J. Phys. Chem. 1983,87,2436-2443
2436
where Re(c) = Koe(c)/Roa(c)and Re(b) = Koe(b)/Koa(b) are relative retention times. The following retention data are available for the solute pair, a = n-heptane and e = di-n-propyl ether: Re(,) = 0.782, Re(b)= 0.664 (W. L. Zielinski, Jr., Doctoral Dissertation, Georgetown University, Washington, DC, 1972). From density data,16 Voe= 138.8 cm3 mol-'; thus, basing the r's on molar volumes (Table I), re = 1.72. Also, we estimate that the oxygen moiety's contribution to the molar volume of di-n-alkyl ethers is 6.51 cm3 mol-' at 30 OC. Therefore, fie = 0.0469 and fk = 0.0216, and from eq A3
which differs from eq 2 (and, hence, eq 1) in the text by the correction term E. Substituting eq A4 into eq A6 and again employing r values based on molar volumes (Table I), we have t = (1.84 - ra)4,[0.021 - 0.0224,] or t =
0.0215(1.84 - ra)$q,+c
(A7)
where the closeness of the constant to fk is a coincidental result. The largest correction encountered is with CHC13 (ra = 1.00) at 4, = 0.483, for which t = 0.0045. This corresponds zfdc(Aw34/kT) = 0.022 (-44) to a correction of but 1 % (Q = 0.453) and is only slightly larger than the estimated experimental error in Q (*0.002). Considering now the solute in question (subscript a), eq Note that, if van der Waals volumes (and, r and f values 55 of ref 1 (with zrjZa= 1) and eq A2 yield therefrom) were used in the above evaluation, the E results (A51 would differ by not more than 0.0002 from those calculated Q + t = DdC+ In [ l + (Ka,"/Voc)4,1 via eq A7. where Registry No. CCh, 56-23-5;CHC13,67-66-3;CHC12Br,75-27-4; t = (pa - ra)&[(r;l - rb-l) - Z ~ ~ , ~ ( A W ~ ~ / ~ T(A61 ) ~ J , I CHBr,Cl, 124-48-1;CHBr3, 75-25-2; benzene, 71-43-2.
Temperature-Induced Phase Transition and Structural Changes in Micellar Solutions of Sodium Oleate Observed by Raman Scatteringt P. T. T. Wong" and H. H. Mantsch Division of Chemistry, National Research Council of Canada, Ottawa, Ontario, Canada K I A OR6 (Received: October 4, 1982; In Final Form: October 26, 1982)
Raman spectra of aqueous sodium oleate in the coagel and micellar phases have been measured as a function of temperature over the temperature range from -40 to 40 OC. The temperature-inducedphase transition between the micellar and coagel phases on both heating and cooling has been characterized. The transition exhibits very high hysteresis, the critical micellization temperature of 0.42 M sodium oleate being observed at 27 "C, while the critical coagelization temperature of this system was found at 11 "C. Changes in the spectra, including the polarized Raman spectra of the micellar phase, have been used to discuss short-range structural changes of various functional groups in sodium oleate. The Raman spectra indicate that, up to 40 "C, the penetration of water molecules into the sodium oleate micelles is insignificant.
Introduction The temperature dependence of the infrared spectrum of 0.38 M sodium oleate in D20 has been reported recently.' Structural changes occurring at the critical micellization temperature of this system were inferred from changes observed in the infrared spectra in the frequency regions of the CH2 and C02- stretching and CH2 bending modes. However, infrared bands in the skeletal C-C stretching region which are highly sensitive to the molecular conformation could not be monitored due to the strong water absorption, and the C=C stretching mode is infrared inactive. Furthermore, the Raman spectra of sodium oleate in the CH2 stretching and CH2 bending NRCC No. 21242. 0022-3654/83/2087-2436$0 1.50/0
regions are expected to differ from the infrared spectra in the same regions due to the dispersion of these optical modes. Thus, complementary information concerning temperature-dependent structural changes and the nature of the phase transition can be obtained by a study of the corresponding Raman spectra. There are only few Raman spectroscopic studies on micelle formation of surfactants at the critical micelle concentration,24 and none of these dealt with the tem(1) Cameron, D. G.; Umemura, J.; Wong, P. T. T.; Mantsch, H. H.
Colloids Surf. 1982, 4,131. (2) Kalyanasunderam, K.; Tomes, J. K. J . Phys. Chem. 1976,80,1462. (3) Okabayashi, H.; Okuyama, M.; Kitagawa, T. Bull. Chem. SOC.Jpn. 1975,48, 2264. (4) Rosenholm, J. B.; Stenius, P.; Danielsson, I. J. Colloid Interface Sci. 1976, 57, 551.
0 1983 American Chemical Society
The Journal of Physical Chemistry, Vol. 87, No. 13, 1983 2437
Micellar Solutions of Sodium Oleate
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