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J. Phys. Chem. 1981, 85, 1445-1457
7 "C (from 64 to 57 "C) upon addition of 0.5 M NaC1" by using the temperature dependence of Mapplor Triton X-100in water with no salt reported in ref 4. Going from 30 to 37 "C, the increase of M observed in ref 4 is -45%, a value close to that reporteriy Kuriyama for the 0.5 M NaCl addition at constant temperature. Our results for Ma are in very good agreement with those obtained by Balmbra et al.l in the range 25-45 "C. The authors of ref 1 propose an exponential law for the growth of Mappwith T. Several other workers have successively proposed the same law,18but the validity of this law was never checked close to T,.Indeed the deviation of our data from the exponential law becomes very large in the range 45-50 "C. The plot of Figure 2 shows that the data do not follow the power-law behavior when e is larger than 7 X (temperature below 30 "C). The overall picture provided by all of the available experimental data1m3on C12Eedilute aqueous solutions is that there are three temperature regions, each characterized by a distinct behavior. In the first region, 5 < T 15 "C, Mappis nearly constant3 and is probably coincident with the true molecular weight of the individual micelle. In the second region, 15 < T < 30 "C, Mappincreases exponentially.'8 It is possible that this behavior is entirely due to nonideality effects, but no quantitative theory is yet available. In fact the predictions of theories of critical phenomena apply only to the asymptotic region where static and dynamic parameters obey (17) T.Nakagawa in "Nonionic surfactants",M. J. Schick, Ed.,Dekker, New York, 1967, p 558. (18) A. Goto, R.Sakura, and F. Endo, J. Colloid Interface Sci., 67,491 (1978).
a simple power-law dependence on the reduced temperature. In the third region, 30 "C < T < T,the solution behaves as a critical binary mixture, and therefore the light-scattering experiment sees only the effects associated with the large increase of the correlation range of concentration fluctuations. the situation may be pictorially described by saying that, in proximity to the critical point, the motion of the micelles is correlated over a distance E which is much larger than the micelle size, so that the lightmattering measurement does not probe the individual micelle, but the growth and decay of large statistical clusters which include micelles and water. This picture bears some resemblance to the secondary aggregation picture discussed by Ottewill et aL3and by Tanford: but the description of critical effects cannot be reduced to a simple secondary aggregation process. A last point to be mentioned is that the linearity of the plots I, vs. c, as reported in ref 1,2,and 4,was probably considered by many authors an indication that the micellar solution is ideal over a large temperature and concentration range and, therefore, that the experimental data reflect directly individual micelle properties. Such an argument is, however, deceiving, as shown by the observation of Balmbra et al.l that the I, vs. c plots, when extrapolated to low concentrations, give an apparent critical micelle concentration (cmc) which is 10 times larger than the true cmc. Accurate measurements18performed at low concentraion show indeed that I, is not a linear function of c and that Mappconsiderably increases with c in a very narrow concentration range above the cmc.
Acknowledgment. This work was supported by CNR/CISE Contract no. 80.00016.02.
Phase Boundary Curves in Toluene, 1-Butanol, and Aqueous Sodium Aikylbenzenesuifonate Systems Patience C. Ho Chemistry Divlslon, Oak RMge National Laboratmy, Oak Ridge, Tennessee 37830 (Received; November 4, 1080)
Miscibility relationships in systems containing toluene, 1-butanol,water, and sodium alkylbenzenesulfonates are reported. The sulfonates studied included benzene, p-toluene, p-ethylbenzene, 2,4,6-trimethylbenzene, p-cymene, and 2,5-&isopropylbenzene. In a triangular representation with a constant ratio of 1 mol of sulfonate/kg of water as one component, the phase boundary curves are fairly symmetrical with respect to the alcohol apex (number of alkyl carbons on benzene ring of benzene sulfonate) less than 3, but highly asymmetrical for SAC greater than 3. The amount of 1-butanolrequired to produce miscibility decreases with the increasing for SAC SAC in the aqueous-rich region (>40% aqueous solution) but increases in the toluene-richregion (>W%toluene) when SAc= 4 and 6. One system, containing sodium 2,5-diisopropylbenzenesulfonate,was studied at eight aqueous solution concentrations at 25 "C from 0.25 to 3.0 mol of sulfonate/kg of water. Phase relationships for limiting three-component systems were also determined. Under the boundary curves of the system containing 0.50,1.0, and 1.5 m aqueous solutions, regions with three liquid phases in equilibrium were observed at 25 "C. The regions of the three coexisting liquid phases varied with changing temperature and composition. Opalescence can be seen at several compositions, especially near the S-shape sector of the phase boundary curves, an observation which, along with low interfacial tension between phases, suggests proximity of critical end points.
Introduction The ability of polar organic compounds to promote miscibility between hydrocarbons and aqueous solutions is well-known. Surfactants and alcohols can effect clear
microemulsions.' The long hydrocarbon chains typical of surfactants are not required, however. Compounds such (1) Hoar, T. P.; Schulman, J. H. Nature (London) 1943, 152, 102.
