J . Chem. SOC., Faraday Trans. I, 1981,78, 1377-1388 Viscosity B Coefficients of Some Alkyltrimethylammonium Bromides and the Effect of Added Alkan-1-01s D O ~ A N E. G U V E L ~ ~ Department Physicochimie des Solutions, Universite Pierre et Marie Curie, 11 Rue Curie, 75231 Paris, France Received 20th February, 198 1 The viscosity B coefficients for aqueous solutions of alkyltrimethylammonium bromides and decyltri- methylammonium bromide containing various concentrations of aliphatic alcohols have been determined at 25 OC. Viscosity B coefficients for the alkyltrimethylammonium bromides were positive and increased as the alkyl chain length increased; the B coefficient increase per methylene group was 0.084. The addition of aliphatic alcohols decreased the viscosity B coefficient of decyltrimethylammonium bromide.As the alcohol concentration was increased the measured partial molal volume of decyltrimethylammonium bromide first decreased and then increased, and this was correlated with the viscosity B coefficient. The addition of alcohol is thought to effect the solvent structure and solute-solvent interactions by changing the composition and dielectric constant of the environment. The viscosity B coefficient is considered to be a measure of long-range forces, solvent structural effects and size and shape factors.' Feakins et aL2 developed a relationship between the relative viscosity, viscosity B coefficient and partial molal volume of the solute, applying transition-state theory. They examined the effect of methanol on viscosity B coefficients of electrolytes.The solute-solvent interactions in aqueous alkyltrimethylammonium bromides and alkysulphate solutions have been examined by Tanaka et al.3 in terms of the Jones-Dole equation. Additional valuable information about solute-solvent interactions can be obtained from partial molal volume studies. Kaneshina et al.4 reported that partial molal volume (E) values below the critical micelle concentration of the sodium alkyl sulphates decreased at low added methanol concentrations and then increased. This result was supported by the observation of Vikingstad and K~ammen,~ who studied the effect of alkan-1-01s on the partial molal volume of sodium decanoate, and the increase in was related5 to the hydrophobic hydration of the surfactant monomer.In earlier studies6* the effects of alkan-1-01s on the hydrodynamic and volumetric properties of micellar systems of alkyltrimethylammonium bromides in aqueous solution were examined. In this work the effect of alkan-1-01s on water structure and the surfactant-solvent interaction in the singly dispersed state are discussed in terms of the viscosity B coefficient and the partial molal volume of the surfactant monomer. EXPERIMENTAL MATERIALS The preparations and purification of the alkyltrimethylammonium bromides and the purification of the alkan-1-01s (methanol, ethanol, propanol and butanol) have been described elsewhere.6 Water was doubly distilled from an all-glass still of specific conductance < 1 x R-' cm-l. t Present address: School of Pharmacy, University of Bradford, Bradford BD7 IDP.13771378 VISCOSITY B COEFFICIENTS DENSITY AND VISCOSITY MEASUREMENTS The densities of the alkyltrimethylammonium bromides C,TAB (x = 10, 12, 14 and 16) and decyltrimethylammonium bromide (C,,TAB) solutions containing various concentrations of alkan-1-01s at 25 f 0.02 'C were made using a Paar density meter model DMA 02. The viscosity measurements were carried out at 25 f 0.02 OC using two U-tube capillary viscometers. The viscometers were calibrated with pure water and 20% sucrose solutions according to British Standard 188.