Reprinted from

COLWIDSANDSURFACESAH~~A: PHYSICOCHEMICAL AND

ENGINEERING ASPECTS

Colloids and SurfacesA: Physicochemical and Engineering Aspects 112 (1996,55--62

Hydrocarbon and alcohol effects on sulfonate adsorptionon alumina

Edward Fu, P. Somasundaran *, C. Maltesh 1

Langmuir Center for Colloids and Interfaces. Department of Chemical Engineering. Materials Science and,Wining Engineering. Columbia University. Nf"" York. NY 10017. liSA

ELSEVIER

COLLOIDS AND SURFACESA: PHYSICOCHEMICAL AND ENGINEERING ASPECTS

AN INTERNATIONAL JOURNAL DEVOTED TO THE PRINCIPLES AND APPLICATtONS OFCOLLOID AND INTERFACE SCIENCE

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ACOLLOIDSANDSURFACES

ELSEVIERColloids and Surfaces

A: Physicochemical and Engineering Aspects 112 (l996) 55-62

Hydrocarbon and alcohol effects on sulfonate adsorptionon alumina

1

Edward Fu, P. Somasundaran *, C. Maltesh 1

Langmuir Center for Colloids and lnterfa<'cs. Depclrtment of Chemical Engineering, Materials Science andMining Engineering, Columbia University, New York. NY 10027. USA

Received l3 October 1995; accepted 9 January 1996

Abstract

Adsorbed surfactant aggregates are finding applications in areas such as soil washing and ultrafiltration. In orderto optimize these processes it is imperative to fully elucidate the effects of the solubilizates and additives on surfactantadsorption and aggregation. The effect of alcohol and hydrocarbon additives on the equilibrium adsorption ofisomerically pure n-decylbenzene sulfonate on alumina is studied here. Dodecane increased sulfonate adsorption bymore than one order of magnitude at concentrations of < 10 -4 moll-I sulfonate. At higher sulfonate concentrations

the adsorption change was much less marked. The effects of varying the dodecane levels between I and 16.7 vol.%were surprisingly small. In contrast, addition of propanol decreased sulfonate adsorption under all conditions becausethe alcohol increased the power of the solvent towards the surfactant. Medium and long chain alcohols were foundto interact synergistically with the surfactant, decreasing the onset of both hemimicellization and micellization.Sulfonate adsorption increased in pre-micellar solutions but decreased in micellar solutions. In addition, adsorptionof sulfonate was found to be identical at low levels of decanol, both of which were well above the aqueous solubilitylimit. This suggested that the effect of the additive is limited by its solubility in the phase from which adsorptiontakes place.

KeY\4'ords: Alcohols; Alumina; Hydrocarbons; Sulfonate adsorption

modification (2,3]. Adsorption of ionic and non-ionic surfactants as single components has beenthe subject matter of several studies using classicaltechniques to determine adsorption density, zetapotential, hydrophobicity and wettability in con-junction with relatively new techniques such asemission, magnetic and vibrational spectroscopies[4--6]. These investigations are usually carried outwith a single pure surfactant dissolved in aqueoussolution, with a single pure adsorbent suspendedin it. In contrast, there has been limited work withmixed surfactant systems containing, for example,oil and alcohol in addition to the surfactant. Suchsystems are of both theoretical and practical impor-

i. introduction

Adsorption and aggregation of surfactants onsolids can occur with marked effects on interfacialand colloidal behavior [1] and drastically alterthe solid/liquid interface. Indeed many industrialproducts/processes such as flotation, flocculation,dewatering, enhanced oil recovery, lubrication,paints, coatings, adhesion, cosmetics, pharmaceut-icals and detergency derive their efficacy via surface

. Corresponding author.I Present addrcss: Corporate Research. Nalco Chemical

Company. Naperville. IL 60563. USA.