0022-3654/81/2085-1445~01.2~l~0 1981 American Chemical
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The Journal of Physical Chemistry, Vol. 85, No. 10, 1981
as salts of benzene- or toluenesulfonate also can promote mutual solubility; Neuberg2 introduced the term “hydrotropic” to describe this property, both of organic salts and of inorganic salts which “salt” organic compounds into aqueous phases. To obtain basic information which might clarify the complex microemulsion multiphases encountered in the aqueous brines/hydrocarbon/surfactant/alcoholsystems used in enhanced oil recovery by micellar floods, as well as the behavior of other aqueous/organic systems, we have been investigating phase behavior of simpler systems. These systems comprise fewer and pure components. In addition, the “surfactant” component has in most cases had fewer alkyl carbons than usually thought necessary for micelle formation. Strong but smooth trends have been found with systematic variations in these compounds, which we refer to by the name “protosurfactants”. For example, increasing the degree of alkyl substitution from sodium benzenesulfonate to sodium diisopropylbenzenesulfonate increased the toluene solubility in water from -0.01 to -0.21 mol of toluene/kg of water for concentrations of 1mol of sulfonate/kg of water, and from -0.03 to -2.3 mol of toluene/kg of water at 2.5 m sulfonate a t 55 0C.3 With four-component systems containing alcohol and high concentrations of sodium alkylbenzenesulfonates (2.5 mol/kg of water), similar trends of the effect of alkyl substitution were ~ b s e r v e dthat ; ~ is, less alcohol was necessary for miscibility for a given composition with higher alkyl substitution on the sulfonate. In addition, phase boundary curves of four-component systems plotted on triangular diagrams (water and sulfonate at a constant ratio taken as a single component) were relatively symmetrical with respect to the alcohol apex. Similar behavior was seen with alkylbenzenecarboxylate salts.5 With different hydrocarbons, other components being fixed, more alcohol was required as the number of alkyl carbons of the hydrocarbon increased.6 At lower concentrations of sodium alkylbenzenesulfonates and -carboxylates substituted by four or more alkyl carbons, with some cosolvent, the phase boundary curves were no longer symmetrical. More cosolvent was required to effect miscibility in the toluene-rich region. Opalescence was observed in several compositions in the neighborhood of miscibility boundaries in the asymmetric region. Close examination disclosed that three phases were present for some of the compositions. These observations appear in some respects similar to patterns reported for systems in which tricritical points (at which three phases merge simultaneously into one) are believed to occur (see, for example, ref 7-9). Tricritical points, and changes in properties as compositional or physical parameters are varied to approach them, are of considerable current interest in theories of ~olution.l*~~ consequently, boundaries of immiscibility in the liquid regions of the fourcomponent system water/sodium diisopropylbenzene(2)Neuberg, C. Biochem. 2. 1916,76,107. (3) Ho.P. C.: Ho, C.-H.: Kraus, K. A. J . Chem. Eng. Data 1979,24, 115. (4)Ho,P.C.; Kraus, K. A. J. Colloid Interface Sci. 1979,70, 537. (5)Ho,P.C.; Ogden, S. B. J. Chem. Eng. Data, 1979,24,234. (6)Ho,P. C.; Kraus, K. A. J. Chem. Eng. Data, 1980,25,132. (7)Radyshevskaya, G. A.;Nikurashina, N. I.; Mertslin, R. V. J. Gen. Che. USSR (Engl. Transl.) 1962,32,673. (8) Widom, B. J.Phys. Chem. 1973,77,2196. (9)Lang,J. C., Jr.; Widom, B. Physical A (Amsterdam) 1976,81,190. (10) Griffiths, R.B.; Widom, B. Phys. Reu. A 1973, 8, 2173. (11)Griffiths, R. B.J. Chem. Phys. 1974,60,195. (12)Moldover, M. R.; Cahn, J. W. Science, 1980,207,1073. (13)Cahn, J. W. J. Chem. Phys. 1977,66,3667. (14)Scott, R. L.Chem. Thermodyn. 1977,2,238. (15)Fox, J. R.J. Chem. Phys. 1978,69,2231.
Ho
sulfonate/toluene/l-butanol,as well as in the limiting three-component systems, have been investigated in considerable detail. No attempt to locate possible tricritical points has been made, but the information presented here may assist any who may wish to do so. Experimental Section Toluene and 1-butanol (certified ACS grade) from Fischer Scientific Co. were used without further purification Sodium benzenesulfonate, p-toluenesulfonic acid monohydrate, and 2,4,6-trimethylbenzenesulfonicacid were obtained from Fluka, A. G.; the acids were converted to the sodium salts by neutralization with 10% NaOH. Sodium p-ethylbenzenesulfonate, sodium p-cymenesulfonate, and sodium 2,5-diisopropylbenzenesulfonate were synthesized as described ear lie^^ The phase diagrams for the four bounding ternary systems were obtained by the method of titrating the mixture of two components with the third component, the end point being taken as either the clear point or the cloud point. The miscibility boundaries in the four-component systems were determined for plane sections of a tetrahedron representing composition, in which the ratio of two of the components, water/organic salt, was fixed. Mixtures of this aqueous solution and toluene were titrated with cosolvent to clear points, and mixtures of aqueous solution and 1-butanol or mixtures of 1-butanol and toluene were titrated with either toluene or aqueous solution to the cloud points. Weighed amounts of two components were placed in 8-mL test tubes with screw-on, Teflon-lined caps containing small holes which could be closed with a valve; the total sample size ranged from 0.5 to 1.0 mL. The mixtures were maintained at 25 f 0.1 “C in a thermostat for -1 h. Then the third component was added from a syringe drop by drop. After the addition of each drop, the tube was put back to the thermostat for up to -5 min to allow the temperature to reach constancy again. Mixing was accomplished with a “vortex” mixer. The aqueous organic salt solutions were prepared from distilled water, and concentrations are expressed in terms of molality, m (mol/kg of HzO). All quantities were determined by weighing, and compositions are presented as weight percentage in both three- and four-component systems. In the search for the number of coexisting phases in the immiscible region, samples to be tested were placed in graduated centrifuge tubes. The total mass of the sample was 5-6 g. The tube was closed with a glass stopper and was mounted vertically in a water bath with the temperature controlled at 25 f 0.1 “C; it was allowed to stand for 2 days to 2 weeks before determining the number of coexisting phases and the phase volumes. The compositions of the phases in equilibrium were analyzed as follows. Toluene and 1-butanol were analyzed with a Perkin-Elmer Sigma 3 gas chromatograph with flame ionization detector. The column was packed with Tenax GC 60/80mesh from Applied Science Laboratory. Sulfonate was analyzed by weighing the residue after evaporation of volatile components. All compositions are presented as weight percentage, and the weight percentage of water was estimated by subtracting the weight percentage of other components from 100. Duplicates in GC analysis agreed to within -5%, as expected from the innate precision of the method, and the error of residue analysis is less than 4 % . Results Four-Component Systems and Various Protosurfactants. At high concentrations (2 mol/kg of H20and
The Journal of Physical Chemistry, Vol. 85, No. IO, 198 1
Phase Boundary Curves 1 -BUTANOL
(a)
1447
(1) H20 ( 2 ) 2.5
E Na-Benzenesulfonate
(3)
11
Na-pToluenesulfonate
(4)
'1
IJa-pEthylbenzenesulfonate
(3)
if
Na-pIsoproWlbenzenesulte
(6)
11
(7) (8)
Na-pQnenesulfonate Na-2-Methyl-5-t-Butylbenzenesulfonate
''
Na-2,5-DiisoppyLbenzenesulfonate
AQTOUS SOLUTION
TOLUENE
1- BUTANOL
?k-bnzenesulfonate
(2)
1.0
( 3)
I'
Na-pToluenesulfonate
(4)
"
Na-pEthylbenzenesulfonate
(5)
"
Na-Z,4,6-~imethylbenzenesulfonate
(61
"
Na-pCymenesulfonate
(7)
Na-2,5-Diisopropylbenzenesulfonate
Figure 1. Effect of substituents on phase relations in toluene/l-butanoVaqueous sulfonate systems (25 1.8 m sodium sulfonate.
