CA2054433A1 - Electroviscous fluid - Google Patents

Abstract

ELECTROVISCOUS FLUID
ABSTRACT
The present invention relates to an electroviscous fluid which comprises a dispersion of 0.1 to SO weight% of wet- method silica particles whose surface adsorbed water has been replaced by an organic compound having in its molecule at least one group selected from the group consisting of a nitrile group, hydroxyl group, and acid group, in an electrically insulating fluid. The wet-method silica particles haave an average particle diameter of 10 to 500 micrometers and a pH that does not exceed 6.5. This electroviscous fluid provides a substantial increase in yield value at low voltages and an excellent shear stability.

Description

S~T BY~ PATE,~T DE~. ;10~ g1 ;1~:glA.~; ~C PAT~T ~EPT.~O~LIN~iSTRATHY~HEN~ 17 ' ' 2054~33 ~L~KCTlR.~:SCO~JS li~UIl~

The p~e~ent in~entlon ~elates to an el~ctr~riscoug ~luid wh~ch ~ a f1uid wh~se vi~co~ity can be ch~n~ed by the lmpre~ion o~ npplica~.iorl of as~
exte~nal ~oltage.
VariouY type~ of theDe ~luids ha~e already been proposed1 and they a~e typlfied b~, f~r exa~ple, dispe~io~ o~ porous ino~ anic par~icle~ (e~ ~., silica, aluolina, talc,~ in ~n e~ectrically in~ulatil~ fluid. In ea~h ca~f~, throu~h the for~a~ion o~ an el~ctrica1 double lay~r by ~ean~ oE wate~ adsorl~et on the paI~ticle ~ur~ace~, the par~icle~ b~co~Q ori~nted in ~e~ponse t~ ah ~xt~rnal ele~t~ic field and the visc~ity increa~e~ ~moxe speci~i~ally, th~s fluid i~ conv~rted int~ a l~ingham ~luid, ~hich exhibit~ a yiald ~alue). This ef~:~ect i~
called the "Winslow ~3fP~". The ~ol~owing dis~tlv~ntages ha~e been a~so&l~ted with ~ a- b~3~ ctrovi~cou~
~luids; the~ h~ limited applicatlon temperalturo~
~approxim~tely lO~C to aooc~, they abrad~ the sur~aunding machine~y~ and ~he particles ~edimont~ ~till, sinc.e ~ilic~ i~ ea8ily o~ai~ed o~ an indu~trial basis and i8 higl~ly a~en~ble to imp~ov~m~nt and msnipu1ation, ik has ~een consid~red potet~ti~lly use~ul for cortain sector~ o applica~cion, for ~ample~ machln~ry which would be u~ed in the vicinit~r o~ ~oom t~mpe~a~ure and ~h~h wau:Ld und~rgo llttle abr~;Ln~ motlon. ~ilics-b~sPd electrt~vi~ce~u~ ~luids ar~ dlsclo~ed in Vnited States Pat~nt N~ber 3,~47,507 anc1 in J~pane~e 2atent Appli~ation I aid Oper~ [R~k~i or ll~ex~minç~ N~ber 6l-44998 [44,q9~ ], ~1t in e~ach C~80 ~he~ e~hll~i'c an imp~acticall~ weak Win~lo~ ef~ect. Alæo, Jap~ne~e l~aten~
Application Laid Cpen Nu~ber 01-284~95 ~2~4~595~8 disc1~e~ an electro~ co-Y~ fluid in the fu~7~ of a SENT BY:~CC P.4TENT DEP1. ;10-28-91 :10:41~ C PATE~T l)~T.~GOWLIN~STRAT11Y&HE~E;;~ 3~7 20~4~33 di8p~r~ion in an electrically insulating fluid of wet-method silica who~e ~urface ~dsor~ed Wi~te~ has bean epls.c~-:l by pol~alel~t ~lcohol. Ba~et nn the form~tian o~ an electri~ o~ble l~yer b~r the polyY~lent alcoh~l, thi~ el~c1:ro~isco~l~ fluid exhibits an electrovi~cous ~havlor ~oI~e or less eqll~l to that of the dispersion of ~h~ un~odifled ~ilica, bu~ al~o r~tains it~
c~a~ac~eri~tic~ at hi~h~r t~mper~tures (9OC). Howevos, ~eh ir~ thi~ ca~Q, the i~t2n3ity of the Winslnw effect i8 ~till m~rely ~ore or l~s~ ~qual to that o:e the prio~
w~t-method ~ilica-~a~cd ~stsms. Mo~reover, b~cau~e the d~alectric con~nt of the polyvalenl~ alcohol decline3 with inc~eastn~ temperature, tha Win~low ~fect 8till decline~ at ~lghex temp~rat~res.
As a cons~squ~nce ~ al 1 o~ the~e hereto~ore propo~ed ~leCtr~vi8cou8 Iluid,Q r~n~ain un~atie~actory rc~
a prao~ical sta~dpai~t.
The pre~erlt inventlon i~troduces a silica diap~r~ion- type el~ctrovi~cous fl~id ~hich devel~ps a l~inslDw ef~ect ~ufficient to sati~fy indu~trial ~pplioatiorl~. The pre~en'c invento2^ car~ied o~t exten~ive inve~ atio~ ~ith a view to solvin~ tt~ aforementi~ned proble~, and di~cove~ed a~ a re~ult ~hat t~e aforemen~ion~d probl~ms are ~u~s~ntially reduced by the u~e a~ the ~i~per~e pha~e of ~ilica p~epared by replacing the water a~sorbed ~n th~ surface of we~-method ~ilica wit}~ ~ partic~l~r type o~ compour~d. The p~esent invention wa~ developed based on this di~cove~y.
The ob~ect ~ th~ pr~3ent invl~ntion i~ the introduction of ~n electrovi~cous ~luid w~ich d~elnp~ an ezc~elle~t Win~low e~ect. The ob~ee::~ o~ the p~e~ent inv~nI;ion ig al~o t~ utili2e a di~pcr~ion of O. l to 50 ~eight percent silica particles which ~:ompri~e wet-meths~d slïica p~rticles whose ~l~rfaee adso~b~ water ha~ b~el~

