowed to stand over the weekend.
The reaction mixture is filtered, and the residue Is washed with distilled waterand dried in a steam chest followed by drying in a vacuum oven at 110C for 6
hours.
2099126
,9
Exampie A-2
A reaction vessel is charged with 40.5 parts (0.25 mole) of Solka
Floc BW-I00 cellulose and 400 parts of water. The mixture is stirred and purged
with nitrogen whereupon 5 parts of a 0.1 molar solution of ceric ammonium
nitrate in I Normal nitric acid are added followed by the addition of 7.1 parts
of acrylamide as a solid. After about 3 hours, another 5 parts of the ceric
ammoniurn nitrate solution are added and stirring is continued overnight. The
reaction mixture is then filtered, and the residue is washed with water, dried In
a steam chest for 16 hours and then In a vacuum oven at 120C for 18 hours.
The product obtainR in this manner contains 0.99% nitrogen.
ExamDle A-3
A reaction vessel is charged with 40.5 parts (0.25 mole) of CF-I I
cellulose, 7.1 parts of acrylamide (0.1 mole) and 300 parts of water. The mixture
is s~irred and purged with nitrogen whereupon 10 parts of a 0.1 molar solution of
ceric ammonium nitrate in I Normal nitric acid are added over a period of 2.5
hours. Stirring is continued overnight and the reaction mixture is filtered. The-residue thus obtained is washed with water and dried in air. The solid is
transferred to an aluminum dish and dried in a steam chest for 2 days and in a
vacuum oven at 120C for 18 hours. A wbite solid is obtained which contains
1.91% nitrogen.
ExamDle A-4
A reaction vessel is charged with 40.5 parts (0.25 mole) of CF-11
cellulose, 17.8 parts of acrylamide (0.25 mole) and 300 parts of water. The
mlxture is stirred and purged with nitrogen for I hour whereupon 10 parts of a
0.1 molar ceric ammonium nitrate solution in I Normal nitrlc acid are added overa period of 2 hours and 15 minutes. The mixture is stirred overnight and then
filtered. The residue is washed with water, dried in air for 2 hours, dried in asteam chest for 16 hours, and finally dried in a vacuum oven at 120C for 16
hours. A white solid is obtained which contains 4.85% nitrogen (theory, 6.0%).
2~99~26
-20-
~- Examole A-5
A reaction vessel is charged with 400 parts of water and 197 parts
(0.5 mole) of an aqueous solution containing 58% by weight of the sodium salt ofAMPS monomer. The pH of the mixture is adjusted to about 4.0 by adding about
0.6 part of AMPS monomer. To the reaction mixture there is an added 81 parts
(0.5 mole) of CF-ll cellulose. The reaction mixture is stirred and purged with
nitrogen, and after about 1 hour, 10 parts of 0.1 molar solution of ceric
ammonium nitrate in 1 Normal nitric acid are added over a period of about 2.5
hours. The mixture is stirred for about 36 hours, transferred Into a glass dish and
dried in a steam chest followed by drying in a vacuum oven at 125C for 24
hours. The dried material Is milled for 24 hours and flltered through a 45 mesh
sieve. A white powder is obtained which contains 3.48% nitrogen (theory, 3.59),
7.89% sulfur (theory, 8.21), and has a sulfate ash content of 17.65% (theory,
18.09).
ExamDle A-6
A reaction vessel is charged with 81 parts (0.5 mole) of CF-11
cellulose, 200 parts of water and 14.4 parts (0.2 mole) of acrylic acid. The
mixture is stirred and purged with nitrogen whereupon 10 parts of a 0.1 molar
ceric ammonium nitrate solution in 1 NormaL nitric acid sre added over a period
of about 2 hours. StJrring is continued for about 2 days and the mixture is
filtered. The residue is washed with water and dried in air for 24 hours. The
resldue then is dried in a steam chest for several days and then ball-milled for6 hours to yield the desired product.
ExamDle A-7
A reactlon vessel is charged with 81 parts (0.5 mole) of CF-ll
cellulose and 400 parts of toluene. The mixture is heated to a temperature of
about 108C while purging with nitrogen. After cooling to room temperature,
76.5 parts (0.1 mole) of a toluene solution containing 26.5% by weight of a
maleic snhydrlde styrene copolymer (0.42 RSV) and 0.2 parts (0.0016 mole) of 4-
N,N-dimethylaminopyridine catalysts are added. The mixture is heated to about
2099126
--21--
-- 60C, and after about 2 hours, 10 parts of dimethylformamide are added to the
mixture. Heating is continued with stirring for about 3 days. After cooling to
room temperature, the mixture is filtered, and the residue is washed with
toluene. The residue then is dried in a steam chest for about 4 days. A white
S powder is obtained.
