Electrorheological fluids with hydrocarbyl aromatic hydroxy compounds

A mixture of a carbon-based hydrophobic base fluid, an electrorheologically active solid particle, and an aromatic hydroxy compound substituted with a hydrocarbyl group containing at least about 6 carbon atoms shows good dispersion characteristics and good electrorheological activity.

BACKGROUND OF THE INVENTION 
The present invention relates to electrorheological fluids and devices, and 
a method for improving the dispersive stability of such fluids. 
Electrorheological ("ER") fluids are fluids which can rapidly and 
reversibly vary their apparent viscosity in the presence of an applied 
electric field. ER fluids are generally dispersions of finely divided 
solids in hydrophobic, electrically non-conducting oils. They 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. 
ER fluids may be used in applications in which it is desired to control 
the transmission of forces by low electric power levels, for example, in 
clutches, hydraulic valves, shock absorbers, vibrators, or systems used 
for positioning and holding work pieces in position. 
ER fluids have been known since 1947, when U.S. Pat. No. 2,417,508 was 
issued to Winslow, disclosing that certain dispersions of finely divided 
solids such as starch, carbon, limestone, gypsum, flour, etc., dispersed 
in a non-conducting liquid would undergo an increase in flow resistance 
when an electrical potential difference was applied. In the extensive work 
which has followed this discovery, many variations of ER fluids have been 
discovered, in which the solid phase, the liquid phase, or other 
components have been varied. One feature of many ER fluids is that a 
dispersant (also referred to as a surfactant) is required in order to 
maintain the finely divided solids dispersed through the liquid medium. 
The use of a dispersant, however, has been reported to lead to diminished 
electro-rheological activity in some systems. 
Among the various attempts to provide an improved ER fluid are the 
following: 
Japanese application 03/170600 (Tonen Corp.), Jul. 24, 1991, discloses an 
electro-viscous fluid comprising an electric insulating fluid, porous 
solid particles, a dispersant, and a polyhydric alcohol. The dispersants 
can include sulfonates, phenates, phosphonates, succinimides, amine, and 
nonionic dispersants including e.g. sorbitan monooleate. 
Japanese application 04/120194 (Tonen Corp.), Apr. 21, 1992 (available as 
Derwent Abstract 92-180972/22), discloses electroviscous fluid containing 
at least one of partially etherified and esterified products of polyhydric 
alcohols in a base electroviscous fluid consisting of an electrically 
insulating fluid, porous solid particles, and dispersant. Dispersants 
include sulfonates, phenates, phosphonates, succinic imides, amines, and 
non-ionic dispersants. 
European publication 395 359 (Tonen Corp.), Oct. 31, 1990, discloses an 
electrically insulating medium containing dispersed solid particles, an 
acid, base, or salt, a polyhydric alcohol, an antioxidant, and optionally 
an agent to assist dispersing of the solid particles (e.g. a sulfonate, 
phenate, phosphonate, succinic acid imide, amine or non-ionic dispersing 
agents). 
European Application 342,041 (Toa Nenryo), Nov. 15, 1989, discloses an 
electrically insulating liquid, a porous solid particulate matter, water, 
and acid, base, or salt. A dispersant can also be used, for example, 
non-ionic dispersants such as sulfonates, phenates, phosphonates, succinic 
acid imides, and amines. 
U.S. Pat. No. 2,970,573, Westhaver, Jul. 20, 1976, discloses electroviscous 
fluids comprising particles of modified starch dispersed in high 
concentration in a dielectric oil, the particles containing an 
electrolyte. Dispersants are also disclosed, usually of the water-in-oil 
type. 
U.S. Pat. No. 3,367,872, Martinek et al., Feb. 6, 1968, discloses an 
electroviscous fluid comprising a non-polar oleaginous vehicle, such as a 
mineral oil, a particulate solid, and optionally other ingredients such as 
a surface active agent. Nonionic agents include ethers and esters formed 
by reaction of ethylene oxide with a variety of compounds such as fatty 
alcohols, alkyl phenols, glycol ethers, fatty acids, [etc.]. 
It has now been found that a certain class of dispersant imparts good 
dispersive stability to ER active particles in carbon-based fluids, while 
providing a fluid which maintains good ER activity. 