* The viscosities were calculated from average flow times, t , and densities, d, based on the equation. q = d(Ct-:) where the characteristic constants C and B of the viscometers were 3.5 x lop3, 3.8 x lop3 and 36.52, 0.3, respectively. The accuracies of the density and viscosity measurements were (2f 1) x g C M - ~ and O.Ol%, respectively, and the density of water was taken as 0.9971 g cm-3.9 RESULTS AND DISCUSSION VISCOSITY STUDIES Jones and Dole, studying dilute electrolyte solutions, ShowedlO that the viscosity of electrolytes can be related to the following relationship q = qo(l + A d C t BC) (2) where ylo is the viscosity of solvent, C is the concentration, and A and B are the characteristic constants of the solute.Since pre-micellar aggregation was not observed in the solutions of ionic surfactant an association of monomers below the critical micelle concentration (c.m.c.) is unlikely to occur. Therefore the viscosity data of aqueous surfactant solutions and decyltrimethylammonium bromide solution containing various concentration of alkan- 1-01s below the c.m.c. were examined by the Jones-Dole equation.Eqn (2) can be rearranged as A plot of (qr- l)/z/C against d C yields the constants A and B. Eqn (2) is generally used to provide information about the solute-solvent interaction. The viscosity of unsolvated spherical colloidal suspensions can be represented by (4) Einstein's equation" qr = 1+2.50 where CD is the volume fraction of the solute; by combining with eqn (2), eqn (4) becomes 2.5 CD = A d C + BC. ( 5 ) Since the A2/C term can be neglected in comparison with BC, and 0 = CV, where Vis the partial molal volume, then eqn ( 5 ) takes the form 0.0025 V = B. (6) In the ideal case the B coefficient is a linear function of the solute partial molal volume ( V ) with a slope equal to 0.0025.12 The B coefficient can be interpreted1 as consisting of two terms B = Bsize + Bsolv (7)D.E. G U V E L ~ 1379 where Bsize is the effect of solute and Bsolv is the contribution arising from solute-solvent interaction. Thus Bsolv12 Bsolv = B-0.0025 V. (8) In order to check the accuracy and precision of the viscosity technique for the investigation of solute-solvent interactions in dilute solutions alone and with the added alcohols, the B values of a series of alkyltrimethylammonium bromides (C,TAB) below the critical micelle concentration in aqueous solutions were determined by a least-squares fit of a plot of (v, - l)/z/C against d C . The viscosity A and B constants obtained for C,TAB and the standard errors for the estimation of viscosity constants, including correlation c’: iefficients, are given in table 1.The A coefficients for C,TAB, which represent the contribution from interionic electrostatic forces,13 were small. Fig. 1 illustrates the dependence of (qr- l ) / d C on z/C, which is linear up to the c.m.c. of C,TAB, and then increases non-linearly as the concentration increases. The linear increase in (q, - l ) / d C below the c.m.c. is a result of the structuring of water molecules around the hydrocarbon chain of the surfactant molecule and the solvation of the hydrophilic group.6 However, the change in the slope of the plots (at c.m.c.) is related to the release of ordered water molecules around the surfactant monomers, and the apparent increase in (qr- l)/z/C above the c.m.c. is considered to be due to the presence of associated monomers, electrostatic interactions and hydration.6 Fig.2 shows that there is a linear increase in the B coefficient with increasing hydrophobicity of the surfactant molecule. This can be attributed to the hydrogen-bonded cluster size produced through hydrophobic interactions.6 The B values obtained for C,,TAB and C,,TAB, 0.77 and 0.95, respectively, compare favourably with those found by Tanaka et al.,3 (0.76 and 0.91 for C,,TAB and C , ,T A B, respectively ). The relationship between the B coefficient and the alkyl chain length for C,TAB can be expressed by the following linear equation (9) B = a + B(CH,)CH where a and B(CH,) are constants. The value obtained for B(CH,) (0.084) is in good agreement with those reported for alkyltrimethylammonium bromides14 (0.080), amino acids15 (0.084) and alkyl sulphates16 (0.079), whilst being slightly higher than the value (0.076) per methylene group given by Tanaka et al.3 The ionic B values (Bion), obtained by Kaminsky’s17 procedure using his data for Brian ( - 0.042), are given in table 1.The present data show that the ionic Bcoefficient follows similar trends as does the B coefficient, and that the B coefficient increases linearly with increasing for C,TAB was linear with a slope (0.0051) higher than the value (0.0025) given by eqn (6). This result is related to the non-ideality which occurs