0927-7757/96/S15.00 01996 Elsevier Science 8. V. All rights reservedP/I 50927-7757(96)0354-0

E. Fu el aL!Co/loid- .5w:(oc('s A: Ph}'sic(J("MrrL Eng. Aspects 111 (1~} 55-6156

be studied and the results interpreted, if there isan understanding of the interactions that occur inmore basic systems. In this work, adsorption of anisomerically pure surfactant, n-decylbenzene sulfo-nate, on alumina was studied in the presence of oiland alcohol additives. This surfactant has a rela-tively simple structure and is resistant to thehydrolysis common for fatty acids and amines.Mixtures of sulfonated surfactants are potential oilftooding surfactants because of their high oil/waterinterfacial activity.

2. Experimental

Materialsz.

2.1.1. SurfactantThe surfactant, n-sodium decylbenzene sulfo-

nate, was synthesized in our laboratories and thedetails are provided elsewhere [12]. Character-ization by IH- and 'JC-NMR. mass spectrometryand high performance liquid chromatography(HPLC) showed the surfactant to be at least 98%

isomerically pure.

tance because of their capacity to form micro-emulsions and their applicability to industrialsituations such as enhanced oil recovery anddetergency. In addition to emulsification. adsorbedsurfactant aggregates can solubilize oil or alcoholas in the incorporation of such molecules intomicelles. Increased attention is being paid currentlyto the solubilization of hydrocarbons and alcoholsin adsorbed surfactant aggregates primarilybecause of the projected applications in soil wash-ing. filtration. thin films, separations, catalysis, etc.[1.8]. Partitioning of model hydrophobic solutessuch as naphthol to the silica-water interface inthe presence of long chain cationic surfactants hasbeen widely studied by Monticone et al. [9]. Ithas been reported that the adsorbed surfactantaggregates are capable of solubilizing the insolubleor non-adsorbing solutes to a greater extentthan simple micelles. Substrate porosity has littleeffect on the uptake of the solute but pH andother solution parameters alter solubilizationprimarily due to changes in solute dissociationcharacteristics.

The literature indicates that the behavior ofadsorbed aggregates is similar to that of micellesin the presence of alkanes [10]. Atypical behaviorwas observed for alcohols primarily because of theavailability of increased solubilization sites (thecore and the hydrophobic perimeter), whereasalkanes are solubilized only in the hydrocarboncore. The presence of alcohol increased the adsorp-tion of surfactant (sodium dodecylsulfate) on alu-mina. and with an increase in alcohol chain lengthsurfactant adsorption was further enhanced. Ina similar study. Esumi et al. [11] reported thatthe effect of alcohol on surfactant adsorption de-pends upon the nature of the alcohol. For ex-ample. hexanol reduccs the polarity of adsorbedlithium dodecylsulfate (LiDS) or lithium perftuoro-octane sulfonate (LiFOS) layers significantly butincorporation of heptanuorobutanol into theLiFOS bilayer alters the polarity only slightly.Interestingly. there was little effect of either alcoholon the surfactant adsorption itself. These contrast-ing effects of alcohols on surfactant adsorptionsuggest that the operating mechanisms are complexand need to be probed further. Adsorption fromcomplex systems such as microemulsions can only

1.1.2. lnorganicsSodium chloride, used to control ionic strength,

was of ultrapure grade (99.999%) and was used asreceived from Aldrich Chemicals.

2.1.3. Hydrocarbonsn-Dodecane (99% pure) from Aldrich Chemicals

was used as received. The alkane was utilized as amodel for oil in this study.

2.1.4. Alcoholsn-Propanol. n-pentanol and n-decanol were

purchased from Fisher Scientific. and were of certi-fied reagent grade.

2.1.5. AluminaLinde A high purity alumina (90% alpha and

10% gamma) was purchased from Union Carbide.The specific surface area as measured using aQuantasorb apparatus by the BET method was 15m2 g-i. Electron micrographs of the samples

E. Fu et ai/CDlloid\" Sur:faces A: Physicochenl. £IIg. Aspet;fi l Jl(J.")5$.c::61 S1

showed them to be irregularly shaped and to haverough surfaces.

the entire concentration range studied. The pH ofthe system was not adjusted and was allowed toattain its equilibrium value of ~8.2. Ionic strengthwas maintained at 0.1 M NaCI. It must be men-tioned that with the exception of propanol, theinitial levels of alcohols studied were above thesolubility limits for each of the additives. Thisresulted in the formation of two-phase liquid sys-tems and stable emulsions at high surfactant levels.The aqueous volume was maintained at 10 ml forall experiments and thus the initial fluid volumesof the samples varied with the level of oil or alcoholadded. From partitioning experiments it was foundthat sulfonate did not partition into the oil phase.