SUMMARY OF THE INVENTION 
The present invention provides an electrorheological fluid comprising (a) a 
carbon-based hydrophobic base fluid; (b) an electrorheologically active 
solid particle; and (c) an aromatic hydroxy compound substituted with a 
hydrocarbyl group containing at least 6 carbon atoms. The invention 
further comprises a process for improving the dispersive stability of an 
electrorheological fluid of a carbon-based hydrophobic base fluid and an 
electrorheologically active solid particle, said process comprising adding 
to the electrorheological fluid an aromatic hydroxy compound substituted 
with a hydrocarbyl group containing at least 6 carbon atoms. The invention 
further comprises electrorheological devices which contain a fluid of this 
type.

DETAILED DESCRIPTION OF THE INVENTION 
The first component of the composition of the present invention is a 
carbon-based hydrophobic base fluid. The term "carbon-based" is intended 
to be approximately synonymous with "organic" and to refer to materials 
other than silicones (which can also be hydrophobic). This base fluid is a 
preferably a non-conducting, electrically insulating liquid or liquid 
mixture. Examples of such fluids include transformer oils, mineral oils, 
vegetable oils, aromatic oils, paraffin hydrocarbons, naphthalene 
hydrocarbons, olefin hydrocarbons, chlorinated paraffins, synthetic 
esters, hydrogenated olefin oligomers, and derivatives and mixtures 
thereof. The choice of the hydrophobic liquid phase will depend largely on 
practical considerations including compatibility of the liquid with other 
components of the system, solubility of certain components therein, and 
the intended utility of the ER fluid. For example, if the ER fluid is to 
be in contact with elastomeric materials, the hydrophobic liquid phase 
should not contain oils or solvents which affect those materials. 
Similarly, the liquid phase should be selected to have suitable stability 
over the intended temperature range, which in some cases may extend to 
120.degree. C. or even higher. Furthermore, the fluid should have a 
suitably low viscosity in the absence of a field that sufficiently large 
amounts of the dispersed phase, described below, can be incorporated into 
the fluid. Suitable liquids include those which have a viscosity at room 
temperature of 1 to 300 or 500 centistokes, or preferably 2 to 20 or 50 
centistokes. Mixtures of two or more different non-conducting liquids can 
be used for the liquid phase. Mixtures can be selected to provide the 
desired viscosity, pour point, chemical and thermal stability, component 
solubility, etc. Useful liquids generally have as many of the following 
properties as possible: (a) high boiling point and low freezing point; (b) 
low viscosity so that the ER fluid has a low no-field viscosity and so 
that 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. 
Useful natural oils include animal oils and vegetable oils (e.g., castor 
oil, lard oil, and sunflower oils, including high oleic sunflower oil 
available under the name Trisun.TM. 80, rapeseed oil, and soybean oil) as 
well as 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. 
Synthetic lubricating oils include alkylene oxide polymers and 
interpolymers and derivatives thereof where the terminal hydroxyl groups 
have been modified by esterification or etherification. They include 
polyoxyalkylene polymers prepared by polymerization of ethylene oxide or 
propylene oxide, the alkyl and aryl ethers of these polyoxyalkylene 
polymers, and mono- and polycarboxylic esters thereof, for example, acetic 
acid esters, mixed C.sub.3 -C.sub.8 fatty acid esters, and C.sub.13 oxo 
acid diester of tetraethylene glycol. 
Another suitable class of synthetic liquids comprises the esters of 
monocarboxylic acids or dicarboxylic acids with a variety of alcohols and 
polyols. Monocarboxylic acids include e.g. hexanoic acid, heptanoic acid, 
octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic 
acid, octadecanoic acid, stearic acid, oleic acid, and isomers of such 
acids. Dicarboxylic acids include e.g. phthalic acid, succinic acid, alkyl 
succinic acids, alkenyl succinic acids, maleic acid, azelaic acid, suberic 
acid, sebacic acid, fumaric acid, adipic acid, linoleic acid dimer, 
malonic acid, alkylmalonic acids, alkenyl malonic acids. Suitable alcohols 
include e.g., butyl alcohol, hexyl alcohol, dodecyl alcohol, 2-ethylhexyl 
alcohol, ethylene glycol, diethylene glycol monoether, and propylene 
glycol. Specific preferred examples of such esters include di-isodecyl 
azelate, available under the name Emery.TM. 2960, and isodecyl 
pelargonate, available under the name Emery.TM. 2911. These and other 
esters are well known to those skilled in the art. 
