Selective flocculation in heterosterically stabilised nonaqueous dispersions

Colloids and Surfirces. 1(%980) 6 Eketier ScientificPrrblishing

(Received August

349-360 Company,

13th. 1979;accepted

349 Amsterdam

-Printed

in EnaC form October

in Belgium

9th, 1979)

AESTRACT The hzipient flocculation behaviour aE poLy(vinyL acetate) p&icle.s stabiked by polystyrene and of poCyacrylonitriCe pzticles stabilised by paCylsobutyIene has heen irwestigatedasafunctionof temperatureusingcyclo~n~eastbedlspesionmedium_EtPrras folrndthat~epoIy~nestabil~p~~~Elorrulafedatho~anupperdldloweF criticaltem~er&rewhilethepoIykobu~Iene stabikzd parti~esftaccuIatedoc~yat.t upper critical tempe=ture_ These critic& Roccu~tion temperatireS 4xxceIated qualitatively withthereCewantthetatempecatures ofpolystyrene andoE polyisabutyienewhendissahed & cycCopentane_ Wkea the homostericalCy stabiEed dispersions were m-wed together in cyclopeutaue to give a hetemstericaiCy stab-d nanaqueous dispersion, it was found that selective RoccuCation oftheMicestc&cpIaceas a functionof temperature.This indicatesthat polymer stabilisedparticles can diMnguish Ys&” fkom “uon-seEE” and behave tidepeadently under certain conditions, These results are dkcusaed wit& the theor&d framework that has been dewCoped For heterosterically stabi&ed nonaqueous dispersion_

Recent experimental and theoretical results on dihite sterically skabilised d&persons (Napper, 1977; Croueher azd Hair, 1978; 1979 a, b) have led to an under&an&g of some of the basic principles that co&r01 steric stab&ation in nonaqueous nwdia. For example, it is now recognised that the limits of stability of such dispersions correspond to the t? tempera&es of the st.ahiIising polymeric moiety in the dispersion medium, provided that de sorption of the steric barrier is not a complicating factor- These rest&s can be explained when the theory of Stitbam et zd_ (1975) % wupled tith the x(T) parameter obtaked from coqesponding states theory (Fati=on and DeEmas, 1969; Croucher and Hairs 1979a)When different core po&mers are stabILised by the same poIymeric stabiliser in a cti&m~n~organic dispersion medium, it has been olwtrved (Croucher axd Hair, f919c) that the dispersion behaves thermodynamically as if it were a system Df homopaxticles, indicating that different core par-

Ina dilutedispcrsion~efrceenergyof interpenetration oftwoparticlcs isdominated bythe mixkgterm (Napper,1977;Crouches andEXair,~978, 297Sa)-Tbeproblemoftbe miKingor~~~ene~~onof~opoL~er chainsinsoEutionhasbeen~tedby Flory and Krigbaum(1950) and ad~p~for~~~~ystabiIisedp~c~es byS1&hamefa.L(~9?5) whogave thefree ene~~ofcloa? aaproachoftwo~~~ystabiIisedparticlesin theinferpenetrationdomain(i.e_whenL=Gd< 2L)as

Priheredisthedistanceof Separationof~es~ilisingchainsandLis the ~hicknessofthes~b~~~gSarrier,w is~ewei~tofpolymerics~iliser perunrt~aceareaof~hep~c~e,o isthemdiusoftheparticle,~~ isthe pa&al specificvoIumeof~es~ricstabi2iser,V~ isthenoIarvoMrneofthe dispersionmediumsndNisAvagadro'snumber,~is amexstueofthe strengtho~the~~~ction~t~~nUledis~~0~ medium andthesteric stabiliserandSdescribesthedistancedependenceofthefreeenergyof int43penetrationInthecascof a~rnarypoZymerso~utiontfreterm(#--_)~~~fi~ energy expressionisreplacedby(l-xXr2 -xl3 +xz3)andAq for a heterostericaUysM%sed dispersionisgivenby Feiginand Napper(1978) as

heqn~2)w~,u,and_xg havethesame meaningasineqn(Z)wherethe subscriptlrefers~~edisp~onmediumand2 and 3refertoth~fxo po~ymerFcstericstab~~_~en2and3are~esamepoI~~mer,~en~~~= = 0 anti ecp (2) reduces ko ecp (I) as would be expected- It wi4.L X23 be foundconvenientforthkdiscussiontotiteeqn(2)intheform

X13*

and AGF

(x23

) =

nNw2

w

ta

(y)