The Func~ionalized PolYsiloxane
The electrorheological fluids of the invention contain from about
0.1% up to about 25% by weight, based on the weight of the hydrophobic liquid
phase of at least one functionalized polysiloxane. The functionalized
polysiloxanes utilized in the ER fluids of the present invention are useful for
improvlng the dispersion of the sollds throughout the vehlcle; in malntalnlng the
stability of the dlspersions; Increasing the strength of the ER response; and, In
some instances, moderating the conductivity of the ER fluid. Preferably, the
functionalized polysiloxanes are soluble in the hydrophobic liquid phase. The
functionalized polysiloxanes contain at least one functional group capable of
being absorbed or adsorbed on the surface of the cellulosic particles contained
in the ER fluids.
In one embodiment, the functional groups in the functionalized
polysiloxanes used in the electrorheological-fluids of this invention include the
amJno, amldo, imlno, sulfonyl, sulfoxyl, cyano, hydroxy, hydrocarbyloxy,
mercapto, carbonyl (including aldehydes and ketones), carboxy, epoxy, acetoxy
phosphate, phosphonyl and haloalkyl groups. These polysiloxanes generally have
a molecular welght above 800 up to 10,000 or 20,000.
The functional polyslloxanes may be linear or branched dlorgano
polysiloxanes as represented generall~ by Formulae I and 11, respectively.
Y~SiO~2O~--Si Y3 or ~1)
m n
2099126
YI~SIiO~ liO~IiO~ i Y3 (Il)
P I P
(X-Si-13
O p
X-Si-X
wherein each X is independently an alkyl, aryl or cycloalkyl group, each of yl
to Y3 is independently X or a functional group capable of being absorbed or
adsorbed on the swface of the cellulosic particles provided that at least one ofYl to Y3 Is not X, m is a number from about 10 to about 1000, n is a number
from 0 to about 10, and each p Is independently a number from 0 to about 1000
provided that at least one p is at least about 10.
Specific examples of functional groups Yl-Y3 in the abo~re formulae
include amino, amido, imino, sulfonyl, sulfoxyl, cyano, hydroxy, hydrocarbyloxy,mercapto, carbonyl, carboxy, epoxy, acetoxy, phosphate, phosphoryl, or haloalkylfunctional groups, or salts or mixtwes of such groups. When Yl and/or Y3 are
functlonal groups and y2 is X in Formula î, the polyslloxanes or siloxanes are
referred to as terminally functionalized slloxanes. When yl and Y3 are X and
y2 is a functional group in Formula 1, the siloxanes are referred to as Internally
functionallzed sillcones.
Throughout thls speclficatlon, It is to be understood that the
Internal functional groups y2 In Forrnula I (and IA) may be distrlbuted randomlywithin the polyslloxane chaln, and the representation of the slloxane in Formulae
such as I and IA should not be interpreted as requiring that all of the SiO groups
having a functlonal group y2 are attached In sequence in a block.
209~126
In one embodlment, each X group is Independently selected from
alkyl or alkaryl groups hav~ng from 1 to about 20 carbon atoms such as methyl,
ethyl, vinyl, propyl, butyl, isopropyl, hexyl, dodecyl, octadecyl, or 2-phenylpropyl
groups. Examples of cycloallphatic X groups include cyclopentyl, cyclohexyl, or
cyclooctyl groups. Alternatively, X may be an aryl group containing from 6 to
about 8 carbon atoms such as phenyl, benzyl, styryl, tolyl and xylyl.
Values of m, n and p in Formulae I and 11 may be varied as
indicated above to provide polysiloxanes having desirable molecular weights. Thevalue of n also may be varied to provide functionalized polysiloxanes having an
increased or decreased functional group content.
In another preferred embodiment, the functional polysiloxanes
which are useful in the ER fluids of the present invention include polysiloxanesas represented by the following formulae
YI ~SiO 3~y2 ~ Si _y3, Or (IA)
m n
CH3~ CH3~ CH3
CH3 CH3 CH3
P~ I P
~CH3-SI-CH3)
O. P
CH3-Si-CH3
y2
whereln each of Yl-Y3 Is independently an alkyl or a functional group selected
from -R'N(R)2, -R'OR2, -R'SH, or -R'COOH, or salts thereof, wherein R' is a
2099126
-24-
divalent group consisting of C, H and optionally O and/or N; each R is indepen-
dently hydrogen or an alkyl group contalning I to about 8 carbon atoms; R2 is
hydrogen, an alkyl or aryl group containing up to about 8 carbon atorns,
propylenyloxide, -(C2H4O)a-(C3H6o)b-R3 wherein a and b are independently
numbers from 0 to 100 provided at least one of a or b is at least 1; R3 is H,
acetoxy, or a hydrocarbyl group; m is a number from about 10 to about 1000; n
is a nurnber from 0 to about 10, each p is independently a number from 0 to
about 1000 provided that at least one p is at least 1; and further provided thatat least one of yl_y3 is not an alkyl group; or Y' and y2 in Formula I are methyl
groups and Y3 is an alkylene oxide polymer block.
