Nuclear magnetic resonance study of ion hydration. 3. Anisotropic

Feb 14, 1985 - water molecules undergo anisotropic rotational motion as an axially symmetric ... motions. The first two, i.e., translational and rotat...
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5098

J. Phys. Chem. 1985, 89, 5098-5101

Nuclear Magnetic Resonance Study of Ion Hydration. 3. Anisotropic Rotational Motion of Water Molecules Bound to the Aluminum(II1) Ion K. Miura,* K. Hashimoto, H. Fukui, Kitami Institute of Technology, 165 Koencho, Kitami 090, Japan

E. Yamada, and S. Shimokawa Faculty of Engineering, Hokkaido University, N13 W8 Kita- ku, Sapporo 060, Japan (Received: February 14, 1985; I n Final Form: July 8, 1985) The IH spin-lattice relaxation times, Ti, of the separate free and coordinated water signals of aqueous A1(C10J3 solutions have been independently measured at temperatures between +10 and -65 "C and with varying salt concentrations. All inversion-recovery measurements of T I showed a single exponential form in the above temperature range. Under our low temperature condition, only the intramolecular proton-proton interaction undergoing rotational motion contributes to TI. The experimental results showed that the difference between the two signals' TI values of the free and coordinated waters arises as the temperature falls below ca. -20 OC. We have been able to explain the experimental results by assuming that the coordinated water molecules anisotropically rotate as ellipsoidal molecules at low temperatures, whereas the bulk water molecules isotropically rotate as spherical molecules throughout the temperature range. We have applied the theory of spin-lattice relaxation due to the anisotropic rotational diffusion by Woessner to the analysis of the motion of the coordinated water molecules and obtained the following conclusions: (1) At low temperatures and low aluminum concentrations,the coordinated water molecules undergo anisotropic rotational motion as an axially symmetric ellipsoidal body whose axis of symmetry is the C2 axis of the H 2 0 molecule; (2) The motion of the hydration water molecule is slowed for low A1 concentrations.

Introduction In the previous papers1,*in this series, we reported changes of the water proton chemical shifts due to ion hydration. These changes of the chemical shifts provide information on the static properties of ion-water complex formation. In addition to that, however, it is also important to have information concerning the dynamical motion of the water molecules in aqueous salt solutions in order to have a better understanding of ion-water interactions. Up to the present a number of investigations relating to the dynamics of the hydration shell have been performed by the use of N M R technique^.^ There are three kinds of motions in water molecules, namely, translational, rotational, and vibrational motions. The first two, Le., translational and rotational motions, are measurable with N M R instruments. The rate of the translational motion of the water molecules in the first coordination sphere can be estimated from the exchange rate between the bound and free waters, which is obtained from line shape a n a l y s i ~line ,~~~ width measurement at half-height of the water signals,b8 and the transverse relaxation time, T2,measured by the pulsed N M R method.9 Information on the rotational motion of water molecules can be acquired from measurement of the longitudinal relaxation time, T,,loand that of the ''0signal width." For many metal ions, it has been found that on the bound water molecules in solutions the rotational diffusion rate about the axis 0-M (M = metal ion), RII,is more rapid than that of the 0-M axis itself, R,.12 However, for the A13+ ion Hertz et a1.I0 have concluded that these two rotational diffusion rates, RIland R , , of the water molecules in the first hydration sphere are almost equal to each other in aqueous AlC13 solutions at room temperature. This conclusion indicating the isotropic rotation of the water molecules bound to the AI3+ ion was obtained from the mea(1) Fukui, H.; Miura, K.; Ugai, T.; Abe, M. J . Phys. Chem. 1977, 81, 1205-1 209. (2) Miura, K.; Fukui, H. Inorg. Chem. 1980, 19, 995-997. (3) Hertz, H. G . "Water, A Comprehensive Treatise", Franks, F., Ed.; Plenum Press: New York, 1973; Chapter 7. (4) Fiat, D.; Connick, R. E. J . A m . Chem. SOC.1968, 90, 608-615. (5) Wawro, R. G.; Swift, T. J. J . Am. Chem. SOC.1968, 90,2792-2796. (6) Swift, T. J.; Connick, R. E. J . Chem. Phys. 1962, 37, 307-320. (7) Connick, R. E.; Fiat, D. J . Chem. Phys. 1966, 44, 4103-4107. (8) Neely, J. W.; Connick, R. E. J. A m . Chem. Soc. 1972,94,3419-3424. (9) Grant, M.; Jordon, R. B. Inorg. Chem. 1981, 20, 55-60. (10) Hertz, H. G.; Tutsch, R.; Versmold, H. Ber. Bunsenges. Phys. Chem. 1971, 75, 1177-1191. (1 1) Connick, R. E.; Wiithrich, K. J . Chem. Phys. 1969, 51, 4506-4508. (12) Hertz, H. G.; Tutsch, R.; Bowman, N. S. J . Phys. Chem. 1976, 80 4 17-425.

