CA2104405A1 - Electrorheological fluids based on synthetic sheet silicates - Google Patents

Abstract

ABSTRACT

Electrorheological fluids based on synthetic sheet silicates Electrorheological fluids have been developed which essentially comprise an aluminum-free metal silicate hydrate which has a sheet structure, a dispersant and an inert aprotic dispersion medium. The metal silicate hydrate preferably is of the kenyaite, magadiite and/or kanemite type. The dispersion medium is preferably a silicone oil having a viscosity range of from 0.5 to 1,000 mPas and/or a mineral oil or a paraffin oil having a viscosity range of from 0.1 to 1,000 mPas. The metal silicate hydrate is added to the electrorheological fluid in a concentration of from 1 to 50% by weight.

Description

HOECHST AKTIENGESELLSCHAFT HOE 92/F 260 Dr.KH/St DESCRI PTION

Electrorheological fluids based on Isynthetic ~heet silicates Electrorheological fluids (ER fluid), thus called in order to e~tablish a clear demarcati.on against the electroviscous phenomena in charged colloids known from the literature (T.Cu Jordan, M.T. Shaw, IEEE Tra:ns.
Electr. Insul., Vol. 24, No. 5, 1989, 849 et se~.), are dispersions of finely particulate, polarizable solids in inert (hydrophobic) and electrically nonconcluctive liquids, whose flow behavior changes ~ubstantially in an electric $ield.

Sufficiently strong electric fields thu~ result both in a change in vi8c09ity and in the development of a distinctive yield strength, i.e. at shear force& below a limiting shear force the fluid behaves as an elastic solid. From a rheological point of view, the fluids change from ~imple liquid~ (Newtonlan system) to p~eudo-plastic liquids (Bingham bodies).

This behavior, known ~ince the 40'~ (US Patents 2,417,850and 3,047,507) can be achieved in suitable fluids by means of both electric direct voltage and alternating voltage (T.W. Martinek US Patent 4,502,973). In doing ~o, it is technically desirable to accompli~h a low ~o negligible current flow. The electrorheological effect reacts to changes in the electric ~oltage level within a very short time, typically with time constants in the millisecond range. These sy~tem~ known as "smart fluids"
can be u~ed industrially when transmitting and a~tenuat-ing large force~ with the aid of low electric outputa over short periods, auch as, for example, in dampexs, ~ibrator~, clutches, a~ hydraulic valveR and in active undercarriages. A distinctive ad~ance when moving from '' '. ' ' . ~
.

2 ~

conventional passive sy~tem~ to electrorheological systems i~ possible by electrical adjustment of the viscosity yield strength to the instantcmeou~ state of motion. Such active feedback ~ystems are increasingly required for overcoming the technical problems of moving systems.

The industrial use of an ER fluid requir,e~, in addition to an adequate ER effect, a high temperature stability and chemical stability of the fluid, low electric co:n-ductivity, negligible electrophoretic effect~, lowabra~iveness an~ adequate ~hearing and ~edimentation stability. In each case, the fluid must be readily redispersible even after prolonged ~tanding and, in contact with elastomeric materials, must not produce a swelling or dissolving effect.

In the case of most of the ER fluids repre~enting the prior art, the dispersed phase compri~es polyelectrolytes (US Patent Nos. 3,970,573, 3,047,507, 4,992,192, 4,~94,198), zeolite~ and ~ilica gels (German Patent Nos. 3517281 A1, 356g34 A1~ or else exotic inorganic compounds such as Li hydrazinium sulfate (US Patent No. 4,772,407) whose effect i~ achieved by loading the di~persed phase with considerable amounts of water (up to 20%). Owing to solvation of the ions present and to ~urface charge~, the water fractiona permit an increa~e in the ionic conductivity and thus generate the polariz-ability of the di~per3ed particles which i~ required ~or the ER effect. The particle~ polarized in the electric field agglomerate owing to dipole-dipole interaction and yenerate an increased viscosity, hydrogen bond formation playing an additional role. The efect i~ re~ersible.
Such water-containing ~ystems tend to be ~ubject to electrolysis, have low chemical ~tability and are often corrosive. Moreover, the u~eful temperature range in which these ER fluid~ can be employed reversibly i~
limited to below 110C.

:
- : . .. ... . , :
- . ': ' : . .

21 ~L~0 ~

Hitherto existing electrorheological fluid~ ba~ed on coated metallically conductive particles, polarizable or semiconducting polymers and anhydrou~ aluminum silicates not only produce insufficiently ~table di~per~ions but also suffer from ER effects which are too ~mall, conduc-tivities which are too 1QW to be industrially acceptable, and, with the exception of the organic ~aterial~, from their high material-6pecific abra~ivene~cl.