Poly alpha olefins and hydrogenated poly alpha olefins (referred to 
sometimes as PAOs) are also useful in the present invention. PAOs are 
derived from alpha olefins containing 2 to 24 or more carbon atoms such as 
ethylene, propylene, 1-butene, isobutene, 1-decene, and so on. Specific 
examples include polyisobutylene having a number average molecular weight 
of 650, a hydrogenated oligomer of 1-decene having a viscosity of 8 cst at 
100.degree. C., ethylene propylene copolymers, and the like. An example of 
a hydrogenated poly alpha olefin is available under the name Emery.TM. 
3004. 
Other examples of possibly suitable liquids include liquid esters of 
phosphorus-containing acids such as tricresyl phosphate, trioctyl 
phosphate, and the diethyl ester of decylphosphonic acid. 
The amount of the carbon-based hydrophobic base fluid is normally the 
amount required to make up 100% of the composition after the other 
ingredients are accounted for. Often the amount of the base fluid is 
10-94.9 percent of the total composition, preferably 36-89 percent, and 
most preferably 56-79 percent. These amounts are normally percent by 
weight, but if an unusually dense dispersed solid phase is used, it may be 
more appropriate to determine these amounts as percent by volume. 
The second major component of the ER fluid of the present invention is an 
electrorheologically active solid particle, which is to be dispersed in 
the liquid component. Many ER active solids are known, and any of these, 
as well as their equivalents, are considered to be suitable for use in the 
ER fluids of the present invention. 
One preferred class of ER active solids includes carbohydrate based 
particles and related materials such as starch, flour, monosaccharides, 
and preferably cellulosic materials. The term "cellulosic materials" 
includes cellulose as well as derivatives of cellulose such as 
microcrystalline cellulose. Microcrystalline cellulose 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 commercially important functional and rheological 
properties can be produced. Microcrystalline cellulose can be obtained 
from FMC Corp. under the name Lattice.TM. NT-013. Amorphous cellulose is 
also useful in the present invention; examples of amorphous cellulose 
particles are CF1, CF11, and CC31, available from Whatman Specialty 
Products Division of Whatman Paper Limited, and Solka-Floc.TM., available 
from James River Corp. Other cellulose derivatives include ethers and 
esters of cellulose, including methyl cellulose, ethyl cellulose, 
hydroxyethyl cellulose, hydroxypropyl cellulose, sodium carboxymethyl 
cellulose, cellulose propionate, cellulose butyrate, cellulose valerate, 
and cellulose triacetate. Other cellulose derivatives include cellulose 
phosphates and cellulose reacted with various amine compound. Other 
cellulosic materials include chitin, chitosan, chondrointon sulfate, and 
viscose or cellulose xanthate. A more detailed listing of suitable 
cellulosics is set forth in copending U.S. application Ser. No. 
07/823,489, filed Jan. 21, 1992 (Case 2598R). 
In another embodiment, the ER active solid particles are particles of 
organic semiconductive polymers such as oxidized or pyrolyzed 
polyacrylonitrile, polyacene quinones, polypyrroles, polyphenylenes, 
polyphenylene oxides, polyphenylene sulfides, polyacetylenes, 
polyvinylpyridines, polyvinylpyrrolidones, polyvinylidene halides, 
polyphenothiazines, polyimidazoles, and preferably polyaniline, 
substituted polyanilines, and aniline copolymers. Compositions of the 
above and related materials, treated or doped with various additives 
including acids, bases, metals, halogens, sulfur, sulfur halides, sulfur 
oxide, and hydrocarbyl halides can also be employed. A more detailed 
description of certain of these materials can be found in copending U.S. 
application Ser. No. 07/774,397, filed Oct. 10, 1991 (case 2594R/B). A 
highly preferred organic polymeric semiconductor is polyaniline, 
particularly the polyaniline prepared by polymerizing aniline in the 
presence of an oxidizing agent (such as a metal or ammonium persulfate) 
and 0.1 to 1.6 moles of an acid per mole of aniline, to form an acid salt 
of polyaniline. The polyaniline salt is thereafter treated with a base to 
remove some or substantially all of the protons derived from the acid. A 
more complete description of polyaniline and its preferred method of 
preparation is set forth in copending U.S. application Ser. No. 
07/774,398, filed Oct. 10, 1991 (case 2593R/B). 
Inorganic materials which can be suitably used as ER active particles 
include carbonaceous powders, metals, semiconductors (based on silicon, 
germanium, and so on), barium titanate, silver germanium sulfide, 
ceramics, copper sulfide, carbon particles, silica gel, magnesium 
silicate, alumina, silica-alumina, pyrogenic silica, zeolites, and the 
like. 