2.1.6. WaterAll water used in the experiments was distilled

three times in a glass still, and then deaerated withnitrogen to remove carbon dioxide.

2.2. Methods

2.2.1. Adsorption0.5 g samples of alumina were transferred to

25 ml flasks and the desired amounts of NaCIsolution added to wet the mineral. The flasks weresealed and the suspension equilibrated for 1.5 h ona wrist-action shaker located inside an incubator.The surfactant and any additives were thenpipetted into the flask. If oil was to be used in theexperiments, it was first dispersed in the surfactantsolution by ultrasonication (Labline Ultratip 9100system, 30 W power for I min) and the resultantemulsions were then pipetted into the flasks.Alcohol, when used, was pipetted directly into theflasks since it was more difficult to keep it dispersedin dilute sulfonate solutions. The suspensions con-taining the surfactant and the mineral were furtherequilibrated for 4 h on a wrist-action shaker.Following this, solids were separated by centrifu-gation at 4500 rev min - I in an incubator. Aliquots

of the supernatant were then removed for analysis.

3. Results and discussion

The aim of the present study was to determinechanges in sulfonate adsorption on alumina in thepresence of oil and alcohol additives. The adsorp-tion of n-decyl benzenesulfonate (n-DBS) on alu-mina in the presence of varying amounts of n-dodecane is shown in Fig. 1. The adsorption of n-DBS alone on alumina is characteristic of ionicsurfactant adsorption on oxide minerals with fourwell-defined regions. Models to account for thisbehavior were previously proposed based uponelectrostatic and hydrophobic interactions [14,15]and confirmed by several spectroscopic and calori-metric studies [16-19]. Surfactant aggregation onparticles (solloid formation, hemimicellization)occurs at a residual concentration of ~ 9 x 10 - 5

mol 1- 1. In the presence of dodecane the adsorp-tion in the lower concentration region (region I) isenhanced, with a slight increase in adsorption alsooccurring in the micellar region (region IV).Neither the hemimicellization concentration northe critical micelle concentration (CMC) seem tobe affected by the presence of the hydrocarbonalthough the adsorption density at the onset ofhemimicellization is about 15 times higher. Testsupernatants in the premicellar range were clear,without a visible oil phase, while more concen-trated systems exhibited increasing turbidity withincreasing sulfonate concentration. Turbidity is anindication of emulsification with more residual oilin micellar systems. Interestingly, increasing the

2.2.2. Anal}'sesSulfonate concentrations above ~ 2 x 10-4 mol

11 were determined using a two-phase titrationtechnique with dimidium bromide-disulphine blueas the indicator [13]. Sulfonate concentrationsbelow 2 x 10 - 4 mol 1- I were measured by UV

absorbance at 223 nm. For measurements of alco-hol (decanol only), the components were separatedusing HPLC (the mobile phase was a 70: 30 mix-ture of acetonitrile and 0.01 M tetrabutylammon-ium phosphate solution, refractive index detector,CIs bonded silica column).

2.3. Condition,~

All experiments were carried out at 75"C toensure complete solubility of the surfactant over

E. Fu et aI./Colloidr Surfaces A: Ph}'sicochem Eng. Aspects 111{J996) ;5542sa

Adsorption behavior of n-DBS on alumina in the presence of varying dodecane levels (i. 9.1 and 16.7%).Fig.