The R group in the above formulae is a divalent group conslstlng
of carbon, hydrogen and optionally oxygen and/or nitrogen whlch may be an
aliphatlc or cycloaliphatic group. Thus, the dlvalent R group may be an alkyleneor cycloalkylene group, oxyalkylene or oxycycloalkylene group, or an amino
alkylene or amino cycloalkylene group attached to the silicon atom. Specific
examples of R include -CH2-, -CH2CH2-, -CH2-CH2-CH2-, cyclohexylene,
CH2CH2 . -OCH2CH2CH2-, -NCH2cH2-~ -cH2cH2cH2N(H)cH2-cH2-~ etc
In one embodiment, R is a divalent group containing from I to about 3 carbon
atoms.
The functional groups whlch may be present in the polyslloxanes
useful In thls Inventlon include amino groups. The amino functlonal groups may
be characterized by the partial formula -R N(R)2 whereln R is as defined above
and each R is independently hydrogen or an alkyl group containing from I to
about 8 carbon atoms or an aryl group containing 6 to about 8 carbon atoms. The
terms amino group or amino functlonal group as used In thls application
Include the above-identified amines and salts thereof including quaternary saltswhlch may be obtained by technlques known to those skilled in the art. Speclfic
examples of amlno functlonal groups whlch may be present on the polysiloxanes
used in the present inventlon Include -CH2NH2, -CH2N(H)CH3, -CH2N(H)C6HI I,
-CH2CH2CH2NH2, -CH2CH2CH2N(CH3)2, -cyclohexylamine, -OCH(CH3)CH2NH2,
2099126
-25-
OCH(CH3)CH2CH2NH2, -C3H6N(H)C2H4NH2~ -CH2CH2CH2N-(CH3)H CH3-
cOOe, etc. An example of a cornmerclally available amine terminated
polysiloxane is PS510 from Petrarch Systems, Bristle, Pennsylvania which is an
aminopropyl terminated polydimethylsiloxane having a molecular weight of about
2500. Baysilone OF4061 is a cyclohexylamine terminated polydimethylsiloxane
available from Mobay Chemical Corporation, Pittsburgh, Pennsylvania. An
example of a quaternary ammonium salt terminated polysiloxane useful in the
present invention is Tegopren 6922 which is reported to be a polysiloxane
polyammonium acetate and which is available from Goldschmidt Chemical Corp.,
Hopewell, Virginia. Another example of an internal amino functional
polysiloxane is GP-4 Silicone Fluid available from Genesee Polymers. The
polysiloxane is represented by the formula
~ I ~ CH3~_ SiMe3 (111)
CH3 C3H6NH2
58 4
Another comrnercially available amino functionalized polysiloxane
is GP7100 from Genesse which is an amine-alkyl modified methalkylaryl silicone
having a theoretlcal molecular weight of 7800.
She functlonal groups contained within the functionallzed
polyslloxanes used in the present Invention may be charscterized by the formula
-R OR2 wherein R is a divalent group as defined above, and R2 Is hydrogen, an
alkyl or aryl group containing up to about 8 carbon atoms, propylenyloxide,
-(C2H4O)a-(C3H6o)b-R3 wherein a and b are independently numbers from 0 to
100 provlded that at least one of a or b is at least one, and R3 is hydrogen,
acetoxy, or a hydrocarbyl group. Speclfic examples of sucli functional groups
include -CH2CH2OH, CH2CH2CH2OH, -CH2CH2OCH3, -CH2CH2O phenyl,
OCH2CH20H, -CH20-propylenyloxide~ -CH20(CH2CH20)pH, -CH20(CH2-
2099126
CH2O)pCH3- -CH2O(cH2cH~cH3)o)pH~ -CH2O(CH2CH(CH3)O)pCH3, where p is
a number from I to about 100, -CH2CH2~O~(c2H4O)a(c3H6o)b-H where a and b
are independently numbers from I to 100, etc.
Examples of commercially available polysiloxanes functionalized
with one or more -R'OR2 group are as follows.