higher) of the protosurfactant component, miscibility boundaries in plane-section (aqueous/ hydrocarbon/alcohol) representations tend to be fairly symmetrical with respect to the alcohol apex. This is illustrated in Figure la, reproduced from ref 4, for the systems containing toluene, 1-butanol, and 2.5 m aqueous solutions of benzenesulfonates, substituted with zero to six alkyl carbons. The region adjacent to the alcohol apex is single phase, and at least two phases are present below the curves. The trend to higher solubilizing effect of the protosurfactant as its degree of alkyl substitution increases is shown by the smaller amounts of alcohol necessary to effect miscibility. Analogous trends with alkyl substitution are found in solubilization of toluene in three-component systems without alcohoL3 At lower alkylbenzenesulfonate molalities in four-component systems, the symmetry of the boundaries with respect to the alcohol apex vanishes for protosurfactants of higher alkyl substitution. This is illustrated in Figure Ib, in which miscibility boundaries are given for systems of toluene/ 1-butanol/aqueous 1 m solutions of sodium alkylbenzenesulfonates, from benzenesulfonate to 2,5-di-
OC):
(a) 2.5 m sodlum sulfonate; (b)
isopropylbenzeneeulfonate (results given in Table I). These may also be compared with the symmetrical curves in Figure 2, which summarizes previously unpublished results for systems containing toluene, 1-propanol, and aqueous 1 m solutions of substituted benzenesulfonates (results assembled in Table P4C30 There is a distinct displacement of boundary in Figure l b of this paper toward higher alcohol on the toluene-rich side with sodium 2,4,6-trimethylbenzenesulfonate.With cymene and diisopropylbenzenesulfonates, the asymmetry becomes striking, and in the toluene-rich region, the progression to lower alcohol requirement for miscibility with increasing number of alkyl carbons on the protosurfadant is no longer followed. The single-phase systems near the aqueous side (right) of the distorted curves were in some cases opalescent. One difference between the systems of Figures 1and 2 is the 1-propanol and water are completely miscible at 25 "C (see Figure 2 and ref 16), whereas 1-butanol and water are not. However, the asymmetry cannot be explained (16)Baker, E.M. J. Phys. Chern. 1955,59, 1182.
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Ho
The Journal of Physical Chemistry, Vol. 85,No. IO, 7981
T A B L E I: C o m p o s i t i o n s of Toluene/l-Butanol11 m Aqueous Alkylbenzenesulfonate Systems at Boundaries between Oneand Multiliquid Phases (26 “C)
wt % 1s o d i u m sulfonate of benzene
p-toluene
p-ethylbenzene
2,4,64rimethylbenzene
p-cymene
toluene butanol
96.2 90.2 68.2 39.3 29.2 21.3 12.5 3.9 2.0 1.9 1.3 72.2 33.8 30.7 21.2 19.0 17.6 9.1 4.8 0.1 68.1 44.4 33.2 27.4 27.0 16.6 12.4 2.5 0.2 51.8 39.2 28.6 27.9 26.2 21.8 7.4 0.3 79.4 70.1 64.2 55.6 47.2 45.4 42.8 41.9 41.8 39.2 39.0 37.9 37.1 36.9 36.2 34.9 34.8 33.6 33.4 32.0
2.9 9.0 29.3 52.6 59.1 64.3 65.6 62.7 56.5 57.5 45.9 26.2 55.1 56.3 59.4 59.4 58.8 46.1 27.6 0 29.2 46.8 50.4 49.3 49.5 42.4 34.8 16.8 0 41.6 50.1 49.4 47.0 44.8 38.3 17.2 0 19.2 27.5 32.3 39.7 46.4 47.9 50.7 50.7 50.3 43.0 41.8 35.8 54.1 53.6 55.3 55.0 55.2 55.9 35.7 57.2
wt % 1soln
0.9 0.8 2.5 8.1 11.7 14.4 21.9 33.4 41.5 40.6 52.8 1.6 11.1 13.0 19.4 21.6 23.6 44.8 67.6 99.9 2.7 8.8 16.4 23.3 23.5 41.0 52.8 80.7 99.8 6.6 10.7 22.0 25.1 29.0 39.9 75.4 99.7 1.4 2.4 3.5 4.7 6.4 6.7 6.5 1.4 7.9 17.8 19.2 26.3 8.8 9.5 8.5 10.1 10.0 10.5 30.9 10.8
by this difference, at least not completely. Similar distortions in boundaries have been observed with toluene/butyl cellosolve/aqueous sodium p-tert-butylbenzoate systems (Figure 8, ref 17); butyl cellosolve and water are also completely miscible at the temperature of these systems. One of the systems, that containing sodium 2,5diisopropylbenzenesulfonate(hereafterthis compound will be denoted by SDPBS) and l-butanol, was investigated in detail. Limiting Three-Component System. Toluenell-buta(17) Ho, P. C.; Kraus, K. A. “Proceedings”; 1980 SPE International Symposium on Oilfield and Geothermal Chemistry, Stanford University, Stanford, CA, May 1980; SPE 8987, p 125.
s o d i u m sulfonate of
p-cymene
2,5-diisopropylbenzene
t o l u e n e butanol
31.8 31.2 30.6 30.5 30.0 29.3 29.2 28.2 28.0 27.6 27.2 26.4 18.5 13.2 10.0 4.5 1.9 63.6 56.2 54.6 53.1 52.3 48.7 47.7 45.6 45.3 45.3 44.9 44.3 42.6 41.6 40.6 40.4 40.6 37.9 35.6 34.8 34.6 34.6 34.0 34.0 33.6 33.0 32.3 29.9 29.0 27.6 26.9 26.8 26.0 25.6 25.3 24.4 24.3 18.7 6.0
57.1 33.0 33.2 51.5 58.1 31.6 58.2 31.2 58.2 55.8 31.6 54.4 24.6 19.9 17.8 11.4 8.6 32.9 38.4 39.6 41.1 41.5 44.1 44.8 25.6 46.7 30.7 28.2 47.7 24.9 23.9 50.2 50.2 50.1 51.6 53.1 53.8 53.6 53.8 42.1 42.0 21.0 43.0 55.5 46.5 56.8 57.7 56.9 50.5 19.1 56.4 56.8 57.0 56.5 14.1 5.8
soln
11.1 35.8 36.2 18.0 11.9 39.1 12.6 40.6 13.8 16.6 41.2 19.2 56.9 66.9 72.2 84.1 89.5 3.5 5.4 5.8 5.8 6.2 7.2 7.5 28.8 8.0 24.0 26.9 8.0 32.5 34.5 9.2 9.4 9.3 10.5 11.3 11.4 11.8 11.6 23.9 24.0 45.4 24.0 12.2 23.6 14.2 14.7 16.2 22.7 54.9 18.0 17.9 18.6 19.2 67.2 88.2
nol/water phase behavior at 25 “C is available from measurements of Moisio, given in ref 18, and at 30 “C in ref 19. Measurements on the other three are given in Table 111. For l-butanol/SDPBS/toluene, which has only a liquid and solid and a single liquid region, adequate definition for present purposes is believed to be given by the solubility of the organic salt in the alcohol, in the (18) Ho, P. C.; Kraus, K. A,; Johnson, J. S., Jr.; Lietzke, M. H.; Thomas; Moisio M.; Ogden, S. B.; Bumette, R. G.; Hydzik, R. J. Biennial Report from Oak Ridge National Laboratory to Fossil Fuel Extraction/Department of Energy BETC/W26-12 (April 1977-March 1979). (19) Seidell, A,; Linke, W. F. “Solubilities of Inorganic and Organic Compounds”,Supplement to 3rd ed.; D. Van Nostrand: New York, 1952; p 633.
