Polymer/Surfactant InteractionsE.D. GODDARD and R.B. HANNAN, Union Carbide Corporation, Tarrytown, NY 10591

ABSTRACT AND SUMMARY

Polyelectrolytes and oppositely chargedsurfactants form precipitation complexes which, inmany cases, can be completely resolubilized byexcess surfactant. In general, maximum precipitationappears to correspond to a single layer of surfactantadsorbed on the polymer, and the resolubilizedform to a double layer of surfactant. Prior toformation of the latter, the complexes are highlysurface active. An analysis of the solubility diagramsof a cationic hydroxyethyl cellulose derivative, anda homologous series of sodium alkyl sulfates, hasprovided a value of the adsorption energy, <1>, ofthese surfactants into the first layer. The value of<1>, viz., 1.1 kT per CH2 group, is somewhat higherthan the corresponding value for micelle formation.Studies with a number of surfactants show thatpolymer/surfactant interaction is most favorable (a)the longer the hydrocarbon chain of the surfactant,(b) the straighter the chain', and (c) when the headgroup is terminal to the chain. Departures fromthese conditions reduce the extent of interactionand render difficult resolubilization of the complex.From results on a range of polymers, it is concludedthat resolubilization of the precipitated complex isalso difficult if the charge density of the polymer istoo high.

INTRODUCTION

Interactions in solution between surfactants and watersoluble macromolecules have been under study for 30years or more. Earliest work seems to have been carriedout on protein, anionic surfactant systems (1-5);depending on whether the protein was below or above itsisoelectric point, precipitation was observed, or was notobserved, respectively, However, even above the isoelectricpoint, association took place and in both cases wasrelated stoichiometrically to the number of positivelycharged sites on the protein.

More recently, interaction between surfactants and anumber of nonionic polymers, such as polyethyleneoxides (PEa) (6), polypropylene oxides (PPO) (7),polyvinylpyrrolidone (PVP) (8), polyvinylalcohol (PVA)

(9,10), polyvinylacetate (PVAc) (9,10), andmethylcellulose (MC) (11), has been reported, and thisfield has been reviewed by Breuer and Robb (9). Forreaction with ionic surfactants, the reaction sequence isreported (9) to be PYA < PEa < MC < PVAc " PPO ~

PVP; and for (the weaker) reaction with cationicsurfactants, it is reported to be PVP < PEa < PVA < MC< PVAc ~ PPO. Aside from the effect of residual charge,it is clear that interaction increases with increasinghydrophobicity of the polymer. In fact, it has been foundpossible to solubilize certain water insoluble polymers,e.g., PVAc (10) and polyvinylformal (12) by addition ofanionic surfactant. In general, interaction betweennonionic surfactants and uncharged polymers appears tobe very weak.

In several recent publications we have reported on thestrong association reactions which take place between acationically charged derivative of hydroxyethyl cellulose(Polymer JR) and anionic surfactants, as studied bysurface tension (13,14), solubility diagram (13,14),electrophoresis (14), and dye solubilization (15,16)methods. Perhaps the most cogent evidence of the strongassociation which can occur in such systems was thecomplete change in the characteristics of an alkyl sulfatemonolayer accompanying the introduction of a minute(10 ppm) amount of the cationic polymer into thesubsolution (14).

In the present paper we will examine in some detailthe influence of structural features in the anionicsurfactant on the interaction with the cationic polymer,and also enquire into the generality of the phenomena wehave reported by examining the interaction patterns of anumber of commercially available cationic polymers withthe anionic surfactant, sodium dodecyl sulfate (SDS).Finally, a small amount of information is reported on theinverse system, viz., anionic polymer, cationic surfactant.The work is concerned largely with the construction ofsolubility diagrams of the polymer/surfactant mixturesand includes a small section on the surface tensionbehavior of selected systems.