Another class of suitable ER active solid particles is that of polymeric 
salts, including silicone-based ionomers (e.g. the ionomer from amine 
functionalized diorganopoly-siloxane plus acid), metal thiocyanate 
complexes with polymers such as polyethylene oxide, and carbon based 
ionomeric polymers including salts of ethylene/acrylic or methacrylic acid 
copolymers or phenol-formaldehyde polymers. Especially preferred is a 
polymer comprising an alkenyl substituted aromatic comonomer, a maleic 
acid comonomer or derivative thereof, and optionally additional 
comonomers, wherein the polymer contains acid functionality which is at 
least partly in the form of a salt. Preferably in such materials the 
maleic acid comonomer is a salt of maleic acid in which the maleic acid 
comonomer is treated with 0.5 to 2 equivalents of base. Most preferably 
this material is a 1:1 molar alternating copolymer of styrene and maleic 
acid, the maleic acid being partially in the form of the sodium salt. This 
material is described in more detail in copending U.S. application Ser. 
No. 07/878,797, filed Apr. 1, 1992 (case 2610R/B). 
Other miscellaneous materials which can be used as ER active solid 
particles include fused polycyclic aromatic hydrocarbons, phthalocyanine, 
flavanthrone, crown ethers and salts thereof, including the products of 
polymeric or monomeric oxygen- or sulfur-based crown ethers with 
quaternary amine compounds, lithium hydrazinium sulfate, and ferrites. 
Certain of the above mentioned solid particles are customarily available in 
a form in which a certain amount of water or other liquid polar material 
is present. This is particularly true for polar organic particles such as 
cellulose or ionic polymers. These liquid polar materials need not 
necessarily be removed from the particles, but they are not generally 
required for the functioning of the present invention. The acceptable 
amounts of such liquid polar material is discussed in more detail below. 
The particles used in the ER fluids of the present invention can be in the 
form of powders, fibers, spheres, rods, core-shell structures, etc. The 
active material can be an ER-active core which is covered by an insulative 
or protective shell or an inert core which is covered by an ER-active 
shell. 
The size of the particles of the present invention is not particularly 
critical, but generally particles having a number average size of 0.25 to 
100 .mu.m, and preferably 1 to 20 .mu.m, are suitable. The maximum size of 
the particles would depend in part on the dimensions of the 
electrorheological device in which they are intended to be used, i.e., the 
largest particles should normally be no larger than the gap between the 
electrode elements in the ER device. 
The amount of such polymer particles in the ER fluid should be sufficient 
to provide a useful electrorheological effect at reasonable applied 
electric fields. However, the amount of particles should not be so high as 
to make the fluid too viscous for handling in the absence of an applied 
field. These limits will vary with the application at hand: an 
electrorheologically active grease, for instance, would desirably have a 
higher viscosity in the absence of an electric field than would a fluid 
designed for use in e.g. a valve or clutch. Furthermore, the amount of 
particles in the fluid may be limited by the degree of electrical 
conductivity which can be tolerated by a particular device, since the 
polymeric particles normally impart at least a slight degree of 
conductivity to the total composition. For most practical applications the 
polymeric particles will comprise 5 to 60 percent by weight of the ER 
fluid, preferably 10 to 50 percent by weight, and most preferably 15 to 35 
percent by weight. Of course if the nonconductive hydrophobic fluid is a 
particularly dense material such as carbon tetrachloride or certain 
chlorofluorocarbons, these weight percentages could be adjusted to take 
into account the density. Likewise if the particles themselves are 
particularly dense, such as certain compounds of barium, they may 
necessarily be present in a larger percentage by weight. Practical 
considerations might dictate that a volume percent concentration 
calculation would be more appropriate in such circumstances. Determination 
of such an adjustment would be within the abilities of one skilled in the 
art. 
The third major component of the ER fluid of the present invention is an 
aromatic hydroxy compound substituted with a hydrocarbyl group containing 
at least 6 carbon atoms. The term "aromatic hydroxy compound" includes 
phenols (which are preferred), bridged phenols, in which the bridging 
group is an oxygen atom, a sulfur atom, a nitrogen atom, a carbon atom 
(including an alkylene group), and the like, as well as phenols directly 
linked through covalent bonds (e.g. 4,4'-bis(hydroxy)biphenyl), hydroxy 
compounds derived from fused-ring hydrocarbons (e.g., naphthols and the 
like); and polyhydroxy compounds such as catechol, resorcinol and 
hydroquinone. Mixtures of one or more hydroxyaromatic compounds also may 
be used. When the term "phenol" is used herein, it is thus to be 
understood that this term is not intended to limit the aromatic group of 
the phenol to benzene. Accordingly, it is to be understood that the 
aromatic group as represented by "Ar" may be mononuclear or polynuclear. 