because of the hydration of monomers and electroviscous effects. The value of Bsize indicates an increase with increasing alkyl chain length.However, in contrast to Bsize, the values of Bsolv were reasonably constant for the various C,TAB used. In fact, the major contribution to the B coefficient arises from Bsize and is related to the solute-size structuring effect on water structure through hydrophobic interactions. (fig. 2). Thus a least-squares fit of a plot of B against PARTIAL MOLAL VOLUME STUDIES The partial molal volume of a solute in solution provides important information on the nature of solute-solvent interaction^.^ The apparent partial molal volume ofTABLE l.-V~scos~ry B COEFFICIENTS FOR THE ALKYLTRIMETHYLAMMONIUM BROMIDES IN WATER AT 25 OC ~~~~ - standard standard C error error E7 below ~ r - 1 110-3 mol tiona tiona coeffic- below / mol for the for the correla- /cm3 dm+ c.m.c.6 estima- estima- tion m o P C,TAB c.m.c.4 C dm-3 A (4 B (B) ient Bsize Bsolv c.m.c. Bion B; B(CH,) 60 50 40 30 20 10 16 14 10 4 2 1 3 2 1 0.8 0.6 0.7 0.6 0.5 0.4 0.1 I 0.202 0.185 0.170 0.148 0.123 0.091 0.121 0.1 12 0.078 0.059 0.047 0.106 0.084 0.079 0.072 0.068 0.077 0.075 0.07 0.059 65 16.8 3.7 0.8 0.015 0.017 0.04 0.046 1.86 5.41 7.36 1.54 0.77 0.95 1.13 1.27 0.99 0.061 0.191 0.07 1 0.999 0.991 0.959 0.995 1.32 -0.55 258.2 1.42 -0.47 278.1 1.62 -0.49 318.5 1.80 -0.53 352 5 m cl - 2 3 0.812 - 4 4 tu cl s 2 crl 0.992 -0.042 0.084 2 m z 4 m 1.172 - - - 1.312 - a All errors assumed in (qr - l ) / d C .FIG. 1 .-Plots of (q, - D. E. GUVELi 1381 I c.rn.c I 1 I 1 0.1 0.2 0.3 0.4 dC A, Cia; 0, Clz; 0, Cia; x 9 Cl6.l)/dC against d C for the alkyltrimethyl ammonium bromides in water at 25 O C : FIG. 2.-Plots of the viscosity B coefficients against the partial molal volume and alkyl chain length for the alkyltrimethylammonium bromides : 0, carbon number; V, partial molal volume.1382 VISCOSITY B COEFFICIENTS decyltrimethylammonium bromide in aqueous solution with added alkan- 1-01s was calculated from18 (10) where no, n and n, are the numbers of moles of water, surfactant and additive, and M,, M and M, are the corresponding molecular weights. To obtain the partial molal volume (c) of the monomer below the c.m.c., the calculated a value was plotted against concentration and extrapolated to zero. - M n,M,+nM+n,M, a V = - - (dp, T,non2 d d2 EFFECT OF ALIPHATIC ALCOHOLS ON PARTIAL MOLAL VOLUME In previous work7 the effect of alkan-1-01s at higher concentrations on the partial molal volume (E) of dodecyltrimethylammonium bromide was examined.The value for C,,TAB showed an increase with increasing alcohol concentration, and for higher added alcohol concentrations (> 1 mol dm-3) there was no evidence of a minimum in E. In order to examine the effect of alkan-1-01s on solute-solvent 260 7 258 E 6 256 - 0 rn 13” 2 54 1 0.1 OI.3 0’5 0.7 0.9 1.1 alcohol concentration/mol dmd3 FIG. 3.-Effect of concentration of added alcohols on the partial molal volume of decyltrimethylammonium bromide below the c.m.c. at 25 O C : 0, methanol; A, ethanol; 0, propanol; +, butanol. I interactions in the singly dispersed state of C,,TAB, a series of aliphatic alcohols (methanol, ethanol, propanol and butanol) at different concentrations (0.2- 1 mol dm-3) was added to aqueous solutions of C,,TAB.Fig. 3 shows that the added alcohols have a considerable effect on for C,,TAB. Dealing first with methanol, at low alcohol concentrations decreased slightly showing a minimum in E, then increased as the alcohol concentration was raised. Ethanol was less effective with regard to changes in E, and the minimum became less pronounced as the chain length of the alcohoIs increased. This effect has also been observed by Kaneshina et aZ.,4 who have reported that the values of sodium alkyl sulphates decreased at low alcohol concentrations and then increased. This result was also confirmed by the observationD.E. G U V E L ~ 1383 for sodium dodecanate by Vikingstad and K~ammen.