1x231

kTS

Thecombinationalcon~bution~o~efreee~e~in eqn(2)(thefactor H)promotesstabil!itywhiEexEZ afid~~,,whi~hareirzvariabIypos~tive for nonaqueoussysfzms,promote instability(Croucher andH%r,1979a)_Tbe in~ction~~~nthe~wo~ricstab~~i_e_~23,~~p~bleofpromoting stabili&or instabilitydependinguponwhetherithasapositiveornegative vaLuerespectiveLgi_TbisimpEes that apairofmutuallycompatiblepolymers, x2S < O,wiH promoteinst&i.Etywhileapair of incompatiblepofymers,~,, > OwilI promo~s~~~ofthedispersions_ThesignofAG~~eq~(2)is determined bythesignof('/r-~~~)+(~-~~~)~~~~_~e~roflacc~ation wiUoccurifthisCermkneg&Eve, AGr O_ Fe&in andNapper(l978) havecommentedfhatES forexamplex sz > Y&x~3 < %a~~d x23 is positive,then seLectivehomofloccuIationof theIaticescontainingsterkstabiIiser3cortfd takepIace_Tbisfnfersthat porymercoatedp~c~esareab!e~odiscrimina~~ between"seK" and "'no~self"whenundergoing~ro~iancollisFo~_T~ interes~gpredictionisconErmed experFment&ly theresukdescribed

When Lt = IL3 =Ltheneqn(6)simpIifiestogiveth~ corresponding expressronforhomos~ricalIy~~biiisedparticLes(Smi~h~etal.,1975) aswotidEleexpected~ RothL,-andSaretemperature-dependenf.q~ti~es,however,inthis paper~e~~~themasco~~~sincetheirvari-atonissmaIlcomp~ed~o thechangesti~~ withtemperature.

titles,

Eis knownfEommodernpolymersolution~heory(Ftory,f970; Pa~rsan,19~9)thatthe~~ipparametersapp~~gineqn(2)aremade up of~~oc~~ICI~~~~a~~(i)aconEaetenergy dissimilaritycontribution which isassac~a~~thformIngpoLyrnersolvent(2--1)contactsin thedispersion reIa~~ve~~hepo~ymer--poEymer(2-Z)andsoLven~soLvent~I-l)con~c~, and(Z) a~~volumediss~~betweenthe polymerand thesoIvent_The can~ctenergycontibu~ioninX~~i_ foundtoincre~ewItErdecre~ing temperature,andistheprimarycauseofiwipientflocculationattheLower critic&floccula~i~n~mperature(LCFT), whSethefreevohune dissimilarity contributionto~~~increaseswithincreasingtemperature andcause flocedationto accura~~heuppercriticaLfloce~a~ion~empe~~~(UCFT)(Croucher andHalr,L979a), ~~rmsof~ecorrespo~dlngs~atestEreorydisc~sedpre_ viousIy(Croercherand Hair,2979a)~ii~be~~~enas

wherethefirs~termontherighthandsideofeqn(7)referstothecontact energy dissimilarity contributionandtie secondterm representsthefree _ _ volumedissimilarr -tyCOl!l~bU~O~ t0 X jj -&is themolarconfigurational isthemo!arconfigura~ionatheat capaciky_ energyofcomponentiandC& preferto Analyticalexpressionscanbewritt43nforvg andrfja&houghwe treat~hemasexperimen~parame~~.Bo~hUi~dCp~icanbec~~~ated usingtheF~ory(l97O)modeL forthe confiitionaLproperties, i.e. -i$

= pixv,*

g;L

(8)

and

wherePEe, Q*and Ti* refertothe pressure,vo~ume,and~emperaturereductionparameters andtiequa&ities mark~.ppithatifdearetheredueed q~titi~whicharerelated~Kough~heequationofs~te

353

tion of temperature. The reduction parameters required for appI2catiot-t of the theory can either he obtained using the prescription of FIory (29’70) or taken from the literature_

The solverrts, toIuene (Eastman), chloroforzn(Calendon Labs.), heptane (Mathezzon, CoIeman and Bell), cyclohexane [Chemical SampIes Co.), and cyclopenfane (Matheson, Coleman and Bell) were used as received_ T&e monomers, acryIonifxZe (Eastman), methyl CethacryIate [Matheson, Coleman and Bell) and vinyl acetate (Mathe~on, Coleman and Bell) were ail distied before use and kept over 4 A moIecuIar sieves, TIZP poIymers used as steric stabllisers are shown in Table 1 together tith the suppliers and the GPC characderisation data TABLE

I!