dodecane concentration from 1 to 16.7 vol. % doesnot cause any further increase in the sulfonateadsorption. Emulsions were observed for the 9.1and 16.7 vol. % dodecane systems at high sulfonateconcentrations and the data show a large degreeof scatter in these cases, making comparison withthe reference isotherm difficult. For both the 9.1and 16.7 vol. % dodecane cases, there was excessoil at the end of each experiment and observationsof agglomeration and floc extraction into the oilphase were made. As mentioned earlier, there wasno measurable partitioning of the sulfonate intothe oil phase, possibly due to the ionic characterof the functional group. As a result, adsorptiondeterminations were direct when aqueous and oilphases were separate as was observed in the pres-ence of I and 9.1 vol. % dodecane. For tests doneat 16.7 vol. % dodecane there was a significantvolume of emulsion which could be measuredeasily. In this case, measurements were madeassuming the emulsion lo be a separate phase. Theresults are summarized in Table I for the systemcontaining 16.7 vol. % dodecane and it is evident

that the emulsion layer contains the highest surfac-tant concentration. A clear trend that developsfrom the volume readings is the increase in emul-sion at the expense of free hydrocarbon as surfac-tant levels are raised. Both observations areconsistent with the fact that emulsions are stabi-lized by surfactants. Nevertheless, the three sulfo-nate adsorption isotherms obtained in the presenceof dodecane are similar and there is no significantdifference below a DBS concentration of 2 x 10-4mol 1- l. At higher sulfonate concentrations, theadsorptions at 9.1 and 16.7 vol. % dodecane differfrom that at 1 %. Adsorption at the two high levelsseems to follow a similar trend in that the slopesof the isotherms decrease at 2 x 10 - 4 mol 1- l, and

do not reach a plateau like the isotherms at 0 and1 % dodecane. Before attempting to interpret thisbehavior it should be noted that very stable emul-sions form at the high sulfonate and dodecaneconcentrations. There will be some errors associ-ated with the surfactant analyses under these condi-tions and the data will be less reliable.

It is interesting that sulfonate adsorption is

E. Fu et al.lColloid!' Surfaces A: Ph}'sicochem. Eng. Aspects 112 (1996) _\"5-62 59

Table lConcentration and phase volume measurements of supematant~ from n-DBS adsorption tests on alumina. Initial dodecaneconcenlralion= 1.67% by volume

Volume (ml)[nitialconc. (moll-i)

Emulsion Oil Aqueous Emulsion Oil

3.0 X 10-J4." X 10-34.1 X 10-34.9 X 10-35.3 X 10-J6.1 X 10-36.2 X 10-J9.6 X 10-31.2 X 10-21.6 X 10-2

9.08.78.69.29.29.19.08.27.71.9

0;3

1.1

1..7

1.2

i1

1.4

1.3

2.1

2.3

2.4

1.10.91.00.40.50.50:40.10.10.1

7.8 X lO-4l.3 X 10-31.2 X 10-3l.4 X 10-3l.6 X 10-32.2 X 10- 3

2.2 X 10-34.0 X 10-36.2 X 10-38.6 X 10-3

L6 X 10-36.1 X 10-15.4 X 10-11.6 X 10-31.8 X 10-36.1 X 10-35.8 X 10-31.6 X 10-19.9 X 10-3Ll X 10-2

~O~O~O~O~O~O~O

8.2 )( 16-4

19)( ro-31.6 x ro-324)( ro-326)( ro-33.0)( ro-329)( 10-35.3)( 10-38.0)( 10-31.0 )(10-1

4.4 x {O-s4.4 x 10-55.1 X 10-s5.0 x 10-55.4 X 10-s6.2 x 10-s6.6 x 10-s8.6 x 10-s8.0 x 10-s1.2 X 10-4

I[ and lli. An increase in propanol concentrationto 10 vol % decreased the adsorption further. Thereis no region I detected in the presence of alcohol.The tendency for propanol to reduce sulfonateadsorption is clearly shown in Fig. 3. The trend isevident as adsorption decreases from 6.2 x 10 - 5mol g -I in the absence of propanol to 4.4 x 10-7mol g - 1 at 50% propanol. This decrease is attrib-

uted to the increased solubility of sulfonate inwater/propanol mixtures. It was observed thatconcentrated n-DBS solutions at room temper-ature formed precipitates as the solubility limitwas exceeded; when propanol was added theseprecipitates dissolved. An increase in solvent powerleads to reduced surface activity and hence reducedadsorption.