The polynuclear groups can be of the fused type wherein an aromatic 
nucleus is fused at two points to another nucleus such as found in 
naphthyl, anthranyl, etc. The polynuclear group can also be of the linked 
type wherein at least two nuclei (either mononuclear or polynuclear) are 
linked through bridging linkages to each other. These bridging linkages 
can be chosen from the group consisting of alkylene linkages, ether 
linkages, keto linkages, sulfide linkages, polysulfide linkages of 2 to 
about 6 sulfur atoms, etc. 
The aromatic hydroxy compound can likewise contain one or more hydroxy 
groups; most commonly, however, there will be only one hydroxy group on 
each aromatic nucleus. 
The aromatic hydroxy compound is substituted with at least one, and 
preferably not more than two, hydrocarbyl groups containing at least 6 
carbon atoms. As used herein, the term "hydrocarbyl substituent" or 
"hydrocarbyl group" means a group having a carbon atom directly attached 
to the remainder of the molecule and having predominantly hydrocarbon 
character. Such groups include hydrocarbon groups, substituted hydrocarbon 
groups, and hetero groups, that is, groups which, while primarily 
hydrocarbon in character, contain atoms other than carbon present in a 
chain or ring otherwise composed of carbon atoms. The presence of the 
hydrocarbyl group is believed to impart to the compound a degree of 
compatibility with the carbon-based hydrophobic base fluid, so that the 
compound can effectively function as a dispersant. 
Suitable hydrocarbyl groups include cycloalkyl groups, aromatic groups, 
aromatic-substituted alkyl groups and alkyl-substituted aromatic groups. 
Other suitable hydrocarbyl groups include substituents derived from any of 
the polyalkenes including polyethylenes, polypropylenes, polyisobutylenes, 
ethylene-propylene copolymers, chlorinated olefin polymers and oxidized 
ethylene-propylene copolymers. It is preferred that the hydrocarbyl 
substituent be an alkyl substituent. More preferably the alkyl group will 
contain 9 to 100 carbon atoms, and more preferably still 20 to 30 carbon 
atoms. Preferred hydrocarbyl groups include polyisobutyl groups and 
polypropyl groups having the desired number of carbon atoms. 
Examples of suitable hydrocarbyl-substituted hydroxy-aromatic compounds 
include the various naphthols, the various alkyl-substituted catechols, 
resorcinols, and hydroquinones, the various xylenols, the various cresols, 
aminophenols, and the like. Examples of various suitable compounds include 
hexylphenol, heptylphenol, octylphenol, nonylphenol, decylphenol, 
dodecylphenol, tetrapropylphenol, eicosylphenol, polyisobutylphenol, 
polypropylphenol, and the like. Examples of suitable 
hydrocarbyl-substituted thiol-containing aromatics include 
hexylthiophenol, heptylthiophenol, octylthiophenol, nonylthiophenol, 
dodecylthiophenol, tetrapropylthiophenol, and the like. Examples of 
suitable thiol- and hydroxyaromatic compounds include 
dodecylmonothio-resorcinol, 2-mercaptoalkylphenol where the alkyl group is 
as set forth above. 
The hydrocarbyl substituted aromatic hydroxy compound, whether mononuclear, 
polynuclear, bridged, etc., can further contain other substituents. Among 
the possible substituents are alkyl groups containing fewer than 6 carbon 
atoms, carboxyl groups, amino groups, hydroxy groups, alkylenehydroxy 
groups, ester groups, nitro groups, halogen groups, nitrile groups, ketone 
groups, and aldehyde groups. 
The amount of the hydrocarbyl-substituted aromatic hydroxy compound in the 
present invention is an amount sufficient to improve the dispersive 
stability of the composition. Normally the effective amount will be 0.1 to 
20 percent by weight of the fluid, preferably 0.4 to 10 percent by weight 
of the fluid, and most preferably 1 to 5 percent by weight of the fluid. 
Hydrocarbyl-substituted aromatic hydroxy compounds are prepared by methods 
which are well known to those skilled in the art, such as by alkylation of 
aromatic hydroxy compounds. Such methods are discussed in the article 
entitled "Alkylation of Phenols," in Kirk-Othmer "Encyclopedia of Chemical 
Technology," Second Edition, Volume 1, page 894 to 895, Interscience 
Publishers, division of John Wiley and Company, N.Y., 1963. 