An internal carbinol functional silicone polymer is available from
Genesee Polymers Corporation, Flint, Michigan, under the trade designation
E~P-69 Silicone Fluid. This fluid is reported to be characterized by the
following formula
(CH3)3SiO~S~O~CH3~--Si(CH3)3 (IV)
CH3 C3H6H
96 6
EXP-68 Silicone Fluid is another carbinol functional polysiloxane
from Genesee Polymers which is reported to be characterized by the formula
(CH3)3SiO ~ SiO ~ ICH3~ Si~CH3)3 (V)
CH3 C3H6OH
56 8
GP-167 sllicone fluid a ailable also from Genesse Polymers Is a
polydimethyl slllcone fluid containing the group.
~Si-CH2CH2CH20CH2CH-cH2
Thls fluld has an equivalent weight per epoxide group of 6000.
20991Z6
-27-
EXP-32 Silicone Fluid avallable from Genesee also is an epoxy
functional polydimethyl siloxane which has the structure
~ CH3 ~ ~ CH3 ~
(cH3)3siotsio ) t SiO ) - Si(CH3)3 (Vl)
CH3 y
96.5 5.5
where Y is -C3H6OCH2-CH-CH2. This material has an epoxy equivalent weight
(calculated) of 1515 and a calculated molecular weight of 8300. Another epoxy
functionalized silicone is glycidoxypropylmethyldimethyl siloxane available fromPetrarch Systems under the designation PS922.
One type of commercially a~ailable polyether polydimethylsiloxane
copolyrners useful in the invention may be characterized by the following general
formula
~CH3)3SiO ~SiO ~ ICH3 ~Si(CH3)3 (Vll)
CH3 x PE y
where PE ~ -CH2CH2CH2O(C2H4O)m(C2H6O)n-Z; x, y, m ~ n are number~, and
Z is hydrogen or a lower alkyl group. These products may be obtalned by
graftlng a polyether to a llnear polydlmethylslloxane through a hydrosilation
reactlon. Example of such materlals include the SILWET~ surfactants from
Union Carbide and the Tegopren silicone surfactants from Goldschrnidt
Chemical Corp., Hopewell, VA, Including the following:
2099126
Name (C2H,~O) (C3H6~ Z Mw
SILWET L-77 yes no -CH3 600
SILWET L-7001 yes yes -CH3 20,000
SILWET L-7500 no yes -C4Hg 4,000
SILWET L-7604 yes no -H 4,000
Tegopren 5847 yesl yes~ -H 800
Tegopren 5863 yes2 yes2 -H 15,000
80/20 wt.%
- lo 2 40/60 wt.%
Alkoxy-end blocked silicone copolymers are available wherein the
polyalkylene oxide groups are attached to the ends of the silicone backbone
through Si-O-C bonds. These products have the general formula
(CH3Si)y zl(OSi(CH3)2)ax yO~PEly (Ylll)
wherein PE = -(C2H4O)m-(c3H6o)n-z~ and Z is a lower alkyl group. By varying
x, y, m and n, a variety of such silicones havc been prepared. One commercially
available product is SlLWEr L-720 which contains both ethylene oxide and
propylene oxide moieties and is butoxy terminated. This silicone has a molecularweight of 12,000.
The functional group of the functionalized polysiloxane may be a
mercapto group such as, for example, -R'SH where R' is a divalent group as
described above. Commercially available mercapto-modified polysiloxanes
include products available from Genesee Polymers Corporation under the
deslgnations GP-72-SS, GP-71-SS and GP-7200. GP-72-SS contains mercapto
propyl side chains in addition to the conventional methyl group substituents andmay be characterized by the following formula
2099126
-29-
(CH3)3SiO~ SiO~CH3~Si(CH3)3 (IX)
CH3 x C3H6SH y
This product has a viscosity at 25C of from 273-297 centistokes. GP-71-SS may
also be represented by the above formula wherein x is 83 and y is 2. The
molecular welght of this fluid is reported to be 6,600 and the fluid contains 1%SH. The viscosity at 25C is 150 centistokes. GP-7200 silicone fluid is a
mercapto functlonal methyl alkyl (-C12H25) alkaryl (-CH2-CH(CH3)phenyl).