EXPERIMENTAL PROCEDURES

Solubility studies: Surfactant concentrate was added to

TABLE I

List of Cationic Polymers

Name

Gafquat 755

Carteretin F-4

Merquat 100

Merquat 550Calgon MS02

Reten 220

Jaguar C-13

PEl - 18PHA

Description

Quaternized vinyl pyrrolidone/aminoethylmethacrylate copolymerCopolymer of adipic acid/dimethyl­aminohydroxy propyl diethylene triamine

Poly (N,N-dimethyl-3,S methylenepiperidinium chloride): DMDACCopolymer of DMDAC and acrylamidePoly (N,N-dimethyl-3,S methylenepiperidinium chloride)Copolymer of acrylamide//3 methacryloxyethyl trimethyl ammonium chloride

Quaternized guar gum derivativePolyethylene imine

Experimental poly N(hydroxy-2 propyl)piperazine, 57% quaternized with trimethylammonium chloride

561

Side chain

Side chain

Side chainBackbone

Backbone

BackboneBackbone

Side chain

Side chain

Backbone

Backbone

pH of 0.1%solution

7.2

7.5

4.2

4.6

7.2

4.2

7.16.0

7.4

562 JOURNAL OF THE AMERICAN OIL CHEMISTS' SOCIETY VOL. 54

C C C• ••

ObservedMaximumPrecipitation

C•

ChargeNeutralization

/ST/

~ ST X. ~ c

'P P P •VST / PC ~'( C C C C C• S'r SP sp· sp· ·SP • ••

VST/VST STVST C C H C C". sp-SP· ••••

/ST SP T ST C SP SP SP/ • T. ••

/ VSP S SP SP

~ ...-i ST ST C .C CC T C""'.. ./ VSP VSP VSP I VSP\

/ VSP VSP/

/

T =TURBIDH = HAZYP = PRECIPITATIONS = SLIGHTV =VERYC =CLEAR

10' c---------------------,

aavcr.....,~

FIG. 3. Solubility diagram of the Polymer JR-400!sodiumdecyl sulfate system.

RESULTS AND DISCUSSION

Effect of Alkyl Sulfate Chain Lengthon the Polymer JR Interaction

Figures 1-4 represent the solubility diagrams ofmixtures of Polymer JR and sodium dodecyl (SDS),tetradecyl, decyl, and octyl SUlfates, respectively. Figure1, for SDS, has previously been reported and analyzed. Inbrief, at higher concerntrations of polymer (> 0.2 %) theline of maximum precipitation is straight, has a slope onthe log-log plot of 45° corresponding to constantcomposition of the precipitated complex, and,furthermore, coincides with the stoichiometric charge

10'2L-;:---l.----'............LL~"'--;-_L- .......................J..J_;:-'-.........-J--..........u.J'-U

10- 2 10" 10° 10'"10 SODIUM DECYL SULFATE

polymer. Solutions were prepared from a stock solutionof polymer with a relatively high concentration of SDSwhich was then diluted serially with polymer solution ofthe same concentration. A Rosano Tensiometer wasemployed for the measurements. Because of surfaceageing, values were taken 1 hr after generating a freshliquid surface.

Materials: The SDS sample was a specimen from BDH,Poole, England. It was subsequently recrystallized threetimes from water and three times from ethanol. Thetetradecyl, decyl, and octyl sodium sulfates were obtainedfrom Eastman Kodak.

Tergitol Anionic 4 is a Union Carbide material;Tergitol 15-S materials referred to in the text wereexperimental products based on a straight chain, 11-15 C,random secondary alcohol. Aerosol MA and Sipon ESethoxy sulfates, described in the text, were specimensfrom American Cyanamid and Alcolac, respectively.

Polymer JR-400 is a product of Union CarbideCorporation. It is quaternary nitrogen substitutedcellulose ether of molecular weight around 400,000 (17).The other cationic polymers used were Gafquat 755(GAF Corporation); Cartaretin F-4 (Sandoz); Merquats100 and 550 (Merck); Reten 220 (Hercules); CalgonM-502 (Calgon); polyethyleneimine (PEl, Dow); JaguarC-13 (Stein-Hall); and, poly-N (hydroxy-2 propyl)piperazine, partially quaternized (PHA, experimental).Further details concerning these polymers appear in TableI.

///

~P C

TC C•

C•C C• •

T•

C•

T•

ST•

C•VSPVST•

SP

SP

C•

ObservedMaximumPrecipitation

C•

C•

C•

C•

C•

C•

T = TURBIDH =HAZYP = PRECIPITATIONS =SLIGHTV = VERYC = CLEAR

T =TURBIDH =HAZYP =PRECIPITATIONS = SLIGHTV =VERYC =CLEAR

~ Ap/

C C TT T SP P. PPPSP C C C. . /. ......T. T T

C T )""•• p.p. P Observed• • / SP P. Maximum

Charge // s:••T Precipitation

Neutralization~/ T·T

/ ·C/ .