The Journal of Physical Chem;stry, Vol. 85, No. 10, 1981 1449
Phase Boundary Curves I-PROPANOL
(2) 1 0
No-Bcnrcncrulfonatc
--
No p-Tolucncrulfonatc Na p Ethyl bcnrcncrulfonata Na -2.4,6-Trlmclhylbcnzenerulfonate N o -p-Cymrncrulfonatc Na -2,s- Dklsopropyl btnzenc~ultona te
Figure 2. Effect of substituents on phase relations in toluene/l-propanol/aqueous sulfonate systems (1.O m sodium sulfonate, 25
OC).
9-LIQUID S- SULFONATE (C12H4703SNa) H- HYDRATE(C,zH1703SNa 4H20)
c12'1703SN'
A
H
Figure 3. (a) Toluene/l-butanoVwater (25 O C ) . (b) 1-Butanokodium 2,5dilsopropylbenzenesulfonate/toluene(25 O C ) . (c) 1-Butanol/sodlum 2,5diisopropyibenzenesuifonate/water(25 ' C ) . (d) Water/sodium 2,5diisopropylbenzenesulfonate/toluene (25 OC).
hydrocarbon, and in the mixtures of alcohol and hydrocarbon. The sulfonate/ 1-butanol/water and sulfonate/ toluene/water systems were studied in considerable detail. The results are graphically presented in Figure 3a-d. To facilitate discussion, points3 are not shown, and small phase regions are exaggerated (specifically the one-liquid-phase regions near the water apex of toluene/l-butanol/water
(Figure 3a) and near the toluene apex of toluene/water/ sulfonate (Figure 3d) and the narrow H (hydrate/ll (liquid) and ll/S (sulfonate) regions of Figure 3d. Water and 1-butanol have limited miscibility. Because of this miscibility gap, and the nearly complete immiscibility of toluene and water, the phase diagram in Figure 3a is fan-shaped, and there is no plait point. In the
1450
The Journal of Physical Chemistry, Vol. 85, No. 10, 1981
TABLE 11: Compositions of Toluene/l-Propanol/l m Aqueous Alkylbenzenesulfonate Systems at Boundaries between One and Multiliquid Phases (25 "C) wt % sodium sulfonate of benzene
l-protoluene panol
p-toluene
p-ethylbenzene
2,4,6-trimethylbenzene
p-cymene
2,5-diisopropylbenzene
1.6 23.0 23.2 29.7 31.1 33.4 40.4 69.0 92.1 1.1 14.5 16.2 23.1 47.0 49.3 68.4 2.8 6.7 29.3 41.2 41.9 63.8 70.5 3.5 5.8 28.6 31.8 42.3 42.6 46.9 62.1 79.2 3.3 31.0 31.7 62.4 67.9 4.1 8.3 22.9 40.6 46.2 47.3 52.0 53.9 57.4 71.3 79.1
25.4 45.5 46.9 45.8 46.8 46.6 44.9 28.3 6.8 18.5 38.9 39.8 42.1 40.1 38.9 28.2 24.4 30.7 39.4 39.2 38.9 30.3 25.8 20.9 28.4 38.4 38.7 31.1 38.2 36.5 30.8 19.3 16.3 36.2 36.1 30.2 27.2 6.8 17.6 31.0 33.8 33.1 31.8 33.3 30.6 31.2 25.3 18.6
soln 73.0 31.5 30.9 24.6 22.1 20.0 14.1 2.7 1.1 80.4 46.6 44.0 33.6 12.9 11.8 3.4 72.8 62.6 31.3 19.6 19.2 5.9 3.7 75.6 65.8 33.0 29.5 20.0 19.2 16.6 6.5 1.5 80.4 32.8 26.2 7.4 4.9 89.1 74.1 46.1 25.6 20.7 20.9 14.7 15.5 11.4 3.4 2.3
C7H8/SDPBS/C4HgOHsystem (Figure 3b) the solubility of SDPBS is less than 0.05 wt % in toluene and 1.8 wt. % in 1-butanol at 25 "C. Most of the phase diagram is occupied by solid-liquid phase equilibria, which are irrelevant to this liquid-liquid equilibrium study. There is no plait point in this system. Figure 3c shows the C4HgOH/SDPBS/Hz0phase diagram, which consists of three independent heterogeneous binary systems. Two systems have liquid-liquid binodal curves: one on the C4HDOHand H 2 0 edge and one near the SDPBS and HzO edge, marked A in Figure 3c. The rest of the immiscible regions involves either sulfonateliquid or possibly hydrated sulfonate-liquid,20t21or sulfonate-hydrate-liquid equilibria, which are irrelevant to this study. There are two plait points, one for each of the liquid-liquid binodal curves. The compositions of phases in equilibrium of the binodal curve on the C4HBOHand (20) Beilstein, 11, 150. (21) Ho,P. C., unpublished work.
Ho
H2O edge are given in Table 111, obtained by titrating a mixture of sulfonate and water with alcohol. Tie lines in area A are drawn schematically, because of the difficulty of determining the compositions of phases in equilibrium in this area. Figure 3d shows the phase diagram of C7H8/SDPBS/ HzO, which also consists of three heterogeneous binary systems. In the region of liquid-liquid immiscibility, the solubility of toluene in aqueous SDPBS increases rapidly with increasing aqueous concentration.* There is no plait point in this ternary system. Plane Sections for Different Ratios of Sodium 2,5-Diisopropyl benzenesulfonate/ Water. Compositions a t miscibility boundaries from 0.25 to 3.0 mol of SDPBS/kg of H20 are presented in Table IV and graphically in Figure 4a (Figure 4b shows the phase boundary curves on planes with fixed sulfonate/water ratios in a tetrahedron). The asymmetry can be seen to move across the diagram from the water-rich to the toluene-rich region as sulfonate concentration increases, and eventually vanishes a t the highest concentrations. Analogous behavior was observed with the toluene/butyl cellosolve/aqueous sodium ptert-butylbenzoate systems previously menti0ned.l' Three-phase Observations. In order to clarify the asymmetry, we kept samples in the immiscible region under the phase boundary curve in systems containing 1.0 m SDPBS (20.9% sulfonate in water) in a thermostated bath (AO.1 "C)from 2 days to 2 weeks and then studied them. Regions with three liquid phases in equilibrium were found. Figure 5 shows the locations where three liquid phases were found at 25 "C. Table V shows the number of phases coexisting at temperatures of 25,38,45 and 55 "C for samples with indicated compositions. The number of phases and the phase volumes at some fixed total composition and the area of three-phase region all change with temperature. Qpalescence was observed with several compositions. Whether this opalescence occurs because of difficulty in separating phases having similar densities22or because of the proximity of a critical (conS6lUte) point is not clear at present. But a sample with mass fraction composition of C7H8= 32.1, C4HDOH= 45.0, H 2 0 = 18.1, and SDPBS = 4.8 has all three liquid phases present at 25 "C with the middle phase occupying -89% of the total volume. As the temperature increased, the volume of the middle phase decreased; the middle phase volume was 79.8% of the total at 38 "C and 77.3% at 45 OC, while at 55 "C only two liquid phases were present. As the temperature rose, the meniscus between top and middle phases fell and that between middle and bottom phases moved up very slowly, and at a temperature between 45 and 55 "C the diminishing phase vanished, leaving two liquids. Near where opalescence was observed, for two samples with mass fractions C7H8 = 48.2, CIHgOH = 29.8, H 2 0 = 17.4, and SDPBS = 4.6 and C7H8= 49.5, C4HgOH = 26.0, H 2 0 = 19.4, and SDPBS = 5.1 (these mixtures are both located in the three-liquid-phase region over the temperature range 25-45 "C), the interfacial tensions (IFT) between the top phase and bottom phase were measured. For the former, IFT was -0.01 dyn/cm (measured a t 45 "C), and for the latter, 0.05 dyn/cm (measured at 38 OC). Measurements were with a spinning drop apparatus23purchased from the University of Texas. Interfacial tensions of two samples located in the twoliquid-phase region over the temperature range 25-38 "C (22) Francis, A. W. "Liquid-Liquid Equilibriums";Interscience: New York, 1963. (23) Cayias, J. L.; Schechter, R. S.;Wade, W. H. ACS Symp. Ser., 1975, No.8, 234.