Polymers used as

steric stabilisers GPC data

Supplier

Pdymer

Mw x 1O-5

MWW

LL

< I!_06

7.6

3-6

PaEystyrene

presarechem-coPittsburgh. PA

PoIyisobutylene

PuZysciences Warrkgton,

PoEy@inyL methyE ether)

Polysciences

OS7

2.0

l?oly(dimethyL

Petrarch Sp&em.s Ledrtomrst, PA

5-4

2-3

doxane)

PA

TZxesewere prepared by dissolving the homopolymer [Z g) in a suitabIe soKvent (50 ml), The monomer (O-15 g) -to be grafted onto the homopoLymer m~zsadded to the soIution aIong wSh azobis @sobutyronitrSe) @W.N) as initiator(O.lg,)_The~eacti~nxvasallowd~ pmceedunderconstant stirring for - 12 h at 348 K_ A cIear solution was obtained, in order to check whether the grafting reaction had succeede& the copoIymer was precipitated by addition of fion-sclventV filtered and vacuum dried- It was &en di~~lved in fresh solvert- a16 its ir spectra recordecL The ir spectxa showed the characteristic stretchiug &que~zci~ of both poIymeric species. The acryIonitrlle graffing was carried out in toIuene, the methyl methacryIa&z graSng was

3, DEspersforz

Summary

Core

po~yymerkutfon

of nonaqueous

dkpersIons

prepared

particIe

Polyacryloti~e

(PAN)

PoIyacryLonitrile

For theheterostericdlystabiliseddispersion f&ehoruostabiEisedpartic~es,i.e_po~yacryLonitrilep~cless~~~~~ and poly(vinyIace~~)partrcles~bi2ised~~po~ys~eue.

samples were heatedat-

1Kperminu';eexceptinthevZcinityofthe~~ti~ffoccuIaticnpo~~where~e~~wasredrrc~~o-O0.1EZ.perminut;e~~Ehe uppercriticalflocculationtempe~~ewasreached_Thiswasobserved visrr~yasthepoinf;a~~~ch~erewasave~ dmmaticreductimx ofbhe nltmberofparticlesin themeasuringvid_

3%

Love-temperature flocculation experiments were carried out in a dry ice +methanoImixture~thecontrolofwhicAwaslessprecise~-t 0_5K)than thatof thesikonehath, Again,~eIo~er~~c~ffocculation~mpera~e ~obse~edvis~yas~epo~tat~~chthe~wasadranzaticreductio~ oftenumber ofparticlesinthemeasurin guiaL,FloccuIationatbo~temperahreswas usuaUyobservedtobeareversiblephenomenoL~_ netero~rically~b~dispe~onsofvariouscombinationsofp~c2es 25°C~~ingv~iousdispersion werealsop~~aredInstopperedvIaIsatmedia,Theparticleconcerrtrationof~esesys~mswas0_2~-6~_%.They wereobservedforfloccuZationat25"Coveraperiadofdays_ RESULTS

AN-D DISCDSSION

Cl~caLpoLymersoLutionth~ry CTompa,1949;Scott,1949) forternary systemsoftwo po&nersinacommonsoIventpredicts ttiatastablehomogenoussoIuti~ncanbeformed,irrespectiveofwhether ~23 isposi5ve or 13 ispositive,~ef~nctionoftfie negative.undersuitabIeconditions_When~ solve~tistodil~~the2--3con~c~~Sn~esoI~tionsuchthat~,, has a negligiblecontributiontothefkeenergy ofthesystem, Whenx,, isnegativea~blesolution~beforrneda~~conce~~tions_~asterie;llIv stabiliseddispersionanegative~~~ would promoteinstabiIity(cf, eqn_(2)) while a positivex 13 woultipromo~stabilI~_ThereforealLdispersionsin whichxz3 Ispo~tivewo~dbeexpec~to5es~lepro~d~~e~spersron mediumisagoodsolventZorthestericstabiEsers_ When xz3 isnegativethe dispersionwouldbeexpected~obestablewhenthesy~~mhasbeendiluted suchtha~the2--3con~c~havebeenm~imised~threspecttofhe~-2 and1-3o~~c~-Thesep~ctionshavebeenconfirmed~pe~errtalLy

TABLE3 Stable

Core

diIMe

hetemstericdiy

poEymer/dabifiser (1)

stabiKsed CGre

nonaqueous

poEymer/stabiEser

dispersions (2)