C/TTS TT. / .. ../

C /c:· /.//C C• •

T AC VST ST C C C•• • •• •IJ P

C STC VST C

• ~ S~ ••C VST STC TSTST C

Charge •••• • • •Neutralization~/ SP

ST/C VST XT T VST. ..,-....

/VSA VSP

C C ~~T VST C• ,.'•••• rI.C/C VSP/ SPVST

,.... • ST•••-:.CC VST CVSPVST••/ ~"-.C

VSP j VSP

CYST C C C C• •• •••SP

C C C CC C• • 'Je ••••

C CVSP VSPC C C

·vsp ,~s;· •

-3 C C C C SP C10 L_~3~.-I--L....I...J....J...W..L.:42.....,J~L.l..J...J...LiL.l---..-:L-LJ....L.l..LLU

10 1~ 10~ 10°"10 SODIUM DODECYL SULFATE

1O.41......::--L~..J....L..J...L.JUJ...-=-..l.-J....J...J..I...I..l..LL...:---L--L....L...I.....L.LLJJ

10'3 10. 2 10" 10°% SODIUM TETRADECYL SULFATE

10° 1=""""--------------,--.....,

FIG. 1. Solubility diagram of the Polymer JR-400!sodiumdodecyl sulfate system.

FIG. 2. Solubility diagram of the Polymer JR-400!sodiumtetradecyl sulfate system.

polymer concentrate, to which the appropriate amount ofwater had been added, in small vials. These were shakenby hand and set aside for 1-3 days, and the appearance ofthe liquid and the precipitation ratings were adjudged byeye. The tests were conducted at room temperature(23 ± 2 C).

Surface tension: Surface tension was studied as afunction of SDS concentration at a fixed concentration of

DECEMBER, 1977 GODDARD AND HANNAN: POLYMER/SURFACTANT INTERACTIONS 563

•

14

•

10 12SURFACTANT CHAIN LENGTH

10·5~--_-.L .-.. -'-_---I

8

10°C H C C C H• • • • • •

P P P P P

C H CHC0 • • ••0 Pc C c P SP C'<:t C Ca:: • • • • .H•..... P P P SP

~

10" C ST C C C C C• • • • • •SP VSP SP SP

IOI~-----------------.....,

-::::::...!! 10-2

oE-

FIG. 5. Logarithm of the equilibrium concentration, ceo ofvarious sodium alkyl sulfates vs. their chain length. n. Conditionscorrespond to maximum insolubility of the Polymer JR/alkylsulfate complexes.

I0'12

0L..'"""2---l_L.......L...L...I...u...ILJ.O"'·,--'---'-...........L.L.L.LI.....O"""o--'---'--'--'-................10'

% SODIUM OCTYL SULFATE

101.----------------------,

T ; TURBIDH ; HAZYp; PRECIPITATION ObservedS; SLIGHT

MaximumV; VERY

Charge PrecipitationC ; ClEAR

Neutralization/

10°C C /C T C C C HC• • / . • • ••••

/ SP P PSP

/ C T T C C CC CH0 / • • • ••• ••0 / SPS SPSPSP SP'<:t /ci:: / T VST C C..... / • • ••~ / VSPSP S SPSP

/10-1 / C C C T ST C C CSH

/ • • • • • • •••/ VSP VSP \ VSP, VSP

VSP VSP

FIG. 4. Solubility diagram of the Polymer JR-400/sodiumoctyl sulfate system.

neutralization line of the mixed polymer, surfactantsystem. In this condition we picture each positive chargeof the polymer as having a negative surfactant moleculeadsorbed onto it in head-to-head configuration. At lowerconcentrations of polymer, the slope of the maximumprecipitation line increases, until at <0.01 % polymer itbecomes 90° and independent of polymer concentration.As the concentration of surfactant at a certain polymerconcentration is increased beyond that required formaximum precipitation, resolubilization of the precipitateoccurs and eventually the systems become completelysoluble. We have postulated (13,14) that this processcorresponds to the adsorption of a second layer ofsurfactant and the transformation of the polymer into asoluble polyanion. Turning to the tetradecyl sulfatesystem (Fig. 2), we see qualitatively similar behavior,except that the 45° linear region is more extended, andthe transition to the higher slope regions occurs at lowerpolymer concentrations. In the case of the decyl sulfateshown in Figure 3, the 45° line of maximum precipitationis correspondingly displaced to higher surfactantconcentration, and the transition concentrations are alsohigher. Finally, for the octyl sulfate system no 45° slopeline is detectable in the concentration range examined,only a vertical segment is observed and this is displaced toan even higher surfactant concentration (see Figure 4).