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surement of the ' H spin-lattice relaxation time, TI,at 25 "C, at which the observed value of T , is the average of the T I from the coordinated water and the T1 from the uncoordinated water. Moreover, at this temperature the measured T I contains contributions from both the translational and rotational motions. Therefore, their conclusion regarding the motion of the waters bound to AI3+ may include some ambiguity. It is well-known that when aluminum salt solutions are cooled to low temperatures, the proton N M R signal of water separates into two components corresponding to coordinated and uncoordinated water molecule^.^^-^' This phenomenon comes from the fact that at sufficiently low temperatures the exchange between the coordinated and bulk water molecules is slow enough to permit the observation of separate absorption signals. With this condition, we have two advantages to investigating the motion of the hydration water. First, the rate of translational motion is too slow to contribute to the spin-lattice relaxation. Second, we can determine the relaxation times of the bound and bulk waters independently.22 Consequently, we can expect more exact information concerning the rotational motion to be obtained by measuring the Tl's of the separate signals of the free and coordinated waters at low temperatures. The purpose of the present work is to investigate the rotational motion of the water molecules in aqueous AI(C104)3 solutions by measuring T I at temperatures lower than +10 OC, at which separate signals from the bound and free waters are available.

Experimental Section Materials. Water was distilled and passed over cation- and anion-exchange resins. The A1(C104)3-6H20was synthesized and purified as follows: Special grade A1C13.6H20was dissolved in 20% perchloric acid, (13) Schuster, R. E.; Fratiello, A. J . Chem. Phys. 1967, 47, 1554-1555. (14) Fratiello, A,; Schuster, R. E. Tetrahedron Lett. 1967, 4641-4644. (15) Fratiello, A,; Lee, R. E.; Nishida, V. M.; Schuster, R. E. J . Chem. Phys. 1967, 47, 4951-4955. (16) Fratiello, A,; Schuster, R. E. J . Chem. Educ. 1968, 15, 91-93. (17) Fratiello, A,; Lee, R. E.; Nishida, V. M.; Schuster, R. E. J . Chem. Phys. 1968, 48, 3705-3711. (18) Matwiyoff, N. A,; Darley, P. E.; Movius, W. G. Inorg. Chem. 1968, 7., -2173-2174. - - -(19) Fratiello, A,; Lee, R. E.; Nishida, V. M.; Schuster, R E. Inorg. Chem.

__

1969 -._ _R -, , 69-77_.

(20) Schweitzer, G. K.; Stephens, J. F. Specrrosc. Letr. 1970, 3, 11-22. (21) Fratiello, A. Progr. Inorg. Chem. 1972, 17, 57-92. (22) Koch, W.; Wawer, I.; Hertz, H. G. Z . Phys. Chem. (Frankfurl am Main) 1982, 132, 161-174.

0 1985 American Chemical Society

Rotational Motion of H 2 0 Bound to Al(II1)

The Journal of Physical Chemistry, Vol. 89, No. 23, 1985 5099

300 -

-0,.

COORDINRTEO

----O,O

BULK

-

-

250

Q

-

-

- 200 E

I=

150 Figure 1. The proton magnetic resonance spectrum of an aqueous Al(C10J3 solution at -40.9 OC. The mole ratio between H20and AI is 3 1 5 1 . The signals arising from bulk water (BH20) and the water molecules in the AI" hydration shell (CHZO)are labeled.

