ELECTRORHEOLOGICAL FLUIDS CONTAINING CELLULOSE AND FUNCTIONALIZED POLYSILOXANES

Abstract: Electrorheological fluids are described which comprise a hydrophobic 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 which is capableof 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 devices; and linear damping devices such as shock absorbers, engine mounts and hydraulic actuators.

Description: ELECTRORHEOLOGICAL FLUIDS CONTAINING CELLULOSE AND FUNCTIONALIZED POLYSILOXANES Field of the Invention This invention relates to electrorheological fluids. More particular¬ ly, this invention relates to electrorheological fluids containing cellulosic particles as the dispersed particulate phase. Background of the Invention Electrorheological (ER) fluids are dispersions which can rapidly and reversibly vary their apparent viscosity in the presence of an applied electric field. The electrorheological fluids are dispersions of finely divided solids in hydrophobic, 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 sufficiently strong electrical field. When the field is removed, the fluids revert to their normal liquid 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 electric 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 liquid 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 to the dispersion. This observation has been referred to as the Winslow Effect. Subsequently, investigators 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 linear or quadratic, depending on fluid composition and the experimental techniques. Measurement of yield stress can be achieved by extrapolation of stress vs. strain curves, sliding plate, controlled stress, or capillary rheometers. Electrorheological fluids which have been described in the literature can be classified into two general categories: water containing; 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 principally associated with the dispersed phase to exhibit significant ER properties. However, from an application standpoint, the presence of water generally is undesirable since it may result in corrosion, operating temperature limitations (loss of water at higher temperatures), and significant electrical 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 hydraulic oil compositions having a large Winslow effect containing an electrical insulating oil, a water-soluble electrolyte, a liquid having a high dielectric constant, and microcrystalllne 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 include all salts which are dissociable into cations and anions such as, for example, sodium 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 highly compatible with elastomeric materials. U.S. Patent 4,702,855 describes electroviscous fluids which are composed of aluminum silicate particles in an electrically non-conductive liquid and a suitable dispersing 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 having a molecular weight above 800. The functional polysiloxanes are included in the fluid at a concentration of 1 to 30% based on the weight of aluminum silicate particles. U.S. Patent 4,772,407 (European Patent Application 319,201) describes an electrorheological fluid exhibiting desirable properties at low current densities and at high temperatures in the complete absence of adsorbed water or water of hydration. In one embodiment, the fluid comprises lithium hydrazinium sulfate dispersed in silicone oil and containing an appropriate suspension stabilizing agent. Among the suspension stabilizers described are the amino-, hydroxy-, acetoxy-, or alkoxy-functionalized polydimethyl siloxanes. Block and graft copolymers are described which are also useful as stabilizing agents. Japan Published Application Hei-1- 197595 describes electroviscous fluids composed of silicone oil, an amino denatured silicone oil or alcohol 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 silicone oils are functionalized polydimethyl silicones where the functional groups are amino or alcohol functional groups. All of the examples 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 silicone with 40 parts of either epoxy functionalized, carboxy functionalized, polyether functionalized or mercapto functionalized silicones. Japanese Published Application Hei-1-207396 describes electrovis¬ cous fluids composed of a mixture of silicone oil and an amino denatured or alcohol denatured silicone oil, a crystal cellulose and a multi-functional alcohol such as ethylene glycol, propylene glycol or butanediol. The mixtures of straight silicone and functionalized silicones used in the invention comprise 100 parts of the straight silicone and 40 parts of the amino or alcohol functionalized silicones. Japan Published Application Hei-2-26633 describes electrorheolog¬ ical fluids which are composed of a dispersoid that consists of hydrous silicate, a liquid phase that consists of non-conducting hydrophobic liquid, and dispersing agent. Polyether denatured silicone oil or epoxy polyether denatured silicone oil is utilized as a dispersing agent. The use of these denatured silicone oils is reported to improve the stability of the electrorheological fluids. The dispersoid content of the fluid is generally 20 to 50%, the content of the dispersing agent is from 1 to 20%, and the remainder is a liquid phase. Summary 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 which 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 devices; and linear damping devices such as shock absorbers, engine mounts and hydraulic actuators. Detailed Description of the Invention Unless otherwise specified in the disclosure and claims, the following definitions are applicable. The term "hydrocarbyl" 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 with the present invention include the following: (1) hydrocarbon groups or substituents, that is aliphatic (e.g., alkyl or alkenyl), alicyclic (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 alicyclic group); (2) substituted hydrocarbon groups or substituents, that is, those containing nonhydrocarbon substituents which, in the context of this 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 do not adversely affect the performance of a material when it is used in an 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 skill in the art and include, for example, sulfur, oxygen, and nitrogen. Moieties such as pyridyl, furanyl, thiophenyl, imidazolyl, and the like, are exemplary of hetero groups or substituents. 