2136
Langmuir 1992,8, 2135-2139
Thermodynamics of Microemulsion Formation. 1. Enthalpy of Solution of Water in Binary (Triton X 100 Butanol) and Ternary (Heptane + Triton X 100 Butanol) Mixtures and Heat Capacity of the Resulting Systems
+
+
S. P. Moulik,' M. L. Das, and P. K. Bhattacharya Department of Chemistry, Jadavpur University, Calcutta 700 032, India
A. R. Das Polymer Science Unit, Indian Association for the Cultivation of Science, Jadavpur, Calcutta 700 032, India Received February 22, 1991. In Final Form: May 12,1992
The enthalpies of solutionof water in binary mixturesof Triton X 100 (TX 100) and butanol and ternary mixtures of TX 100,butanol, and heptane as well as the heat capacities of the resulting ternary (TX 100, butanol, and water) and the quaternary (heptane, TX 100,butanol, and water) mixtures were measured. The enthalpy changes to form solvated mixed TX 100 and butanol and stable microemulsions, holding maximum water (expressed per mole of water addition), were essentially negative. The measured heat capacities were greater than the calculated heat capacities based on ideal mixing. The results indicated interactions among the components, leading to the formation of internally organized media, contributed by the deaggregation and solvation of the amphiphiles. Introduction The multicomponent compositions of microemulsions make the systems complex. The componentscan undergo various specific and nonspecific interactions leading to equilibrium states having isotropic, thermodynamically stable solutions of different consistencies. The dispersions can be water in oil, oil in water, and water and oil both in comparable proportions (bicontinuous) with variable internal structures. Under the condition of low water content, the surfactant and cosurfactant form aggregates which dissociatewith increasing water addition and orient on the surface of the microdroplets, stabilizing the dispersion. The recent and past literature have witnessed thrust on the phase-forming behaviors of ternary and quaternary microemulsion-forming solutions,l+ elucidation of their internal structure and dynamic behavior,'-1° and their uses as liquid membranes11-14 and reaction media.1518 The thermodynamic studies on the formation (1) Bourrel, M.;Schechter,R.S.MicroemulsionsandRelatedSystems; Marcel Dekker, Inc.: New York and Basal, 1988. (2) Shinoda. K. Roe. Colloid Polvm. Sci. 1983. 1 . 68. (3) Ghosh, 0.;Mill&, C. A. J. Phis. Chem. 1987,'91, 4528. (4) Friberg, S. E. Colloids Surf. 1982,4, 201. ( 5 ) Bisal, S. R.; Bhattacharya, P. K.; Moulik, S. P. Indian J. Chem. 1989, B A , 550. (6) Bisal, S. R.; Bhattacharya, P. K.; Moulik, S. P. J. Surf. Sci. Technol. 1988,4,121. Das, M. L.; Bhattacharya, P. K.; Moulik, S. P. Colloids Surf. 1990, 49, 247. (7) Gulari, F.; Bedwell, B.; Alkhafaji, S. J.ColloidInterface Sci. 1980, 77, 202. (8) Kotlarchyk, M.; Huang, J. S.; Chen, S. H. J.Phys. Chem. 1985,89, 4382. (9) Lang, J.; Jada, A., Malliaris, A. J. Phys. Chem. 1982, 92, 1946. (10) Bisal, S. R.; Bhattacharya, P. K.; Moulik, S. P. J. Phys. Chem. 1990,94, 350. (11) Xenakis, A.; Tondre, C. J. Phys. Chem. 1983,87,4737. (12) Tondre, C.; Xenakis, A. Faraday Discuss. Chem. SOC.1984, 77, 771. (13) Xenakis, A.; Tondre, C. J. Colloid Interface Sci. 1987,117,442. (14) Tondre, C.; Xenakis, A. J. Colloid Polym. Sci. 1982, 260, 232. (15) Letts, K.; Mackay, R. A. Inorg. Chem. 1975,14, 2993. (16) Bunton, C. A.; Buzzaccarini, F. J. Phys. Chem. 1981, 85, 3139.