in which the molar ratio of HC104 to A13+was 3.5:l. The solution was concentrated by heating it until it ceased to generate hydrogen chloride gas. The solvent was then evaporated under reduced pressure and the residual solid was dried under vacuum. The Al(ClO4)3 formed was recrystallized from ethanol three or four times until the concentration of Fe3+become lower than the lower limit of detection (5 ppm). We prepared seven different aqueous solutions as samples, which differed from each other in the Al(C104)3 concentration. The mole ratios, H20/A1, in each sample were 16.1, 19.6, 23.5,26.1, 31.5, 35.0, and 39.6, respectively. The A13+concentration was determined by chelatemetric titration with EDTA at 100 OC. The pH of the solutions was ca. 2 and was independent of the aluminum concentrations of the samples. NMR Measurements. The 'H N M R spectra were obtained on a JEOL FX-200 Fourier-transform spectrometer (200 MHz for 'H) equipped with a JEOL NM-PVTS2 variable-temperature unit. The spin-lattice relaxation times, T I ,were obtained by the inversion-recovery method using the pulse sequence of (-1 80' pulse -t-90° pulse -T-)n.For each measurement of T1, more than 15 different pulse intervals ( t ) were used. The delay time (7') was 10 s because all the absorption signals had T I values shorter than 0.5 s. The number of pulse sequences ( n ) was 4. Measurements of ' H N M R were performed by using 5-mm-diameter tubes at temperatures of +10 to -65 "C. The accuracy in the temperature measurement was within f 0 . 2 "C. Prior to the experiment, the effect of dissolved oxygen in a sample was examined. The T1 of the undegassed sample was compared with that of the degassed and sealed sample at the same temperature and salt concentration. It was confirmed that the difference between both the Tl's was small and within the experimental error in our temperature range. Therefore, the undegassed samples were used for our experiments.

Results and Discussion T1 of Coordinated and Bulk Water Protons. As described previously, when aqueous solutions including the Al( 111) ions were cooled, exchange of water molecules was considerably slowed and separate proton signals were observed for the bulk water and the coordinated water bound to A13+. This phenomenon is illustrated in Figure 1. The integration of the separate peak area (BH20and CHl0) in Figure 1 indicated that the hydration number of A13+ is about six. This hydration number is the same as that in the results of Fratiello et al." Therefore, the peak CHIOin Figure 1 arises from water molecules in the first hydration sphere. We measured the spin-lattice relaxation times, T I ,of the coordinated and free water molecules as a function of temperature for seven samples with different Al(C104), concentrations. All inversion-recovery measurments of Tl showed a single exponential form throughout the temperature range. This means that the exchange rate between the coordinated and bulk water molecules

IE0

I

50 -80

-60

-40 T

-20

0

20

[OC)

Figure 2. The IH spin-lattice relaxation times, TI, of the coordinated and bulk water signals as a function of temperature, T , at high (0 and 0 ) and low (0and m) aluminum concentrations. The mole ratios of H20 to AI are 19.6 (0 and 0 ) and 31.5 (0 and W), respectively.

is negligibly small at the temperatures at which the coordinated and uncoordinated water signals have different TI ~ a l u e s . 2The ~~~~ results for the two solutions with high and low aluminum concentrations in the samples measured are shown in Figure 2. Figure 2 indicates that the T I values of the coordinated and bulk water protons are equal at relatively high temperatures, but the difference between the two Tl's arises as the temperature falls below ca. -20 "C. The other five measured solutions showed a similar trend. The minimum value of T,(bulk) is about 95 ms, which is in good agreement with the theoretical [Tl(bulk)],i, of 102 ms, calculated with the H-H distance of ice (r" = 1.645 A, rOH= 1.01 A, LHOH = 109"). The differences between the T , values of the coordinated and uncoordinated water molecules were especially large at low temperatures and low aluminum concentrations. The difference between the bulk and coordinated T,'s seems to reflect the dynamics of the water molecules in the hydration shell of the aluminum ion. We will attempt below to explain the experimental results by assuming anisotropic rotational motion of the coordinated water. Figure 2 shows that at low salt concentrations the minimum of T I(coordinated) is longer than that of T,(bulk). Moreover, [Tl(coordinated)],in is at a higher temperature than [ Tl(bulk)],i,. These should be attributed to the anisotropic motion of the coordinated water molecule. Anisotropic Rotational Motion of the Coordinated Waters. We can expect that the measured relaxation rates, l / T l , in this experiment will not contain a contribution from the translational motion in either the bound or the free waters, because the spinlattice relaxation time depends on rapid motions as fast as the Larmor precession. Therefore, we have to explain the experimental results by the rotational motion contribution to T 1 . Moreover, the correct explanation should be able to account for the experimental fact that the two Ti'sof the coordinated and uncoordinated water signals are equal at high temperatures, but they differ from each other at low temperatures. The intermolecular protons are widely separated from each other compared to the two intramolecular protons. The rotational relaxation rate is inversely proportional to the sixth power of the dipole-dipole distance, and so the rotational intermolecular contribution to T I ,which interacts within the clusters such as (H20), and Al(H,O):+, can be safely neglected.I0 Furthermore, the contributions from the proton-cation (A13+)and the protonanion (Clod-) magnetic dipole-dipole interactions are also neg(23) Lambert, J . B.; Keepers, J. W. J . Mugn. Reson. 1980, 38,233-244.

