Dec., 1963
SELECTIVE ADSORPTIONOF ALCOHOL
As mentioned previously6 the interactions described here might be due to London forces between side chain and polymer backbone. It seems that the probability of fitting the side chains into resin cavities increases with cross-linkage, ie., with the abundance of the organic matrix material in the vicinity of the interacting ions. Another way of stating this would be that the average value of Tik, the distance between a bond belonging to the amino acid and one of the resin matrix, becomes smaller with cross-linkage. The London forces, which are proportional to z&,&/?+ika, l 3 where Ori and Crk are polarizabilities of bonds belonging to the amino acid and t o the resin, respectively, should therefore increase with cross-linkage. The specific free energy does not increase very much with resin cross-linkage in the phenylalanine resin interaction. Both the high negative AH- and ASvalues remain almost constant. This means that the interaction between the benzene rings of phenylalanine (13) J. 0. Hirschfelder, C. F. Curtis, and R P. Bird, “AIolecular Theory of Gases and Liquids, ’ John Wiley and Sons, Inc., Kew York, N. Y., 1954, Chapter 13.2
2547
and of the polystyrene backbone are already very strong in the dilute gel. The great negative entropy change indicates a strong localization of the benzene rings, probably in a surface-to-surface manner, l 4 so that the proximity of additional polymer has little influence on the interaction energy. The strong and localized binding might in part be due to a cooperative effect of the resin polystyrene matrix. This suggestion is in accord with the fact that no spectral changes, indicative of complex formation, were detected in mixtures of sodium toluenesulfonate and phenylalanine solutions when compared to the spectra of the pure compounds. Acknowledgment.-The
author wishes to thank Mr.
S.de Groot for his assistance in carrying out the experiments. (14) It has been shown by Coulson and Davies [Trans. Faraday Xoc., 48, 777 (195p)l t h a t the dispersion forces for unsaturated compounds are atrongly orientation dependent. They calculated a n interaction energy of 2.7 kcal./mole for the parallel orientation of hexatriene molecules a t a distance of 4 A. This can he compared to our value of 4.2 kcal./mole a t a somewhat smaller distance betaeen benzene rings.
SELECTIVE ADSORPTION STUDIES BY RADIO TRACER TECHNIQUE. IV. SELECTIVE ADSORPTIVITY OF ALCOHOL AGAIKST SURFACE ACTIVE AGENT AT THE AIR-SOLUTION INTERFACE BYKGz5 SHINODA AND JUN XAKANISHI Department of Chemistry, Faculty of Engineering, Yokohama National University, M i n a m i k u , Yokohama, J a p a n Received April 19, 1963 Selective adsorption of alcohol against surface active agent a t air-solution interface in aqueous solution of agent containing a small amount of alcohol has been studied by the aid of radioactive alcohol. All the experiments were carried out below the critical micelle concentration. Selective adsorptivities of RBOH (dodecanol) to R12S041;a and R14SQ4n’awere 284 and 55, those of RloOHto RI2SO4nTaand RllCOOK were 31 and 117, and those of RBOH to Ri2S04Na and RtlCOOK were 3.9 and 11, respectively. The selective adgorptivity of alcohol against agent was roughly proportional to the c.m.c. value of agent, and it has increased about three times per one addition of methylene group to alcohol. The added salt depresses the c.m.c. of agent and the adsorbability of agent increases inversely proportionally t o the c.m.c. As the result the selective adsorptivity of alcohol against agent decreases proportionally to the c.m.c. decrease. For example, the selective adsorptivity of R8OH against Rd304Na decreased from 3.9 to 1.9 in the presence of 0.0214 N NaNOa. From these correlations it is possible to estimate the selective adsorptivity for the other pairs of alcohols to agents.
Introduction Rather distinctive changes of the properties are often observed in solution of surface active agent due to the addition of a small amount of These distinctive changes may result from a high selective adsorptivity of alcohol against agent a t the So far as me know, however, there was no paper which intended to determine the selective adsorptivity of alcohol against agent. The present investigation was undertaken in order to determine the selective adsorptivity by the aid of radioactive alcohol and to understand the effect of added alcohol on the surface chemical properties of solution of surface active agent. Experimental Materials.-Radioactive dodecanol l-CI4, decanol l-Cl4, and octanol l-Ci4 whose specific activities were 2.10, 2.74, and 3.31 (1) G. D. Milesand L. Shedlovsky, J . Phys. Chem., 48, 57 (1944). (2) L. Shedlovsky, J. Ross, and C. IT. Jacob, J . Colloid S a . , 4 , 25 (1949). (3) M. Nakagaki and K . Shinoda, BUZZ. Chem. Soc. Japan, 27, 367 (1954). (4) G. Aniansson, J . Phys. Chem., 55, 1286 (1951). ( 5 ) G. Kilsson. qbzd.. 61, 1135 (1967). (6) A . Wilson, M. B. Epstein, and J. Ross, J . Collozd Scs., 12, 345 (1967).