Our previous analysis (14) led to the followingequation describing the equilibrium in these system

(Ct - Ce)

This equation refers to the condition of maximuminsolubility; [Pl is the polymer concentration, Ct is thetotal concentration of added surfactant, and Ce is theconcentration of surfactant required to maintainequilibrium with the precipitated complex. The equationmakes it clear that as [Pl tends to zero, virtually all theadded surfactant is required to maintain Ce, and, hence,why the precipitation line becomes vertical. It isqualitatively obvious, from inspection of Figures 1-4, thatthe affinity of the association reaction decreases stronglyas the chain length of the surfactant decreases. Thisconclusion is emphasized by Figure 5 in which we plotthe logarithm of the Ce values, i.e., the concentrations

10,2........,:-''---~.........,..u...LJ..-:----'--...L-'--'- ..........u..L._...J-~ .........-'-L-U.I

10'2 10'1 10° 101

% TERGITOL ANIONIC 4

FIG. 6. Solubility diagram of the Polymer JR-400/TergitolAnionic 4 system.

corresponding to the vertical lines in Figures 1-4, of thealkyl sulfates against their chain length; the plot is linear.The data allow a quantitative estimate of the interactionenergy to be made.

The equilibrium governing the adsorption of anionic

564 JOURNAL OF THE AMERICAN OIL CHEMISTS' SOCIETY VOL. 54

10'r----------------------, 10'~-----------------____,

SH ST H C C C C C ST C C H H C10° • • • • • ~ P 10° • • • • •• •P P P P P P P P P PC ST ST C C C C H

00 • • • • • • •0Pc ~c ... C P P P SP 0

"""C C C. H """ C C H H H HCC• • . . .' • cr: Ccr:

V~:''''' .... SP P SP • • • • • • •••.... -,P P P P SP

'If!. ..' '. 'If!..' ..

C T .'C C C · C SHC10-' • • :. • • •

VSP VSP :.

SP 10"

/ c T C H H H H C• • • • • • • •VSP VSP VSP VSP

All solutions clear at 13.5% Surfactant

10'2L....",-l----L--'-.l...J...L...UJ....,.....--L--L...L..l-W...I...l..L;;---...l-...l-.L.J...J...J...!-u

10-2 10-1 10° 10'

0/0 TERGITOL ANIONIC 45-S SULFATE

FIG. 7. Solubility diagram of the Polymer JR-400/Tergitol45·S sulfate system.

la'~--------------------,

C VST C C C HH10° • • • • • •P P P P P

C C C C CHH0 • • • • • •0

C P C P P SP""" C C VST Ccr: • • • • • • H.... P P'If!.

C C C C C C VSH10-1 • • • • • •SP SP

All solutions clear at 12% Surfactant

10-2 L-:~--..J~...l.-L.li-L.I......;----..J_L....L--L...1...J....L..L..I--;:-_.L-..I.-..J'---'-J....W..w

10-2 10" 10° 10'

0/0 AEROSOL MA

FIG. 8. Solubility diagram of the Polymer JR-400/Aerosol MAsystem.

surfactant onto a positively charged polymer can beexpressed as

C-adS. =0 Cb ~xp 1(e Wo + n <l» / kTf

~here Cb is the equilibrium concentration of surfactant insolution, Cads is the concentration of adsorbed surfactantin undefined units, Wo is the electrostatic potentialaround the polymer, n is the number of CH2 groups inthe surfactant chain, <t> is the adsorption energy per CH2group, and k and T are the Boltzmann constant andabsolute temperature, respectively. If we considerconditions corresponding to maximum precipitation andcharge neutralization, the equation simplifies to

c'acts =0 c e exp (n <l> /kT) = a constant.