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Miura et al.

I

.

.*

I

3;. I

Figure 3. The model used for the motion of the water molecules coordinated to the AI3+ ion.

ligible. As a consequence of these simplifications, we can use the single molecule approximation for either the bound or the free waters. We postulate here that only the intramolecular protonproton interaction operating within a single H 2 0 molecule undergoing rotational motion contributes to the measured relaxation rates of the water protons for either the bound or the free waters. We need three more assumptions in order to interpret the difference between the Tl’s of the coordinated and bulk water protons. These three assumptions are as follows: (i) Bulk water molecules rotate isotropically. Namely, the motion of bulk molecules is described by a spherically symmetric rotation in which the Brownian motion is represented by the single rotational diffusion coefficient, R. On the other hand, coordinated water molecules rotate anisotropically as an axially symmetric ellipsoidal body does. Namely, the motion of coordinated molecules is described by axially symmetric rotation in which the Brownian motion is represented by two rotational diffusion coefficients, Le., the rotational diffusion coefficient about the symmetric axis, R I I ,and that about the two equivalent axes perpendicular to the symmetric axis, R,. We introduce here the anisotropy parameter, u, which is defined as the ratio of R, to Rll. That is = R,/Rll

2

0.02

0.04 XRI

0.06

Figure 4. The three rotational diffusion coefficients, R (O), R,,(a), and R,/R,, (= c) (A), a t the temperature of [Tl(coordinated)],i, as a function of the mole fraction of AI(C10,)3, xAl. The curve for R,,coincides with the curve for R in the region higher than xAl = 0.05.

magnetogyric proton ratio, r” is the proton-proton distance in the water molecule, and wH is the Larmor angular frequency of the proton. In our experiment, wH = 4 X lo8* s-]. The above formulae for Tl(aniso) become the same as the well-known T,(iso) formula in the isotropic rotational motion if u is set equal to unity. That is

where y = oH/R, and 1/ R = 6 ~with ~ the , usual correlation time TC.

Equations 2 and 5 indicate that the ratio, [Tl(aniso)],,,/T1(iso)],,,, is the function of the anisotropy parameter u alone. It is easily shown that 1 5 [T,(aniso)lrnin/[T~(iso)l,,n 5 4/3

(6)

(1)