Example A. Synthesis of Surfactant. 
One thousand parts by weight phenol and 64 parts by weight Amberlyst 15.TM. 
sulfonic acid functionalized resin (semi dry) are charged to a reactor at 
52.degree.-60.degree. C. The contents are heated with stirring under a 
stream of nitrogen and maintained at 125.degree.-130.degree. C. for two 
hours. To the reactor is added 1116 parts propylene tetramer and the 
mixture is maintained at temperature for three hours. Agitation is stopped 
and, after settling for 30 minutes the reaction mixture is sent to a 
stripping column where volatiles are removed. The resulting produce 
contains less than 0.5% residual propylene tetramer and less than 1% 
residual phenol. 
Example B. Synthesis of Surfactant 
Example A is substantially repeated except as follows: One thousand parts 
by weight of synthetic phenol and 50 parts Super Filtrol.TM. Grade 1, a 
sulfuric acid-impregnated filter aid, are charged to a reactor and heated 
to 50.degree. C. Propylene tetramer, 1,226 parts, is rapidly added, with 
stirring, maintaining the temperature below 60.degree. C. Stirring is 
discontinued and the material is allowed to settle for 4 hours. The 
material separates into two layers; the upper layer is decanted, filtered, 
and stripped, to yield the product. The lower layer, which is largely the 
filter aid, is recharged with sulfuric acid and used as a heel for 
subsequent batches. 
Example C. Synthesis of Surfactant 
Example B is substantially repeated except that the starting materials are 
126 parts by weight phenol and 1000 parts by weight C.sub.24 -C.sub.28 
olefin fraction from Gulf. 
Example D. Synthesis of Surfactant 
Two hundred seventy-five parts by weight phenol and 126 parts toluene are 
charged to a reactor and the contents heated to 49.degree. C. Seven and 
one-half parts BF.sub.3 are introduced to the reactor with stirring 
through a submerged line, maintaining the temperature below 55.degree. C. 
One thousand parts by weight polyisobutylene are added while maintaining 
the temperature at 38.degree. C. maximum. The contents are maintained at 
35.degree.-38.degree. C. for 8 hours. Lime is added to neutralize the 
excess BF.sub.3, and the contents are filtered. 
The contents are subjected to stripping followed by vacuum stripping at 
150.degree.-270.degree. C. to provide the desired product. 
The composition of the present invention can further contain other 
additives and ingredient which are customarily used in such fluids. Most 
importantly, it can contain a polar activating material other than the 
three aforementioned components. 
As has been mentioned above, certain of the ER-active particles, such as 
cellulose or polymeric salts, commonly have a certain amount of water 
associated with them. This water can be considered such a polar activating 
material. The amount of water present in the compositions of the present 
invention is typically 0.1 to 30 percent by weight, based on the solid 
particles. More generally the amount of polar activating material (which 
need not be water) will be 0.1 to 10 percent by weight, based on the 
entire fluid composition, preferably 0.5 to 4%, and most preferably 1.5 to 
3.5 weight percent, based on the fluid. The polar activating material can 
be introduced to the ER fluid as a component of the solid particles (such 
as absorbed water), or it can be separately added to the fluid upon mixing 
of the components. Whether the polar activating material remains dispersed 
through the bulk of the ER fluid or whether it associates with the solid 
particles is not precisely known in every case, but such details are not 
essential to the functioning of the present invention. Indeed, even the 
presence of a polar activating material is not essential to the 
functioning of the fluids of the present invention or to the dispersant 
characteristics of the surfactant. Rather it is observed that some ER 
fluid systems function more efficiently when the polar activating material 
is present. Accordingly, it is sometimes desirable not to dry cellulose 
thoroughly before it is used in the ER fluids of the present invention. On 
the other hand, for fluids which will be exposed to elevated temperatures 
during their lifetime, it is often desirable that no water or other 
volatile material be present. For such applications the use of an 
alternative polar material, having significantly lower volatility, can be 
useful. 