The functional groups of the functionalized polysiloxanes useful Jn
the present invention may be -R'COOH groups where R' is a divalent group as
defined above. An example of a commerclally available carboxy-terminated
polysiloxane is PS-573 from Petrarch Systems, Bristol, Pennsyl~ania which is
characterized by the formula
f Cl H3 ~ ICH3
HOOC(CH2)3 tSiO ) - Si(cH2)3cooH (X)
CH3 x CH3
Another carboxy-terminated siloxane is PS409 from Petrarch
Systems which is identified by the structure
HWC~6P3~ ,CH3 ~_ CH3 _~CH3~_ CH3
a~3 ~H3 n / ,0 \\a~3 CH3 (X~)
~a13- S1_a13)
CH3_ St-a13
C3H6WOH
The functlonal groups may be other carbonyl-containing groups such
as aldehydes, ketones, acetoxy, etc. For example, a polydimethylsiloxane can be
2099126
-30-
~- terminated with groups such as ~Si-CH2-C(O)CH3, ~Si-CH2C(O)H; ~Si-
CH2C(O)CH3, etc.
Examples of other functionalized polysiloxanes include (3-
cyanobutyl) methylvinylsiloxane (PS934, Petrarch); (cyanopropyl) methyl-
methylphenylsiloxane copolymer (PS910, Petrarch); poly(acryloxypropylmethyl)
siloxane (PS901.5, Petrarch); polymethyl-3,3,3-fluoropropylsiloxane (PS182,
Petrarch~.
Salts of the above-described functional groups are also
contemp1ated as useful derivatives. In addition to the quaternary ammonium
salts, salts of the hydroxy, mercapto, sulfonyl and sulfoxyl groups can be used
including alkali and alkaline earth metal salts.
The term functionalized siloxane or polysiloxane as used in this
application includes block copolymers comprising non-functionalized siloxane
units and hydrocarbon units containing functional groups such as those describedabove. These types of copolymers may be random or block copolymers.
The electrorheological fluids of the invention contain from about
0.1 to about 25% by weight of the functionalized polysi!oxanes based on the
weight of the hydrophobic liquid phase. More often the fluids will contain from
about 0.5 to about 10% by weight of the functionalized silicones based on the
weight of the hydrophobic liquid.
The ER fluids of the present invention may be prepared by mixing
the above-described celluloslc particles (as the dispersed phase) with the selected
hydrophobic liquid phase and the functionalized silicone. The cellulosic particles
may be comminuted to certain partlcle sizes if desired.
In one embodiment, desirable and useful ER fluids are provided in
accordance with the present invention which are essentially non-aqueous or
essentially anhydrous. Small amounts (for example, less than about 1% based on
the total weight of the fluid) of water may be present which may, in fact, be
essentlally impossible to remove from the cellulose, but such amounts do not
hinder the performance of the ER fluids of the present invention.
2099126
In addition to the hydrophobic liquid phase, the dJspersed
particulate phase of cellulose, and the functionalized polysiloxane, the ER fluids
of the present invention may contain other components capable of imparting or
impro~ring desirable properties of the ER fluid. Examples of additional
components which may be included in the ER fluids of the present invention
include organic polar compounds, auxiliary dispersing agents, viscosity index
improvers, organic or inorganic acids, salts or bases, etc. The amount of the
above additional components included in the ER fluids of the present invention
will be an amount sufficient to provide the fluids with the desired property
and/or improvement. Generally, from about 0 to about 10% by weight, and more
often from about 0 to about 5% by weight of one or more of the additional
components can be included in the ER fluids of the present invention to provide
desirable propertles including vlscoslty and temperature stability. It Is hlghlydesirable, for example, that the particulate dispersed phase remain dispersed
over extended periods of time such as during storage, or, if the particulate
dispersed phase settles on storage, the phase can be readily redispersed In the
hydrophobic liquid phase.
The Or~anic Polar ComDounds
In one embodiment, it Is desirable to include in the ER fluids of the
present inventlon at least one organic polar compound. Thus, the ER flulds may
contain from 0.1 up to about 10% by welght, based on the total weight of the ER
fluid, of one or more organlc polar compound. The polar compounds are desirable
particularly when the ER fluids contaln less than 1% of water. In another
embodJment the ER fluid contalns from about 0.1 to about 2% of the polar
compound. Examples of useful organic polar compounds include compounds such
as carboxylic acids, amines, amides, nitriles, alcohols, polyhydroxy compounds,
nitro compounds, ketones and esters. Examples of amides include acetamide and
N-methyl acetamide. Polyhydroxy compounds are particularly useful in the ER
fluids of the present invention, and examples of such polar compounds Include
ethylene glycol, diethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol,
2099126
glycerol, penta~rythritol, etc. Examples of other polar compounds include
propronitrile, nitroethane, formic acid, trichloroacetic acid, diethanolamine,
triethanolamine, ethylene carbonate, propylene carbonate, pentanedione,
furfuraldehyde, sulfolane, diethyl phthalate, etc.