The u~e of semiconducting organic materials is thwarted by the instability (redox sen~itivity) and the price of the materials known hitherto. Thus no products are kno~n to be marketed at pre~ent.

The object of the invention i~ therefore to develop an inexpensive and efficient ER fluid which on the one hand has a high electroactivity and a low electric conduc-tivity in the required industrially relevant temperature range (up to 140C), and on the other hand has good dis-persion stability and low abrasiveness. Variou~ synthetic sheet silicates were prepared as anisotropic, dopable, highly polarizable dielectrics and were di~persed in inert oils, using various disper~ing aids if required.

It was found, surpri~ingly, that the abovementioned requirements are met if aluminum-free metal ~ilicate hydrates having a ~heet structure are used.

The invention therefore relates to electrorheological fluid~ containing e~sentially aluminum-free metal ~ilicate hydrate~ having a ~heet structure, a di~per~ing aid and an inert aprotic di~persion medium.

The aluminum-free meta~ silicate hydrate3 are es~entially ternary ~ystems compri~ing metal oxide M2O (M preferably Na), silicon dioxide SiO~ and water H2O. The aluminum-free metal ~ilicate hydrates employed for the ~R fluids according to the invention are preferably those of the kenyaite, magadiite and kanemite type. The SiO2/M2o molar .. . .
. .

2 ~ 0 ~

ratio is 2-10 for kanemite, from 8 to 29 for magadiite and ~ 19 for kenyaite. The water content prior to the drying StPp i6 from 0 ~o 30% by weight~

It is further pos~ible to employ in the ER fluids accord-ing to the invention, ~heet ~ilicates doped with metal, ammonium, alkylammonium and arylammonium and mixture3 of the various structural and dopant types.

The metal silicate hydrate~ are employed in concentra-tions of from 1 to 50~ by weightl preferably from 15 to 30% by weight, based on the total weight of the electro-rheological fluid.

The chemically pure preparation of the metal ~ilicate hydrates is carried out according to the hydrothermal process (DE-A-3 400 130, DE-A-3 400 132, DE-A-3 521 227).
Ion exchange with mineral acid~ produces the acidic form of the sheet ~ilicates, and re-doping with suitable metal 6alt or ammonium ~alt solution~ produces novel doped silicate hydrates (DE-A-312 300, F. Wolf, W. Schwieger, 2. Anorg. allyem. Chemie, 457 (1979), 224)o Preferably, the disper~ing aids listed below and their mixtures from neutral and non-neutral ~urfactant~ and ....... are employed:

Cationic ~urfactants:

- dialkyldimethylammo~ium salts, alkyl chain Ca-C22, preferablY ~16~Cls - alkyltrimethylammoniUm salts, alkyl chain CB_C1BI
Pr~:Eerab1Y C16 - C1B
- oxyethylated amine~ R-N(C2H~O)XH (C2H9O)~H, alkyl ~hain CB~C1a~ X+Y S 25 and their ammonium ealts.
- perfluoroalkyltrimethylammonium salts, alkyl chain CB ( 1B ~
- poly-diallyldimethylammonium ealts , - :

:
...
.

2~0~D~

Nonionic surfactants - AB, ABA, BAB block copolymers from a polydimethyl-siloxane block (A) and a polyoxyalkylene block (B) alkylene C length 2, 3, 4 - polydimethyl~iloxane block which has had polyoxyalky-lene blocks grafted thereon - polyethers (MW ~ 107) - ~sters and ~emie~ter~ of the alkanephosphonic and 1-hydroxy-1,1 alkanediphosphonic acids, alkane radiCa1B CB_C18 Anionic ~urfactantæ

- dialkylnaphthalene~ulfonic acid conden~ed with formal-dehyde as the Na salt, alkyl chain: C8 C18 - diphenyl ether ~ulfonic acid condensed with formal-dehyde as the triethanolamine salt - 1 mol of 3-ring nonylphenol novolak + from 10 to 20 mol of ethylene oxide as the triple aulfosu~cinic acid semiester Na salt - 1 mol of 7-ring nonylphenol novolak I from 10 to 120 mol of ethylene oxide - 1 mol of 7-ring nonylphenol novolak + from 10 to 120 mol of ethylene oxide as the mixed ester ~ro~
benzoic acid and maleic acid with bound Na sulfite a~
the Na ~alt - cro~slinked copolymers ~rom acrylic acid and acrylamide - crosslinked polyacrylates - copolymers from acrylamide and 2-acrylamido-2-methyl-propanesulfonic acid - copolymer from 2-acrylamido-2-methylpropanesulfonic acid and methacrylamido-N,N-dimethylmethylamine - l-hydroxyalkane-1,1-dipho~phonate as the alkyl-ammonium, dialkylammonium, Na and Li salt~ alkane radicals: C8-C18~ alkyl radicals in the ammonium ion C2~C1s - alkanepho~phonate a~ the alkylammonium, , ~. , .
, , , ,. .