SENT BY:D~C PATENI DE~. .lO-~-gl ;10:41A~; ~C PA~ DEPl.~O~LI.~STRATHYOE~ 17 - 20~4433 3 o repl~ced by ar~ or~anic eompoun~ ~hich contalns within its molecule at lea~t one nit~ile ~roup~ hydra:~;Yl gr~up, or acid ~roup, ~nd wherein the w~t-method ~ a p8rti~:1e5 hP.ve an ave~ge p~rtlcle d~m~ter o~ 10 ~o SOO
microm~ter~ arld ha~re a pH that doe~ llot exceed fi . 5, in an electrically insulating fl~l~d. ~ ~urther obJect o~ the pre~en~ ittventi~n i~ to p2~0vi~1e an electI~o~i~c~ou~ fluid whlch pro~ide~ a sub~tantial increase in yield ~alue at l~w vol~ge~ and ~ cellent ~he~ ~t~bili.~y.
The prQ~ent invention relates t~ e.n electrn~ co~ fluid c~pri~ing ~ di~persl~n of silica p~rticl~s in $n elect~ic:~lly insulating :~luid, the imp~o~vement compri8ing u~ing 0.1 to 50 wei8;htX wet-me~hod ~ilica par~icles who~ ~ur~ac~ ad~rbed water 1~a~ been replace~ by atl o~g~nic compo-md ha~inE~ ln it~ ~oleo~le At l~a~t orle ~ ro~lp 6elected frtsn~ t~e gro~lp consi~qtlng o~ a nitrile group, llyd~oxy} ~.rnup, or acidl g3:0up, wh~rein the wet-method silica paxtlcle~ have an aver~ge p~r$icle ~ize of 10 to 500 micromet~r~ and a pH of no~ gr~ater th~n 6.5. T~e p~ (hydrog;en lon ~centr~tlon) o~ the wet-method ~i~ica particles are preer~1y n~e~8ured in a t~ wei~ht percent a~ue~u~ su3pen~i~n, hDwever the method of tihg~ the partic:les ~or pH is hot c:ritical to the pr~sent invention .
T~ ~xpl~in the precedin~; in ~reAter detail, the wet-~oethod silica particles employed by ~che pre~ant inventior~ are prepared ~y the prclducti~n o~ silic~ by ~ch~
addition of Q~isl ~Ldex wet condition~ to wat~r ~la~
startiRg m~teri~l. The~e wet-method ~ilica particl~ ~re an ldeal d:L~per~e phase or ~lectr~ cous fl~id~ bec~ e their ~urfaces po~e~s a layer of ads~rbed water, which is ideal ~or t~ develop~ent of tbe Winslow effect, an~
becau~e they ha~e opti~al partiol~ Their average ~rti~le ~i~e ~hould ~all within t~e range o~ lO to 500 SENT BY~ PATENI DEI~. ;iQ-2g-91 ;lD:4~AN: ~ PATP~T DE~.~0~LI.~ST~ ~;# ~/17 4 2~4~3~