Hence, the slope of the log, 0 Ce vs. n plot has the

10" 100

0/0 TERGITOL 15-S-3 SULFATE

FIG. 9 Solubility diagram of the Polymer JR-400/TergitolIS-S·3 EO sulfate system.

value <t> /2.3 kT, and from Figure 5 we obtain a value of<t> of 1.1 kT. This value is somewhat higher than the freeenergy of micelle formation of this kind of surfactant,viz., 0.8 kT/CH2 group (18). The energy of clusterformation corresponds more closely to that of"hemimicelle" , formation of ionic surfactants onoppositely charged mineral surfaces (19).

Effect of Anionic Surfactant Structureon the Polymer JR Interaction

The above results, and those reported by us previously,involved straight chain surfactants in which the alkyl chainwas primary' to the anionic head group. [For convenience,in this category we include a linear alkyl benzenesulfonate (13).] We will now examine departures from thisstructure. Tergitol Anionic 4 is a fourteen carbonsecondary sulfate in which the anion is attachedapproximately midway along the main chain which itselfpossesses some branching. Figure 6 shows that the solubilitydiagram has become more complex, the salient featurebeing that with this surfactant it has become moredifficult, i.e., more surfactant is required, to solubilize thecomplex. We note, however, the unusual clear zonearound the 1% surfactant level at a polymer concentrationof 0.1%.

Figure 7 presents corresponding, and similar, data forthe Polymer JRjTergitol Anionic 45-S sulfate system. Thelatter surfactant is based on a straight chain 14-15 carbonhydrocarbon in which the alcohol, and hence, sulfategroups are secondary and random along the chain. Wenote again the difficulty in solubilizing the complex athigher surfactant concentration, and also the appearanceof an even larger delineated "clear zone" at lower levels of

, 0

the polymer. For both systems the 45 maximumprecipitation line is evident at higher polymerconcentration, and the slope increases at lower polymerlevels. Results for the Polymer JRjAerosol MA system(dimethylamylsulfosuccinate) are given in Figure 8. In thiscase not only are resolubilization difficulties encountered,but the maximum precipitation line, in the rangeinvestigated, is almost vertical.

Certain features concerning the affinity of the

DECEMBER, 1977 GODDARD AND HANNAN: POLYMER/SURFACTANT INTERACTIONS 565

1010°10-1

100 C H T VT C C C C C• • • • • • •• •P P P PC VST ST C C C H VST

0 • • • • • •••0 Pc P P P VST""" C CCI:: • • • C.C.HIeC...., P P P~

10" C VST C C C C HVST C• • • • • • •••SP SP SP SPC ST C C SH SH H C• • • • • • • •SP SP VSP VSP

0/0 SDS

FIG. II. Partial solubility diagrams of a series of polycation/sodium dodecyl sulfate systems. The lines drawn correspond toconditions of maximum precipitation.

10'21"'0"""2;-'---'..............L..J....u....ll.J..0-.·,-J.-.j-J--'-L..LL1.u0~0:--..L..--'--J.....L..J...J...I..u1 01

%TERGITOL 15-S-7 SULFATE

10'r:-------------------.....

FIG. 10. Solubility diagram of the Polymer JR-400/TergitolIS-S-7 EO sulfate system.

mon feature in each solubility scheme is the slope of 45 v

of the lines of maximum precipitation at higher polymerconcentrations (>0.1 %). Presumably, these lines corres­pond to charge neutralization through adsorption of asurfactant ion at each cationic site along the polymerchain although the stoichiometry is not readily verifiableas many of the polycations have an incompletely identi­fied structure and/or contain an amino functionality forwhich the ionization state was not determined. An ex­ception to this was the fully quarternized homopolymerMerquat 100 (and also Calgon M502) for which theobserved polymer/SDS ratio of 1:2 at maximum precipita­tion closely corresponds to a calculated molecular weightresidue, per cationic charge, of 162. Two of the polymers,

10 r--------------------,

polymer/surfactant interaction, as judged by theformation of the maximum precipitation line (firstsurfactant layer) and resolubilization of the complex(second surfactant layer), now start to emerge. Interactionis most favorable (a) the longer the hydrocarbon chain ofthe surfactant, (b) the straighter its chain, (c) when theanionic head group is terminal to the chain. Conditionsare least favorable in a surfactant molecule likeAerosol-MA where the alkyl groups are short andbranched and the head group is centrally positioned inthe molecule. The reason for the "clear zones" insolubility diagrams of Polymer JR and Tergitol Anionics 4and 45-S sulfate is not apparent: it may be connectedwith a salting-out phenomenon as the surfactantconcentration is increased.