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 substituents in this invention are essentially free of atoms other than carbon and hydrogen and are, therefore, purely hydrocarbon. The Hydrophobic Liquid Phase The electrorheological fluids of the present invention comprise a hydrophobic liquid phase which 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- Iene hydrocarbons, olefin hydrocarbons, chlorinated paraffins, synthetic esters, hydrogenated olefin oligomers, and mixtures thereof. The hydrophobic liquid phase selected for a particular ER fluid should be compatible with the other components, and the other components are preferably soluble in the hydrophobic liquid phase which may comprise mixtures of two or more of the above-identified fluids. The choice of the hydrophobic liquid phase also will depend in part upon the intended utility of the ER fluid. For example, the hydrophobic liquid should be compatible with the environment in which it will be used. If the ER fluid is to be in contact with elastomeric materials, the hydrophobic liquid phase should not contain oils or solvents which attack or swell, or, in some cases even dissolve elastomeric materials. Additionally, if the ER fluid is to be subject to a wide temperature range of, for example, from about -50°C to about 150°C, the hydrophobic liquid phase should be selected to provide a liquid 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 liquids may be used for the hydrophobic liquid phase. Mixtures may be selected to provide the desired viscosity, pour point, chemical and thermal staoility, component solubility, etc. For example, mixtures of hydrocarbons with polysiloxanes may be used to dissolve hydrocarbon components such as the viscosity modifiers discussed below. Liquids useful as the hydrophobic continuous liquid phase generally are characterized as having as many of the following properties as possible: (a) high boiling point and low freezing point; (b) low viscosity so the ER fluid has a low no-field viscosity 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 wide range of applied electric field strengths; and (d) chemical and thermal stability to prevent degradation on storage and service. Silicon-based oils such as the polyalkyl-, polyaryl-, polyalkoxy-, or polyaryloxysiloxane oils and silicate oils comprise a particularly useful class of synthetic hydrophobic liquids. 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. In one embodiment, the silicone-based oils are polysilicones such as alkyl phenyl silicones or siloxanes. The alkyl phenyl silicones can be prepared by the hydrolysis and condensation reactions as described in the art such as, for example, in An Introduction to the Chemistry of the Silicones, by Eugene G. Rochow, John Wiley & Sons, Inc., New York, Second Edition (1951). The silicone-containing fluids may be polysiloxanes having units of the general formula wherein n has a value 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 aliphatic 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 organyl groups including halogenated aryl groups, alkyl and aryl ether groups, aliphatic ester groups, organic acid groups, cyanoalkyl groups, etc. The organyl groups, in general, contain from 1 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, in 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 mixed alkyl, aryl and 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 in all cases contain from 1-5 halogen atoms each. These silicone fluids may, of course, also be physical mixtures of one or more of the polysiloxanes in which R is as defined above. 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 1 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 groups include phenyl, benzyl, styryl, tolyl, etc. Specific examples of alkyl siloxanes useful as the hydrophobic liquid phase include: polydimethylsiloxane; polymethylethylsiloxane; poly- vinylmethylsiloxane; polydiethylsiloxane; polymethylhexylsiloxane; polymethyloctylsiloxane; polymethyloctadecylsiloxane; polymethyl- tetradecylsiloxane; polymethylhexadecylsiloxane; polymethylcyclohexylsil- oxane. Preferred silicone oils generally have a viscosity at 25°C of from about 1 up to about 300 or 500 or about 100 centistokes. In another embodiment;, 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 wherein R l is an alkyl group containing from 1 to about 6 carbon atoms and R 2 is a hydrogen atom, halogen, or an alkyl group containing from 1 to 3 carbon atoms. Specific examples of the alkyl phenyl polysiloxanes of the type containing the repeating structure (II) include methyl phenyl silicone, methyl tolyl silicone, methyl ethyl phenyl silicone, ethyl phenyl silicone, propyl phenyl silicone, butyl phenyl silicone and hexyl propyl phenyl silicone. 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 size 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 25°C. 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 25°C of 100 centistokes. Another synthetic silicone is a methyl phenyl polysiloxane sold by General Electric Company under the tradename SF-1038. The viscosity of this material at 25°C ranges from about 50 to about 500 centistokes. Other methyl phenyl polysiloxanes are those marketed by Dow Corning as Dow Corning 550 Fluid which has a viscosity at 25°C of about 100 to 150 centistokes, and Dow Corning 710 Fluid having a viscosity at 25°C 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 methyl phenyl silicone and hexyl 4-propylphenyl silicone, respectively. 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 useful 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 derived from coal or shale are also useful oils. 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 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 polycarboxylic esters thereof, for example, the acetic acid esters, mixed C ~Cg fatty acid esters and C | Oxo acid diester of tetraethylene glycol. Another suitable class of synthetic lubricating liquids comprises the esters of dicarboxylic 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 fumarate, dioctyl sebacate, diisooctyl azelate, diisodecyl azelate, dioctyl phthalate, didecyl phthalate, dieicosyl sebacate, the 2-ethylhexyI diester of linoleϊc 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 C j 2 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 olefins containing from 2 to about 24 or more carbon atoms such as ethylene, propylene, 1-butene, isobutene, 1-decene, etc. Specific examples include polyisobutylene having a number average molecular weight of 650; a hydrogenated oligomer of 1-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 liquids include liquid esters of phosphorus- containing acids such as tricresyl phosphate, trioctyi phosphate and the diethyl ester of decylphosphonic acid. Other specific examples of hydrophobic liquids which may be utilized in the ER fluids of the present invention include, for example, mineral oil, di-(2-ethylhexyl) adipate; di-(2-ethylhexyl) maleate; dibenzylether, dibutylcarbitol; di-2-ethyIhexyl phthalate; 1 , 1-diphenylethane; tripropylene glycol methyl ether; butyl cyclohexyl phthalate; di-2-ethyIhexyl azelate; tricresyl phosphate; tributyl phosphate; tri(2-ethylhexyl) phosphate; penta-chlorophenyl phenyl ether; brominated diphenyl methanes; olive oil; xylene; toluene, etc. Commercially available oils which may be used in the ER fluids of the invention include: Trisun® 80 oil, a high oleic sunflower oil from The Lubrizol Corporation; 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. 