snicrome~er~ ~nd pr~erably fQll~ within the ran~;e o~ 50 ~o 200 micrQmeters. When th~ p~rti~le size i~ le~ than 10 r~lcrom~er~, the particles e:chibit a lsr~e c-rientability, hut the in~erpa~rt~cl~ ~orce~ are small and a 8Ati~actory ~risco~ity Will tlOt be a~hi~v~d. On the other ha~nd, at pa:rticle ~ize~ in excess uf 5Q() microme~ , the oria~ntability 1~ dir~ini~hed ~nd the thick~tling ~ect is redllcecl. Mor~o~er, at su~h di~nen~ions, the particle ~ize itsel k~giIas to po~e si~nificant problems. The partiel~ shap~ ~hould be as cloeo to truly apheric~l as po~si~le. Wh~n the p~rticl~Y
~ubstan~ially de~iate from ~pha~i~31, ~h~ effe~t ive interpartiol~ conta~t ~rea declineæ ~nd the ~ohasive orceg a~e ~hen weak. W~th re~ard to the particle size distri~ution, the narrow~r the bet~ce~. The pa~ le orien~abi~i~y becorn~ increasin~sly unl~s~rsn a~ t:he particle si ~e di~trib~lti~n be~omes narrow~r, ~hich provides fo~ a m~re efïi~l~n~ v~sso~ity rise. V~riou~ rne~hs~d~ c~n b~
devi~ed for the production of ~ilic~ particles which have a n~rr~r particl~ si~e d~st~ibutiosl ~n~l are as clo~e t~
~pherical a~ po3~ible, b~t ~uch particl~s a~e obt~ined ~ainl~r by de~ ng a t~lli t:a~le drying proce~ . Fo~
ex.~snple ~ 8pray d~yin~ ~Qthods Elre ~d~al .
Xn addition to the propert~e~ di~cu~d abuve, the q~antit~r of ion in the ~ilica iB al90 a c~uci~l facto~ in determinln~ the ta~ge~ce~ Win~low ef~ec~. While not li~ltine the present i~ ntion to an~r pa~ti~:ular theory, it i8 ~e~ieved that the prlncipal inn pre~ent in the ~iliCA i~: the sodill~ ion, and thiæ i~mainly th~
excess from the ~odium io~ u~ed in ~rder to neutrali~e the ~olid acid p~esent ~ ~n impllrity in the water gl~l818 rting ~hate~riQl. Accordingly, th~. ~luidlty ~f the ~ilica i~ goYerned by t~as magnitllde o thi~ gu~ntity of sodi~l~ ion. Accor~in~ ta ~xpe~imen~s by the i nventor, SEh~ BY:D~ PATENT DEPT. ;IQ-28-91 ;10~ CC PAT~T Da~T -GOW~IN~STRAl~&HE~E;;~ ~17 ~, 2~4433 the pre~enc~ of f~e~ ion in t~e silicQ brin~Y a~out a retardatior~ in par~icle ~rIentation. A clear e~ample of thi~ phenomenon i~ the insta~ility ir~ ~qhear stre~ at a constan~ or va~riable ahear rat~ that is ob~erved when ~n electric field is applied to an e~l~c~rovi~cous lCluid pr~apa~d ~y the di~pe~ion o~ Inreu ion-con~ainlng w~t-metho~ ~qilica. In the case o;~ free ioD-containing p~rticle~ thi~ i~ tho~ght to be due to an incs~ase in the ti~oe req1lired for orient~tion oî the randoml~
diqtributed p~r~icle~ due to the relatively long ~ime as~oci~te:l with ion movem~nt. Th~ res-llt is th~
a.pp~a~an,oe of in~tabili~y u~der dyns~ic conditions. ~t is ~or this rea~on l:h~t wet-method ~1 lica depleted o~
~ree ion ~e. ~., soditlm ion, ~c. ~ l~ optimal for the development of ~ eful Winslow ~ffect. Pure ~et-~ethod 8ilic~ gellerally exhibit:3 fluidit~ in the acid regi~n, therefore acid~c ~ilica i8 i~eal. The ~luldity inde:c ac:cor~ing to the pre~ent i~ ntion i~; deined a~ ~ollow3:
th~ p}l of a 4 Wt2~ aqeOU9 8~115perl8iC-I~ of ~aid si~ica mUBt no'c exc~ed ~. 5 ~nd ~nore p;re~erably dcles not e~ceed 5 .5 A usef~ll Win~low e~ec~c doe~ not alppear at ~ralue8 in exce~ 6.5. In ord~r to ~tain wet-m~hod sllic~
whiLch h~ sueh a flllidity, the ~Xce8B ~odiun2 ion n~us~ be remaved to ~he m~ximum po~ le. e~ctant, or, alter1~atively, a pure! water ~la~s whlch contai~ only træce~ o~ ~olid acid mu~t be ~tnployed ~ the ~tar~in~
mat~ri~l .
No Yp~iflc re~tri~t:ion~ a~e placed on the wet-method ~ilsca ~m~loye~l b~r th~ prese~t invention :1~
long as it sati~ies tha p~p;~rt:i.e~ di~cu~ed abo~e. It may be ~e~lected ~Cro~ ~n~oll8 ~ommerci~l w~t-wethwd sili~as, for ~xample, ~ip~il A Q- 5 from ~ippon Si.lica Kogyo R~bu~l~iki Kai~h~ and it.~ aqui~ralent~.