The Journal of Physical Chemistry, Vol. 85, No. 10, 1981 1451
Phase Boundary Curves
TABLE 111: Ternary Systems: Compositions a t Boundaries between Phases at 25 "C and Compositions of Phases in Equilibrium wt % system
1-butanol
1-butanol/sodium 2,5-diisopropylbenzenesulfonate/ toluene (boundary between one- and two-liquid phases)
0
29.7 49.8 87.8 98.2
water/sodium 2,5-diisopropylbenzenesulfonate/ toluene (boundary between one- and two-liquid phases)
1-butanol/sodium 2,5-diisopropylbenzenesulfonate/ water (boundaries between one- and two-liquid phases)
8.0
13.5 16.4 29.7 47.8 49.3 55.5 56.0 66.1 71.0 73.6 79.6 30.5 30.9 31.1 36.3 40.6 43.4 49.1 53.3 54.6 59.8 62.0a 73.3 83.2 98.2 0
(boundary between two-liquid and solid phases)
2.4 3.3 4.4 4.7 5.7 6.0 9.5 18.3 19.5 22.6 24.0 24.3 24.4 26.5 26.7 26.9 26.9 26.9 27.0 27.0 27.5 27.8 24.1 24.6 25.3
sulfonate
toluene
99.95 70.0 49.8 11.7 0 0.4 1.1 0.5 1.0 1.5 2.3 0
0
52.5 51.2 46.3 36.1 33.2 30.6 26.4 23.3 22.5 21.3 21.0 12.7 7.0 1.8 20.9 20.8 31.1 28.1 27.3 23.5 32.2 29.0 30.8 30.5 31.3 31.7 33.9 33.0 37.1 35.3 42.4 39.9 42.7 41.4 51.2 41.0 46.9 42.9 36.4 48.6
End point was not sharp.
97.6 93.0 90.5 85.0 81.1 77.7 79.1 92.0 85.2 81.7 67.4 49.0 47.2 41.0 40.8 30.9 26.9 24.8 20.4 17.0 17.5 22.6 27.6 26.2 26.0 24.5 23.4 22.9 19.4 17.0 14.0 16.8 0
79.1 76.8 65.6 67.5 68.0 70.8 62.8 61.5 50.9 50.0 46.1 44.3 41.8 42.6 36.4 38.0 30.7 33.2 30.4 31.6 21.8 31.5 25.3 33.0 39.0 26.1
equilibrium compositions, wt % top phase bottom phase top phase bottom phase top phase bottom phase
water
1-butanol
water
sulfonate
73.6 47.8 71.0 56.0 66.1 55.5
24.8 49.0 26.9 40.8 31.0 40.6
1.6 3.2 2.1 3.2 2.9 3.9
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The Journal of Physlcal Chemlstty, Vol. 85, No. IO, 1981
Ho
TABLE IV: Compositions of Toluenell-Butanol/AqueousSodium 2,5-DiisopropylbenzenesulfonateSystems at Boundaries between One and Multiliquid Phases (25" ) wt % wt % concn of aq concn of aq 1soln mol/kg 1soln mol/kg of H,O toluene butanol soln of H,O toluene butanol soln
0.25
0 0
1.0 1.8 2.4 2.9 3.5 3.7 4.2 4.2 4.6 4.8 5.3 14.6 31.4 37.3 40.5 68.5 0.30
0 0
1.5 2.5 3.2 3.3 3.9 4.3 4.6 5.0 6.1 6.8 7.4 7.9 8.7 11.1 15.8 22.2 27.5 51.1 63.1 0.36
0.50
0 0
1.0 1.7 1.8 2.4 3.4 3.8 4.0 4.1 5.3 5.5 6.3 6.6 7.9 8.1 9.1 9.8 4.1 4.2 4.2 4.5 4.8 4.9 5.0 5.5 7.0 7.3 7.3 9.5 9.9 10.7 11.9 12.8
47.8 73.6 4.7 74.2 7.5 8.6 8.7 9.7 11.1 74.1 74.1 13.1 74.0 70.6 60.0 55.5 52.9 29.1 56.0 71.0 5.1 45.8 7.1 72.2 39.4 9.1 35.9 32.8 72.4 9.8 17.7 12.9 17.1 71.2 69.2 65.4 62.0 44.1 33.8 61.8 66.1 60.0 70.3 4.7 5.5 71.4 7.3 71.2 48.8 5.6 43.3 40.9 10.5 11.9 34.8 14.7 18.4 64.7 6.9 7.0 56.0 70.8 61.4 70.5 71.2 71.7 71.4 71.3 43.9 39.3 71.0 69.3 23.0
52.2 26.4 94.3 24.0 90.1 88.5 87.8 86.6 84.7 21.7 21.3 82.1 20.7 14.8 8.6 7.2 6.6 2.4 44.0 29.0 93.4 51.7 89.7 24.5 56.7 86.6 59.5 62.2 21.5 83.4 74.9 79.2 74.2 17.7 15.0 12.4 10.5 4.8 3.1 38.2 33.9 39.0 28.0 93.5 92.1 25.2 88.9 24.8 47.1 89.1 51.2 52.8 82.9 80.2 57.1 76.2 71.8 31.2 88.9 88.8
39.5 24.4 33.7 24.5 23.3 21.3 21.3 21.4 46.6 50.8 18.3 18.8 64.2
1.5
2.0
13.5 13.8 18.4 23.9 28.6 33.9 35.6 36.1 38.7 40.1 41.2 42.6 53.1 56.1 57.6 78.5 15.3 25.6 32.8 39.7 43.9 46.6 47.7 50.0 52.7 54.3 55.4 56.9 57.3 57.6 58.4 59.7 60.1 61.6 63.2 64.2 65.2 66.4 67.2 67.7 69.2 69.3 70.4 70.6 70.8 71.1 75.6 77.6 82.3 86.7 90.3 92.0 12.1 14.7 16.3 28.5 28.9 32.2 35.9 40.6 44.6 45.9 50.8 53.4 62.7 68.3 73.5 77.3 79.6 80.8
81.8 82.3 82.9
25.4 26.0 67.5 64.6 61.2 58.2 56.3 55.4 54.0 52.6 52.1 50.6 42.2 40.0 38.4 20.6 9.1 13.5 15.2 15.1 15.9 16.0 15.5 16.7 15.8 16.4 16.5 36.1 35.6 36.5 16.7 34.0 33.9 32.8 17.2 17.7 30.1 18.2 28.5 18.1 18.7 26.8 18.8 19.7 26.1 20.7 21.8 20.4 16.2 12.3 9.0 7.5 6.3 6.7 7.5 10.5 12.0 11.3 13.4 13.8 13.8 14.2 13.8 13.1 15.3 13.8 13.0 12.5 11.8 12.1 10.8 11.5 12.1