mc./mole, respectively, were obtained from the Daiichi Pure Chemicals Co. Ltd. These alcohols were synthesized by reduce tion from respective fatty acids of highest purity at the Radio Isotope Laboratory of the company. Sodium dodecylsulfate and dodecanoic acid were the same materials used in the preceding experiment^.^ Sodium tetradecylsulfate was synthesized from fractionally distilled tetradecanol. It was further purified by extraction with ethyl ether and recrystallization from ethanol and water.8 Aqueous solutions of these materials were further purified by foam fractionation prior to the experiments. Procedures.-The apparatus used was similar to that shown in Fig. 1 of the previous paper,’ but the horizontal tubing was shorter in length and filled out with solution in order to promote the circulation of the solution due to the movement of bubble^.^ The foam stability was very good due to the presence of alcohol. As the alcohol moderately evaporates near loo”, simple drying of solution could not apply for the determination of radioactivity of solution. A h e d volume of sample solution was oxidized with potassium persulfate. The carbon dioxide was then adsorbed with barium hydroxide solution and filtered, and finally the radioactivity of BaC08 was measured, from which the amount of alcohol in solution was determined. The concentration of surface active agent in solution of collapsed foams was de(7) K. Shinoda and K. Mashio, J . Phys. Chem., 64, 54 (1960). (8) L. H. Princen, Ph.D. disaertatie, Utrecht, 1955. (9) K. Shinoda and K. Ito, J . Phys. Chem., 66,1499 (1961).
2548 0
2
6
4
8
TABLE I ALCOHOL AGAINSTS U R F A C E ACTIVE AGBST AT AIR-SOLGTION( AQCEOUS) IKTERFACE
S E L E C T I V E L4DSORPTIVITY O F
.*
$p 40
1
Alcohol---------
RI2OH-R,,SO4Na
rn
4 8 12 16 Concentration of alcohol X 103 (mmoles/l.).
Fig. 1.-Selective adsorptivity of RIzOH against R14S04Na (1.37-1.43 mmole/l.) and RsOH against R:&04Sa (6.34-6.45 mmole/l.) as functions of alcohol concentration. termined by weighing and drying known weights of solution. Assuming the interior of foams was the same composition as solutions, the selective adsorptivity, a, was determined from the ratio of mole ratios of alcohol to agent in the adsorbed layer and in bulk ~olution.~,
a =
c,,
Call
7
C,I and C,I’ are the concentrations of alcohol in the bulk and in collapsed foams, and C and C‘ are the concentrations of agent in the bulk and in collapsed foams, respectively.
Results and Discussion Selective adsorptivity of alcohol against agent at air-solution interface has been determined for several combiiiatioiis of R120H, RloOH, or R80H with the sodium alkylsulfate or potassium dodecanoate. The mole ratio of alcohol to agent in the adsorbed layer changed with the change of the mole ratio in bulk solution, while the selective adsorptivity remained constant as showii in Fig. 1. The averages of the data for respective combinations of alcohol to surface active agent are summarized in Table I. All the experiments were performed below the c.m.c. of agent containing alcohol, otherwise a quantitative interpretation of the results is complicated and inaccurate due to the preferential aggregation of alcohol in the micelles. The c.m.c. value of surfactant coiitaiiiiiig a small amount of alcohol was estimated by the equation obtaiiied previously. IO Wilson, Epstein, and Ross6 have determined the amount of alcohol and agent in the adsorbed layer from which the apparent selective adsorptivity of dodecanol against RI2SO4Nahas been calculated as about 15-29. As the concentration of the solution was above the c.m.c., their value was very much smaller than the present result, 284 f 20. Selective adsorptivity of alcohol against surfactant was determined by the radio-tracer technique. As the selective adsorptivity is based on the ratio of radiocouiits, it is not affected by many serious disturbances in thc absolute values for radioactivity. In the coursc of bubble geiicratioii, thc radioactivity iii solutioii tlccreased appreciably because the alcohol liad higher adsorptivity than the surface active agent and was removed more rapidly in the foam. Radioactivities of respective samples were about 200-10,000 c.p.m., and the mean deviation of radioactivity of the samples prepared from the same solutioii was about 3-10y0. (10) K. Shinoda, .I Phys Chem. 68, 1130 (IfL54).
Agent (c.m.c. in mole/l.)