(17)Schomacker, R.; Stickdorn, K.; Knoche, W. In Reactions in Compartmentalized Liquids; Knoche, W., Schomacker, R., Eds.; Springer-Verlag: Berlin and Heidelberg, 1989.
behavior of microemulsions and the energetics of the interaction of the componentsare comparatively rare. The single and multiphase formation of microemulsions and their internal structure and particle aggregation are vital pieces of information necessary for their preparation, application, and use. But the knowledge of their internal arrangement, structure, and interaction need augmentation through thermodynamic studies. Although the complex nature of microemulsions has restricted rapid growth of the thermodynamic status, several direct calorimetric studieshave appeared in recent literature. Kertes et al.1B-22 have made systematic studies on the enthalpy of mixing of soap, alkanols, and oil in binary as well as ternary combinations and have attempted to analyze the resulta in the light of probable interactions at the molecular level. Partial molar enthalpies of water and surfactant in pentaethylene oxide dodecyl ether/hexadecane/water have been determined by Olofsson et alSz3Their interest centered around the interaction of water with the polyethylene oxide groups in the form of a microemulsion. Roux-Desgranges et aLZ4have reported the heat capacities of toluene in the water/dodecyl sulfate/ 1-butanol/toluene microemulsion. They have observed a large change in the apparent molal heat capacity of toluene in the aqueous end, whereas the changes are more gradual toward the toluene end. The good prospect of calorimetric studies on microemulsion-forming systems and relatively less abundant physicochemical investigations on the water/Triton X 100 (18) Das, M. L.; Bhattacharya, P. K.; Moulik, S. P. Langmuir 1991,7, 636. (19) Kertes, A. S.; Chaston, S.; Lai, W. C. J. Colloid Interface Sci. 1980, 73, 94. (20) Kertes, A. S.; Lai, W. C. J. Colloid Interface Sci. 1980, 76, 48. Ibid. 1980,1, 197. (21) Lai, W. C.; Kertes, A. S. Colloids Surf. 1982, 4, 379. (22) Kertes, A. S.; Tsimering, L.; Garti, N. Colloid Polym. Sci. 1985, 263, 67. (23) Olofsson, G.; Kizhing, J.; Stenius, P. J. Colloid Polym. Sci. 1986,
,,, n&LO. ro
111,
(24) Rous-Desgranges, G.; Roux, A. H.; Grolier, J. P. E.; Viallard, A. J . Colloid Interface Sci. 1981, 84, 536.
Q743-7463/92/2408-2135$Q3.QQ/Q0 1992 American Chemical Society
Moulik et al.
2136 Langmuir, Vol. 8, No. 9,1992 (TX 100)/butanoUheptanesystem have prompted us to do this investigation. The enthalpies of solution of water in the binary mixtures of TX 100 and butanol and the ternary mixtures of TX 100, butanol, and heptane have been measured together with the heat capacities of several mixtures near the threshold limits of water addition to yield stable single-phase microemulsions. The results are presented and discussed in what follows.