21~ L~ Q ~

dialkylammonium, Na and Li salts, alkane radicals:
C8-C18, alkyl radicals in the ammonium ion C2-Cl8 - N-oleylsarcosine-Na - N-oleylmethyltaurine-Na - alkyl-oxyalkylenesulonic acid, alkyl radical: C8-C18 2-7 oxyalkylene unit3 - 2,4,6-tributylben~ene-1-polyethersulfonic acid, 2-7 oxyalkylene units - p-alkylbenzene~ulfonates, alkyl radical: C9-C~9 - dialkylmethanesulfonic acids, ~um of the carbon atoms o~ the alkyl radical~ i~ 14.
- sodium 0-oleylisethionate - alkyl polyethersulfonates, alkyl radical C9-Cl4, 2-7 oxyalkylenes - alkyl polyethercarboxylic acids, alkyl radical C9-C14, 2-7 oxyalkylenes - alkylaminQpropanepho~phonates - copolymer~ from acrylic acid and 10~ by weight v~
diallylaminomethylenephoaphonic acid diallylaminomethylenediphosphonic acid tetraethyl diallylaminomethanediphosphonate allylamino-bis(methylenepho~phonic acid) diethyl diallylaminomethylenephosphonate Betaines - betaine salt from the ~ub~titution reaction of mono-chloroacetic acid and alkyldimethylamines, alkyl radicalS C8-Cl9 - betaine ~alt from the ~ub~titution reaction of mono-chloroacetic acid and alkylamidopropyl-N,N-dimethyl-amine, alkyl radical6 C6-C19 - betaine salt from the substitution reaction of mono~
chloroacetic acid alkyl ester and alkyldimethylami~es, alkyl radicals in both ca5es C6-C18 - betaine ~alt from the sub~titution reaction of alkyl ~35 monochloroacetateandl-hydroxyethyl-2-alkylimidazole, alkyl radicals in both ca~e~ C6-Cl9 - : ', . ~ , . ' ' , :

: - -, ., ~ . , : . - - : : :
, . , ~ , ~. . . : . ,: . ' .. . . . . .

`- 2 1 ~

The base oils employed can be inert aprotic dispersion media. Preferably, ~ilicone oil~ in a vi~co~ity range of from 0.5 to 1,000 mPas and mineral or paraffin oil~ in a viscosity range of from 0.1 to 5,000 mPas are employed.

The following method~ were found to be beneficial for preparin~ the ER fluids:

Method 1) The sheet-structure metal eilicate hydrates are di~per~ed in an alkaline (pH = 8-14), aqueous solution of di~pers-ing aids having a content of from 2 to 30~ by weight,preferably from 2 to 10~ by weight of di~per~ing aid based on the amount of ~ilicate used (silicate/so].ution 1:2) and stirred at temperaturea from 60 to 80C for 3 to 10 hours.

A~ter removing the aqueous phase by filtration or centri-fuging, the moist solid i3 dried at temperature~ of from 80 to 180C, preferably of from 120 to 140C.

After initial grinding and renewed disper~ing, if requi~ed, in silicone oil or mineral oil, the resultant mixture is ground in a ball mill.

Method 2) After drying of the sheet ~ilicate at from 120 to 240C, preerably 140C or 180C, to con~tant weight, the ~heet ~ilicate is disper~ed with from 2 to 30% by weight of di~persing aid, ba5ed on the amount of ilicate, in ~ilicone oil or mineral oil and i8 stirred for ~e~eral hours. The dispersion is then grou~d in a ball mill.

Method 3) Correspo~d~ to method 2) but without the drying step.

,.
.
- , ~, , ~

o ~
- ~ -Method 4) The sheet ~ilicate i~ dried in a manner similar to method 2). It is disper~ed in aprotic, nonpolar solvents together with a disper~ing aid (batch quantitie~ from 2 to 30~ by weight of the ~heet ~ilicate) and i~ ~tirred for several hours at temperature~ which correspond to from 60 to 80% of the boiling point of the sol.vent. The solvent i~ removed by filtration or centrifuging, the remaining ~olid is dried, grou~d once more and disper~ed in silicone or mineral oil. Thi~ oil disper~ion i~ then ground in a ball mill.
I

The invention provides the following advantageq:

Sheet-structure aluminum-free metal silicate hydrates, especially metal-doped silicate hydrates, dried to con-stant weight surpri~ingly exhibit distinctly :Largerelectrorheological effects ~han those a~ociated with dielectric materials of di~ferent types, while the intrinsic vi~cosity i9 very low. The fluid3 are water-free, and are active even above 110C. The ER effect increa~es with temperature, the conductivity remaining low. Electrical power ab~orbed of from 10 to 20 m~ per square centimeter of electrode ~urface at 20C and from 80 to 120 mW/cm2 at 140C are typical values.