Suitable polar activating materials include water, other hydroxy-containing 
materials as alcohols and polyols, including ethylene glycol, glycerol, 
1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 2,5-hexanediol, 
2-ethoxyethanol, 2-(2-ethoxyethoxy)ethanol, 2-(2-butoxyethoxy)ethanol, 
2-(2-methoxyethoxy)ethanol, 2-methoxyethanol, 2-(2-hexyloxyethoxy)ethanol, 
and glycerol monooleate, as well as amines such as ethanolamine and 
ethylenediamine. Other suitable materials are carboxylic acids such as 
formic acid and trichloroacetic acid. Also included are such aprotic polar 
materials as dimethylformamide, dimethylsulfoxide, propionitrile, 
nitroethane, ethylene carbonate, propylene carbonate, pentanedione, 
furfuraldehyde, sulfolane, diethyl phthalate, and the like. 
While the polar material is believed to be normally physically adsorbed or 
absorbed by the solid ER-active particles, it is also possible to 
chemically react at least a portion of the polar material with the 
polymer. This can be done, for example, by condensation of alcohol or 
amine functionality of certain polar materials with an acid or anhydride 
functionality on the polymer or its precursor. 
The ER fluids of the present invention find use in clutches, valves, 
dampers, positioning equipment, and the like, where it is desirable to 
vary the apparent viscosity of the fluid in response to an external 
signal. Such devices can be used, for example, to provide an automotive 
shock absorber which can be rapidly adjusted to meet the road conditions 
encountered during driving. 
EXAMPLES Examples 1-19 
compositions with the following surfactants are examined at 20.degree. and 
60.degree. , and the yield stress (in kPa) is measured in the presence of 
a 6 kV/mm field using a Couette test apparatus. In the Couette testing, 
data is gathered using a custom horizontal concentric cylinder 
electrorheometer. The shear stress is determined by measuring the torque 
required to rotate an inner cylinder separated from an outer cylinder by 
the ER fluid. Because this rheometer uses a lip seal, some seal drag is 
apparent in the measurements. The shear rate is determined from the 
rotation rate assuming couette flow. This device has a shear rate range of 
20 to 1000 s.sup.-1. The electrode gap is 1.25 mm. The rheometer can 
evaluate fluids over the temperature range of -20.degree. to 120.degree. 
C. For each sample tested, the composition contains 25% by weight 
cellulose which in turn contains 2% or 3.5% water (by Karl Fischer), and 
3% by weight of the indicated surfactant, in a medium of Emery 2960.TM. 
diisodecyl azelate. 
TABLE I 
______________________________________ 
Ex. Surfactant 
______________________________________ 
1* none 
2 C.sub.24-28 alkyl-substituted phenol 
3 polyisobutylene (mw 940)-substituted phenol 
4 propylene tetramer substituted phenol 
5 matl. of Ex. 2, formaldehyde coupled 
6 polypropylene (500 M.sub.n)-alkylated phenol 
7* glycerol monooleate 
8* 3-decyloxysulfone 
9* sodium alkyl sulfonate 
10* nonylphenoxypoly(ethyleneoxy)ethanol 
11* sorbitan sesquioleate 
12* diethoxylated oleyl alcohol 
13* ethoxylated oleic acid (600 MW) 
14* oleylamine 
15* oleic acid 
16* ester of polyisobutenyl succinic anhydride with 
pentaerythritol 
17* bis(2-hydroxyethyl)tallowamine 
18* Hypermer KD3.sup.a 
19* polyisobutenylsuccinic anhydride adduct with 
poly(ethyleneamines) 
______________________________________ 
.sup.a polymeric dispersant from ICI, structure not known. 
*designates a comparative example 
The results of the testing show that the samples in which the surfactants 
of the present invention are employed exhibit high yield stress in the 
presence of the electric field. 
Examples 20-49 
Samples as indicated in Table II are prepared and tested as in Example 1. 
In each of these Examples the solid is cellulose, dried under vacuum at 
150.degree. C. for 16-18 hours to provide a water level of less than 1% 
except as noted. The polar activator is ethylene glycol, and the 
surfactant is an alkyl phenol having 24-28 carbon atoms in the alkyl 
group, except as noted. The base fluid is Emery.TM. 2960 (diisodecyl 
azelate) or Emery.TM. 2911 (isodecyl pelargonate), as indicated: 
TABLE II 
______________________________________ 
% % 
Ex. Cellulose, % 
Eth. Gly. 