None of our results were contradictory with eq 6. In fact, the ratios, [ T,(coordinated)],,,/ [ Tl(bulk)],,,, for all samples mea(ii) The three rotational diffusion coefficients, R, Rll,and R,, sured were within the above limitation. We now realize that all are functions of the temperature and the aluminum concentration three parameters R, Rll,and R , can be determined at the parof the solution. ticular temperature of [ Tl(coordinated)],,,. We were able to (iii) The angle between the symmetric axis of rotation for the evaluate these parameters at that temperature by the following coordinated water molecule and the proton-proton vector in this three steps. First, u, Le., R,/RII, was determined by comparing molecule is fixed at 90”. This is shown in Figure 3. We take the experimental ratio, [ T,(coordinated)],,,/ [ T,(bulk)],,,, with a model in which the symmetric axis of rotation, Le., the C2axis + 2f2x,u)],, the theoretical ratios, m , l ) 2f(2y,l)],/[f(x,u) of the coordinated water, coincides with the binding axis in the calculated for various values of u. Next, for a given u, R l lwas complex formation between the AI3+ ion and the water oxygen. estimated from the particular value of x giving the maximum for Under the above three assumptions, we will analyze the rotathe function, Lf(x,u) + 2f(2x,u)]. Finally, we obtained R at the tional motions of the coordinated and bulk water molecules. We of [ T1(coordinated)],,, by comparing the experican utilize for this aim the formulae for T , by W o e s ~ n e and r ~ ~ ~ ~ temperature ~ mental ratio, T,(bulk)/[T,(bulk)],,,, with the theoretical ratio, ShimizuZ6for an ellipsoidal body. 1.4252/1f(y,l) 2f(2y,l)], in which 1.4252 = [f(y,l) 23 WoessnerZs has shown that the nuclear spin-lattice relaxation (2y,l)Imx. The three parameters R, Rl,,and R,/RIl (= u) at the time, T,(aniso), for two interactive protons fixed in a molecule particular temperature of [ Tl(coordinated)],, are plotted against undergoing axially symmetric anisotropic rotation is given by the mole fraction of A1(C104)3, xAl,in Figure 4. 1 3 KO 2’YH4h2 Figure 4 shows that the rotational velocity of the bulk water, = -[f(x,u) + 2f(2x,u)] (2) R, monotonously decreases with increasing salt concentration, but Tl(aniso) 10 4~ r H H 6 W H RIIof the coordinated water has a maximum at a mole fraction where of ca. 0.04. Moreover, R, of the hydration water is abruptly slowed as the mole fraction of A1 decreases. The concentration 3 (4 2a)x 1 6ax dependence of the bulk water motion R is the same as that usually f(xd = (3) 4 x2 ( 6 ~ ) 4~ x2 (4 2u)’ observed for rotational diffusion. This is easily accounted for by the higher microviscosity for bulk water at higher concentrations. = WH/RII (4) However, the coordinated water motion shows quite a different dependence on the concentration. The behavior of R,,suggests In eq 2 w, is the magnetic permeability in vacuo, yH is the the presence of two opposed sources of resistance for the motion, one of which is the microviscosity effect and gives for Rllthe same (24) Woessner, D. E. J . Chem. Phys. 1962, 36, 1-4. dependence on the concentration as R, but the other source of (25) Woessner, D. E. J . Chem. Phys. 1962, 37, 647-654. resistance makes R,,slower for lower concentrations. Furthermore, (26) Shimizu, H. J . Chem. Phys. 1962, 37, 765-778. IJ

+

+

~

-( -) +

+-

+

+ +

+

J. Phys. Chem. 1985, 89, 5101-5106 for R , , the latter source, giving slower motion for lower concentrations, is much stronger than the former viscosity contribution, providing the same concentration dependence as R . Therefore, the slowdown of R , is more rapid than that of RIlfor lowering the concentration of Al. The anisotropy parameter u, Le., R , / R I I of , the coordinated water molecules abruptly falls from unity (indicating isotropic rotation) to zero (completely anisotropic rotation) when the aluminum concentration is lowered. The higher resistance for motion for low concentrations can be attributed to AI-H20 coordination bond formation in the hydration shell provided that the bond strength is larger for low concentrations. Thus, we arrive at the conclusion that the structure of the hydration shell becomes looser as the salt concentration increases. This conclusion is supported by another piece of evidence reported by Hertz et al.1° that the interaction between neighboring hydrated ions destroys the ordered structure of the hydration sphere. The destruction of the hydration shell will lower the heights of the potential barriers against the rotational motions in the shell.

5101

Particularly, the motion of the A1-0 axis itself, Le., R , is much accelerated by this destruction. Our experimental results showed that difference between the two Tl’s of the coordinated and bulk water signals becomes greater at lower temperatures and lower aluminum concentrations. This means that R , / R I I (also maybe R I I / Ris) smaller at lower temperatures and lower A1 concentration^.^^ However, the two T,’s were equal at temperatures higher than -20 O C at any Al(C10& concentration. Therefore, the conclusion of Hertz et al. that R l l is equal to R , will be correct only at the higher temperature.

Acknowledgment. This research was supported in part by the Scientific Research Fund of the Japanese Ministry of Education (Grant No. 57740307). Registry No. H20,7732-18-5. (27) At temperatures low enough to satisfy x,y so)/T,(iso) is equal to 2(R/Rl,)/(1 + u ) .