In further compari~on with ER fluids based on aluminum-containing ~heet ~ilica~es, the ~luids accordi~g to the inventio~ are free-flowing, non-thixotropic and, very importantly, produce stable disper~ions. ER fluids with alumo~ilicates aa the dielectric show ER effects which are ~oo small, in contra~t to tho~e de~cribed here~
conductivitie~ below ~hose which are indu~trially acceptabl~-, and a high material-~pecific abrasiveness owing to which ~ompone~ts within which the fluid is to be employed are destroyed.

Owing to the purity of the mineral material~ employed, : . .. . . . . . . :. . .
- . . . .
'- : .

2 ~ 0 ~

compared to native alumosilicates, precisely defined ER
fluids can be compounded, which i~ the reason for the reproducible preparation and the clefined setting attendant therewith of rheolo~ical properties.

Generating structurally viscou~ properties in the electric field-free state by doping the sheet ~ilicates, and covering with ~urface-active substances also provides very good elec~romechanical properties at high shearing rates, without which the use of these fluids, compared to alumosilicate-based fluid5, for torque transmi~sion~ and clutches would not be possible.

It is also true of the ER fluids prepared in ~ilicone oil as a dispersion medium that they are compatible with rubber like materials and are nontoxic ti.e.
phy~iologically acceptable).

Examples Characterization of the ER fluids The ER fluids are examined in an ~R rotary rheometer from Haake, Karlsruhe, having the type de~ignation CV20 and the measuring ~ystems PQ20, PQ45, SYO.5ER, SVl.OER, SVO.2ER and DA45, gap widths of 0.2, 0.5 or 1 mm and field ~trengths up to 10 kV being employed. Static and dynamic measurementQ are evaluated and direct or alter-nating voltage i5 applied. The measured value~ are logged using a Rheocontroller RC20 and a Roto~ieko RV20 from the same firm. Comparable equipment and the mea~uring and evaluation methods are de~cribed fully in the litera~ure (cf. W. Winslow, J. ~ppl. Phys. 20 (1949) 1137, R.T. Bonnecaze, J.F. Brady, ~. Rheol. 36(1) 1992~.

The tables list, compared to the prior art, the compoRi-tion of the fluids, i.e. dielectric used in base oil with dispersing aid and ~iscosity with and without field and the increa~e factor at 100 ~-1 as well a~ the ætatic yield ':

strength for the purpose of characterization.

The first three formulae in the illu~trative examples correspond to the reference samples, the foll~wing examples to the ER fluids according to the invention, thus illustrating that a variety of compositions of the dispersed phase and different di.~persing aids (cf. Example 4-23) re~ult in di~per~ion~ having good ER properties, especially a good ef~ect at temperatureæ
above llO~C.
1. Inert dispersing medium ~at 25~C):

a) Polydimethylsiloxane (AK 10 Wacker) Viscosity: 9.4 mPas Density: 0.930-0.933 g/cm3 b) Polymethylphenyl~iloxane (TR 50 Wacker) vi~c08ity: 50 i 5 mPas Density: 0.955-0.957 g/cm3 c) Mineral oil Viæcosity: 7. 15 mPas Density: 0.8399 g/cm3 d) Paraffin oil Viscosity: 25~ mPas Den~ity: ~.873 g/cm3 2. Diaperaed solide a) Sheet æilicate kenyaite type 25 b) Sheet ~ilicate magadite type c) Sheet ailicate kanemite type d) Mixture a-c e) Ion-exchanged sheet silicate type a-c 3. Dispersing aid~

.

,.
.

Cationic surfactant~:
- distearyldimethylammonium chloride - perfluorostearyltrimethylammonium ioclide Nonionic surfactants:
5 - AB block copolymers from a polydimethyl~iloxane block (A) and a polyoxyalkylene block (B), alkylene C length 2, (commercially available from Wacker, VP 1633) Anionic surfactants:
- dioctylnapthalenesulfonic acid condensed with formal-dehyde a~ the Na 6alt - 1 mol 7-ring nonylphenol novolak + from 10 to 120 nnol of ethylene oxide - l mol of 7-ring nonylphenol novolak ~ from 10 to 120 mol of ethylene oxide a~ the mixed ester iErom benzoic acid and maleic acid with bound Na sulfite as the,Na salt - croqslinked ~a polyacrylate - 1-hydroxy-dodecane-1,1-diphosphonate a~ the dibutyl-ammonium salt 20 - decanephosphonate as the Na 6alt - 2,4,6-tributylbenzene-1 polyethersulfonic acid, 7 oxyalkylene units - p-dodecylbenzenesulfonate~
- alkylpolyethersulfonate~, alkyl radicals C12 C13 C14 ratio = 30:1:5, 7 oxyalkylenes - copolymer~ from acrylic acid and 109~ by weight of tetraethyl diallylaminomethanediphosphonate Betaines:
betaine ~alt from the ~ub~titution reaction of mono-chlvroacetic acid and stearyldimethylamine - betaine 6alt from the eubstitution reaction of ~tearyl monochloroacetate and 1 -hydroxyethyl 2-stearylimidaæole 21~0~