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. Generally, 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 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 liquid such as a silicone fluid. Other useful weight ratios may be from 20:80 to 50:50. The Cellulosic Dispersed Particulate Phase The electrorheological fluids of the present invention contain cellulosic particles 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 invention 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 less than 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, fibers, spheres, rods, etc. In one embodiment, the cellulosic particles utilized in the present invention are microcrystalline cellulose particles. Microcrystalline cellulose as used herein, is the insoluble residue obtained from the chemical decomposition of natural or regenerated cellulose. Crystallite zones appear in regenerated, mercerized and alkalized celluloses, differing from those found in native cellulose. By applying a controlled chemical pretreatment to destroy molecular bonds holding these crystallites, followed by mechanical treatment to disperse the crystallites in aqueous phase, smooth colloidal microcrystalline cellulose gels with commercial- ly important functional and Theological properties can be produced. More particularly, in the hydrolysis of cellulose, the amorphous portions of the original cellulose chains are dissolved, 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 washing steps are subjected to a mechanical disintegra¬ tion to produce a material having particle sizes in the range of less than 1 up to about 250 or 300 microns. Within this range, the particle size and size distribution are variable, it being understood that the size and size distribution can be selected to suit a particular end use. Microcrystalline cellulose prepared in this manner is characterized by its extremely low content of ash which is attributed to the fact that 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 fluids of the present invention may be reduced by drying the cellulose for an extended period at temperatures from about 50°C to about 150°C, generally under vacuum. Amorphous cellulose is also useful, and examples of useful amorphous cellulose particles, are CF1, CF11 and CC31 available from Whatman Specialty Products Division of Whatman Paper Limited, Maidstone Kent, ME 142LE. CF1 is identified as a long fiber powder cellulose with a fiber length of 100-400 micron and a mean diameter of 20-25 μm. CF11 is a medium fiber amorphous powder cellulose with a fiber length range of from 50 to 250 micron and a mean diameter of 20 to 25 μm. CC31 is identified as a very pure microgranular powder cellulose. The ash content of these three cellulose materials is about 0.015%. Useful cellulose particles are also available from the James River Corporation, Cellulose Floe Division, Hackensack, New Jersey 07601 under the general designation Solka-Floc®. Examples of various grades of Solka- Floe available include AS-1040 (average fiber length 160 microns and ash content 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 0.21%); 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 LATTICE™ 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 cellulose. Examples of cellulose esters include cellulose propionate, cellulose butyrate, cellulose valerate, cellulose triacetate, etc. These cellulose ethers and esters are available commercially in a var ' e y of molecular weights, and the particular molecular weight chosen for use ir ER fluids of the present invention may be varied over a wide range depending un the particular derivative 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 cellulosics also can be used in the ER fluids. These include chitan, chitosan and chondrointon sulfate. Viscose or cellulose xanthate obtained by reacting cellulose with an alkali and thereafter with carbon disulfide can also be used as a cellulosic derivative in this invention. Other cellulose derivatives which may be utilized as the cellulosic particles in the ER fluids of the present invention include cellulose phosphates and cellulose reacted with various amine compounds epichlorohydrin triethanol¬ amine reaction products; etc. Examples of commercially available amine containing derivatives of cellulose include ECTOLA cellulose (epichlorohydrin triethanolamine); DEAE cellulose (diethylaminoethyl cellulose); PEI cellulose (polyethyleneamine cellulose); QAE cellulose (diethyl-[2-hydroxypropyl] aminoethyl cellulose); and TEAE cellulose (triethylaminoethyl cellulose). Cellulose phosphate is another useful derivative and is available from Sigma Chemical Company. Cellulose derivatives also include cellulose reacted with or coated with various silicon compounds including, for example: dimethyl silicone in the presence of a catalyst such as di-t-butyl peroxide; epoxy silicone 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 acid as a catalyst. The cellulose derivatives which may be utilized as cellulosic particles in the ER fluids of the present invention also may be copolymers 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 acids, esters or salts, and (a) a sulfo acid monomer such as represented by the formula (R 1 ) 2 C=C(R 1 )Q a Z b (A) wherein each R j is independently hydrogen or a hydrocarbyl group; a is 0 or 1; b is 1 or 2, provided that when a is 0, then b is 1; Q is a divalent or trivalent hydrocarbyl group or C(X)NR 2 Q'; each R 2 is independently hydrogen or a hydrocarbyl group; Q ! is a divalent or trivalent hydrocarbyl group; X is oxygen or sulfur; and Z is S(O)OH, or S(O) 2 OH; or (b) a polymer of at least one of said monomers. In Formula A, R^ and R 2 are each independently hydrogen or hydrocarbyl. In a preferred embodiment, R j and R 2 are each independently hydrogen or an alkyl group having from 1 to 12 carbon atoms, preferably to about 6, more preferably to about 4. In a preferred embodiment, R j and R are each independently hydrogen or methyl, preferably hydrogen. Q is a divalent or trivalent hydrocarbyl group or C(X)NR 2 Q'. Q' is a divalent 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)(NR 2 )Q'. The hydrocarbyl groups each independently 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 aromatic 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, dime thy lethyl, diethylethyl, and butylpropylethyl groups, preferably a dimethylethyl group. In one embodiment, Q is C(X)NR 2 Q' and Q' is an alkylene having from about 4 to about 8 carbon atoms, such as dimethylethylene. Specific examples of useful sulfo acid monomers include vinyl sulfonic acid, ethane sulfonic acid, vinyl naphthalene sulfonic acid, vinyl benzene sulfonic acid, vinyl anthracene sulfonic acid, vinyl toluene sulfonic acid, methalyl sulfonic acid, 2-methyl-2-propene-l -sulfonic acid and acrylamido hydrocarbyl sulfonic acid. A particularly 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- acrylamido methane sulfonic acid, 2-acrylamido propane sulfonic acid, 3- methylacrylamido propane sulfonic acid and l,l-bis(acrylamido)-2-methyl propane-2-sulfonic acid. Specific examples of other monomers which can be