S'CS
Experimental Section Materials. The materialsn-heptane (Hp),Triton X 100 (TX loo), and butanol (Bu) used were the same as reported earlier.s.8 Doubly distilled conductivitywater (specific conductivity 2-3 S cm-' at 30 OC) was used for the preparations and mixing. Apparatus. A Tronac Model 458 automatic titration calorimeterwas used for calorimetric measurements at a temperature of 25 O C . The calibration of the apparatus was checked by measuring the enthalpy of reaction of hydrochloric acid and sodium hydroxide. The accuracy of the calorimeter was 0.5% on 2 cal. For heat capacity measurements,the thermistor constant was determined by comparing the heat absorbed by known amounts of a pair of pure liquids (water and heptane) taken in the reaction vessel. Procedure. The reaction vessel was charged with 25 mL of the titrant mixture, and the buret was fded with the titer (water). The whole system was immersed in the 60-L-capacitywater bath maintained at a temperature of 25 k 0.0002 "C by a Tronac PTC probe. When the thermal equilibrium was reached, the titer was delivered in the titrant mixture at the rate of 0.316 mL/min under a constant-stirring condition. The heat change was recorded in equivalentsof millivolts on a Houston Instrument's Ominscribe D5000 strip chart recorder with time and processed in the usual manneP* to convert into enthalpychanges. The heat capacities of the mixture before and after titration were determined, and the mean was used in the calculation of enthalpy. In each experiment,a definite quantity of water in the range 0.1-1.5 mL was added from the buret to 20 mL of a mixture of either TX 100 and Bu or TX 100, Bu, and Hp under constant stirring and the heat evolved was estimatedby the procedure describedabove. A 20-mL sample of the binary or ternary mixturecontained 0.030.3 or 0.12-0.19 mol of components, respectively,to which 0.0060.08 or 0.005-0.06 mol of water was added, respectively. The measured enthalpieswere, therefore, integral quantities. Allthe mixing compositions were made to fall slightly above the phase boundary line (Figure 1). The solutions were, therefore, homogeneous and isotropic. We observed that a minor shift toward the biphasicside hardlyaffectedthe courseof the thermochemical runs. On the basis of the following principle, the absolute heat capacities of the microemulsions were determined. A known quantity of heat was sent into the solution with the help of the calibration heater, and the change in temperature was recorded in millivolts. Using the thermistor constant (Tk= 0.032 894 "C/ mV) and appropriate correction for the low heat capacity of the reaction vessel, the heat capacityof the solution was found. This was expressed in joules per mole of the solution.
Rssults and Discussion In Figure 1,the triangular phase diagram of the water/ TX 100/Bu/Hp system at 25 OC is presented. The open circles along the phase boundary line indicate the compositions at which heat capacities were measured. The full circles represent compositions at which enthalpies of solution of water in TX lOO/Bu/Hp were determined. In constructing the diagram, s (surfactant) and cs (cosurfactant) were kept fixed at a 1:l ratio (w/w). The concentrations in the diagram are expressed in weight percent. (25) Hopkins, H.P., Jr.; Jahagirdar, D. V.; Moulik,S. P.; Aue, D. H.; Webb, H.M.; Davidson, W. R.; Pedley, M.D. J. Am. Chem. SOC.1984, 106,4341. (26) EBtoyh, D. J.; Christensen, J. J.; Izatt, R.
M.Erperiments in Thermometnc Titrimetry and Titration Calorimetry; Brigham Young University Press: Provo, UT, 1974.
loo%/
Y
Y
Y
Y
Y
"
Y
Y
Y
\ loo'/. 0
W
Figure 1. Triangular phase diagram of the (TX100 + Bu)/ heptane/watersystem at 25 OC, s:cs = 1:l (w/w). Open and closed circles represent compositions for heat capacity measurements. Enthalpy of solution runa were conducted for closed circle compositions.
I
'7 0-001 nu/ "S+CS)
Figure 2. Heat capacity of the ternary TX 100/Bu/water system vs %/%+a profile at 25 OC: curve 1,calculated by eq 1; curve 2, experimental C, vs %/n,+,; curve 3, profile at 25 O C .
Heat Capacities of Ternary and Quaternary Mixtures. The heat capacities Cp of ternary TX 100/ Bu/water mixtures at a 1:ls:a ratio (w/w), at different mole ratios of water and s + cs, i.e., ndna+cs,and expressed per mole of the mixture are presented in Figure 2 along with the heat capacities ( C p ) d ccalculated by eq 1where ni is the number of moles of the ith component of molar heat capacity, (Cp)i.