RnOH
RioOH
RsOH
RI4SO4Na(0,002) 55 i 5“ [ 81 PI [16] 1 . 9 =!= 0.3’ RlZS04Na (0.0040) [I401 in 0.0214N NaXOp RI2SO4Na(0.0081) 284 f 20‘ 31 It 7 d 3 . 9 It 0.2G RiiCOOK (0.027) [lOOO] 117 i 10’ 11 i 2g The following footnotes refer t o number of measurements, temperature, “C., concentration range of agent (mmoles/l.), concentration range of alcohol (mmoles/l.), respectively. ’ 6, 20, 1.43-1.37, 0.0084-0.0010. 8, 25, 3.98-3.88, 0.0062-0.0052. 10, 25, 5.78-5.59, 0.0084-0.0019. 10, 25, 6.41-6.31, 0.00590.0031. ‘ 12, 25, 6.45-6.34, 0.0177-0.0098. 3, 20, 25.5, 0.04270.0380. 7, 20, 25.6-25.4, 0.315-0.270.
’
’
The background was about 28-30 c.p.m. throughout this study.
Theory The logarithm of the selective adsorptivity multiplied by IcT is equal to the difference between the standard free energy of adsorption of alcohol and agent. The energy of adsorptioii of alcohol and agent increases with their hydrocarbon chain length, but in the latter, tlie electrical energy required a t the adsorption is large and expressed as11,12
e4
=
- K,kT In C,
+ const.
(2)
where K , = 0.6 is an experimental ccnstaiit and C, is the conceiitration of gegenians in mole/l. Thus
kT In
CY
=
in‘w - m u - K,kT In C,
+ const.
(3)
\There m’ and m are the iiuniber of carbon atoms in hydrocartoii chain of alcohol and the agent, w , is the energy of adsoiptioii per methylene group and approximately 1.08 kT. Introducing the following relationll in eq. 3
kT In [c.ni.c.]
= -mw
-
K,kT In C,
+ const.
(4)
we obtain lii a
=
1.0Sm’
+ ln [c.in.c.] + const.
(5)
Equation 5 expresses that the selective adsorptivity iiicreases three times per one addition of methylene group in alcohol and is proportional to the c.m.c. It is clear from Table I that the agreement between the theory, eq. 5 , and the experiments is satisfactory. These relations also agree with the other experimental facts that the adsorbability of agent is inversely proportional to tlie c.m.c.13and that of alcohol increases according to the Traube’s rule. Similarly, the added salt lowers the c.ii1.c. and enhances the adsorbability ol‘ agelit. For example, the c.1n.c. of Rj2SO1Kalo\wls fro1110.0081 to 0.0040 lklOlC/~.“i l l 111(. ~)lC’SC’llCC’ Ol‘ 0.021 I S KaT\-08, and the selective adsorptivity of octaiiol against R12S04Ka falls off from 3.9 to 1.9. From these (11) K . Shinoda, in “Colloidal Surfactants,” ilcademic Press I n c . New Yolk, iY.Y. 19G3, Chapter I , g. 41. (12) K. Shinoda, J . Phys. Chem , 6 0 , 1439 (l9bG). (13) K. Shinoda. J. Collozd Scz., 18, 174 (1963). (14) R. J. Williams, 1. N. Phillips, and K . J. JIysels, Trans Famda!l Soc.. 61, 728 (1956).
Dec., 1963
DONKAN EQUILIBRIA IZ: POLYMETHACRYLIC ACID-SODIGM CHLORIDE SYSTEMS
correlations it is possible to estimate the selective adsorptivity for the other pair of alcohols against agents. The numbers with bracket in Table I are the estimated values. The present results may be equally applicable
2549
for the adsorption a t the interface between the aqueous solution and the oleophilic phase. Acknowledgments.-We wish to thank Mr. S. Sugiura for his cooperation in this project.
DONNAN EQTJILIBRIA IN CROSS-LINKED POLYMETHACRYLIC ACID-SODIUM CHLORIDE SYSTEMS BY RICHARD L. GUSTAFSO~ R o h m and Haas Company, Research Division, Philadelphia 87, Pennsylvania Received April 22, 1968 Measurements of uptake of sodium chloride by a polymethacrylic acid resin which has been cross-linked with 57, divinylbenzene have been measured at various degrees of neutralization in aqueous solutions which were 1.0, 0.4,0.1,and 0.02 in ionic strength a t 25'. Mean molal activity coefficients, y** = yr,e"v/2RT, of sodium chloride in the resin phase have been calculated after suitable corrections have been made for salt occlusion on the surface and in the macro-pores of the resin. Values of y** have been shown to decrease with decreasing ionic strength at a constant degree of neutralization, C Y , of the carboxylic groups of the resin. It has been shown that this effect is not the result of anion-adsorbing impurities or resin heterogeneity. Similar variations of y*+ with ionic strength have been shown t o occur in cases oi rigid inorganic zeolites and in solutions of linear polyelectrolytes. The experiniental values of y** in the resin systems were found t o be in poor agreement with theoretical values of yri calculated on the basis of Katchalsky and Michaeli's theory of highly swollen polyelectrolyte gels. The discrepancies were particularly large a t low ionic strengths. Consideration of the equilibria involved suggests that the activity coefficient of the chloride ion in the gel phase decreases markedly with decreasing ionic strength a t a constant vallue of CY, whereas the activity coefficient of the sodium ion remains relatively constant.