>> 1, the ratio T,(ani-

Interaction of Poly(ethy1ene oxide) with Sodium Dodecyl Sulfate Micelles: A Fast Kinetic Study by Temperature Jumpt Christian Tondre Laboratoire d’Etude des Solutions Organiques et Colloidal (L.E.S.O.C.,U.A. C.N.R.S No. 406), Uniuersitt? de Nancy I, 54506 Vandoeuure-les- Nancy Cedex, France (Received: February 21, 1985; In Final Form: June 19, 1985)

The modification of sodium dodecyl sulfate (SDS) micelle dissolution-formation relaxation time T~ (and relaxation amplitude) brought about by the addition of poly(ethy1ene oxides) (PEO) is investigated by using the temperature-jump technique with a spectroscopic probe (acridine orange). Whereas small molecular weight additives (dioxane, PEO 1000) have no special effect on these quantities, a very particular behavior is observed with PEO 10000. It is shown that this behavior is in relation with the formation of the stoichiometric polymersurfactant complex, which has been previously observed by means of different static methods. The influence of different parameters on 72 is examined: polymer concentration, surfactant concentration, added salt concentration,temperature. The results are interpreted, with the aid of a mass action law model for polymersurfactant complex formation, as supporting the idea that the complex is constituted of a micelle wrapped up by the polymer chain rather than by a polymer saturated by a linear adsorption of surfactant molecules. The observed features agree with the picture of a polymer-surfactant complex entity having between 0.5 and 1 chain of PEO 10000 per micelle.

Introduction Besides the fundamental importance of the interaction between macromolecules and surface active molecules in biological systems, which have been recognized since a long time,’ other reasons for studying such interactions have appeared in recent years in relation with tertiary oil recovery2 and textile leaning.^ Among the different processes experimented to improve oil recovery, one consists in an injection of surfactant solutions followed by a flooding with polymer solutions. On the other hand, during cleaning processes the adsorption of water-soluble polymer on the textile fibres is expected to modify the surface behavior so as to improve the cleaning. On a fundamental point of view efforts have been made to try to identify the origin of surfactant-polymer interactions depending on the chemical structure of the interacting specie^.^-^ In this work we will restrict ourselves to the situation arising when nonionic water-soluble polymers (poly(ethy1ene oxide), PEO) are mixed with micellar solutions of an ionic surfactant (sodium dodecyl sulfate, SDS). One may expect in this case different kinds of polymersurfactant complexes to be formed. Such complexes have been extensively studied by various techniques, which most ‘Part of this work was presented at the “Fast Reaction in Solution” DGI cussion Group Meeting (Chemical Society, London, and Max Planck-Gesellschaft) Gbttingen, R.F.A., 3-5 Sept 1980.

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of the time show the Occurrence of a change of the studied physical property for a well-defined stoichiometry between the polymer and the surfactant, in addition to the change due to the modified critical micellar concentration. This is true for measurements using surface t e n ~ i o n ,c~o,n~d u ~ t i v i t y , v~ iJs~c ~ s i t y , ~NMR J ~ chemical shift and counterion r e l a ~ a t i o ndialysis ,~ equilibrium,’’ etc. Two extreme explanations have been proposed to account for this situation: Jones, for instance, has suggested9 that the stoichiometry observed when the SDS concentration is changed (the PEO concentration being fixed) corresponds to the point where ~~

(1) Robb, I. D. In “Anionic Surfactants. Physical Chemistry of Surfactant Action”; Lucassen-Reynders, Ed.; Marcel Dekker: New York, Surfactant Science Series, Vol. 11, Chapter 3. (2) Nagarajan, R. Polym. Prepr. ( A m . Chem. SOC.,Diu. Polym. Chem.) 1981, 22, 33-8 (1981). (3) Larcheres, G.;Lamy, P.; Papillon, B. “Physicochimie des Composes Arnphiphiles”; Editions du C.N.R.S.: Bordeaux, France, 1978; Colloques Nationaux du C.N.R.S. No. 938. (4) Cabane, B. J. Phys. Chem. 1977, 81, 1639. (5) Cabane, B.; Duplessix, R. J . Phys. 1982, 43, 1529. (6) Gilanyi, T.; Wolfram, E. Colloids Surf. 1981, 3, 181. (7) Pincus, P. A.; Sandroff, C. J.; Witten, T. A. J . Phys. 1984, 45, 725. (8) Nagarajan, R. Chem. Phys. Left. 1980, 76, 282. (9) Jones, M. N. J. Colloid Znferface Sci. 1967, 23, 36. (10) Francois, J.; Dayantis, J.; Sabbadin, J. Eur. Polym. J . 1985, 21, 165. (1 1) Shiraharna, K. Colloid Polym. 1984, 252, 978.

0 1985 American Chemical Society