Both (Cp)oband ( C p ) d c decrease with the calculated heat capacities are fairly lower than the correaponding experimentalvalues (Table I). The dgerence, i.e., ACp = (Cp)obe- ( C p ) d csteadily increases with the mole ratio of water and s + a. The decreasing trend in the heat capacity shown in the figure is a direct consequence of the lower molar heat capacity of water than those of both TX 100 and Bu; the overall values of course include the structural and interactional contributions in the mixture. Increased solvent structure by way of solvation, aggregation, orientation, etc. is accompanied by increased heat capacity. The extents of the molecular
Langmuir, Vol. 8, No. 9,1992 2137
Thermodynamics of Microemulsion Formation Table I. Heat Capacity. per Total Amount of Quaternary Mixtures in the Form of Microemulsions at 298 I( C,/ (J K-1 mol-') mol % (wt %) compositions ~~
sample 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
water 2.9 (0.5) 5.8 (1.0) 8.4(1.5) 10.9 (2.0) 11.0 (2.0) 15.7 (3.0) 16.0 (3.0) 20.0 (4.0) 20.4 (4.0) 24.5 (5.0) 24.7 (5.0) 26.9 (8.0) 34.9 (8.0) 48.6 (13.0) 61.5 (20.0) 81.4 (40.3) 84.8 (44.1) 89.2 (53.2)
s+cab oil 19.1 (25.5) 78.0(74.0) 22.4 (29.0) 71.8 (70.0) 21.6 (28.5) 70.0 (70.0) 22.3 (30.0) 66.8 (68.0) 26.6 (33.0) 64.4 (65.0) 23.3 (33.0) 61.0 (64.0) 26.3 (37.0) 57.5 (60.0) 27.3 (39.0) 52.7 (57.0) 25.6 (37.0) 54.0 (59.0) 24.5 (37.0) 51.0(58.0) 26.7 (40.0) 48.6 (55.0) 25.0 (38.0) 48.1 (56.0) 23.9 (42.0) 39.8 (50.8) 15.9 (42.0) 30.5 (45.0) 18.0(43.0) 20.5 (37.0) 8.9 (33.5) 9.6 (26.2) 12.4 (47.8) 2.8 (8.1) 10.1 (44.3) 0.7 (2.5)
Standard deviation of (Cp)ob14.6%. ratio (w/w).
&/no 27.00 12.40 8.30 6.30 5.85 3.85 3.70 2.64 2.63 2.10 1.97 1.80 1.16 0.63 0.33 0.12 0.033 0.008
obs 232 238 227 225 224 240 240 257 255 247 249 242 195 177 141 109 96 91
cdc 222 223 219 215 216 208 208 202 201 194 195 190 155 130 133 99 95 87
s + cs composition, 1:l
300 r
Figure 4. Heat capacity profile along the triangular phase boundary curve at 25 O C : open circles, experimental; closed circles,calculated. The lengths of the vertical lines designate C, values aa per the ordinate scale.
Y
11
100
1
0
I
2
4
6
8
1 0 1 2 1 4
"/!v
Figure 3. Profiie of heat capacity vs oikwater ratio for the quaternary TX 100/Bu/Hp/water system at 25 O C : curve 1, calculated by eq 1; curve 2, experimental.
and structural interaction, etc. are revealed in the magnitude of ACp which is positive and steadily rises with water content, revealing onward structure formation and aggregationin the mixture (Figure 2). Dipolar interactions among the ethylene oxide groups of TX 100, the hydroxyl group of Bu, and water contribute to this effect along with the hydrophobic interaction. The heat capacities of the quaternary mixtures (microemulsions) marked along the phase boundary line in Figure 1 indicate that the change in composition from a water-continuous to an oil-continuous state results in an increasedheat capacity (curve 2, Figure 3). The calculated values (curve 1)are all lower, and the difference becomes more prominent at o:w (oikwater) compositions of 2-3, where the microemulsion texture tends to become bicontinuous. This is a reflection of the internal structural changes of the microemulsion on the heat capacity. The bicontinuous microemulsions having stabilization by way of oriented amphiphiles toward both oil and water have a considerably organized microstructure and higher observed specificheat. The heat capacities are profiled with the compositions of the phase diagram in Figure 4; the contours demonstrate a visual revelation of the sway of (Cp)obs with phase boundary compositions of the quaternary system. The ups and downs of the heat capacity in the diagram are commensurate with the alteration of the internal structure of microemulsions. In conformitywith expectations, the deviations are minimums toward the oil and water ends.
.