Other Additive_
The ER fluids of the present invention also may contain at least
one organic or inorganic acid, base or salt. In one embodiment, the acids, basesand salts are included in the ER fluids of the present invention to improve the
ER strength. Examples of acids include inorganic acids such as sulfuric acid,
hydrochloric acld, nitric acid, perchloric acid, chromic acld, phosphoric scld and
boric acid. Examples of organic acids include acetic acid, formic acid, propionic
acid, butyric acid, isobutyric acid, valeric acid, oxalic acld, and malonlc acid.
Inorganic bases which can be utilized include hydroxides and carbonates of alkali
metals and alkaline earth metals. Organic amines are exarnples of basic organic
compounds. Speclflc examples of useful bases Include sodlum hydroxide,
potassium hydroxide, calcium hydroxide, sodium carbonate, sodium bicarbonate,
potassium phosphate, sodium phosphate, aniline, methylamine, eehylamine, and
ethanolamine. Examples of salts which may be used include halides of alkali
metals and alkaline earth metals, and alkali metal salts or organic acids.
Speciflc examples Include llthlum chlorlde, sodlum chlorlde, potassium chlorlde,magneslum chlorlde, calclum chlorlde, barium chloride, llthJum bromide, sodium
bromide, potassium bromide, silver nitrate, calcium nitrate, sodium nitrite,
ammonium nitrate, potasslum sulfate, sodlum sulfate, ammonlum sulfate, and the
alka1i metal salts of formlc acld, acetlc acid, oxalic acid and succinic acid.
The amount of the acid base or salt included in the ER fluids of the
present inYention may be ~raried o~rer a wide range depending upon the other
components of the ER fluid and the desired effect. In one embodiment, the ER
fluid wil1 contain up to about 20% by weight, based on the weight of the organicpolar compound, of at least one organic or inorganic acid, base or salt.
2099126
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In some instances, it may be desirable to add materials which are
soluble in the ER fluid and which are capable of increasing and stabillzing the
viscosity of the ER fluids when the fluid is not under the influence of an
electrical field. Materials which have been described In the literature as
viscosity modifying agents In lubricating oils may be used for this purpose in the
fluids of the present invention. Viscosity modifying agents generally are
polymeric materials characterized as being hydrocarbon-based polymers generally
having a number average molecular weight of between about 25,000 and 500,000,
more often between about 50,000 and 200,000. The viscoslty modifiers may be
included in the ER fluids of the present invention in amounts from about 0 to
- about 10% or more as required to modify the viscosity of the fluid as desired.
Polyisobutylenes, polymethacrylates (PMA), ethylene-propylene
copolymers (OCP), esters of copolymers of styrene and maleic anhydride,
hydrogenated polyalpha-olefins and hydrogenated styrene-conjugated diene
copolymers are useful classes of commercially available viscosity modifiers.
Polymethacrylates (PMA) are prepared from mixtures of methacry-
late monomers having different alkyl groups. Most PMA's are viscosity modifiers
as well as pour point depressants. The alkyl groups may be elther straight chainor branched chain groups containing from l-to about 18 carbon atoms.
The ethylene-propylene copolyrners, generally referred to as OCP
can be prepared by copolymerizing ethylene and propylene, generally in a
solvent, using known catalysts such as a Ziegler-Natta initiator. The ratio of
ethylene to propylene in the polymer influences the~oil-solubility, oil-thlckenlng
abillty, low temperature viscosity and pour point depressant capability of the
product. The common range of ethylene ccntent is 45-60% by weight and
typically is from 50% to about 55% by weight. Some commercial OCP's are
terpolymers of ethylene, propylene and a small amount of non-conjugated dlene
such as 1,4-hexadiene. In the rubber industry, such terpolymers are referred to
as EPDM (ethylene propylene diene monomer).
2099126
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Esters obtained by copolymerlzing styrene and maleic anhydride In
the presence of a free radical initiator and thereafter esterifying the copolymer
with a mlxture of C4 18 alcohols also are useful as viscosity-modifying additives.
The hydrogenated styrene-conjugated diene copolymers are
prepared from styrenes such as styrene, alpha-methyl styrene, ortho-methyl
styrene, meta-methyl styrene, para-methyl styrene, para-tertiary butyl styrene,
etc. Preferably the conjugated diene contains from 4 to 6 carbon atoms.
Examples of conJugated dienes include piperylene, 2,3-dlmethyl-1,3-butadiene,
chloroprene, isoprene and 1,3-butadiene, wlth isoprene and butadiene being
partlcularly preferred. Mlxtures of such conjugated dlenes are weful.