Dispersion medium

Sign

of x+,

PANJpotyisabutyyEene

PlHMA~poLy(dimethyl siloxane)

u-heptztne

+

PVAc/poEysmene

P_lN@dyisobuty~eue

cyclohesane

+

PANJpoly(vinyi methyl

tohtene

-

cbcoroform

-

PVAcpoEystyrene

ether) PVAclpolystyrene

PAN&oLy(vinyL efher)

methyl

356

byminir,gnumerouss~~~ys~~particles~getherin avarietyof nouaqueousdispersion mediaat25°C.Theconcentrationof particles rangedfrom 0.2totL6 IAei~t%.~esystems~~~aresho~inTable3, bothpositivea.ndnegatEvevaIuesof~ 23 are representedintheIisLKtwas found~a~~ePANp~~c~~~iiised~~poIy~~y~methy~e~her)~~ tithPVAcpa&iclesstabilkedwith polys~~~neinchIoroformffocculated as~eparCjcleconcent-;atoaincreased_~~preciseeoncen~tion atwhich thisoccurred hasnotbeenquantit&ively detehed andfixrther experimen-

~workneedstobeunde~enon~~~m,

TZrehe~ros~eric~ystab~systemstudiedasafrrnctionoftempe~~e used PAN p~c2es~ilised~~hpoIyIsobu~~enepI~; PVAc par%c~es st!abiKsed with poLystyrene-Cyclope&anewasempIoy~dasthedispersion medium.The individualhemostericaZLy~biPiseddispe~onsweEeaIso studiedtithrespectto ~heirlrmcipientflocc~tionbehaviourasa~ction oftern~~~e_Thesesystemswere chosenbecauseoftheavaik&iLity of thermodynam~cda~onpoLyIsobutylene~cycIopen~e(Bardin andpatterson,1969)and poiystyrene+cyclopentane@aekietal~,l973)so~u~ious and because the:c23 vz&eforpoIystyrene+poLyisobutyIeneisapo.sitive quantity(Hyde zndTanner,l968)whichis moreEypicalforamb&ure of polymersthanisanegative~,,_ ~eincip~eentflocculationr~~ areshowninTa~le4-ThePVAcp~cles~~

forthe homo&eric&ysta~iqstems withpolystyrenein

cyclopentaneshowboth.araupperand aLowercriticdnocc~tion~mperatureand these correla~qu~~tiv~y~~~etwo8 temperaturesreported (SaekietaL, ~913)for~epoLys5yrene-tcye~open~e~s~m_OnLyan uppercritical flaccuiationtemperaturewas foundforthe PANparticles stahSkedt;y poryisobuty~eneincycropentaneand.thisPrrasalsofoundto Correla~q~~~~v~y~~tfieindependen'LLyrepo~~~he~Eempe~~~e (BaEdirrar.dPa~rson,1969)associa~wi~~~eIowercriti~soEution temperakzeforthepolyisobutyleue +cyciopentauesoIution~Thedispersion couEako becookdto 243 KwithoutanysignofLow-temperatureincipient flocculation tzddngplace,

Summvy

of Incipient

System

flaccuIation

U-K

m easuremeuts

in cyclopentaxe

Kal?Tm

PAN~polykobutyIene

455

-

PVAc/ppolystyrene --

Q10

280

*,lK

eulK

461

-

421

293

-

351

Combining eqns (I), (6 j (when L = L, = L3 j and (7) allows the free energy afunctionoftemperature_Suhof interpenetration, AG, MXobepredictedas , stitutingeqns (8)--(10) into eqn (7) gives_ at the point of incipient ffoccuIation(Croucher andHair,l979a)

2(4#3 - f&,‘”1=:A v;

u2 55

213_

1

f

113

-

r2

ill)