61.1 60.2 14.1 11.5 10.2 7.9 8.1 8.5 7.3 7.3 6.7 6.9 4.7 3.9 4.0 0.9 75.6 60.9 52.0 45.2 40.2 37.4 36.8 33.3 31.5 29.3 28.1 7.0 7.1 5.9 24.9 6.3 6.0 5.6 19.6 18.1 4.7 15.4 4.3 14.2 12.1 3.9 10.8 9.7 3.1 8.2 2.6 2.0 1.5 1.0 0.7 0.5 81.6 78.6 76.2 61.0 59.1 56.5 50.7 45.6 41.6 39.9 35.4 33.5 22.0 17.9 13.5 10.2 8.6 7.1 7.4 6.2 5.0
Phase Boundary Curves
The Journal of Physical Chemistry, Vol. 85,No.
lo, 1981
1458
TABLE IV (Continued) concn of aq soln mol/kg ofH,O
3.0
toluene
wt % 1butanol
83.5 83.6 84.6 86.2 86.5 89.0 92.2 93.4 26.5 42.9
11.2 13.5 13.4 11.4 11.2 9.7 7.0 6.0 8.1 11.7
a
mncn of aq soln mol/kg of H,O
soln 5.3 2.9 2.0 2.4 2.3 1.3 0.8 0.6 65.4 45.4
wt % 1butanol 11.0 11.0 10.8 10.6 8.0 7.1 5.8 4.6 2.6
toluene 52.1 62.5 64.1 67.2 81.4 85.9 90.8 94.5 97.1
soln 36.9 26.5 25.1 22.2 10.6 7.0 3.4 0.9 0.3
1 -BUTANOL
A
NO-2,S- DIISOPROPYLBENLENESULFONATE ( I ) H20
(21 0 25 m
I31 0 3 0 m 14)
036 m
151 0 5 0 m
TOLUENE
AQUEOUS SOL"
(2) 1 0 m
( 3 ) 1 5 rn (4) 2 0 m ( 5 ) 3 0 m Na-2.5-di1sopropylbcnzcncsulfonorc
( C I ~ H ~ ~ O ~ S N O )
a. - L l O U l D S- SULFONATE
A
Figure 4. Effect of concentration of sodium 2,5diisopropylbenzenesulfonateon miscibility of the toluene/l-butanol/water system (25
OC).
1454
The Journal of Physlcal Chemlstty, Vol. 85, No. 10, 198 1
Ho
1 -BUTANOL SYSTEM TOLUENE~l.0UTANOL-IOmNo.2. 5. DIISOPROPYLLIENZENESULFNATE L 25.C)
-
0OUNOIRY 0ETWLEN ONE- I N 0 MULTI.PH4SE
TWO COEXISTING LIQUID PHlSES
0
THREE COEXISTING LIQUID PHISES
2
00
Z0$a
a
f
N E -
rl
e D
TOLUENE
v
v
v
v
v
v
SOLUTION
Flguro 5. Toluene/ 1-butanol/ 1.O m sodium 2,5diisopropylbenzenesulfonate (25 OC).
were measured with another apparatus." For mass fraction C7H8= 46.3,C4HgOH= 13.5,HzO = 31.8, and SDPBS = 8.4,the IFTbetween top and bottom phases was -0.1 dyn/cm, and for C7Hs = 31.4,C4HgOH= 7.2, HzO = 48.6,and SDPBS = 12.8,it was -0.4 dyn/cm at 38 "C. The slight difference of refractive indexes between adjacent phases in the three-liquid-phase systems and the high temperature sensitivity preclude reliable measurements of the interfacial tensions between top and middle and between middle and bottom phases at present. Some analyses, of the equilibrated phases are given in Table VI, and the volume fraction of each phase is also given in this table. In systems with three liquid phases, in most cases, the percentage volume of the middle phase is more prominent than the other phases. Whenever opalescence exists, the analysis of the phases in equilibrium becomes difficult and material balance is poor. The distribution of sulfonate in each phase of the three-phase system was found surprisingly to be almost equal. The analysis of other components in some of the three-phase systems also has been carried out; however, material balance was poor, and only for one case and only for the percentage of sulfonate are results given. In two-phase systems, the analysis of phases is much easier to perform than in three-phase systems. The volume fraction of each phase and the distribution of sulfonate are mainly dependent on the location of the overall compositions; in toluene-rich regions, the ratio sulfonate to water in the top phase is lower than in the bottom phase, opposite to the systems in regions with less toluene. Mixtures covering most of the area in the immiscible region of the system containing 0.5,1.5,and 2.5 m SDPBS were also studied at 25 OC (results given in Table VII) in order to study the trends as the asymmetry vanished with increasing aqueous concentration. As expected, threeliquid-phase regions can be found in all systems with asymmetrical boundary curves, and they are located mostly near the S-shape sector of the boundary curves. It is interesting that no three-liquid-phase region was found in the system with 2.5 m SDPBS at 25 O C .
2
(24) Gash, B.;Parrish, D.R. J. Pet. Technol. 1977, 29, 30.