The sulfonate adsorption isotherms in the pres-ence of 1% pentanol and decanol are also shownin Fig. 2. Both pentanol and decanol increaseadsorption at lower sulfonate concentrations butreduce the plateau adsorption. Interestingly theshape of the isotherms in the presence of all threealcohols is similar.

The alcohol adsorption as a function of residualDBS concentration was also determined and theresults are shown in Fig. 4. Uptake of decanol wasdetermined to be very near 100% below 4 x 10-5moll-I n-DBS. The residual alcohol was below thedetection limit of HPLC. Assuming a parking areaof 20 A 2 for alcohol adsorbed in a vertical orienta-

tion to the surface, monolayer coverage is achieved

increased only in region I wherein the predominantadsorption mechanism is electrostatic interactionbetween the sulfonate ion and the alumina surface.It is unlikely that dodecane enhances electrostaticattraction forces between the sulfonate species andalumina sites but it is possible that sulfonateaggregation is enhanced at the interface resultingin enhanced adsorption. The slopes of the iso-therms in region I in the absence and presence ofdodecane are however very similar, suggesting thatthe electrostatic driving force is not altered. Belowthe hemimicellization concentration, the surfactantwill adsorb as individual molecules or as dimers.This will increase the hydrophobicity of the surfacelocally creating sites where the alkane can coads-orb. Coadsorbed dodecane can enhance sulfonateaggregation at the interface, resulting in increasedsurfactant adsorption. Once sulfonate forms hemi-micelles and bilayers at the solid-liquid interface,the oil will be solubilized into these aggregates andthe effect on adsorption is reduced. Similarly, theoil will preferentially solubilize into micelles in thebulk at higher sulfonate concentrations, resultingin minimal effects on adsorption. Similar resultshave been reported in a study of dodecane adsorp-tion/abstraction on alumina [20].

The results obtained for the effect of alcohols ofvarying chain length on the adsorption of n-DBSare given in Fig. 2. Addition of 1% propanoldecreases the adsorption measurably below6 x 10 - 5 mol 1- 1 and also through most of regions

E. Fu el al./Col/oids Surfaces A: Physicochem. Eng. Aspects 112 (1996) 55-6260

00

~

"0.~0i£~c

oS"3'"

Fig. 2. Adsorplion behavior of n-DBS on alumina in the presence of alcohols of chain lenglh varying from propanol to decanol.

I~IO-

?O~E 1.10

,;'"

~~"i..

!~Of)

0 10 !n 30 40 5n 60

n-Propanol, voJ '.

Fig, 3, Adsorption behavior of n-DBS on alumina as a functionof n-propanol concentration.

E. Fu et aL I'Colloid5 Surfaces If: PhJ'sicochem. Eng. Aspe~ts JU( l~) 5.1-6:) 61

at 1.2 x 10-4 mol g-i. The measured adsorption isI x 10-3 mol g-l, indicating that alcohol formsmultilayers at the interface. So use of the termabstraction would be more precise to describe theloss of decanol. At higher surfactant levels, decanolabstraction begins to decrease. A reduction of thedecanol concentration from I to 0.25% did notaffect the sulfonate adsorption but the shape of thedecanol abstraction curve wa.~ similar.

Adsorption at the solid/liquid interface is gov-erned by: (i, electrostatic interactions between thesulfonate ions and charged surface sites; (ii) hydro-phobic interactions between adsorbed sulfonateions as well as between sulfonate and the additivein solution and at the interface; (iii) changes insolvent power stemming from the dissolution ofthe additive; and (iv) shielding of the ionic headgroups by coadsorbed non-ionic heads. In bulksolution, alcohols reduce electrostatic repulsionsat the micellar surface, enhance surfactant micelli-zation and reduce the CMC. However, this trendwas found to be reversed for short chain alcoholsat high concentration levels because under theseconditions the solvent power towards the surfac-tant was increased. Such increase in solvent powerexplains the reduction of sulfonate adsorption inthe presence of propanol (Fig. 3). However, theincreased level of molecular associations caused byhigher alcohols will result in increased sulfonateadsorption when pentanol and decanol are present.The greater effect of decanol over pentanol rel1ectsthe chain length dependence of the alcohol/sulfo-nate interactions. An interesting observation is thatthe sulfonate adsorptions in the presence of I and0.25% decanol were identical. This may appearpuzzling considering the strong synergistic inter-actions that occur between the decanol and thesulfonate. It must be recalled, however, that dec-anol is present at levels above its miscibility withthe aqueous solution and therefore its activity insolution is identical in both cases.