Comparative Example 1 In accordance with Example 3 of Patent Application EP 0361106 Al, the ER fluid based on al pitch was pre-pared. Dispersing aids were not used, analogously to the patent application.

Comparati~e Example 2 The ER fluid was prepared by Advanced Fluid Sy3tems ~td.
It iB an ERF fluid based on a lithium polyacrylate according to UK Patent No. 1570234.

Comparative Example 3 Sample according to Patent Application DE 3536934 Al having 40% by weight of aluminum silicate as the dis-persed phase and ~Raysilon as the dispersing aid (5~ by weight), prepared in accordance with Example 4.

Example 4 5 g of disper~ing aid ~dioctylnaphthalenesulfonic acid condensed with formaldehyde as the Na salt) are dissol~ed in 1 1 of water. This solution in a thermostatted vessel has 100 g of aynthetic kenyaite dispersed into it by Z0 means of a Pendraulik Dissolver LD50. The temperature is kept at 70C for 30 min. The suspension i8 centri~uged and the residue is dried at 140C in vacuo to con~tant weight. The material thus coated is then preground and screened. The fraction having particle BiZes c 32 ~m is suspended in 70~ by weight silicone oil (A~10) and is homogenized, in a number of grindin~ pas~es, in a Fryma bead mill, Co ball mill type, to a fineneæs of 1-2 ~m d5~.
The disper~ion thus obtained is non-thixotropic, free flowing and non-settling.

. . .
.:. . : . . . : . ~ .
' ' ' ', ' ' ~'', ' ' . '~ ~, .
- . . . .

Example 5 According to the preparation method describ2d in Example 4, an ER fluid is prepared uæing synthetic magadiite as the solid and a mixture of a 7-ring nonylphenol novolak and ethylene oxide as the di~persing aidL.

Example 6 Preparation in analogy to Example 4, using 1-decanephos-phonic acid as the di~persing aid.

Example 7 Preparation in analogy to Example 4, using block (poly-siloxane)-polyoxyalkylene (VP 1633 Wackerchemie) as t:he dispersing aid.

Example 8 Preparation in analogy to Example 4, u~ing a quaternary ammonium compound ~betaine from stearyl monochloroacetate + stearyldimethylamine) as the di~persing aid.

Example 9 Preparation in analogy to Example ~, u ing a mixture of synthetic kenyaite/magadiite (70:30) and Na polyacrylate (MW 106) as the dispersing aid.

Example 10 Preparation in analogy to Example 9, u~ing a dibutyl-ammonium salt of l-oxydodecane-l,1-diphosphonate a3 the dispersing aid.

Example 11 Preparation of an ER fluid with synthetic kanemite as the -. . ~ ., - :

., . . ~ . . .

', :' ' "' ' ' . :, :. ' ' : ' . . : ~ ~
.

: .: , ~ : ,: : ~ , :.

L~ /~

dielectric material and Baysilon OF (commercially avail-able from Bayer) as the dispersing aid. The formulation is carried out in accordance with Example 4.

Example 12 Preparation in analogy to Example 4, using a 7-ring nonylphenol novolak with ethylene oxide as a mixed ester from benzoic acid and maleic acid with bound Na sulfite as the dispersing aid.

Example 13 Preparation of an ER fluid, u~ing a mixture of synthet:ic kenyaite/magadiite (cf. Example 9) and a distearyl-dimethylammonium chloride as the dispersing aid. Mo aqueous preparation step was used (cf. Example 4), and the dispersion was prepared directly in the bead mill using 16 passes.

Example 14 Preparation in analogy with Example 13, using mineral oil as the base liguid. The disperRing aid is a dioctyl-naphthalene~ulfonic acid conden~ed with ~ormaldehyde a~ .
the Na salt.

Example 15 Preparation in analogy to Example 4, using Li ion-exchanged kenyaite and l-oxydodecane-1,1-diphosphonate as the dispersing aid.

25 Example 16 -Preparation in analo~y with Example 4, except that magadiite was used instead of kenyaite, with dibutyl-ammonium p-dodecylbenzenesulfonate aB the dispersingi~id.

:, :.. , ... - ... .. .. . ....... . . . . . . .
: :-,. .: ~ :: . .. . .
.
... . ~ . . . . .. ..