E-
00
0
0
h
P
.^
n 4
Discussion The curves of Figures 1, 2, and 4 separate one-liquidphase regions from regions of more than one phase on plane sections, defined by constant sodium sulfonate/water ratios, of the tetrahedron representing concentrations of
F?
o m
c
."."4-0 4
8a
0
Phase Boundary Curves
The Journal of Physical Chemlstty, Voi. 85, No. 10, 1981 1455
TABLE VI: Compositions of Phases in Equilibrium: Toluene/l-Butanol/Water/Sodium 2.5-Diiso~ro~vlbenzenesulfonate (25" C) compositions, wt % phase vol, toluene 1-butanol sulfonate water (vol %) overa11 48.5 29.6 4.6 17.3 top phase 11.1 3.6 88.4 middle phase 5.8 bottom phase 6.2 0.5 overall 32.2 44.9 4.8 18.1 6.9 34.6 44.3 top phase 5.2 15.9 88.9 middle phase 31.1 44.9 19.2 4.8 4.2 0.3 bottom phase 5.3 5.6 88.7 overall 49.5 19.4 5.1 26.0 top phase 4.1 10.6 middle phase 81.2 5.9 bottom phase 6.9 2.3 31.4 overall 7.2 12.8 48.6 top phase 96.4 25.0 2.9 0.3 0.4 11.1 bottom phase 16.5 75.0 7.2 65.2 overall 75.2 14.9 2.1 7.8 top phase 85.9 6.0 0.7 78.3 15.0 14.1 bottom phase 12.0 22.6 13.1 52.3 overall 31.8 8.4 46.3 13.5 top phase 31.2 0.4 86.4 12.1 0.6 bottom phase 68.8 13.2 24.0 14.0 48.8 a IFT = interfacial tension.
A IC4H~OHI
*2
IFTO (top vs. bottom phase), dyn/cm 0.01 (45"C)
0.05 (38"C)
0.395(38"C)
0.112 (38"C)
D(HzO)
Flgure 6. Schematic illustration of coexisting three-liquid phases in the isothermal compositlon tetrahedron.
the four components in the total system. The compositions of the liquid phases, when more than one are present, will not in general be found on the plane sections; i.e., tie lines cannot be drawn on the planes. Except at singular points, the boundary curves will be between one-liquid-phaseand two-liquid-phase regions. One exception would be at a tricritical point, an improbable occurrence. Another would be at the juncture of two two-liquid-phase regions, the composition on the boundary curve being the composition of a liquid phase common to the two regions. An infinitesimal composition difference might exist between one and three phases at such a point, which should correspond to an indentation on the boundary curve. Opalescence in the single phases in regions where three phases were observed close to the boundary curve (Figure 5) makes its location somewhat uncertain and blurs indications of possible indentations. A complete definition of the system would require the determination of large numbers of the compositions of phases in equilibrium with one another, or equivalently the tie surfaces. With the limited results reported here, a discussion of the relationship between the phases seen
in the limiting three-component systems on the tetrahedron faces and the miscibility boundaries in the fourcomponent plane sections, in particular the three-phase regions near the asymmetric boundaries, may be of interest. In this regard, the 1-butanol/sodium diisopropylbenzenesulfonate/water (Figure 3c) and the toluene/lbutanol/water (Figure 3a) are the most interesting. In Figure 3c, there are two liquid-liquid two-phase regions, with plait points, which should be the origin of quaternary consolute curves in the interior of the tetrahedron when toluene is present. Only a single liquid-liquid region is seen in Figure 3a, with no plait points. From Figure 5, there is a volume in the interior of the tetrahedron, cut by the 1 m sulfonate plane section, which represents compositions at which three phases coexist. A possible representation of the three-phase space, which suggests relationships to the phase diagrams of the tetrahedral faces, is shown schematically in Figure 6.25 (25) Private discussion with Professor John E. Ricci.
1456
The Journal of Physlcal Chemistry, Vol. 85, No. 10, 1081
Ho
TABLE VII: Compositions of Toluenell-Butanol/Aqueous Sodium 2,6-DiisopropylbenzenesulfonateSystems in Immiscible Multiphase Region at 26 “C concn of aq compositions, wt % phase volume,a vol % soln, mol/kg of H,O toluene 1-butanol soln no. of ohases t m b 0.5 5.0 65.2 29.8 2 99.1 0 0.9 9.2 51.9 38.9 2 83.7 0 16.3 9.9 30.1 60.0 2 95.9 0 4.1 10.3 54.5 35.2 86.4 0 13.6 35.1 15.0 49.9 28.6 47.6b 22.8 45.0 15.0 40.0 66.7 24.4 8.9 15.1 25.1 59.8 12.5 0 87.5 15.1 64.9 20.0 97.9 0 2.1 29.0 15.2 55.8 14.6 0 85.4 19.9 33.0 47.1 43.2 11.4b 45.4 20.0 20.0 60.0 3 12.5b 12.5 75.0 41.3 23.6 35.1 3 26.7 10.0 63.3b 30.0 2 5.0 65.0 17.1 0 82.9 35.0 20.0 45.1 43.2 0 56.8 35.0 45.0 20.1 86.5 0 13.5 40.0 15.1 44.9 45.4 0 54.6 55.0 34.9 10.1 57.5 0 42.5 55.0 39.0 6.0 99.0 0 1.0 59.7 25.4 14.9 84.4 0 15.6 59.8 15.3 24.9 71.7 0 28.3 70.0 15.1 15.0 85.1 0 14.9 75.0 20.0 5.0 2 96.8 0 3.2 80.3 9.7 10.0 2 0 89.4 10.6 89.4 5.3 5.3 2 96.7 0 3.3 1.5 14.9 5.1 80.0 2 3.2 0 96.8 29.9 10.0 60.1 2 0 9.1 90.9 46.0 13.0 41.0 2 0 23.5 76.5 55.3 36.5 1 or 2 (fuzzy) 8.2 62.0 32.0 1 or 2 (fuzzy) 6.0 66.7 15.0 19.3 . 1 (fuzzy)b 71.0 4.1 25.0 2 62.5 0 37.5 71.0 25.1 3.9 1 (fuzzy)b 15.8 11.9 72.3 3 10.6 87.2 2.2b 74.0 19.0 3 7.0 96.7 O.lb 3.2 79.6 16.9 3.5 99.0 2 0 1.0 83.7 7.0 9.3 2 15.2 84.8 0 84.8 10.1 5.1 2 93.0 7.0 0 2.5 24.9 9.4 65.7 2 37.1 57.8 5.1 2 44.8 11.3 43.9 2 56.9 38.0 5.1 65.1 24.9 10.0 75.0 18.0 7.0 78.6 15.4 6.0 15.4 83.2 1.4 10.1 83.7 6.2 88.9 4.9 6.2 2 89.2 9.3 2 1.5 94.7 2.0 3.3 2 t = top phase; m = middle phase; b = bottom phase. Opalescence.