The effects of propanol observed here are con-trary to that proposed using the two-site adsolubili-zation model of Lee et al. [10]. However, for thehigher alcohols (pentanol and decanol) sulfonateadsorption is enhanced significantly at low surfac-tant adsorptions. It can be said that the two-siteadsolubilization model will be valid above a criticalalcohol chain length.

Hydrocarbons do not have a strong influenceon the CMC of surf act ants [21]. This much weakereffect, as compared to that of alcohols, has beenattributed to their solubilization primarily in thehydrocarbon core of the micelle, while alcoholscan also reside in the palisade layer and reducethe free energy of micellization. Solubilized hydro-carbons do not alter micellization and this is alsoseen in Fig. 1 as neither the onset of micellizationnor hemimicellization is measurably affected. Itwas also seen that the sulfonate adsorption is notvery sensitive to the amount of oil present in thesystem. The aqueous activity of an additive deter-mines ils effect on adsorption. Since the concen-tration of dodecane present was above its aqueoussolubility limit and sulfonate did not partition intothe oil phase the effect was minimal. Increasingthe amount of oil, however, tends to increase theoil/water interfacial area. This would result in areduction of surfactant activity in the aqueousphase (and lherefore adsorption) as more surfactantmolecules would adsorb at the oil/water interface.Comparison of the adsorption isotherms in Fig. 1suggests that the curves are similar below a sulfo-nate concentration of 2 x 10 - 4 mol 1- 1. Under

these conditions, there is insufficient surfaclant toprevent coalescence, and so the oil/water interfacialarea is minimal. Above ~ 2 x 10 - 4 mol 1- 1 sulfo-

nate, the emulsions become more stable andadsorption at the oil/water inlerface may be quitehigh. Emulsions that appear milky white typicallyhave dispersed droplets in the size range I-50 I.1m[22]. So for example, at an oil/water ratio of 0.1,assuming a parking area of 25 A 1 for sulfonate and

10 I.1m spherical particles, sulfonate equivalent to4 x 10-4 kmol m-3 can be accommodated at theinterface. Under the same assumptions, 1l.1m drop-lets can adsorb 10 times as much surfactant.Therefore, emulsions of moderate oil volume canaffect the aqueous activity of sulfonate. The reduc-tion in sulfonate adsorption observed in the twohigh oil systems between 2 x 10-4 and 3 x 10-3mol 1- 1 is attributed to such effects. However, the

adsorption decrease would have been expected tobe the greatest for the 16.7% dodecane system, butthis is not supported by the data in Fig. I.

In highly concentrated surfactant systems, thetotal quantity of surfactant could far exceed the

62 E. Fu et aI.ICo//oids SIu:faces .-4: Ph>.sicochem. Eng. Aspects l/l ( I~) 55-iS2

Referencesquantity that could be adsorbed at the oil/waterinterface and the fraction of surfactant depletedfrom the aqueous solution would then be quitelow. From Fig. 1 it is indeed seen that above3 x 10 - 3 mol 1- I there is no reduction in adsorp-

tion for the 9.1 and 16.7% dodecane systems.

4. Summary

Adsorption of sulfonate from mixtures with alco-hols and alkanes was studied at the alumina-waterinterface. The aim was to identify the role ofadditives in the case of adsorption from micro-emulsions using dodecane as a model for oil.Dodecane tends to increase adsorption, particu-larly in region I of the isotherm, but sulfonateadsorption is not very sensitive to the initial levelof the dodecane under the conditions tested. Shortchain alcohols (propanol) decreased sulfonateadsorption due to their effect on surfactant solubil-ity in the bulk. Medium and long chain alcoholsincreased the sulfonate adsorption in premicellarsolutions and decreased it above the CMC. Thiseffect is attributed to the decrease in the onset ofhemimicellization and an even larger effect on theonset of micel1ization. Decanol abstraction wasnearly 100% at low sulfonate concentrations, butdecreased at higher sulfonate concentrations asalcohol became increasingly solubilized andemulsified.