, . . . . . ..
. ,, . , , . , c : ' . :' ' '' ' ' '~ ' : ' ' ' ' " . ' Example 17 Preparation in analogy to Example 16 t using calcium p-dodecylbenzenesulfonate as the d.ispersing aid.

Example 18 Preparation in analogy to Example 16, using paraffin oil as the base oil and calcium p-dodecylbenzenesulfonate as the ~urfactant.

Example 19 Preparation in analogy to Example 16, using a d~decyl polyether~ulfonate with 7 ox~ethylene units a~ the surfactant.

Example 20 Preparation in analogy to Example 16, u~ing a copolymer from acrylic acid and 10~ by weight of tetraethyl diallylaminomethanediphosphonate a~ the ~urfactant.

Example 21 Preparation in analogy to Example 16, u~ing a copolymer from acrylic acid and 10~ by weight of tetraethyl diallylaminomethanedipho~phonate as the di~persing aid and paraffin as the base oil.

Example 22 Preparation in analogy to Exam~le 16, using 2,4,6~tri-butylbenzene-1-polyethersulfonic acid compxising 7 oxy~
ethylene unit~ a~ the ~urfactant.

Example 23 ~o g of magadiite are dried to constant weight at 180C.

. . . . :: :

. .
- ..

.
. -.. ... . . . . . .
- ~ :

- 16 ~
This is then introduced into 1 1 of a ~olution of silicone oil AK10 and ~he betaine from a:Lkyl monochloro-acetate and 1-hydroxyethyl-2-alkylimidazole and stirred for 3 hours at 90C using a Pendraulik Dissolver LD50.
The amount of betaine in thi~ case is 5~ ;by weight of the sheet silicate amount u~ed. Thi~ oil ~u~pen~ion i~ then ground in a Co ball mill MS12 in a numbe:r of pa~ses.

Example 24 Preparation in analogy to Example 4, using di~tearyl-dimethylammonium chloride ~s the di~per~ing aid.

Example 25 Preparation in analogy to Example 4, u~ing perfluoro-~tearyltrimethylammonium iodide as the di~persing aid.

Table 1 Composition of the illustrative fluid~
,.~_ ~ _ = _ I
Sample ~oil) Surfactant S fraction T fraction . _ .... ~ ~---~ I
1 Mesophase None 25 _ .. , . . . ... _ ._ _ 2 Li pOly acrylate _ . _ . . . , ~ __ 3 Al silicate Baysilon OF 40 5 (AK10) _ _ . _ ~_ ~ ~
4 Kenyaite Naphthalene- 48 2.5 tAK10) sulfonic acid/ .
formaldehyde condensate :
_ __ ~

5 Magadiite 7-ring nonyl- 43 2.5 (TR50) phenol novolak +
_ ~ ~thylcne oxidc ~ ~ _ - . . . ~ . . : . . .
. .. . . ~ ..
.. ..

.. : .

, ,`,'' ' ~ ~

2 ~ Q ~

Sample Dielectric Surfactant S fraction T fraction ¦
l (oil) I ~ ~ ~ ~

6 Kenyaite l-Decanephos- 34 2.5 (TR50) phonic acid I _~_ ~ ~ . . ~

7 Kenyaite Block (poly- 46 2.5 (TR50) siloxane)-(poly-oxyalkylene~
I ~ _ _ __ ~ _ ~

8 Kenyaite Stearyldimethyl- 41 2.5 (TR50~ betaine ester quat . __ _ . .__ _ . ~

9 Kenyaite/ Sodium 35 2.5 magadiite polyacrylate (TR50) _ ._ _, _~ _ . ~ . . .~_ 5 ¦ 10 Kenyaite/ 1-Oxydodecane- 35 1 magadiite 1,1-diphos-(70:30) phonate (TR50) .. ~ ~ . ~ . .... .
11 Kanemite Baysilon 39 2.5 (AK10) _ .
12 Kenyaite 7-ring nonyl- 48 2.5 (TR50) phenol novolak ethylene oxide.
esterified with benzoic acid and maleic acid . . ~ , ~ .
13 Kenyaite/ Distearyldi- 37 2 magadiite methylammonium l ~70:30) chloride ¦
(TR50) l _ . .. ~ ~
14 Kenyaite/ Naphthalene- 37 2 magadii~e sulfonic acid/
~70:30) formaldehyde (mineral condensate oil) __ . .. , _ ___ . . .
, .