copolymerized with cellulose include acrylamide, methacrylamide, methylenebis(acrylamide), hydroxymethylacrylamide, acrylic acid, methacrylic acid, methyl acrylate, ethyl 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 derivatives useful in the ER fluids of the present invention also may be block or random polymers obtained by reacting cellulose with other polymers such as styrene-maleic anhydride copolymers in the presence of catalysts. For example, cellulose can be reacted with 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. Example A-l A reaction vessel is charged with 40 parts (0.247 mole) of Solka Floe BW-100 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 solution 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 are added 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 water and dried in a steam chest followed by drying in a vacuum oven at 110°C for 6 hours. Example A-2 A reaction vessel is charged with 40.5 parts (0.25 mole) of Solka Floe BW-100 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 1 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 ammonium 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 120°C for 18 hours. The product obtained in this manner contains 0.99% nitrogen. Example A-3 A reaction vessel is charged with 40.5 parts (0.25 mole) of CF-11 cellulose, 7.1 parts of acrylamide (0.1 mole) and 300 parts of water. The mixture is stirred and purged with nitrogen whereupon 10 parts of a 0.1 molar solution of ceric ammonium nitrate in 1 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 120°C for 18 hours. A white solid is obtained which contains 1.91% nitrogen. Example 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 mixture is stirred and purged with nitrogen for 1 hour whereupon 10 parts of a 0.1 molar ceric ammonium nitrate solution in 1 Normal nitric acid are added over a 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 a steam chest for 16 hours, and finally dried in a vacuum oven at 120°C for 16 hours. A white solid is obtained which contains 4.85% nitrogen (theory, 6.0%). Example 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 of AMPS 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-11 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 125°C for 24 hours. The dried material is milled for 24 hours and filtered 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). Example 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 are added over a period of about 2 hours. Stirring 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 residue then is dried in a steam chest for several days and then bail-milled for 6 hours to yield the desired product. Example A-7 A reaction vessel is charged with 81 parts (0.5 mole) of CF-11 cellulose and 400 parts of toluene. The mixture is heated to a temperature of about 108°C 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 anhydride styrene copolymer (0.42 RSV) and 0.2 parts (0.0016 mole) of 4- N,N-dimethyiaminopyridine catalysts are added. The mixture is heated to about 60°C, 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 powder is obtained. The Functionalized 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 improving the dispersion of the solids throughout the vehicle; in maintaining the stability of the dispersions; 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 amino, amido, imino, 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 weight above 800 up to 10,000 or 20,000. The functional polysiloxanes may be linear or branched diorgano polysiloxanes as represented generally by Formulae I and II, respectively. Y 3 , or (I) m -22- wherein each X is independently an alkyl, aryl or cycloalkyl group, each of Y to Y is independently X or a functional group capable of being absorbed or adsorbed on the surface of the cellulosic particles provided that at least one of Y 1 to Y 3 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. 1 Specific examples of functional groups Y -Y in the above formulae include amino, amido, imino, sulfonyl, sulfoxyl, cyano, hydroxy, hydrocarbyloxy, mercapto, carbonyl, carboxy, epoxy, acetoxy, phosphate, phosphoryl, or haloalkyl ι ^ functional groups, or salts or mixtures of such groups. When Y and/or Y are functional groups and Y is X in Formula I, the polysiloxanes or siloxanes are referred to as terminally functionalized siloxanes. When Y 1 and Y are X and 2 Y is a functional group in Formula I, the siloxanes are referred to as internally functionalized silicones. Throughout this specification, it is to be understood that the internal functional groups Y in Formula I (and IA) may be distributed randomly within the polysiloxane chain, and the representation of the siloxane in Formulae such as I and IA should not be interpreted as requiring that all of the SiO groups having a functional group Y are attached in sequence in a block. In one embodiment, each X group is independently selected from alkyl or alkaryl groups having from 1 to about 20 carbon atoms such as methyl, ethyl, vinyl, propyl, butyl, isopropyl, hexyl, dodecyl, octadecyl, or 2-phenylpropyl groups. Examples of cycloaliphatic 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 II may be varied as indicated above to provide polysiloxanes having desirable molecular weights. The value 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 polysiloxanes as represented by the following formulae m CH 3 -Si-CH 3 Y < wherein each of Y -Y 3 is independently an alkyl or a functional group selected from -R'N(R) ? , -R'OR , -R'SH, or -R'COOH, or salts thereof, wherein R' is a divalent group consisting of C, H and optionally O and/or N; each R is indepen- 2 dently hydrogen or an alkyl group containing 1 to about 8 carbon atoms; R is hydrogen, an alkyl or aryl group containing up to about 8 carbon atoms, propylenyloxide, -(C 2 H 4 O) a -(C 3 H 6 O) b -R 3 wherein a and b are independently numbers from 0 to 100 provided at least one of a or b is at least 1; R is H, acetoxy, or a hydrocarbyl group; m is a number from about 10 to about 1000; n is a number 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 that at least one of Y 1 -Y ~ . is not an alkyl group; or Y 1 and Y2 in Formula I are methyl groups and Y is an alkylene oxide polymer block. The R 1 group in the above formulae is a divalent group consisting of carbon, hydrogen and optionally oxygen and/or nitrogen which may be an aliphatic or cycloaliphatic group. Thus, the divalent R' group may be an alkylene or 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, -OCH 2 CH 2 -, -OCH 2 CH 2 CH 2 -, -NCH 2 CH 2 -, -CH 2 CH 2 CH 2 N(H)CH 2 -CH 2 -, etc. In one embodiment, R' is a divalent group containing from 1 to about 3 carbon atoms. The functional groups which may be present in the polysiloxanes useful in this invention include amino groups. The amino functional groups may be characterized by the partial formula -R'N(R) 2 wherein R' is as defined above and each R is independently hydrogen or an alkyl group containing from 1 to about 8 carbon atoms or an aryl group containing 