The styrene content of these copolymers is in the rsnge of about
20% to about 70% by weight, preferably about 40% to about 60% by welght. The
aliphatic conjugated dlene content of these copolymers is In the ran8e of about
30% to about 80% by weight, preferably about 40% to about 60% by weight.
These copolymers can be prepared by methods well known In the
art. Such copolymers usually are prepared by anionic polymerization using, for
example, an alkall metal hydrocarbon (e.g., sec-butylllthium) as a polymerizatlon
catalyst. Other polymerlzation techniques such as emulsion polymerization can
be used.
These copolymers are hydrogenated in solution so as to remove a
substantial portlon of their olefinic double bonds. Technlques for accomplishlngthis hydrogenatlon are well known to those of skill In the art and need not be
descrlbed In detall at thls point. Briefly, hydrogenatlon is accomplished by
- contacting the copolymers with hydrogen at super-atmospheric pressures In the
presence of a metal catalyst such as colloidal nickel, palladlum supported on
charcoal, etc.
In general, it Is preferred that these copolymers, for reasons of
oxldatl~e stablllty, contain no more than about 5% and preferably no more than
about 0.5% residual olefinlc unsaturation on the basls of the total number of
carbon-to-ctrbon covalent llnkages within the a~erage molecule. Such
2099126
-35-
unsaturation can be measured by a number of means well known to those of skill
in the art, such as infrared, NMR, etc. Most preferably, these copolymers
contain no discernible unsaturation, as determined by the afore-mentioned
analytical techniques.
These copolymers typically have number average molecular weights
in the range of about 30,000 to about 500,000, preferably about 50,000 to about
200,000. The weight average molecular weight for these copolymers is generally
in the range of about 50,000 to about 500,000, preferably about 50,000 to about
300,000.
The above-described hydrogenated copolymers have been described
- in the prior art. For example, U.S. Patent 3,554,911 describes a hydrogenated
random butadiene-styrene copolymer, its preparation and hydrogenation. The
disclosure of this patent is incorporated herein by reference. Hydrogenated
styrene-butadiene copolymers useful as viscosity-modifiers in the ER fluids of
the present invention are available commercially from, for example, BASF under
the general trade designation "Glissoviscal". A particular example is a
hydrogenated styrene-butadlene copolymer available under the designation
Glissoviscal 5260 which has a number average molecular weight of about 120,000.
Hydrogenated styrene-isoprene copolymers useful as viscoslty modlflers are
available from, for example, The Shell Chemlcal Company under the gerleral
trade designation "Shellvis". Shellvis 40 from Shell Chemlcal Company is
identified as a diblock copolymer of styrene and isoprene having a number
average molecular weight of about 155,000, a styrene content of about 19 mole
percent and an Isoprene content of about 81 mole percent. Shellvis 50 is
available from Shell Chemical Company and is identlfled as a dlblock copolymer
of styrene and isoprene having a nurnber average molecular weight of about
100,000, a styrene content of about 28 mole percent snd an Isoprene content of
about 72 mole percent.
The following examples illustrate some of the fluids of the present
invention. Cellulosel type is dried at 50C under vacuum for 5 hours. Cellulose~
2099126
type is dried at IS0C under vacuum for 24 hours. Silicone (10 cst) is a
polydimethyl silicone oil from Dow Corning.
ER Fluid A Yo/wt.