SENT 8Y:DC~ ~ATENT DEPI`. ,IQ-28-91 ;10:42A.~: ~C PATEKT DE~.~GO~LI~ST~hT~ 7~17 , 6 20~433 Acc~din~ to th pre~ent inventi~n, the water ad~or~esi on ~he ~urface o~ ~his wet~method sllica i~ then replaced by an org~nic compound which cont~ins ~ nit:rile grc-up, hydroxyl group " or acid ~roup . 'Xh~, the su~ace of wet-mathod ~llica i~ norma:lly ccvered with a layer of ~d~o~bed water. ~I-ile ~he particular welght proportion ~or thl~ adsorbed wat~r in ~he total oilica weight ~ill vary with the particul~ typ~ o~ ~t-method ~ilic~, in 8;~nesal it wlll fall wi~h~n the ran8e of 5X to lOZ.
since this l~yer ~f adsorbed wate~ i~ merely hydro~en botlded to a layer of structural w~t~r w~lch resides ~nediately inward, it aan be alo~oot co~pletely eli~inated by h~atin~ to ~round 100~C. However, ~5 discu~ed a~o~e, thi~ adsorbecl ~ter lay~ pl~y~ a si5~nificant role in the df~svelop~ent o~ thQ Winslow ct. Tlle cau~e f~r thi~ is bolle~ed to ~eside ma;nly in the Ihigh diele~ric ~on~ta~t of thet wate~
(approxi~a~ly 8~ at ~oom te~ ature~. However, it~
eas~ Df elimination by heatin~ extingui~he~ the Wlnslow effect. In the pre~en~ in~enti~n, this adso~bed water la~er on th~ sl1rf~ce o wet-method ~iliaa 1~ replaced with an or~anic ~ompound which contaill~ a nitr~ le ~3roup, hydrG~cyl ESroup, or acid group. lhe nitrile grotlp~co~taini~ orga~ic ~ompo~nd a~ speci~ied her~in is exe~plified by ~lip~atic nitrile~ h a6 a~etonitrile, propionitrile, n-capronltrile, ~ccin~nitrile, etc., and b~ aromatic nit~ile~ such as ben~nnitrile, ~lpha-t~luni~rile~ ancl 9~ forth. Th~ hyd~xyl g~clup-c~ntaining co~npo~nd i~ ex~7~pli~iet ~ m~ncnral~3nt alc;:~hol~ such ~Y meth~nol and e~hanol; by cli~alent ~lcohols such 8,~ et~rlene ~lycol, 1, 2-prop~nediol, and 1,4-bu~anediol; and by triv~ t ~Icoh~ls ~ch as el~r~erol Th~ ~Gld group- cslnta~nir~g compound i8 e2templi~ied ~y Qlipha~i c acida ~uc~ ~ ac~3tic acid ant .