6 to about 8 carbon atoms. The terms "amino group" or "amino functional group" as used in this application include the above-identified amines and salts thereof including quaternary salts which may be obtained by techniques known to those skilled in the art. Specific examples of amino functional groups which may be present on the polysiloxanes used in the present invention include -CH 2 NH 2 , -CH 2 N(H)CH 3 , -CH 2 N(H)C 6 H π , -CH 2 CH 2 CH 2 NH 2 , -CH 2 CH 2 CH 2 N(CH 3 ) 2 , -cyclohexylamine, -OCH(CH 3 )CH 2 NH 2 , -OCH(CH 3 )CH 2 CH 2 NH 2 , -C 3 H 6 N(H)C 2 H 4 NH 2 , -CH 2 CH 2 CH2N ffi (CH 3 )H< H 3 - COO θ , etc. An example of a commercially 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 58 4 Another commercially available amino functionalized polysiloxane is GP7100 from Genesse which is an amine-alkyl modified methalkylaryl silicone having a theoretical molecular weight of 7800. The functional groups contained within the functionalized polysiloxanes used in the present invention may be characterized by the formula -R'OR wherein R' is a divalent group as defined above, and R is hydrogen, an alkyl or aryl group containing up to about 8 carbon atoms, propylenyloxide, -(C 2 H 4 O) a -(C 3 HgO) b -R wherein a and b are independently numbers from 0 to 100 provided that at least one of a or b is at least one, and R is hydrogen, acetoxy, or a hydrocarbyl group. Specific examples of such functional groups include -CH 2 CH 2 OH, CH 2 CH 2 CH 2 OH, -CH 2 CH 2 OCH 3 , -CH 2 CH 2 O phenyl, OCH 2 CH 2 OH, -CH 2 O-propylenyloxide, -CH 2 O(CH 2 CH 2 O) p H, -CH 2 O(CH 2 - CH 2 O) CH 3 , -CH 2 O(CH 2 CH(CH 3 )O) H, -CH 2 O(CH 2 CH(CH 3 )O) p CH 3 , where p is a number from 1 to about 100, -CH 2 CH 2 -O-(C 2 H 4 O) a (C 3 H 6 O) b -H where a and b are independently numbers from 1 to 100, etc. Examples of commercially available polysiloxanes functionalized *__ with one or more -R'OR group are as follows. An internal carbinol functional silicone polymer is available from Genesee Polymers Corporation, Flint, Michigan, under the trade designation EXP-69 Silicone Fluid. This fluid is reported to be characterized by the following formula (CH 3 ) 3 SiO Si(CH 3 ) 3 (IV) 96 6 EXP-68 Silicone Fluid is another carbinol functional polysiloxane from Genesee Polymers which is reported to be characterized by the formula 56 8 GP-167 silicone fluid available also from Genesse Polymers is a polydimethyl silicone fluid containing the group. O / \ ≡Si-CH 2 CH 9 CH 2 OCH 2 CH-CH2 This fluid has an equivalent weight per epoxide group of 6000. EXP-32 Silicone Fluid available from Genesee also is an epoxy functional polydimethyl siloxane which has the structure 96.5 5.5 where Y is -C 3 H^OCH 2 -CH-CH 2 . 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 from Petrarch Systems under the designation PS922. One type of commercially available polyether polydimethylsiloxane copolymers useful in the invention may be characterized by the following general formula CH 3 CH 3 (CH 3 ) 3 SiO 4- SiO -j L SiO — ) Si(CH 3 ) 3 (VII) CH 3 χ PE where PE = -CH 2 CH 2 CH 2 O(C H 4 O) m (C H 6 O) n -Z; x, y, m + n are numbers, and Z is hydrogen or a lower alkyl group. These products may be obtained by grafting a polyether to a linear polydimethylsiloxane through a hydrosilation reaction. Example of such materials include the SILWET ® surfactants from Union Carbide and the Tegopren® silicone surfactants from Goldschmidt Chemical Corp., Hopewell, VA, including the following: 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 (CH 3 Si) y . z [(OSi(CH 3 ) 2 )a χ . y O-PE] y (VIII) wherein PE = -(C 2 H 4 O) m -(C 3 HgO) n -Z, and Z is a lower alkyl group. By varying x, y, m and n, a variety of such silicones have been prepared. One commercially available product is SILWET L-720 which contains both ethylene oxide and propylene oxide moieties and is butoxy terminated. This silicone has a molecular weight 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 designations 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 and may be characterized by the following formula This product has a viscosity at 25°C 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 weight of this fluid is reported to be 6,600 and the fluid contains 1% SH. The viscosity at 25°C is 150 centistokes. GP-7200 silicone fluid is a mercapto functional methyl alkyl (-C^H^) alkaryl (-CH 2 -CH(CH )phenyl). The functional groups of the functionalized polysiloxanes useful in the present invention may be -R'COOH groups where R' is a divalent group as defined above. An example of a commercially available carboxy-terminated polysiloxane is PS-573 from Petrarch Systems, Bristol, Pennsylvania which is characterized by the formula Another carboxy-terminated siloxane is PS409 from Petrarch Systems which is identified by the structure H00CC,H c The functional groups may be other carbonyl-containing groups such as aldehydes, ketones, acetoxy, etc. For example, a polydimethylsiloxane can be termϊnated with groups such as ≡Si-CH 2 -C(O)CH 3 , ≡Si-CH 2 C(O)H; ≡Si- CH 2 C(O)CH 3 , 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-fluorαpropylsiloxane (PS182, Petrarch). Salts of the above-described functional groups are also contemplated 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 described above. 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 polysiloxanes 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 cellulosic particles (as the dispersed phase) with the selected hydrophobic liquid phase and the functionalized silicone. The cellulosic particles may be comminuted to certain particle 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 essentially impossible to remove from the cellulose, but such amounts do not hinder the performance of the ER fluids of the present invention. In addition to the hydrophobic liquid phase, the dispersed particulate phase of cellulose, and the functionalized polysiloxane, the ER fluids of the present invention may contain other components capable of imparting or improving 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 properties including viscosity and temperature stability. It is highly desirable, 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 Organic Polar Compounds In one embodiment, it is desirable to include in the ER fluids of the present invention at least one organic polar compound. Thus, the ER fluids may contain from 0.1 up to about 10% by weight, based on the total weight of the ER fluid, of one or more organic polar compound. The polar compounds are desirable particularly when the ER fluids contain less than 1% of water. In another embodiment the ER fluid contains 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, glycerol, pentaerythritol, etc. Examples of other polar compounds include propronltrϊle, nϊtroethane, formic acid, trichloroacetic acid, diethanolamine, triethanolamine, ethylene carbonate, propylene carbonate, pentanedione, f urfuraldehyde, sulfolane, diethyl phthalate, etc. Other Additives 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, bases