This study clearly shows the important role thatalcohol and hydrocarbon additives play on surfac-tant adsorption. While small additive moleculesincrease the solvent power for the surfactant andthus reduce adsorption, larger molecules coaggreg-ate with the surfactant thus lowering the freeenergy of micellization and hemimicellization andenhancing adsorption. Adsorption of the surfactantin the presence of an additive is independent ofthe additive concentration if it is present above itsaqueous solubility limit.

Ackn()"",cdgements

[l] H.S. Hanna and P. Somasundaran. in D.O. Shah andR.S. Schechter (Eds.I, [mproved Oil Recovery bySurfactants and Polymer Flooding, Academic Press, NewYork, 1911, p.253.

[2] P. St)masundaran, A[ChE Symp. Ser., (1915) 1l.[3] G.D. Parfitt and C.H Rochester, Adsorption from

Solution at the Solid-Liquid Interface, Academic Press,New York, 1983.

[4] P. Somasundaran and D.W. Fuerstenau.l. Phys. Chern.,10 (l966) 90.

[5] K.V. Viswanathan and P. Somasundaran. ColloidsSurfaces, 26 (l981) 19

[6] P. Somasundaran and 1.T. Kunjappu, Colloids Surfaces,31 (l989) 245.

[1] 1.H. O'Haver, L.L. Lobban. 1.H. Harwell and E.A.O'Rear ill, in S.D. Christian and 1.F. Scamehorn (Eds.),Solubilization in Surfactant Aggregates, SurfactantScience Series, Vol. 55, M. Dekker, New York, 1995,p.211.

[8] 1.W. Barton. T.P. Fitzgerald, C. Lee, E.A. O'Rear and1.H. Harwell, Sep. $(,;. Technol1 23 (l988) 631.

[9] V. Monticone, M.H. Mannebach and C. Treiner,Langmuir, lO (l994) 2395 (and references cited therein).

[lO] C. Lee, M.A. Yeskie, 1.H. Harwell and E.A. O'Rear,Langmuir, 6 (l990) l158.

[ll] K. Esumi, M. Shibayama and K. Meguro, Langmuir, 6(l990) 826.

[ l2] P. Somasundaran. Adsorption from Flooding Solutionsin Porous Media. Annual report submitted to theDepartment of Energy, National Science Foundation anda Consortium of Industrial Organizations. ColumbiaUniversity, New York, 1981

[l3] V.W. Reid, G.F. Longman and E. Heinerth, Tenside, 4(l961) 292.

[14] P. M)masundaran and D.W. Fuerstenau. J. Phys. Chern.,10 (1966) 90.

[l5] P. Chandar, P. Somasundaran and N.l. Turro, J. ColloidInterface Sci., 111 (1981) 3l.

[16] P. Somasundaran. N.l. Turro and P. Chandar, ColloidsSurfaces. 20 (1986) 145.

[11] P Chandar, P. Somasundaran. K.C. Waterman andN.l. Turro, 1. Phys. Chern., 91 (1981) 150.

[18] A. Sivakumar, P. Somasundaran and S. Thach, ColloidsSurfaces, 10 (1993169.

[19] A. Sivakumar and P. Somasundaran. Langmuir, 10(l994) l31.

[20] K. V. Viswanathan and P. Somasundaran. Soc. Pet. Eng.11(l982Il0l.

[21] K. Shinoda, T. Nakagawa. B. Tamamushi and T.lsemura,Colloidal Surfactants, Academic Press, New York, 1963,Chapter l.

[22] M.l. Rosen. in Surfactanls and Interfacial Phenomena.Wiley, Ne" York, 1918, p. 224.Financial support from the National Science

Foundation, Department of Energy and ARCOExploration and Technology is acknowledged.

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