Eth ox y sulfates comprise the last group of anionicsurfactants examined. Solubility diagrams for PolymerJR/Tergitol 15-S-3 EO sulfate and Tergitol 15-S-7 EOsulfate are presented in Figures 9 and 10. We see thefeatures of 45° precipitation lines at high concentrationand the need for high solubilizing concentrations of thesesurfactants, but no anomalous clear zones. In otherexperiments it was established that the presence ofethoxy groups, per se, does not adversely affect theinteraction, so confirming previous results (20); both atwelve carbon monoethoxy sulfate and a triethoxy sulfate(Sipon ESY and ES) displayed strong interaction features,viz., a 45° precipitation line in the range of polymerconcentration tested (0.1 to 1%) and also relatively lowvalues of resolubilization concentrations.

Interaction of Other Polycations with 50SThe generality of polycation/anionic surfactant inter­

actions is demonstrated in Figure 11 which presentspartial solubility diagrams of mixtures of various poly­cations with SDS. Here, only the lines corresponding tomaximum precipitation are depicted for each system; theremainder of each diagram will be described qualitatively.These' polycations were with one exception commercialsamples and are described in Table I. The degree ofcationic functionality of several of them would vary withpH, but they were used as supplied without adjustment ofpH, since our purpose was to establish the general natureof the interactions rather than specific aspects. A com-

Polymer JR/Non-Anionic Surfactantsand Other Systems

We have reported previously (13) that nonionicsurfactants, such as Tergitol 15-S-9, and betainesurfactants, such as N tetradecyl, N,N dimethylglycine,give no indication of reaction with Polymer JR as judgedby both surface tension and solubility criteria. Cationicsurfactants fit into this category as well. In the same wayit has been found that no interaction occurs betweentetradecyl sulfa t e and the nega tively chargedcarboxymethyl cellulose (21).

Influence of Added Salt on PolymerJR/SOS Interaction

Solubility diagram experiments demonstrated that in­organic salts such as NaCI, Na2 S04, etc., have little effecton the polymer/surfactant preciptation even at the rela­tively high added level of 0.1 %. Only when there was aninfluence on the solubility of one or other of theinteracting components, e.g., formation of magnesiumdodecyl sulfate on adding MgCI2, was some effect seen.These results show that the driving force for the inter­action is associated with the cationic polymer and thesurfactant anion itself, and not other parameters such asionic strength.

566 JOURNAL OF THE AMERICAN OIL CHEMISTS' SOCIETY VOL. 54

60

40

RETEN.220",- SDS\ALONE

---\ \PHA \ \.\ G~~~~_~:_~:'~ \ (... -\

\MERQUAT '" '\j '\',- 550 "'\ JR r.... ~\

........... \ 400 '}l.~"" ..".~ I ~ \,......... "'T'~f"" \\

CARTARETIN F· 4 " ........~.. '~r:"-'-'~\::Z"-~!!!IIrr......_ "..~:.:- ..

t

which the cation is incorporated directly into the back­bone, viz., Merquat 550, PHA, and Carteretin F-4, giverise to a greater S.T. lowering than the remaining poly­mers studied, for which the cationic groups are located onside chains.

In closing this section, mention should be made ofother work recently carried out on polycation/SOS sys­tems. Thus, van den Berg and Staverman (22) investigatedthe binding of SOS onto PEl by a study of the ensuingpH shifts. Likewise, this technique was employed toexamine complex formation in PEI/SOS and PHA/SOSsystems by Vanlerberghe (23) et aL These authors alsostudied the interaction by use of surface tension, wetting,conductance, and electrophoresis techniques.

30 L---J.......L-L.LU.J..l.L,:-----L----L.l...ll.LW.-,----L-J.---W..llli-'-,-----'-.LL.LllUL-----'----J-J....LLllJJ

10-5 10-' 10-3 10-2

SDS MOLARITY

FIG. 12. Surface tension results for a series of polycation/sodium dodecyl sulfate systems at 25 C. Polycation concentrationis 0.1%. Arrows indicate points of maximum insolubility.

viz., Reten 220 and Jaguar C-l3, were investigated atconcentrations low enough to verify the change in slopetowards the vertical.