and 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 acid, nitric acid, perchloric acid, chromic acid, phosphoric acid and boric acid. Examples of organic acids include acetic acid, formic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, oxalic acid, and malonic acid. Inorganic bases which can be utilized include hydroxides and carbonates of alkali metals and alkaline earth metals. Organic amines are examples of basic organic compounds. Specific examples of useful bases include sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, sodium bicarbonate, potassium phosphate, sodium phosphate, aniline, methylamine, ethylamine, 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. Specific examples include lithium chloride, sodium chloride, potassium chloride, magnesium chloride, calcium chloride, barium chloride, lithium bromide, sodium bromide, potassium bromide, silver nitrate, calcium nitrate, sodium nitrite, ammonium nitrate, potassium sulfate, sodium sulfate, ammonium sulfate, and the alkali metal salts of formic acid, acetic acid, oxalic acid and succinic acid. The amount of the acid base or salt included in the ER fluids of the present invention may be varied over a wide range depending upon the other components of the ER fluid and the desired effect. In one embodiment, the ER fluid will contain up to about 20% by weight, based on the weight of the organic polar compound, of at least one organic or inorganic acid, base or salt. In some instances, it may be desirable to add materials which are soluble in the ER fluid and which are capable of increasing and stabilizing 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 viscosity 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 either straight chain or branched chain groups containing from 1 to about 18 carbon atoms. The ethylene-propylene copolymers, 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-thickening ability, low temperature viscosity and pour point depressant capability of the product. The common range of ethylene content 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 diene such as 1 ,4-hexadiene. In the rubber industry, such terpolymers are referred to as EPDM (ethylene propylene diene monomer). Esters obtained by copolymerizing styrene and maleic anhydride in the presence of a free radical initiator and thereafter esterϊfying the copolymer with a mixture of C 4 _^g 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-dimethyl-l,3-butadiene, chloroprene, isoprene and 1,3-butadiene, with isoprene and butadiene being particularly preferred. Mixtures of such conjugated dienes are useful. The styrene content of these copolymers is in the range of about 20% to about 70% by weight, preferably about 40% to about 60% by weight. The aliphatic conjugated diene content of these copolymers is in the range 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 alkali metal hydrocarbon (e.g., sec-butyllithium) as a polymerization catalyst. Other polymerization techniques such as emulsion polymerization can be used. These copolymers are hydrogenated in solution so as to remove- a substantial portion of their olefinic double bonds. Techniques for accomplishing this hydrogenation are well known to those of skill in the art and need not be described in detail at this point. Briefly, hydrogenation is accomplished by contacting the copolymers with hydrogen at super-atmospheric pressures in the presence of a metal catalyst such as colloidal nickel, palladium supported on charcoal, etc. In general, it is preferred that these copolymers, for reasons of oxidative stability, contain no more than about 5% and preferably no more than about 0.5% residual olefinic unsaturation on the basis of the total number of carbon-to-carbon covalent linkages within the average molecule. Such 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-butadiene copolymer available under the designation Glissoviscal 5260 which has a number average molecular weight of about 120,000. Hydrogenated styrene-isoprene copolymers useful as viscosity modifiers are available from, for example, The Shell Chemical Company under the general trade designation "Shellvis". Shellvis 40 from Shell Chemical 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 identified as a diblock copolymer of styrene and isoprene having a number average molecular weight of about 100,000, a styrene content of about 28 mole percent and an isoprene content of about 72 mole percent. The following examples illustrate some of the fluids of the present invention. Cellulose 1 type is dried at 50°C under vacuum for 5 hours. Cellulose" ? type is dried at 150°C under vacuum for 24 hours. Silicone (10 est) is a polydimethyl silicone oil from Dow Corning. ER Fluid A %/wt. CF-1 Cellulose 1 15 EXP-69 2 Silicone (10 est) 83 ER Fluid B CF-11 Cellulose 2 20 UC-L-7600 3 Silicone (10 est) 77 ER Fluid C CF-11 Cellulose 2 20 UC-L-7600 3 Silicone (10 est) 77 ER Fluid D CF-11 Cellulose 2 20 UC-L-7500 3 Silicone (10 est) 77 ER Fluid E CF-11 Cellulose 2 15 EXP-69 2 Glycerol 1 Silicone (10 est) 82 ER Fluid F CF-11 Cellulose 2 15 EXP-69 2 Glycerol/KOH (95/5) 1 Silicone (10 est) 82 ER Fluid G Solka FLOC BW-100 15 EXP-69 3 Ethylene glycol 0.5 Silicone (10 est) 81.5 ER Fluid H CF-11 Cellulose 35 EXP-69 2 Silicone (10 est) 63 ER Fluid I CF-11 Cellulose 30 EXP-69 2 Silicone (10 est) 68 ER Fluid I CC-31 Cellulose 2 20 EXP-69 3 Ethylene glycol 1 Silicone (10 est) 76 ER Fluid K Cellulose Phosphate 15 EXP-69 2 Silicone (10 est) 83 ER Fluid L Cellulose CF-11 20.0 GP 72 SS 3.0 Ethylene glycol 0.75 Silicone (10 est) 76.25 ER Fluid M Cellulose CF-11 25.0 Petrarch PS 563 2.0 Ethylene glycol 1.0 Silicone (10 est) 72.0 ER Fluid N CC-31 Cellulose 2 25 Ethylene glycol 1.5 EXP-69 5.0 Emery 2960 68.5 ER Fluid O Cellulose CF-11 2 20 EXP-69 3 Butyrolactone 1 Silicone (5 est) 76 ER Fluid P Solka-Floc BW-100 15 EXP-69 2 Malononitrile 0.5 Silicone (10 est) 82.5 ER Fluid O Solka-Floc BW-100 15 EXP-69 2.0 Nitrobenzene 0.5 Silicone (10 est) 82.5 ER Fluid R TEAE Cellulose 20 EXP-69 2 Silicone (10 est) 78 The efficiency of the electrorheological fluid is related to the amount of electrical power required to affect a given change in rheological properties. This is best characterized as the power required for an observed ratio of yield stress under field to the viscosity of the fluid in the absence of a field. From fluid requirements vs. device design considerations, a parameter has been defined as the dimensionless Winslow number, Wn, where; Wn = (YS) 2 (PD)(ηo) YS = Yield stress (Pa) PD = Power density (w/m ) = Current density x Field strength ηo = Viscosity with no field 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 20 C C, and in other embodiments, the ER fluids are characterized as having Wn in excess of 100 at the maximum temperature of the intended application. This temperature may be 80°C, 100°C, or even 120°C. While the invention has been explained in relation 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 modifications as fall within the scope of the appended claims.