. :

r--~ ==_ _=
Sample Dielectric Surfactant S -Fraction T fraction ¦
toil) I __ ,, . ,_ __~ . ____ ~
Kenyaite 1-Oxydodecane- 37 2 (Li:Na=1:1) 1,1-diphos-tTR50) phonate ~ _ . ~._ . ~ ._ _ ~
16 Magadiite Dibutylammonium 37 2.5 (TR50) p-dodecylben-l zenesulfonate-I ._ .__ ~_ ¦ 17 Magadiite p-Dodecylben- 42 2.5 (TR50) zenesulfonate Ca salt ~ .. ., . _ ~--~
18 Magadiite p-Dodecylben- 42 2.5 (paraffin zenesulfonate oil) Ca salt _ .. _ ~ . _ ¦ 19 Magadiite Alkylpolyether- 45 2.5 tTR50) sulfonate 7 oxyethylene units .. _ . ... . . . . ~ .. _ ... I
Magadiite Copolymer from 42 2.5 (TR50~ acrylic acid and 10% by weight oF
tetraethyl diallylamino-methanedi-phosphonate _ . . _~ ~ _ , , ~
21 Magadiite Copolymer From 42 2.5 ¦
(paraffin acrylic acid and oil) 10% by weight of tetraethyl diallylamino-methanedi^
phosphonate __ ~_ .. .. _ .____ ~ .

... . . .
.. .
.

o ~

=-- --= = =
¦ Sample Dielectric Surfactant S fraction T fraction l (oil) ~ ~_ ~ . ... . .. ~ _ ~
¦ 22 Magadiite 2,4,6-Tributyl- 37 2.5 (TR50) benzene-1-poly-ethersulfonic acid 7 oxyethylene units I _ . .. ~ . . _ _ ~--~
23 Magadiite Betaine from 34 2 (AK10) stearyl mono-chloroacetate and 1-hydroxy-ethyl-2-stearyl-imidazole ~ ~ _ ~ ~ .... ~
24 Kenyaite Distearyldi- 43 2.5 (AK10) methylammonium chloride . , , . . Il Kenyaite Perfluorostearyl 43 2.5 ¦
(AK10) trimethyl- l ammonium iodide i ~ =~ ,-- -. .~ ~ . .~ ~ ~

. . ~ .

. .
,, .
- , , Table 2 Characteristics of the electrorheological fluids ., _ _ , ,., -, __= ~ = =~, = I
Sample T Visco~ity Vi6cosity Static Factor without 2 kV/mm yield at field st~ength 1OO/E I
C mPa~ mPas Pa , _ ~ ~ _ 120 519~5 459~ ~88 8~9 50 388~3 3067 831 7~9 l 100 _ _ _ _ l 120 _ _ _ _ . .__ _ _ . __ ___ ~_ 220 214~9 88~110~ 41 50 269~4 126611652 ~7 l 100 _ _ _ _ I
120 _ _ _ _ _ _ _ __ ~__ . v . ._ 1 3 20 234~0 655~2 153 2~8 196~9 8~6~1 253 4~5 100 146~6 1246 399 8~5 120 172~6 1657 ~43 9~6 _ - - ___ ~__ 420 ~48~8 768~9 114 5~2 50 94~7 ~210 162 12 100 21~2 1~18 358 68~0 120 24~7 1365 490 S7~3 _ __ __, ~ . __ _1 20728~5 4476392 6~2 50417~7 2761628 6~7 100223~2 60291036 27~0 120332~2 5940108~ ~7~9 __ _ _ _ _ __ r~ _ _ 6 20~30~5 605 14 2~6 1 50113~2 41B 339 3.7 ¦
10083~7 627 417 7~5 l 1~076~9 669561 8~ 1 I_ __ ~ __ ----I
7 20~2~6 1~19313 ~2 1 50313~6 2335 506 7~5 ~-100151~7 45721156 30~0 _ l20 1~0 2 45071263 25.2 ~ .

2 ~ o ~

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¦ Sample T Viscosity vi9c09ity Static Factor without 2 kV/mm yield at field strength 100/a C mPas mPas Pa ~ , . .~ ~___ __ 8 20 1132.0 2716 660 2.
598. ~ 2920 7594.8 100 262.0 5873 8722~ .6 120 319.4 3224 134110.1 . .
9 ~0 464.0 266~ 4155.7 318.0 3796 5g3ll .9 100 283.9 9603 110133. e I
120 236.8 3196 1085~2.4 I . ~ ~. ._ . _--791.0 2776 5683.7 385.6 3048 7087.9 100 376.4 3575 14799.5 120 253.1 3282 141212.8 _ ._~ _ . _ .. _ _ ~1 20 445.2 ~53 62.2 1.0 494.5 495 63.8 1.0 100 262.1 424 35.1 1.62 120 203.0 1485 642. ~ 7.32 , .. _ ~ _ .... _. .
1 12 20 470.6 3091 325 6.5 303.2 2807 430 ~.3 100 153.0 7935 919 52.0 120 151.9 6114 1107 40.5 _ ~ . . __ _ 13 20 307.0 3973 ~32 12.9 229.4 4257 554 18.6 lO0 304.8 667~ 403 21.9 120 162.2 5312 568 32.7 __ . _ , ., .... .. __ _ . . .. ~JI
14 20 201.3 3687 518 18.
173.6 1473 293 8.5 120 63.3 ~100 757 33.6 1 _ ~ ~ ~ ~1 705.3 1743 490 2.5 391.4- 3950 1166 10.1 2~ 357.9 4355 l947 12.2 : - , , , :