CF-I Cellulosel 15
S E~CP-69 2
Silicone (10 cst) 83
ER Fluld B
CF-ll Cellulose2 20
UC-L-7600 3
Sllicone (10 cst) 77
ER Fluid C
CF-II Cellulose2 20
UC-L-7600 3
Silicone (10 cst) 77
ER Fluid D
CF-I 1 Cellulose2 20
UC-L-7500 3
Sllicone ~10 cst) 77
R Fluid E
CF-ll Cellulose2 15
EXP-69 2
Glycerol
Sillcone (10 cst) 82
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ER Fluid F
CF-ll Cellulose2 15
EXP-69 2
Glycerol/KOH (95/5)
Silicone ~10 cst) 82
ER Fluid G
Solka Fi OC BW-100 15
EXP-69 3
Ethylene glycol 0.5
Silicone (10 cst) 81.5
ER Fluid H
CF-ll Cellulose 35
EXP-69 2
S11icone (10 cst) 63
ER Fluid I
CF-ll Cellulose 30
EXP-69 2
Silicone (10 cst) 68
ER Fluid I
CC-31 Cellulose2 20
EXP-69 3
Ethylene glycol
Si11cone ~10 cst) 76
ER Fluid K
Cellulose Phosphste . 15
W-69 2
SJlicone (10 cst) 83
209912~
-38-
ER Fluid L
Cellulose CF-I l l 20.0
GP 72 SS 3.0
Ethylene glycol 0.75
Silicone (10 cst) 76.25
ER Fluid M
Cellulose CF-Il 25.0
Petrarch PS 563 2.0
Ethylene glycol 1.0
Silicone (10 cst) 72.0
ER Fluid N
CC-31 Cellulose2 25
Ethylene glycol 1.5
EXP-69 5.0
Ernery 2960 68.5
ER Fluid O
Cellulose CF-112 20
EXP-69 3
Butyrolactone
Slllcone (5 cst) 76
ER Fluld P
Solka-Floc BW-100 15
EXP-69 2
Malononltrile o.5
Slllcone (10 cst) 82.5
ER Fluid O
Solka-Floc BW-I001 15
EXP-69 2.0
Nltrobenzene 0.5
Silicone (10 cst) 82.5
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-39-
ER Fluid R
Solka-Floc BW-1001 15
EXP-69 2
Propylene carbonate 0.5
Silicone ~10 cst) 82.5
ER Fluld S
Solka-Floc BW-100 15
EXP-69 2
Methyl propronarnide 0.5
Silicone (10 cst) 82.5
ER Fluid T
Solka-Floc BW-100 15
EXP-69 2
Furfuraldehyde 0.5
Silicone (10 cst~ .82.5
ER Fluid U
DEAE Cellulose 20
EXP~9 2
S{licone (10 cst) 78 -
ER Fluid V
Hydroxypropyl Cellulose 20
W-69 2
Ethylene glycol
Sillcone (10 cst) 77
ER Flu~ W
TEAE Ce11ulose 20
EXP-69 2
Slllcone (10 cst) 78
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-40-
ER Fluid X
Carboxyrnethyl cellulose, sodium salt 20
EXP-69 2
Silicone (10 cst) 78
ER Fluid Y
Hydroxyethyl cellulosel 20
EXP-69 2
Silicone ~10 cst) 78
ER Fluid Z
Methyl cellulose 20
EXP-69 2
Silicone (10 cst) 78
ER Fluid AA
Solka-Floc BW-100 15
GP-4 .2
Sllicone (10 cst) 83
ER Fluid AB
Solka-Floc BW-100 15
GP-72-A 2
Sllicone (10 cst) 83
ER Fluld AC
Solka-Floc BW-100 15
EXP-69 2
Slllcone (10 cst) 83
ER Fluld AD
Cellulose CF-112 20
GP-72-A 3
Ethylene glycol 0.75
Slllcone(10 cst) 76.25
2099126
--41--
-- ER Fluid AE
Cellulosic Example A-l 15
EXP-69 2
Silicone (10 cst) 83
ER Fluid AF
Cellulosic of Example A-2 30
EXP-69 2
Sillcone (10 cst) 68
ER Fluid AG
Cellulosic of Example A-3 30
EXP-69 2
Silicone (10 cst) 68
ER Fluid AH
Cellulosic of Example A-4 30
EXP-69 .2
Silicone (10 cst) 68
ER Fluid Al
Cellulosic of Example A-6 20
GP-4 2
Sillcone (10 cst) 78
ER Fluid A I
Cellulosic of Example A-7 25
EXP-69 2
Sillcone (10 cst) 73
ER ~uid AK
Cellulose CF-112 15
EXP-69 2
Slllcone (10 cst) 63
Mlneral oil 20
2099126
-42-
The efflciency of the electrorheological fluid is reJated to the
amount of electrical power required to affect a given change in rheological
propertles. This is best characterized as the power requlred for an obselved
ratio of yield stress under field to the viscosity of the fluid in the absence of a
s field. From fluid requirements vs. device design considerations, a parameter has
been defined as the dimensionless Winslow number, Wn, where;
Wn = (ys)2
(PD)(rlo)
YS = Yield stress (Pa)
PD = Power density (w/m3)
= Current density x Field strength
l~o = Viscosity with no fleld applied (PaS)
In accordance with certain embodiments of the present invention,
electrorheological fluids are provided which are characterized as having a
Winslow Number (Wn) In excess of 3000 at 20C, and in other embodlments, the
ER fluids are characterized as having Wn in excess of 100 at the maximum
temperature of the intended application. This temperature may be 80C, 100C,
or even 120C.
While the invention has been explalned in relatlon to its preferred
embodiments, it is to be understood that various modifications thereof will
become apparent to those skilled in the art upon reading the specification.
Therefore, it is to be understood that the invention disclosed herein is intended
to cover such modiflcations as fall within the scope of the appended claims.