Claims: Claims i. An elect:* .eological fluid comprising a hydrophobic liquid phase, cellulosic particles as ε 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 which is capable of being absorbed or adsorbed on the surface of the cellulosic particles. 2. The electrorheological fluid of claim 1 wherein the hydrophobic liquid phase is a non-functionalized polysiloxane. 3. The electrorheological fluid of claim 1 wherein the polysiloxane is a polydimethylsiloxane. 4. The electrorheological fluid of claim 1 wherein the functional groups comprise amino, amido, imino, sulfonyl, sulfoxyl, cyano, hydroxy, hydrocarbyloxy, mercapto, carbonyl, carboxy, epoxy, acetoxy, phosphate, phosphoryl, or haloalkyl functional groups, or salts or mixtures of such groups. 5. The electrorheological fluid of claim 1 wherein the functionalized polysiloxane is represented by the formulae m wherein each X is independently an alkyl, aryl or cycloalkyl group, each of Y to Y is independently X or a functional group capable of being absorbed or adsorbed on the surface of the cellulosic particles provided that at least one of Y 1 to Y 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. 6. The electrorheological fluid of claim 5 wherein the functional groups comprise amino, amido, imino, sulfonyl, sulfoxyl, cyano, hydroxy, hydrocarbyloxy, mercapto, carbonyl, carboxy, epoxy, acetoxy, phosphate, phosphoryl, or haloalkyl functional groups, or salts or mixtures of such groups. 7. The electrorheological fluid of claim 1 wherein the functionalized polysiloxane is represented by the formulae m n wherein each of Y 1 -Y . is independently an alkyl or a functional group selected from -R'N(R) 2 , -R'OR 2 , -R'SH, or -R'COOH, or salts thereof, wherein R' is a divalent group consisting of C, H and optionally O and/or N; each R is indepen¬ dently hydrogen or an alkyl group containing 1 to about 8 carbon atoms or an aryl group containing 6 to about 8 carbon atoms; R is hydrogen, an alkyl or aryl group containing up to about 8 carbon atoms, propylenyloxide, -(C2H 4 O) a - (C 3 HgO) b -R wherein a and b are independently numbers from 0 to 100 provided o at least one of a or b is at least 1; R is H, acetoxy, or a hydrocarbyl group; m is a number from about 10 to about 1000; n is a number from 0 to about 10, each p is independently a number from 0 to about 1000 provided that at least one p ι q is at least about 10, and further provided that at least one of Y -Y is not an alkyl group; or Y 1 and Y2 in Formula I are methyl groups and Y . is an alkylene oxide polymer block. 8. The electrorheological fluid of claim 7 wherein each of Y - Y 3 is independently a -CH 3 , -R'SH, -R'COOH or -R'OH group or a salt thereof. 9. The electrorheological fluid of claim 7 wherein the 1 functional polysiloxane is characterized by Formula I and Y and Y are methyl groups and Y is an -R'SH or -R'OH group. 10. The electrorheological fluid of claim 7 wherein the functional polysiloxane is characterized by Formula I and Y 2 is methyl and Y I and Y 3 are -R'COOH groups. 11. The electrorheological fluid of claim 9 wherein R' is an alkylene group containing up to 8 carbon atoms. 12. The electrorheological fluid of claim 10 wherein R' is an alkylene group containing up to 8 carbon atoms. 13. The electrorheological fluid of claim 1 comprising from 0.5 to about 10% by weight of at least one functionalized silicone. 14. The electrorheological fluid of claim 1 also containing at least one organic polar compound. 15. The electrorheological fluid of claim 14 wherein the polar compound is a polyhydroxy compound. 16. The electrorheological fluid of claim 14 wherein the fluid also contains up to 20% by weight, based on the weight of the organic polar compound, of at least one organic or inorganic acid, base or salt. 17. The electrorheological fluid of claim 1 comprising less than about 1% by weight of water. 18. An electrorheological fluid which comprises a non- functionalized polysiloxane liquid continuous phase, from about 5 to about 40% by weight of cellulosic particles, and from 0.5 to about 10% by weight, based on the weight of the hydrophobic liquid continuous phase of at least one functionalized polysiloxane represented by the formula m n wherein each of Y -Y is independently CH 3 or a functional group selected from -R*N(R)H, -R'OR 2 , -R'SH, or -R'COOH, or salts thereof; R' is a divalent group containing 1 to about 6 carbon atoms, hydrogen and optionally O and N; R is hydrogen or an alkyl group containing 1 to about 8 carbon atoms or an aryl group containing 6 to about 8 carbon atoms; R is hydrogen, an alkyl group containing q 1 to about 8 carbon atoms, propylenyloxide, or -(C 2 H O) a -(C 3 H 6 O) b -R wherein a and b are independently numbers from 0 to 50 provided at least one of a or b q is at least 1; R is H or a lower alkyl group; m is a number from about 10 to about 1000; and n is a number from 0 to about 10, provided that at least one of Y } -Y 3 is not CH 3 ; or Y 1 and Y 2 are CH 3 and Y 3 is an alkylene oxide polymer block. 19. The electrorheological fluid of claim 18 wherein Y to Y is independently -CH 3 , -R'SH, -R'COOH or -R'OH groups or salts thereof. 20. The electrorheological fluid of claim 18 wherein Y 1 and Y . are CH 3 and Y 2 is an -R'SH or -R'OH group. 