Surfactant 
Base fluid 
______________________________________ 
20* 25 1.50 0 Emery .TM. 2960 
21 30 2.00 3.0 Emery .TM. 2911 
22 30 2.25 3.0 " 
23 30 2.50 3.0 " 
24 30 2.75 3.0 " 
25 10 0.90 2.0 Emery .TM. 2960 
26 10 0.90 4.0 " 
27 10 0.5 4.0 " 
28 10 2.0 2.0 " 
29 10 0.5 2.0 " 
30 10 0.9 4.0 " 
31 10 2.0 4.0 " 
32 30 2.0 3.0 " 
33 30 1.5 3.0 " 
34 30 1.75 3.0 " 
35 30 0.9 3.0 " 
36 30 0.9 2.0 " 
37 30 0.5 4.0 " 
38 30 1.5 4.0 " 
39 30 2.25 3.0 " 
40 15.sup.a 1.0 3.0 " 
41 25.sup.a 1.0 3.0 " 
42 25 1.25 3.0 " 
43 25 1.0 3.0 " 
44 30 1.5 3.0 Emery .TM. 2911 
45 30 3.25 3.0 " 
46 30 1.25 3.0 " 
47* 25 1.25 0 Emery .TM. 2960 
48* 25 1.25 3.0.sup.b 
" 
49 25 1.25 3.0.sup.c 
" 
______________________________________ 
*a comparative example 
.sup.a dried 6.5 hours at 170.degree. C. 
.sup.b surfactant is glycerol monooleate 
.sup.c surfactant is polyisobutylphenol 
The examples within the scope of the invention show good electrorheological 
activity. 
Examples 50-59 
Samples as indicated in Table III are prepared and tested in an oscillating 
duct flow apparatus. In this apparatus data is gathered using an 
oscillating test fixture which pumps the ER fluid back and forth between 
parallel plate electrodes as the field is increased to 6 kV/mm. The shear 
stress is determined by measuring the force required to move the fluid 
through the electrodes. The mechanical amplitude is .+-.1 mm and the 
electrode gap is 1 mm. The mechanical frequency range is 0.5 to 30 Hz, 
which produces a shear rate range of 600 to 36,000 s.sup.-1. The shear 
rate is calculated at the wall of the electrodes assuming Poiseuille flow. 
The apparatus is capable of testing a fluid over the temperature range of 
-20.degree. to 120.degree. C. In each of these Examples the solid is 
polyaniline, used at 20 percent by weight; the surfactant, used at 3 
percent by weight, is as indicated. No polar activator is used. The base 
fluid is Emery.TM. 2960 (diisodecyl azelate), Emery.TM. 2911 (isodecyl 
pelargonate), or Emery.TM. 3004 PAO (hydrogenated poly-alpha olefin) as 
indicated: 
TABLE III 
______________________________________ 
Ex. Base Fluid Surfactant 
______________________________________ 
50* Emery .TM. 2960 
none 
51 " C.sub.12 alkyl substituted phenol 
52 " C.sub.24-28 alkyl substituted phenol 
53* Emery .TM. 3004 PAO 
none 
54 " C.sub.24-28 alkyl substituted phenol 
55* Emery .TM. 2911 
none 
56 " C.sub.24-28 alkyl substituted phenol 
57* " glycerol monooleate 
58* Emery .TM. 2960 
" 
59* Emery .TM. 3004 PAO 
" 
______________________________________ 
*comparative examples 
The results show good electrorheological properties when the surfactant of 
the present invention is used. 
Examples 60-62 
The procedure of Examples 50-59 is repeated except that the solid particle 
is the sodium salt of a 1:1 molar alternating copolymer of maleic 
anhydride and styrene, containing about 5 percent adsorbed water, and 
present in an amount of 40 weight percent of the ER fluid. In each case 
the base fluid is Emery 3004 PAO. The surfactant used is as shown in Table 
IV. 
TABLE IV 
______________________________________ 
Example Surfactant type 
Surfactant amount 
______________________________________ 
60* none 0 
61* glycerol monooleate 
3 
62 C.sub.24-28 alkyl phenol 
3 
______________________________________ 
*a comparative example 
The results show good electrorheological properties when the surfactant of 
the present invention is used. 
Each of the documents referred to above is incorporated herein by 
reference. Except in the Examples, or where otherwise explicitly 
indicated, all numerical quantities in this description specifying amounts 
of materials or reaction conditions are to be understood as modified by 
the word "about." Unless otherwise indicated, each chemical or composition 
referred to herein should be interpreted as being a commercial grade 
material which may contain the isomers, by-products, derivatives, and 
other such materials which are normally understood to be present in the 
commercial grade. As used herein, the expression "consisting essentially 
of" permits the inclusion of substances which do not materially affect the 
basic and novel characteristics of the composition under consideration.