A qualitative description of the unshown portions ofthe solubility diagrams is of interest regarding the easewith which each precipitated system can be resolubilizedby added surfactant. All of the polymers displayingmaximum precipitation at a polymer/SOS ratio less thanor equal to unity, i.e., Jaguar C-l3, PHA, Merquat 100,Calgon M-502, and PEl, proved difficult to resolubilize,requiring large excesses of surfactant. The remaining poly­mers were readily resolubilized in the manner of PolymerJR. It appears that a critical charge density exists abovewhich adsorption of the second, resolubilizing surfactantlayer becomes unfavorable owing to mutual repulsion ofthe ionic head groups.

Surface tension (S.T.) measurements were conductedon several systems at a constant polymer concentration of0.1 %, and the results together with those previouslyreported for Polymer JR/SOS (14) appear in Figure 12plotted against the logarithm of the surfactant concen­tration. Points corresponding to maximum precipitationare indicated by arrows. In all cases it is seen that thepresence of the polymer, itself only weakly surface active,produces a sharp depression of the S.T. at SOS concen­trations below its critical micelle concentration. Similardepressions, but smaller, have been reported for nonionicpolymers in the presence of SOS (6,7). This lowering ofthe surface tension can be ascribed to adsorption ofsurfactant anions onto the polymer backbone, markedlydecreasing its solubility and rendering it highly surfaceactive at the air/water interface. Subsequent resolubiliza­tion of the complex through further addition of sur­factant mayor may not produce a minimum in the S.T.plot, depending on the relative surface activity of thepartially resolubilized complex. Eventual coincidence ofthe S.T. value with that of micellar SOS indicates thatadsorption onto the polymer is completed, the concen­tration of single surfactant ions remains sensibly constant,and further addition of surfactant results in the formationof micelles. Further evidence of this effect was obtainedby dye solubilization experiments on the Polymer JR/SOSsystem (15,16).

It is of interest that the extent of S.T. depressionobtainable by a polycation in the presence of SOSappears dependent upon the position of the cationicfunctionality in the polymer structure. Polymers for

Interaction of Anionic Polymerswith Cationic Surfactants

All the work we have described so far has concernedpolycation/anionic surfactant systems. Considerably lesswork has been devoted to polymer/surfactant systems inwhich the charges are reversed although Saito has re­ported the interaction of polyacrylic acid with cationicsurfactants (24). We have studied the solubility diagramof sodium carboxymethyl cellulose (Hercules L-n and anexperimental hydroxyethyl carboxymethyl cellulose withcationic alkyl trimethyl ammonium chlorides. In thesesystems the polymer/surfactant ratio at maximum pre­cipitation agreed well with that calculated for chargeneutralization, and the difficulty we observed in resol­ubilization of the polymer/surfactant complexes is con­sistent with the relatively high charge density (degree ofsubstitution equal to 0.7) of these polyelectrolytes.

REFERENCES

I. Putnam, F.W., and H. Neurath, 1. Am. Chem. Soc. 66:692(1944).

2. Putnam, F.W., and H. Neurath, Ibid. 66:1992 (1944).3. Karush, F., and M. Sonenberg, Ibid. 71 :1369 (1949).4. Goddard, E.D., and B.A. Pethica, 1. Chem. Soc. 2659 (1951).5. Pankhurst, K.G.A., in "Surface Chemistry," Butterworths,

London, 1949.6. Jones, M.N., 1. Colloid Interface Sci 23:36 (1967).7. Schwuger, M.J., Ibid. 43:491 (1973).8. Fishman, M.L., "Interaction of Sodium Dodecylsulfate with

Aqueous Polyvinylpyrrolidone," Ph.D. Thesis, Polytechnic In­stitute of Brooklyn, 1969.

9. Breuer, M.M., and J.D. Robb., Chem. Ind. 530 (1972).10. Arai, H., and S. Horin, 1. Colloid Interface Sci. 30: 372

(1969).11. Lewis, K.E., and C.P. Robinson, Ibid. 32:539 (1970).12. lsemura, T., and A. Imanishi, 1. Polym. Sci. 33:337 (1958).13. Goddard, E.D., T.S. Phillips , and R.B. Hannan, 1. Soc.

Cosmet. Chem. 26:461 (1975).14. Goddard, E.O., and R.B. Hannan, 1. Colloid Interface Sci.

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[Received May 16, 1977]