21. The electrorheological fluid of claim 20 wherein R' contains from 1 to about 3 carbon atoms. 22. The electrorheological fluid of claim 20 wherein R' is a propylene group. 23. The electrorheological fluid of claim 18 wherein Y is CH 3 and Y 1 and Y 3 are -R'-COOH groups. 24. The electrorheological fluid of claim 23 wherein R contains from 1 to about 3 carbon atoms. 25. The electrorheological fluid of claim 23 wherein R' is a propylene group. 26. The electrorheological fluid of claim 18 also containing at least one organic polar compound. 27. The electrorheological fluid of claim 26 containing from about 0.1 to about 10% by weight based on the total weight of the electrorheo- logical fluid of the organic polar compound. 28. The electrorheological fluid of claim 26 wherein the organic polar compound is at least one polyhydroxy compound. 29. The electrorheological fluid of claim 26 wherein the fluid also contains up to 20% by weight, based on the weight of the organic polar compound, of at least one organic or inorganic acid, base or salt. 30. The electrorheological fluid of claim 18 comprising less than about 1% by weight of water. 31. A clutch valve or damper containing the electrorheological fluid of claim 1. 32. A clutch valve or damper containing the electrorheological fluid of claim 18. [received by the International Bureau on 14 June 1993 (14.06.93) ; original claim 1 amended ; claims 5, 7 , and 18 amended and renumbered as claims 3 ,5, and 11 ; claims 4 and 6 replaced by amended claim 4 ; claims 9 and11 replaced by amended claim. 6 ; claims 13-14 and 16-17 replaced by amended claims 7-10 ; claims 31 and 32 replaced by amended claim 12 (3 pages) ] 1. An electrorheological fluid comprising a hydrophobic liquid phase, cellulosic particles as a dispersed phase and from 0.1 up to 25% by weight, based on the weight of the hydrophobic liquid phase of at least one functionalized polysiloxane containing at least one functional group which is capable of being absorbed or adsorbed on the surface of the cellulosic particles. 2. The electrorheological fluid of claim 1 wherein the hydrophobic liquid phase is a non-functionalized polysiloxane. 3. The electrorheological fluid of claim 1 wherein the functionali¬ zed polysiloxane is represented by the formulae m wherein each X is independently an alkyl, aryl or cycloalkyl group, each of Y to Y^ is independently X or a functional group capable of being absorbed or adsorbed on the surface of the cellulosic particles provided that at least one of γ to Y^ is not X, m is a number from 10 to 1000, n is a number from 0 to 10, and each p is independently a number from 0 to 1000 provided that at least one p is at least 10. 4. The electrorheological fluid of claims 1 or 3 wherein the functional groups are selected from amino, amido, imino, sulfonyl, sulfoxyl, cyano, hydroxy, hydrocarbyloxy, mercapto, carbonyl, carboxy, epoxy, acetoxy, phosphate, phosphoryl, and haloalkyl functional groups, and salts and mixtures of such groups. 5. The electrorheological fluid of claim 3 wherein each X is CH3 , each of Y -Yr is independently an alkyl or a functional group selected from -R'N(R) 2 , -R'OR 2 , -R'SH, or -R'COOH, or salts thereof, R' is a divalent group consisting of C, H and optionally O and/or N, each R is independently hydrogen or an alkyl group containing 1 to 8 carbon atoms or an aryl group containing 6 to 8 carbon atoms, R 2 is hydrogen, an alkyl or aryl group containing up to 8 carbon atoms, propylenyloxide, -^H^ ^-^HgO^-R 3 wherein a and b are independently numbers from 0 to 100 provided at least one of a or b is at least 1; R 3 is H, acetoxy, or a hydrocarbyl group, m is a number from 10 to 1000, n is a number from 0 to 10, each p is independently a number from 0 to 1000 provided that at least one p is at least 10, and further provided that at least one of Y -Y is not an alkyl group; or Y 1 and Y 2 in Formula I are methyl groups and Y 3 is an alkylene oxide polymer block. 6. The electrorheological fluid of claim 5 wherein Y* and Y 3 are methyl groups, Y 2 is an -R'SH or -R'OH group, and R' is an alkylene group ∞nt-dning up to 8 carbon atoms. 7. The electrorheological fluid of claim 1 wherein the fluid comprises from 0.5 to 10% by weight of at least one functionalized silicone. 8. The electrorheological fluid of claim 1 also containing at least one organic polar compound. 9. The electrorheological fluid of claim 8 wherein the fluid also contains up to 20% by weight, based on the weight of the organic polar compound, of at least one organic or inorganic acid, base or salt. 10. The electrorheological fluid of claim 1 comprising less than 1 % by weight of water. 11. The electrorheological fluid of claim 1 comprising 5 to 40 % by weight of the cellulosic particles and 0.5 to 10% by weight, based on the weight of the hydrophobic liquid continuous phase, of the functionalized polysiloxane. 12. A clutch valve or damper containing the electrorheological fluid of any one of the previous claims.

Inventors: PIALET JOSEPH WILLIAM, PIALET, JOSEPH, WILLIAM
Applicants: LUBRIZOL CORP, THE LUBRIZOL CORPORATION
Application year: 1992
Main classification: C10M145
IPC codes: C10M145, C10M157, C10M171, C10N20, C10N40, F16F9