A knowledge of FE at both the LCFT azd UCFT &Lows FE to be calculated fEom equ (IO)_ VaIues for u2 and rz can now be calculated kom the s;mukfianeous equations resu.Ltingkom eqn (II), Using the value of TL * = 4490 K obtained by Bardin and Patterson (1969) we eaIculate C~Y* = O-C24 and by polystyrene in cyclopentane, CfiP 2 = 0_093 for the PVAc latices sabilised Croucher and Hair (1979a) have shown previously that AGF can be w&ten as the S?M of AGF (comb), AGF (contact energy) and AGF (free volume) terms_ UtiEsing eqns (1) and (6)-(10) a!Eows the various contributions to AGF tc be calculated as a function of tempera-e_ These contributions are plotted in Fig_ 1 for a d&ance of separation of the particles of 10 nm using VaIUes for w = 3 X LO-* g cme2, u2 = O-93 cm3 g’, V. = 94-I cm3 morE, tz=ZUOnm andL=lOnm, The comb~a~ionaLcon~~~u~ion~ AGf isa positive quantity which increases linearly ~5th timperature whereas the contact energy and kee volume co&ributions are negative quantities as expected (Croucher and lEfti, 1979a)_ AGF (contact energy) increases t&h increasing temperature while AG:’ (free volume) decreases with increasing temperature, At the LCFT AGF (contact energy) E AGF (f&e volume) therefore both terms co&rib&e almost equa.Hy to tie flocculation process in this system, i-e_AGF becomes negative since 1 AC:’ (contact energy) + AGF (keevohnne) i> jAGy (comb)/ -However atthe UCFTAG~((free voIume)is~edominan~~w~~~causesthelaticestoffaccuIa~_ Addition of the three confxibutions to AGF gives the parabolic shaped temperature dependence also shown in Fig_ I_ For the PAN particLes stabitised by poLyisobu@lene onLy an UCFT was found. It has been deterrn&zed previously (Croucher and Hair, 1979~) that PAN k&ices stabilised by polyisobutylene and dispersed in a variety of normal, branched and cyclic aIkanes will only flocculate at an UCFT_ In these systems, the poIyisobutylene is honmlogous with the a&ane and the contzt energy dissimilarity contribution to x is zero, x is therefore entirely a kee volume dissimilarity effect, Using the value for TI * given pre-tiously with u2 = 0 in eqn (II) gives a value of cI r+ = 0_6?7. The free energy of in&penetratio~ AGF in this system is made up of two contributions AfZp (comb) and AGF (freevohmte) and these are pIotted in Fig. 2 for an interparticIe separation of 20 run using vaEues for w = 6 X 10e8 g cm-*, u2 = LB? cm3 g+ .a=200nmandL=20nm_I~~beseankomFig_2~haf,at ambient temperatures AGF (comb) > AGF (free vchnne) and the dispersion remains stable-As the temperature increases AGF (comb) becomes more positive andAG~(fkeevolume)becomesmore negativeunt%attheUCFT

358

6 3 . SW -0 a 9 Q -2 -4 -f I

270

290

310

370 330 350 TEMPERATURE /K

4IO

390

430

4

I3c

l-

2a lI-

)? IL

I

270

I

290

+

310

I

I

.