~ It is known19 that at low alcohol concentrations the order of solvent structure increases and that the transfer of a hydrocarbon from a non-polar environment to water results in a negative volume change, which reflects the ordering of water molecules around the hydrocarbon chains.20 In this work at low concentrations, the changes in are similar to those in v f o r hydrophobic in alcoholic solutions. The minimum in E indicates the maximum structuring effect of the surfactant monomer on the water-alcohol structure. The minimum and increase in E in the ternary systems are related to solute-solvent interactions. It has been reported5 that the addition of alcohol reduces the electrostriction of water molecules at the ionic head group of the surfactant molecule, which increases the value of V of this group. However, the increase in E at higher alcohol concentrations is due to the effect of alcohols on the water structure, both in terms of a decrease in the hydrophobic hydration of the hydrophobic part of the surfactant monomer, as well as a decrease in the hydrophilic hydration of the ionic head group.' The concentration giving rise to the minimum in E appears to be dependent on the alkyl chain length of the alcohol; the longer the chain length, the greater the effect on because of the hydrophobic effect associated with the hydrophobic part of the alcohol molecule.EFFECT OF ALIPHATIC ALCOHOLS O N THE VISCOSITY B COEFFICIENT The addition of aliphatic alcohols to decyltrimethylammonium bromide affects the viscosity of the surfactant solution by changing the solvent composition. The increase in viscosity is due to the structuring of water molecules around the hydrocarbon chain of the surfactant monomer and solvation of the hydrophilic groups.6 Thus, when various concentrations of methanol were added the relationship between (q, - l)/z/C and z/C differed in the low and high alcohol concentration regions.Fig. 4 shows that (vr - l)/z/C falls linearly as the alcohol concentration increases, followed by a steady increase above the c.m.c. The other alcohols showed similar effects. The viscosity A and B coefficients of decyltrimethylammonium bromide containing various concen- trations of aliphatic alcohols below the c.m.c.in aqueous solution are shown in table 2. They were determined by a least-squares fit of a plot of (qr- l)/z/C against z/C, and include the standard errors for the estimation of viscosity constants and correlation coefficients. It is apparent that the coefficient B changes with increasing alcohol concentration. Changes in B for strong electrolytes with added alcohol have been observed by several 2 1 p 22 Table 2 shows that the addition of alcohol to an aqueous solution of C,,TAB does not contribute in the expected way to an increase in the B coefficient. Thus, at a given concentration of added alcohol (for example 0.2 mol dmP3 methanol), the viscosity B coefficient of C,,TAB decreased while the A coefficient showed an increase, table 2. The decrease in the B coefficient of C,,TAB with equal concentrations of alkan-1-01s was linear in the order butanol > propanol > ethanol > methanol (fig.5). Changes in the B coefficients of strong electrolytes with added ethanol were also observed by Padova,21 who reported that the B coefficient decreased with increasing ethanol concentration until the alcohol concentration was ca. 40% and that the effect of ethanol on B was related to the negative interaction coefficients and the decrease in entropy of the mixed solvents. Feakins et aZ.22 studied the effect of added methanol on the B coefficient of the electrolytes and they observed that small amounts of methanol enhanced the structure of the mixture compared with that of water, and an increase in the structure-breaking effect caused a decrease in the B values of electrolytes.The concentration causing a decrease in the B coefficient for C,,TAB appeared to be dependent on the alkyl chain length of the alcohol; the longer the chain length, the greater the lowering effect on1384 VISCOSITY B COEFFICIENTS B. This can be attributed to the effect of lowering the dielectric constant, which increases as the alcohol chain length increases. Although many studies have appeared5? 