SENT BY:D(~C PATENI DE~. ;10-'~8-9l ;lD:43A.~ P.4TE~`iT DEYr.~O~Ll,~ST~4THY&HE~IDE # ~/17 2~5~3 propionic acid .snd by ars~m~tic aclds such as benzoic acid and phthalic acid. All of the~e are suitnble ~nd no particul~r r~Yt~ic~ion~ apply to the~e cs~l~pounds. Variotl9 method~ ca~ be de~ ed :eor the repl~cement procedure, ~t tho f~llowin~; method hEIs pro~ren to be 8imple an~
~trais!ht~orwa~d. Fi~st, the wet-method ~ilica parti~les are plac~d under a nitrogen ~urrent at 150~C in order to remoY~ the ~ur~ace adsorbed water. A~ter cooling to room tenlpe~ature Inder the nitroge:n c~trrent, I:he. stlb~tituting compo~nd i~ thQn addsd in a qua~nti~y co~re~pondin~ t~ the weizht loss due t~ the de~orbed water wi'ch mlxgng to ph~rsi~al homogenei~:~r in, for example, a mi~cer. Afte~
~uch 8, tre~tment, t~l~ sur~ac~ of 'che wet-method sillca particle~ will be c~vered by ~ l~yer of the sub~ti~utin~
compound. ~ue t~ the high dielectric con~an~ of ~ame, Wi~lo~ effect ca~ be de~eloped which i.~ a~ l~ast equiv~len~ t~ th~t for the ads~rbsd W~te~.
The electro~isco~s $1uid ~ccordin~ to the present invention co~p~i~e~ the di~persion of wet-method 8ilic~ particles a~ ~pec~fied hereinbefore in a~
electri~ally in~ulatin~ fluid. However. the ~l~ct~lc~lly in~ulating ~l~id it~elf is not pa~ticularly rest~icted lon~ as it i~ 8 liqul~ at room temp~r~t~lre And i~
elec~ri~ally in~ulating. Su~h electr~cally in~ulating ~luids ar~ ex~mplifi~d by ~ineral oil~, dibl~tyl seb~cate, ch70rinate~ par~~n~, fluorine oils, ~nd silicone oil9.
Amah~ th~ precedin~, ~ilisone oil~ are prefer~ed for their ~tron~ electric~1 in6ulation~ low t~mp~rat~r~-dependon~ vis~o~ity vari~tion. and so fort~.
These ~ilicone 0115 are exemplified h~ the fl~id diorganopolysilo~anes with the fo~lowin~ chemic~1 ~truct~r~:

SENT BY:DCC PATENI ~EPl. ;10-2~-91 ;1O:d.3AL~ PATE~T DEFYr ~0~Lli~ST~ 9~7 2~4~33 ,~
R--Si~--~5~0)n- S1--R
R R R.
wl~erein R in the prec~ding formula compri~e~ monoval~nt hyds~carl~on groups as ex~mplified b~ alkyl g~uups such as ~oet~yl, e~yl, and prc~pyl, ~nd aryl ~roup~ ch as phenyl and n~phthyl. 1~ i~ prees~x~ed within the p~e~ent in~ntion tlhat methyl comp~ A~ least 302~ of the ~,X'Ot~p9 R. Moreo~rer, whi.le ~he degr~e of poly~erization n i8 not partic~lla~ly ope~:ified~ it prefer~bly ~e$ not e~c~ed 1,000 in order to acllieve a practic$1 Y~Co3ity range.
Value~ not e~ceedling lO0 are even more pre.~e~d, Sil~cone ~ w~ th thi~ at~:ture are ~vailabla in 'che ~orm of a lar~e numbes of comn~er~ial products, for example, SN20Q frwD Tnray l~ow Carnin~ Silico:le Co~pany, Limited.
Fu~he~re, ~o~æ the ~illcone ~il9, fluoro~lk~l-cDnt~inin~ dior~anopolysiloxan~s are par~icula~ly preferr~d because the~ e~hance the Winslow ~ffect ~nd inhi~it the particJ.e ~edime~tati~n cau~ed by 3pecific gravity di~fer0nces. T~e~e are ~oncretely expressed ~y the ollowi~g ~t~ucturai orm~1a:
R ~2 R-n - 9i~ (8iO)~ (Sl~)p- S~-~