Introduction Considerable disagreement exists concerning the nature of electrolyte sorption by ion-exchange resins. More than a decade ago, Baunian and Eichhornl pointed out that results concerning the sorption of hydrochloric acid from aqueous solution by crosslinked polystyrenesulfonic acid gels could not be explained on the basis of Donnan theory if it were assumed that the activity coefficient of HC1 in the gel phase remains high a t low external electrolyte concentrations. It was observed experimentally that abnormally large amounts of HCl were adsorbed by the resin phase from dilute solution. Since that time, several workers2-10 have shown that as the external electrolyte concentration approaches zero, the mean molal activity coefficient, yr+, of the sorbed electrolyte also approaches zero. This behavior is opposite to that observed in aqueous solutions of strong electrolytes, in which case activity coefficients tend toward unity a t infinite dilution. Freemaiill has suggested that the abnormal decrease of yrk with decreasing solution molality, m,, is caused by occlusioii of electrolyte on the bead surfaces aiid by the sorption of eo-ions by resin impurities. By the use of an iterative procedure, he has calculated the quantities of co-ion which must be occluded or sorbed by impurities in order to give good agreement with the equation log yrk = a f bm,, where a and bare constants. (1) W. C . Bauman and J. IEichhorn, J . Am. Chem. Soc., 69, 2830 (1947). ( 2 ) H. P. Gregor, F. Gutoff, and J. I. Bregman, J . Coollozd Scz., 6 , 243 (1951) ( 3 ) 11. 1'. Ciegor and h1. H. Gottlieb, J. rim. Chem. Soc., '76, 3539 (l9S3). (4) C. W. Dames and G. D. Yeoman, Trans. Paradag Soe., 49, 968 (1953). ( 5 ) J. S Maokie and P. Meares, Proc Rog Soc (London), A282. 485 (195.5). (6) G. J. Hills, P. W. ill. Jacobs and N. Lakvhminaraganaiah ?hid., 8262,257 (1961). (7) K. A. Kraus and G. E. Moore, J . AmAChem. Soc ,75,1457 (1 953). (8) M. H. Gottlieb and H. P. Gregoi, zbzd., '76,4639 (1954). (9) F. Nelson and X. A. Xraus, %bid.,80,4154 (1958). (10) J. Danon, J . Phys. Chem., 65, 2039 (1961). (11) D. H. Freeman zbzd., 64, 1048 (1960).
Glueckauf and W a t t ~ ~ ~ have - l ~recently published several papers which support the theory that the observed abnormalities are produced by variations in the degrees of cross-linking within a resin sample. By the assumption of an appropriate distribution of concentrations of functional groups within the resin, it is possible to obtain agreement with experiment on the basis of constant resin activity Coefficients. The validity of the assumption of the high degree of heterogeneity required to obtain a fit of the data is questioned on the basis of proton magnetic resonance studies of Gordoiil6.16 which indicated that several commercially available cation and anion exchange resins possess a high degree of homogeneity. It has been shown by Barrer aiid Meierll' on the basis of data concerning sodium chloride sorption by aluminosilicates, that the ideal Donnaii law based on constant activity coefficients in the zeolite phase is apparently obeyed. It was suggested that the differences in electrolyte sorption that are observed between rigid zeolites and organic ion-exchange resins are associated with the swelling properties of the latter materials. An important point, whicli often seems to have beeii overlooked, is that similar decreases of mean activity coefficients with decreasing electrolyte concentration have been reported1*-21 for a variety of linear polyelectrolytes in aqueous solution. I n these cases the distribution of polymer chains is governed only by (12) E. Gluecktruf and R. E. Watts, Natuie, 191, 904 (1961). (13) E. Glueckauf and R. E. Watts, Proc. Roy. Soc. (London), 8 2 6 8 , 339 (1962). (14) E. Glueckauf, ibid., 8268, 3.50 (1962). (15) J. E. Gordon, Chem. I n d . (London), 267 (1962). (16) J. E. Gordon, J . Phys. Chem.. 66, 1150 (1962). (17) R. M. Barrer and W. $1. Meier, J . Chem. Soc., 299 (1958). (18) A. Xatchalsky and S. Lifson, J . Polymer Sei., 11,409 (1953). (19) G. P. Strauss and P. Ander, J . Bm. Chem. Soc., 80,6494 (1958). ( 2 0 ) Z. Alexandrowicz, J. Polgmer Sci., 43, 337 (1960); 56, 11.5 (1962). (21) &I. Nagasa\va, M. Izumi, and I. Kagawa, ibid., 3'7, 375 (19.59).