6 y ‘ 9 which have concluded that alkan-1-01s at low concentrations in micellar solutions and in water alone increase the ordering of water molecules, the observed results for the B coefficient of C,,TAB in alcoholic solutions do not show similar trends. There are a number of complexities to consider concerning the behaviour of alkan- 1-01s in an aqueous surfactant solutions.The competing effects involved that lead to a negative viscosity B coefficient have yet to be resolved. Cox and W ~ l f e n d e n ~ ~ ‘t “a A’ A. / H , I 0.1 0.2 0.3 0.4 dc FIG. 4.-Plot of (qr - l)/v’C against d C for solutions of decyltrimethylammonium bromide containing various concentrations of methanol at 25 OC: 0, 0.2; V, 0.4; 0, 0.7; A, 1 mol dm-3. concluded that the negative viscosity B coefficient was due to depolymerization of the water structure. Gurney24 reported that if a solute causes a local loosening of the water structure, then the viscosity B coefficient is negative. The existence of a negative B coefficient was also related12 to the incompatible ordering effect of the ion on solvent structure.It is apparent that in the solvent mixture the observed B values do not depend on the solvent composition in a simple way. However, Tominaga et c 1 1 . ~ ~ demonstrated the occurrence of decreased counter-ion binding to the surfactant monomer with increasing alcohol concentration. This finding was in agreement with the observation of Larsen and Tipley,26 who reported an increase in free counter-ion concentration in alcoholic surfactant solution. It is expected that the addition of alcohol gives rise to an increase in the concentration of free bromide ion in terms ofD. E. G U V E L ~ -1 - -3- B -5- - 7- 1385 TABLE 2.-EFTECT OF ALIPHATIC ALCOHOLS ON THE B COEFFICIENT OF DECYLTRIMETHYLAMMONIUM BROMIDE AT 25 *c standard standard error for error for alcohol the the B con.es tima tiona estimationa correlation per mole /moldm-3 A (4 - B (B) coefficient /cm3 rno1-I of alcohol 0.2 0.4 0.7 1 .o 0.2 0.4 0.7 1 .o 0.2 0.4 0.7 1 .o 0.2 0.4 0.7 1 .o 0.36 0.64 0.82 1.08 0.51 0.88 1.02 2.05 0.76 1.16 1.99 2.71 0.84 1.35 2.35 3.49 0.021 0.023 0.078 0.075 0.024 0.03 0.058 0.147 0.04 0.016 0.042 0.1 10 0.029 0.074 0.120 0.042 CH,OH 0.58 0.121 1.48 0.137 1.79 0.426 2.22 0.416 C,H,OH 0.82 0.052 1.7 0.156 3.0 0.302 4.47 0.724 C,H,OH 1.75 0.239 2.26 0.08 4.23 0.206 5.70 0.544 C,H,OH 1.7 0.151 2.45 0.365 4.6 0.593 7.05 0.209 0.893 0.987 0.918 0.968 0.995 0.987 0.990 0.974 0.965 0.998 0.997 0.990 0.992 0.978 0.983 0.999 255.2 - 1.88 254.59 254.88 256.00 255.60 -4.54 254.71 255.06 256.20 256.10 -5.7 255.00 255.36 256.97 256.59 -6.82 256.22 256.52 257.92 a All errors assumed in (qr- l)/z/C.'I i i i i alcohol chain length FIG. 5.-B coefficient of decyltrimethylammonium bromide containing equal concentration of alkan- 1-01s as a function of the hydrocarbon chain length of the alcohol molecule at 25 O C : 0, 0.2; 0, 0.4; V, 0.7; A, 1 mol dm-3.1386 VISCOSITY B COEFFICIENTS -1 - -3 - - 5 - B -7- the changing solvent composition in singly dispersed C,,TAB solution. This was also observed by Larsen and Tipley,26 who noted that the concentration of free counter-ions in aqueous solution of C,,TAB followed the changes in the solvent structure. Since the bromide ion is a structure-breaker, an increase in the free ion concentration will decrease the ordering of water molecules. In addition, as the concentration of alcohol is increased, there is dehydration of the monomer6 and a lowering of the dielectric constant of the solvent mixture.As the dielectric constant decreases, a decrease in charge density2' is expected together with a decrease in the surface ionic field. This might increase the structure-breaking effect of the surfactant monomer, which is in accord with the suggestion of Feakins and Lawrence.28 L. I I I I 254 255 256 257 258 - V,jcm3 mol-' FIG. 6.