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¦Sample T vi5c09ity Vi~co~ity Static Factor without 2 kV/mm yield at field strength 100/s l CmPas mPa~ Pa I. . . . ~ , ,~ ~~
16 2029~ 622 1'i2 2.1 75134 1531 395 11.5 120 97 3137 10~'2 32.2 I - ~ ~ ~_ _ 17 20267 1603 267 6.1 75149 3256 561 21.8 120 98 3040 8~1 31.1 _ ___ . . _ , ___ 18 20 1268 2682 264 2.1 75351 2673 ~33 7.6 120218 1507 7~5 6.9 _ ____ __~
1920 364 1064 170 2.9 194 166~ 507 8.5 120 137 2810 17h9 20 4 2020 335 708 215 2.1 159 1534 413 9.6 120 118 3045 161~ 25.6 . ~ ~ - . ~ _ 21 20 1123 19~5 9~ 1.7 299 1914 387 6.4 _ 120 153 3335 942 21.7 22 20 280 1~48 206 5.2 170 3~72 701 20.3 __ l20 l30 642l 690 49.3 23 20 314 1377 147 4.4 224 1~28 189 8.6 100 158 141B 169 B.9 120 145 1521 1~0 10.~
_ l40 l73 l657 2l4 9.4 24 0 2488 2966 8~2 1.2 2815 10480 1297 3.7 _ 50 l553 9045 la86 _ _ . _ .
:
..

2 ~ Q ~

~ . .: f ~ ~ ~ ~== _ ~Sample T Viscosity Viaco~ity Static Factor without 2 kV/mm yield at field ~trength 100/~ ¦
l C mPas mPas Pa I _._ __ __ _~
2520 3854 ~567 913.~ 0.
100 256~ 4767 ~565 1.7 - .. 120 1779 2118 1~64 1.2 An essential aspect in assessing an ER fluid i~ the determination of the relative power absorbed in the pre~ence of a voltage compared to the field-free state.

TE ' D~
L = - 1 rO Do In this relationship, T iS the ~hearing ~tres~ measured and D is the preset shearing rate. The index E represents measurement results in the electric field, the index 0 those without field. Thi variable wa~ optimized.

The resulting curve~ indicate the ratio ~f the nece~sary mechanical energies to be di~eipated with and wi hout an electric field at variou~ shearing ratea.
This variable is e~ential for the de~ign of industrial components.

Figure~ 1 and 3 depict the relation~hip between the ~hearing stre~ measured a~ a function of the electrical field ~trength and the given ~hearing rate. Figures 2, 4, 5 and 6 depict the relative power absorbed by the ER
fluid~ (power = product of ~ and D) as a function of the ~hearing xate at various temperatures and con~tant field strength .

Figure 7 depicts a novel electrorheological phenomenon.
When an electric field i~ applied, the vi~co~ity of the .- , .. , : . . , . -.
.
.

suspension at shearing rates greater than 5 s-l drops below that of the suspension without a field. When the electric field is switched off, the viscosity then returns to its original value. We call this phenom~non the negative electrorheological effect.

''~ ' ' .
' . ' .

.

Claims (6)

1. An electrorheological fluid essentially comprising an aluminum-free sheet-structure metal silicate hydrate, a dispersing aid and an inert aprotic dispersion medium.

2. The electrorheological fluid as claimed in claim 1, wherein the aluminum-free metal silicate hydrate is a silicate hydrate of the kenyaite type, of the magadiite type and/or of the kanemite type.

3. The electrorheological fluid as claimed in claim 1, wherein the inert dispersion medium is a silicone oil in a viscosity range of from 0.5 to 1,000 mPas and/or a mineral oil and/or paraffin oil, each in a viscosity range of from 0.1 to 5,000 mPas.

4. The electrorheological fluid as claimed in claim 1, wherein the disper ing aid is a cationic surfactant, an anionic surfactant, a nonionic surfactant and acetamide.

5. The electrorheological fluid as claimed in one or more of claims 1 to 3, wherein the metal silicate hydrate is doped with metal, ammonium, alkylammonium and arylammonium.

6. The electrorheolog.ical fluid as claimed in claim 1, wherein the metal silicate hydrate is employed in a concentration of 1-50% by weight, preferably 15-40% by weight, based on the total weight.