whereln ~ i8 de~lned a~ abo~e, R2 i a fluoroalkyl gro~pha~ing 10 or ~ewer carbons, ant m and p a~e intege~ with v~lu~ not e~c~dlng 1,000.
The ~tructure of the afor~nt~ned C~10 fl~oroalkyl group is not particularly specifi~d, b~t the 3,3,3- trifluoropropyl gr~up i~ pref~rred from tha s~andpoint of ~as~ of ~ynthe~ o~de~ to obtain a SENT ~Y:D~ PAT~DE~. :10-28-91 :10:43~M ; ~C PAT~T D~T.~O~L1~S~A~E;~10t17 20~4~3 .qub~t~nti~l enhan~.ement of the Win~low ~ffect, it will be preferable for e~ch ~ola~ule ~o c~nt~in ~t lea~t 30 moleZ
~luoroalkyl g~oup. Moreo~er 9 while ~he degree of polymeriz~ti~n ~ i8 a~in not partic~larly ~pecified, it p~efer~bly doe~ no~ ex~e~d l,OOO in o~do~ to achieve a practic~l visco~ity ra~l~e. ~lue~ not ex~eeding lOO are aven ~re ~re~erred. The m~chaniR~ by which the fluoroalkyl g~oup enhanoes the Winslow efect i~ not clear. It can b~ eonjeetu~e~, howaver, that a ~tron~
intra~Dlecular dipole i8 gen~rated by ~h~ si~ult~neo~s ~resenoe in the molecul~ of the el~c~ron~gati~e fluorine Rtom and electropo~itive ~ilicon ato~ s~pa~ated b~ a ~uita~le distance. Polarization o~ the double layer i 9 the~ pro~oted by ~ontact ~etween thi~ dlpole ~nd the electric~l double l&yer on ~he wet-~ethod silica.
~therwise, fluorin~- containin~ fluida tend to ~ave larger ~pecific gra~i~le~ which rea~lts i~ a~
acco~panying inhibition o~ c~ sediment~ti~n.
The~e ~lu~roal~yl-cont~ining dior~nopoly~;lo~nes are ~omm~rcially avait~ble, for example, as ~S~265 ~ro~ To~ay Dow Cornin~ Silicone ~ompany, Limit~d .
1~ electr~ovisc~ lutd ~ccording t~ the pres¢n~ invention compr~9es the di~per3ion o~ we~-method ~ilica particle~ a~ te~cri~ed h~reinbe~ore in an electrically in~latlng luid as desc~ibed ~rein~efore.
The quanti~y di~p~rsed ~hould f~ll within the r~nge o~
0.1 to 50 w~% ~nd prefer~ly is ~n the range o~ lO to 40 wtZ. A satisfactory thickenin~ ef~ct iB n~t obtai~ed at les~ than O.l wt%. ~t ~ e~ e~ceeding sn wt%~ the vi~c08ity of t~e ~ystem is ~o ~u~stantially inc~ea~ed to be impractica~.

SENT BY:DC~ ~ATENT DE~ 28-91 :10:~3.4.`il; ~CC PhTEhlT DEI~.~O~ CT~ATHY~E~ /17 20~433 The ~lectrovi~cou~ flui~ accordin8 to the pre~ent imention a~ d~cribed ab~ve i~ u~e~ul as the w~rk~ oil or lun~tional oil in p~rtictl].~r types o~
wnchinery, ~r e~campl~, machinar~ wh~ch will b~ emplo~ed in th~ ~icinity o~ roo~ t~mper~ture and wh~3r~ there will be little ~brading motion.
Tho present inyention wlll be e~cplained in ~r~ater detail below ~hrou~h the u~e of illustratlYe and compar ' ~on example~ . In the e~ample~, CQ = centistol~e~
and the vi~cositY is tlhQ value ~t 25~c.
~ e sl~ctrovi~c2ua beha~io~ w~ mea~ured a~
follo~s . lrhe ~e~t f lui~ s~as placed in ~n allllQ;nu~ ~up (in~erior diameter = 42 mnl) ~nto which an aluminum roto~
~di~eter - 40 nn, len~th = CO ~) was subæequentl~
inserted. Th0 resul~ing cylir~drical cell w~s set up ~v~rtically, and the cup wa~ liLn~sarly ac!cel~ted ~rom a ~h~sr rate (D) o~ zero to 330 8 1 ~ r 40 ~conds.
During thls pe~ivd, th~ torque appli~d to the ~otor wa~
m2~ured w~th ~ tor<~ue ~snscr, and this was conve~ted into the shear ~tr~ (s~ an~ the l)-ver~u~-S curve waa drawn vn an x-Y r~c~rd~r. In addltion, the roto~ wa~
electricall~r groul~ded and D-vexsus - S ctlrYes wer~ o r~c~rded while applying a direct-cur~ent volta~e to the c~p. The inter~ec~i~sn oP the e:~trapolatlon Qf tl~e lin~ar ~eg~ent ~i~h the 5~a~cis ~a~ deaign~t~d as ~he yield value at the partic~lar fielt ~trengt2-. ~he ther~nal and ~hear stre~ a~ ty and the ~@di~ntabilit~ ~f the wet-method silica p~rti~les w~3re A~ examlned.
The e~ectroviscosity te~t wa~ al~o a~t up ~n ~u~h ~ ~nner that the cell te~perQture could be ~7ari~d~