-B coefficient of decyltrimethylammonium bromide containing equal concentrations of alkan- 1-01s as a function of at 25 OC: 0, 0.2; n, 0.4; 7, 0.7; A, 1 mol dm-3. The structural attractive forces arise when there is compatibility between structural influences and repulsive forces, and the establishment of structural order near the non-polar solute is favoured.This produces a hydrogen-bonded water network around the surfactant monomer which leads to a decrease in E. However, when there is incompatibility between structural effects, and the disrupted water molecules exceed the structured molecules in the total volume of the solution, then the structure-breaking effect will be reflected in the solute-solvent interactions. Thus, changes in the B values of C,,TAB with added alcohols were more pronounced and became more negative as the alcohol concentration increased. Fig. 6 shows the relationship between the B coefficient of C,,TAB containing the same amount of alkan-1-01s and E at 25 O C . It is apparent that the viscosity B coefficient decreases non-linearly, reaching a minimum value with increasing E.Dealing first with low alcohol concentrations there is little effect on B until the concentration reaches 0.4 mol dm-3. However, the tendency of B to decrease is reduced when the chain length of the alcohol is increased. This is also reflected in a change in E with the added alkan-1-01s (fig. 3). The hydrophobic hydration results in a structured medium where the solute B coefficient is positive and the slope dB/dD. E. G U V E L ~ 1387 - 2. - 4- B - 6 - deviates from the Einstein relation, being more positive for the larger hydrophobic salts.12 This is in accord with the observation for C,TAB in aqueous solutions, whereas the dependence of B on E, fig. 6, shows that the Einstein relation is no longer valid for C,,TAB with added alcohols, owing to the complicated effects of the alcohols on solute-solvent interactions.Fig. 7 indicates that the change in B coefficient per mole alcohol chain length FIG. 7.-B coefficient of decyltrimethylammonium bromide per mole of alcohol as a function of the hydrocarbon chain length of the alcohol molecule at 25 O C : 0, alcohol chain length. of alcohol, derived from a least-squares fit of a plot of B coefficient against alcohol concentration, decreases with increasing alcohol chain length (table 2). However, the effect as the homologous series is ascended is non-linear, which is related to the fact that the hydrophobic effect associated with the hydrophobic part of the alcohol molecule becomes greater as the length of the hydrocarbon chain of the alcohol increases.I thank Prof. R. Schaal and Dr D. Eagland for their comments on this work. R. H. Stokes and R. Mills, Viscosity of Electrolytes and Related Properties (Pergamon Press, Oxford, 1965). D. Feakins, D. J. Freemantle and K. G. Lawrence, J. Chem. SOC., Faraday Trans. 1, 1974, 70, 795. M. Tanaka, S. Kaneshina, W. Nishimoto and H. Takabatake, Bull. Chem. SOC. Jpn, 1973, 46, 364. S. Kaneshina, M. Manabe, G. Sugihara and M. Tanaka, Bull. Chem. SOC. Jpn, 1976,49, 876. E. Vikingstad and 0. Kvammen, J. Colloid Interface Sci., 1980, 74, 16. D. E. Guveli, J. B. Kayes and S. S. Davis, J. Colloid Interface Sci., 1979, 72, 130. 'I D. E. Guveli, J. B. Kayes and S. S. Davis, J. Colloid Interface Sci., 1981, 82, 307. * British Standard, BS 188 (1957). @ G. S. Kell, J. Chem. Eng. Data, 1967, 12, 66. lo G. Jones and M. Dole, J. Am. Chem. SOC., 1929,51, 2950. l2 J. E. Desnoyers and G. Perron, J. Solution Chem., 1972, 1, 199. l 3 H. Falkenhagen and E. L. Vernon, Phys. Z., 1932, 33, 140. l4 J. E. Desnoyers, M. Are1 and P. A. Leduc, Can. J. Chem., 1969, 47, 547. l5 W. Devine and B. M. Lowe, J. Chem. Soc. A , 1971, 21 13. A. Einstein, Ann. Phys, 1906, 19, 289, 191 1, 34, 591.1388 VISCOSITY B COEFFICIENTS K. Tamaki, Y. Ohara and Y. Isomura, Bull. Chem. SOC. Jpn, 1973, 46, 1551. '' M. Kaminsky, Discuss. Faraday Soc., 1957, 24, 171. E. Hutchinson and C. S. Mosher, J . Colloid Sci., 1956, 11, 352. l9 F. Franks and D. J. G. Ives, Quart. Rev., 1966, 20, I . 2o G. Nemethy and H. A. Scheraga, J . Chem. Phys., 1962, 36, 3401. 21 J. Padova, J . Chem. Phys., 1963, 38, 2635. 22 D. Feakins, B. C. Smith and L. Thakur, J . Chem. SOC. A , 1966, 714. 23 W. M. Cox and J. H. Wolfenden, Proc. R. SOC. London, Ser. A , 1934, 145, 147. 24 R. W. Gurney, Ionic Processes in Solution (McGraw Hill, New York, 1953). 25 T. Tominaga, B. T. Stem and D. F. Evans, Bull. Chem. Soc. Jpn, 1980, 53, 795. 26 J. W. Larsen and L. B. Tepley, J . Colloid Interface Sci., 1974, 49, 113. 27 K. Shirahama and T. Kashiwabara, J. Colloid Interface Sci., 1971, 36, 65. D. Feakins and K. G. Lawrence, J . Chem. SOC. ,4, 1966, 212. (PAPER 1 /297)