330

350

379

TEMPERATURE

390 /K

l

I

410

430

450

c

0

AG~E 1 AG~(comb)~_Additior,ofthese twocontibutkmswiUagaingivetheparabolicshapedtemperaturedependencefor AGF, However,in~casetSeLC~~Sexpe~~~;ltaPlyInaccess~'CJIesincethedispersionmedlumfreezesbeforeth~s~~~~mfloccrrlates, ForaheterostericaJlystabiIiseddispersioneqn(3 jshows thatAGrconsIsts~fcon~butionsfromAG~~(~~~),bG~~~~)andAG~(~,,),It shot&i be noted that AC? (xu) can be cakulated by diEsing eqn (4) with eqns (6)~(1O)while AG~(~23)mms obtainedbycombiningeqn(5)witheqns (6~ZQ)_Theh~terostericaiLystabilisedsystemstudied wasamixtureof thehomosteri~y~abifiseddispersio~discuss~above_Therefore,the wi, v,-and L,-valuescisedInthc~c~tionsarethose~~dbeforewhere thesubscriptsl,2and3refertothecyclopentane,polys~en~ andpolyisobutylenerespactively, A vaIue of a = X50 m was used in the heteroStddiZXttfOn cakulations,The :;I3 p arameterwascakulatedusingeqns (?)-(XO)where tiz w~t;akentobe1_225(Fa~~~onandRobard,1978) and assumed constant over the temperdue range of Mezest- TSe value of uz, which is eqtivdent %o X,, /PJ *b theFlory(1970)nom~nclature, was estimated,using theap,?ropria~p~e~rs(~~ory,1910) tobe0_0?3. ThevaIueof-r* usedwas 0_07(PatkersonandRobard,~978)_Thevahzeof segmentatbasis,wzzzfot.mdtobeO_tN whichis ~23rwhe~no~a.Iisedona in goad agreemtmt with the experimental va!ue fcauz5 5y Hyde and Tanner (f968)butmol~t~ananorderofm~i~desmallerthanthe~uec~ItulatedbyFeig:nand Napper(1978).ThevariouscontributionstoAG~, fora~~eofPVAcp~cless~b~~~bypoIy~renepiusPANpartieFesstab~sedbypoIyisobutylene~~ddIspe~~IncycLopen~e,are plo~dinFig_3_BothAG~(~,,j-~dAG~fX~~) have theirusualparabokic shape withAGF(Xt3) beingofagreatzrmagnitudethan bGF(~~~)and overthe reflectsthefactthat~~+ > ~:~_dG~(~~~)ha.s apositivevahe entire~mpem~rar;ge_~d~tion ofthesecon~butions,i-e_dG~In ESg_3,mightbeexp~ct&togkveanonaqueousdispersionwithcZfferent ~mpera~estabilitych~c~~ti~~comparedt~tIrecomponenthom~stericaHystabiIisedsystems_~twas found experimecta#IyhoweverthaCas the he~eros~ricallysCjabiIiseddisp~IonweascooI~~o 28OK,oneofthe systemsffoccuWedand afloc phasewasinequilibtiumwithadisperse phase.Thec!!persionwashe~dat260K~ortwohtiurs and thstwa-phase systemwasfo~dtopers~~Wheatheflocphasewas~ai;~~~from~e s~~e~persion,itwasfoundtobecomp~eeteIysoZubbintuIrrene~~~tingthatthePVAcparticksstabflisedbypoly~&yrenewereEocc-uIatinginde~endenffyofthePANprtiticless~bitisedbypoI~sob~~lene_Uponraisingthe~mpe~~eofEIre~~ersiont~41OK,a~o-phasesystem~~ agaInob~~,~~~ttreP?~~cpartcIe~s~~t~~y ELoccuIating. Uponraising the~mperaturefur:h~~toLCS~K~he"'mo~s~le"po~on ofthedispersion~~eCaccrrf-?ecai_9:thlFANp~icIess~b~,ribypoLYiSObu~ene_ ~~~~~conErrn-~~erec~nep~ictionsofFeiginandNapper(f978) thatsseiective~o~x~ationcan~eplaceundercertain~pecifiedconditions, TIriswo~~perFz:~~sbeIn~tive~~~ezpec~since~~~ i~positive,indicatig

60 I60

-[60

-4c

-6C

I

170

210

t

25050 330 370 TEMPEBATCIRE IK

,

410

1. 450

’

D

contrihu-iions to the fhze energy of close approach of a heterostec%aIIy Ffg- 3_ The dous skbilised dispex+a idz eqx (3)) are plotted as a fuaction of temperatie, me q;aIues for dG>x..) axd 16 %E x1,) are irdica~d on the reft-hsnd scale* while fEre vahxs for AGF(x~,) and aG?are indrc_?ted OP the rfght-hand scale_ The freezing point of the c&persion medium is shown as the vertical dashed line at I79 K_

Bardin. J--M_ and D- Pattersort., L969_ PoIycuer. 10: 247. Croucher. MD, and~E.EEair,1978_~~molecules.LL:874. Coucher, MD_ 2nd BKL. Hair, 1979a J_ Phys,Chem., 83: h7L2_ Croucher, B&D_ and BEG E&r_ f979h In: R.M- Fitch (EXitor), Pdymer

Colloids

Zl,

Cmucher,MD_ andM.LHak.1979c~ lb¶a~~ptsubmittedfoc publicatiorrFe&in, RL and D-H, Napper, 1978, J_ CoUaid Interface Sci, 67: 127, plary. P-J- and WmR Kcigbaum. 1950_ J_ Chem_ Phys_, IS: 1086_ Flwy, P..L, 1974.XDiscxm~FaradaJrsaC,49: 7_ Hyde. AX and AG_ Tanner,1966. J_ CoUotd htexfze ScL, 26: 179. Napper- D-EL. 1977, J_ ColIoidInferface Sci, 58: 390, Pawn, D., 1969, Macromclec~ 2: 672, Pattersoa. D- and G_ 3elmaE, X969_ Trsns Farahy p&c_, 65: 708_ Patterson, D- and k l&bard, 1978, IldacramokcuIes~ 11: 690, Saekl, S_, N, KuS. KOIEIO~and M, Kaueko* 1973- Macromolecdzs, 6: 589Smtt. RE, 1949- 5, Chem- PUPIL, 17: 279Smithy., J-B,, EL Evaus and D.H. Xapper- X975_ A Cheu~ tic_, Faraday I, 71: 285 Tampa, EL, 1949_ ‘Rana. Faraday S&z, 455 1X42-