The ternary face of Figure 3c is the origin of two quaternary two-liquid spaces entering the tetrahedron, one from each of the binodal areas of Figure 3c. Each such space carries a quaternary consolute curve originating from a plait point of Figure 3c. The quaternary three-liquid equilibrium space, which is entirely inside the tetrahedron, arises from contact and interpenetration of the two twoliquid spaces. One special contact (“E”) involves the quaternary consolute curve l2 = l3 from the ternary plait point 1;a similar special contact (“F’) involves the quaternary consolute curve l1 = l2from plait point 2. At E, the quaternary consolute liquid (12 = 13) comes into equilibrium with the liquid l1, giving rise to a triangular equilibrium l1+ l2 13;at F the quaternary consolute liquid (11 = 12) curves into equilibrium with the liquid l3giving rise to a triangular equilibrium l1 + l2 + 13. Between the two limiting line-equilibria, (12 = 13) + l1 at E, and (11 = 12) + l3 at F, there is a three-liquid space, generated by planar triangles of three coexisting liquids,
+
l1 + l2 + 13. These triangles are not parallel to each other; and they collapse to lines, at E and at F. Each of the coexisting liquids, l1 + l2 + 13,generates a curve which, on an arbitrary plane section of the tetrahedron, is a point of indentation on the “phase boundary” curve of the section, the boundary between homogeneous and heterogeneous systems. An arbitrary plane section of the tetrahedron, such as Figure 5, cuts the three-liquid space (11 + l2 + 13) at three points: a on curve 11, b on curve 12,and c on m e 1%These points are the indentations on the “phase boundary” curve of the plane section. The three points (a, b, and c) are not three coexisting liquids, but they delimit a region of the plane section in which three coexisting liquids are observed. A composition x in this region of the plane section gives the three phases 11, 12,and 13, but the compositions of the coexisting liquids are not on the plane section. In general, different compositions x on the plane section give different seta of compositions of the three liquids.
J. Phys. Chem. 1881, 85, 1457-1460
On the arbitrary plane section, a liquid on the “phase boundary” curve is in equilibrium with a second liquid which is not on the same section. A liquid a t one of the indentations (a, b, c) is in equilibrium with two other liquids, with compositions not on the section. For compositions in the three-phase region (“inside” the points a, b, c) two of the phases approach identity as they approach the limiting line-equilibrium, E for (12 = 4) + 11, F for (I1 = 12)+ l3 Near E or near F, critical opalescence may be expected. Any opalescence observed in sets of two or three coexisting liquids not near E or F would arise from lack of separation of liquid phases because of similar densities.22 The loci of the four-component critical relations are unclear at present. But it is likely that the course of the consolute curves from the plait point for 11-12 (binodal curve on C4H90Hand H20 edge) on Figure 3c will pass through part I of the S-shaped curve of the hump in Figure 5 (and in Figure 4b), and the course of consolute curve from the plait point for l2-I3 (binodal curve A in Figure 3c) will pass through part I1 of the S-shaped curve. The low interfacial tensions (in the range of 0.01 dyn/cm) in these regions, mentioned before, is one indication of a critical point being approached. Whether opalescence seen at compositions near the asymmetrical boundary curve is due to the approach to critical (consolute) relations or due to lack of separation of liquid phases is not certain at present. The loci of the two consolute curves are also not defined, but the loci of consolute curves will affect the direction of tie lines in three dimensions and eventually will affect the shape of the phase boundary curves on certain plane sections in the tetrahedron. Where we see no opalescence and find no
1457
three-liquid-phase equilibria, i.e., in the aqueous-rich region in systems studied here, the size of the one-phase region increases rapidly with increasing SDPBS (or tert-butylbenzoate) concentration owing to the rapid increase of miscibility of toluene and l-butanol in the sulfonate (or benzoate) solution. It would be of interest to elucidate the tie lines of quaternary systems, the loci of the critical points at a number of aqueous concentrations at fixed temperatures, to measure the interfacial tensions between coexisting phases, and to locate “tricritid points”, (if there are any). For a tricritical point to occur, the two consolute curves must meet, an occurrence which appears improbable. It is possible, however, that at some temperature, in one of the arrays of similar systems having asymmetric boundaries on plane sections containing different alkylbenzenesulfonates or -carboxylates and alcohols (and possibly hydrocarbons), such a point may occur. Much additional work would obviously be necessary to establish it, and the results obtained to date are believed to be of enough interest to report as they stand. Acknowledgment. I am very much indebted to Professor John E. Ricci of New York University for many helpful suggestions and discussions and to Dr. J. S. Johnson, Jr., Dr. K. A. Kraus, and Dr. F. Dowel1 of the Oak Ridge National Laboratory Chemistry Division for suggestions, discussions, and encouragement during the writing of this paper. This research was sponsored by the Division of Chemical Sciences, Basic Energy Sciences, US.Department of Energy, under contract W-7405-eng-26 with the Union Carbide Corp.
Transport through Liquid Membranes Generated by Cholesterol R. C. Srivastava” and R. P. S. Jakhar Chemlstty Department, Blrk Instituie of Technology and Scbnce, H&n/-33303 1, RaJasthan, Indb (Received: September 6, 1980; In Final F m : February 9, 198 1)
The experiments on hydraulic permeability, electroosmoticvelocity, streaming potential, and current reported in this communication demonstrate that cholesterol, which is an effective surfactant when added to water, generates a surfactant-layerliquid membrane at the interface. At or above the critical micelle concentration (cmc) of cholesterol, the interface is completely covered with the liquid membrane, while below the critical micelle concentration it is only partially covered. The interface used in the present study was a cellulose acetate microfiitration membrane/water interface. Experiments have also been designed to demonstrate the formation of cholesterol bilayers.
Kesting’s liquid-membrane which was originally propounded to account for the enhanced salt rejection in reverse osmosis due to the addition of surfactant additives to saline feed, has also been shown4to (1)R. E. Kesting, A. Vincent, and J. Eberlin, OSW R and D Report no. 117,Aug 1964. (2)R. E. Kesting, Reverse-Osmosis Process Using Surfactant Feed Additives, OSW Patent Application SAL 830, Nov 3,1965. (3) R. E. Keating, W. J. Subcasky, and J. D. Paton, J. Colloid Interface Sci., 28, 166 (1968). (4)R. C. Srivastava and Saroj Yadav, J. Non-Equilib. Thermodyn., 4,219 (1979). 0022-3654/81/2085-1457$01.25/0
be of significance in the systems of biophysical interest. Cholesterol,though very slightly soluble in water, has been shown6$to lower considerably the surface tension of water. Cholesterol has a maximum s o l ~ b i l i t y ~of* ~4.7 pM in aqueous solutions, and the measured surface tension6 of its saturated solution in water is -33 dyn/cm. Its cmc (5)N. L.Gershfeld in “Methods in Membrane Biology”,Vol. 1,E. D. Korn, Ed., Plenum Press, New York, 1974,Chapter 2. (6)N. L.W e l d and R. E. Pagano, J. Phys. Chem., 76,1244 (1972). (7)M. E.Haberland and J. A. Reynolde, Roc. Natl. Acad. Sci. U.S.A., 70,2313 (1973). (8)M. K. Jain, Curr. Top. Membr. Tramp., 6,l-67 (1975).
0 1981 American Chemical Society