SENT BY:DCC PATEI~lT DEFT. il~-23-~1 ;lO:~ PATENT DEPT.~OWLINGST~AlHY~ E;i~12~17 20~4~

Exatn~ .lç 1 Wet-method E~ilica tNipsil AQ-S fr~ln NiPpon ~ilica Ko~yo Kabu~hiki l~a~ ) ~ith an aver~;e particle size of 100 r~icrometer~ ar~d pH - 5 . ~ to h, 5 (4 wt%
a~ ou~ ~U~p~n9ion) W~ dried ~or Z hc~urs under a nitrogen ctl~xent at lSO~C. I~ryin~ ~au~ed this w~t-metho~
~ilica to 8u~fer a weigl-t lo~s oE approximately 9 wt%.
A~Eter the ~ri~d wet-mat~od silica had been ~oole~ t~ oom temp~rature tmder a ni~roESen current, acetoni~c~ile was added in a quantity equal ~ t~2 we~ht loss. Sti~ring i~ a ~xer ~or abo~t 1 h~ur afford~d an ~cetonitrile-tr~ated w~-~ethod 8ilica, lS Wei~ht part~
o~ this acetonit~lle-trea~d ~ilica was ~u~pended and di~persed lt~t~ 8!5 weight part~ trime~hyl~iloxy-~erminated polydir~e~chyl~ ne (~i~co~ity = 100 cs). The electl~ov~ ou~ ~aeha~ior of thi~ 6~spension was then mea~u~ed a~ ell temperature ~ 25C, and th~
m~a~ureloent re~ults are reported in Table 1 belo~.

Exa~Rle 2 The el~ct~oYi~cou~ beh~ior of a ~u~pen~ion prepared a~ in ~s~ample 1 wa~ meastlred at ~ c~ll te~nperatura ~f gOc~ 8,n3 thef~e me~ a3n~nt re~ult~ ar~
reported in ~able 1 belo~.

l~xample 3 Elect3~0viscous fluid in the form o~ the ~t~pen~ion prep~l~ed in l~ mple 1 w~ heated ~or 1 ~eek at 90~C in a~n op~2~ r3y~ rn under air, then I~e~oved ~d oool~d. ~ter thi~ heat trç~atmerllt, the ~le~t~oYi~cou~
behavior of~ th~ re~u:~tin~ ~uspen~ion wa~ ~e~su~ed~ ~nd the~e re~llts a~e r~aporte~l in T~ble 1.

.

~t~'l BY:DCC PATEi\lT ~EPT. ;1~-28-~l ;10:4~ PATEI~'T DFPT.~&O~LI,~JSTR~THY&HE~IDE;~13~17 20~44~3 amP~e. 4 An electroviscou~ fluid in the. form o ~
su~pen~ion was pI~epa~ed a~ ~n ~xample 1~ but in this case usin~ 1, 2- prop~n~diol .in plac~ o~ the acetonitr~ le u8ed ~n Ex8~ple 1. The ele~tro~ ous behavior o~ thi~ ~lui~
was mea~ur~d as in Exampla~ 1, and these re~ult~ are reported ln T~bl~ 1 below.

E~mp~l,e 5 An elec:~r~vi~cous flui~ in th~ fcsrm o ~
8u8pension wa~ pr~pared ~g in Example 1~ but in thi~ ~se uYin~ acetic a~id in place o~ the a~etonitrile u~ed in Exa~pl~ 1. The ~lectrovisc:ou~ beha~a,ior oi~ thi9 fluid wa~
meaaus~ed a3 in Example 1, and thesg re~ults are rep~ted in Tnble 1 below.

E~c~ple 6 A~ elæ!ctrovis~oua Plulcl wa8 prep~red a~ in ~xa~nple 1, but in ~his case ~u~pending ~d di~perslng 15 wtX o~ the ~ a in a 3l3,3-trli~ oropropyl~ethyl-polysiloxane withL a vific~ity o~ 30C cs ~$126S-300GS
fro~ Toray Dow Corning Sili~one Company~ Limited~ in pla~ o~ the p~lydime~hy~siloxan~ with vi~9c08i~:y - 100 C!S
us~d in Exa~ple 1. The electrovis~o~ beha~lvr of thi~
~IYpen~1oD ~as m~asured at a cell telnpe~tur~ ~f 25DG, asld these refiults ~re reposted in Table 1 below.

Co~ i~son E~c~mple 1 ~ n el~ctrovi~cous $1~id in the f~rm of a suspen~ion w~ prepared a~ in Exa~ple 1, but in thi~ case ua~ng th~ W~- me~hod ~ilica prior to it~ acetonitril@
~re~t~e~t in pl~ce o~ the ~cetonit~le-treated wet-~ethod ~ilica empluyed in E~mple 1~ The el~rovis~ou~
behavio~ of ~hi~ w~ measured ~ in Exampl~ 1~ and th~ a~1rement re3~1t~ are r~ported in Table 1 ~low.

SE~T BY:DCC PATE,~ DE~T. ;10-2~-g1 ,1û:4~AM ~ PATE~T DEF~.~GO~LI.~ST~ 17 13 2~4~3 Ço~ari~on Exam~1~ 2 The electro~l~cou~ bel~avior ~f the electrovi~cou~ fluid o~ Comparison EJ~an~ple ~ was luea~ured at a c~ll teulperature ~f 9d~C, and the~e mea~ur~uent results ~rc repo~ted in Table l b~low.

Co~ or~ _:ca~Ple 3 Elect~ovis~ou~ fltlid as p~Rared in Comp~riaon ~xaolple 1 wa~ heated for 1 week at ~O~C: in an open ~ystem under air, thPn ~emov~d and cooled. ~he Ql-a~tro~scous b~3haYior of tlle electrovi~c~u~ ~lui~ obtained fr~m this he~t t~eatment w~ mea~ d ~t ~ cell telQper~tllre o~
25~C, and the~e re8ult~ ~re reported in Table I.

Comp~ri~on E:xample 4 An electrovisc:ou~ 1uid in the fo3~ o:e a su~pension wa~ prep~red a3 in E~aT~ple l, bllt in this ca~o u~ wet-methl)d ~illc~ particle~ wit~ an aVerage p~r'cicle si:~;e of 4 mi~rom~t~r~ and p~ .5 to 6.5 (4 wt%
aq~teou~ su~pen~ion~ ln plnce o t~e ~et-me'chod ~ Q
part~cle~ with an uYerage particle oiz~ of lO0 ~i~ronleter~ u8ed in R~:ampl~ l. The electro~is~o~s beha~ior o thi~ fl~lid w~ a~red a~ in Exampl~ nd these measure!merlt results ~re reporte~ in Tabl~ 1 below.

n l~ca~ 5 An electroviscou~ Jid lh the fnr~ of a ~u~pen~ion wa~ pr~pa~ed a~ in Ex~ple 1~ but i~ t~i~ c~e u~ing wet-m~ d ~ a pa~ticle:s with ~n s~rer~g~
partic~e 6iae of 8.5 mi~r~meter~ and p~E = lO.0 ~ 4 wt~ aqueou~ allapen~ion~ in place of the wet-methocl 9i~ ica particl~s wit~ arl a~rera~;e pa~ticle ~ize o~ lO~
mic~ometer~ a~ used in Exa~ple 1. T~le electrDvi~cou~

.

SENT BY:DCC PAT~'~T DEPr. :1Q-28-91 ;10:4~1t1: KC pATEriT [3EPr.~O~L INCSTRAlHY&~E;#1~17 -14 2~44~3 beh~viol of ~his fluid wn~ mea~ured ~ ln ~x~mple l, ~nd t~ese m~asurement re~ult~ ar~ repor~ed in T~ble 1 below.

TA~le I
~ --_ .~ .. .. _........... .__ 9HEAR PARTICL~
THE~MAL Y~ELD ~ALUESTRE9S S8DIM~
~A~L~ TREAT~ ~_ STAB~LITY ~ IL IT~
1 RVfllun 2XV~m7n ~. .. _ ~ _~. ~
EX. 1 n~ne ~4~ 4gO high mediwa EX. 2 none ~05 460 high m~diun ~X. 390C~l wk 75 l60 hi~h medium ~X. 4 none 215 440 high Tnediun . ~ n~he 200 39n medium m~di~n El~. 6 non~ 315 660 high l~
COMPAR.none 220 4~0 hiqh medlum CxXlli 2R. s~one150 300 high o~ediu~n ~X. 390C/1 wk35 60 high ~diu~n COMPAn .n~De 135 2~0 high mediwn ~X.~

~X. Snone 16~ 325 1~w medi~
.... _ _ ~ ........
Becau~e the el~trovi~co1ls ~ it ~c~c~rdin~5 ~o the pre~ t i~v~ntlon compris~s a disper~ion o~ 0~ l to 50 weight ~r~ent wet~ hod ~ilica parti~les who8e ~urface adsor~ed wat~r ha~ been replaced b~ ~ parti~ular type of or~anic cumpo~nd in an electr~c~lly insulatin~:
flll~d, this electroviscou~ fluid i~ chara~teriz2d by a ~ub~.anti~l in~rea~e ~n yield value ~t low ~olta~es and a~l ~xcelle~ heer ~tability.

.. . .

Claims

CLAIMS:

1. In an electroviscous fluid comprising a dispersion of silica particles in an electrically insulating fluid, the improvement comprising using 0.1 to 50 weight% wet0method silica particles whose surface adsorbed water has been replaced by an organic compound having in its molecule at least one group selected from the group consisting of a nitrile group, hydroxyl group, and acid group, wherein the wet-method silica particles have an average particle size of 10 to 500 micrometers and a pH of not greater than 6.5.