I
4oooi I
;\\-*4 \ o
3000 124000
I
*'
A
A
1000 8000,' /
/
I
J
020
040
060
080
100
120
"w/qs+ CS) Figure 5. Enthalpy of solution of binary and temary mixtures at 25 OC plotted against %/ne+=: curve 1, TX 100/Bu/water, ordinate scale I; curve 2, TX 100/Bu/Hp/water, ordinate scale 11. The AHevalues are expressed in joules per mole whereas they are given in kilojoules per mole in Table 11.
Integral Enthalpy of Solution AHe of Water in Binary and Ternary Mixtures. The thermograms of the enthalpy of solution showed a steady rise in the exothermic heat from the start of water addition to the end. The AHH,declined with an increased w:o ratio in the final mixture. In Figure 5 , enthalpies of solution of water in TX loo/ Bu as well as in TX 100/Bu/Hp are presented. These representative illustrations show the exothermicity of the solution process as a function of composition. The AHH, for the binarymixtures has a systematicrise with increased nw/ns+cs, that is, with increased water content. AH8values are presented in Table 11. The AHsfor the ternary mixtures have shown a reverse trend compared to the binary
Moulik et al.
2138 Langmuir, Vol. 8, No.9, 1992 Table 11. Integral Enthalpy. of Solution of Water in Binary (TX 100/Bu) and Ternary (Hp/TX IOO/Bu) Mixtures, Forming Microemulrionrb at 298 K ndn, n,llh+r. -MJ(kJ mol-') Binary System
27.00 (1) 8.30 (3) 6.30 (4) 3.85 (6) 3.70 (7) 2.63 (9) 2.10 (10) 1.80 (12)
0.07 0.13 0.21 0.30 0.40 0.51 0.62 0.73 Ternary System 0.15 0.40
2.61 5.36 7.44 9.57 10.91 12.18 13.31 14.32 3.60 3.16 3.22 2.85 2.93 2.71 2.37 2.14
0.50 0.60 0.66 0.80 1.00 1.10
*
Standard deviation of AH8 +3.4%. Numbera in parentheses in column 1 correspond to the sample numbera in Table I. LOO0 r 3
3000
I
I/
1000
15
25
35
4.5
1.60kJImol of added water. The exothermicenthalpy of solvation of both TX 100and Bu surpasses the endothermic enthalpy of deaggregation of both TX 1001TX 100 and TX 100IBu species, providing resultant increasing negative AH0 with an increased molar content of water. The nature of variation of the resultant AH0 in the presence of oil is opposits; the AH0 expressed per mole of water addition at low in the presence of maximum oil is a maximum. With a decreased percentage of oil, even though n w / ~ + cincreases, a the AH, systematically decreases. The overall AHBis, however, much lees (nearly one-fourth) than that in the absence of oil. In a microemulsion, water molecules in the micropools have access to undergo solvation interactions with interfacial TX 100 and Bu and to release heat. This is associated with the endothermic enthalpy of deaggregation of oil, where the extent of amphiphile aggregation is greater. All these effects combined together lead to the decline of the exothermic enthalpy of dilution of the microemulsion. For all the compoeitions,the loweringof AH, in part ale0results from the distribution of Bu in oil which becomes inaccessible to the water molecules. (At 25 "Conly 7% (vlv) Bu is soluble in water, resulting in a high distribution constant of Bu between heptane and water.) The results in Tables I and I1 for the quaternary microemulsion systems show a maximum in C, at 20.4125.61 54 mol% of w/s+cs/Hp (cf. Figure 3). The AH, values do not show a maximum or minimum at any composition; the values systematically decline with an increased percentage of water. The maximum in C, corresponds to the formation of an internal structure in the mixture, which hardly affecta AH,.The internal arrangement(orientation and adsorption, etc.) contributes a minimum to AH,; the enthalpy of solution is entirely guided by the enthalpy of deaggregation of the amphiphiles (TX 100 and Bu) and their solvation. The measured integral heats of solution (Qml) in the calorimeter resulted from combined contributions of the heat of deaggregation @dag), hydration (Qhyd), and organization (Qorg) of the amphiphile components such that
" 1 ~lS'CSI
Figure 6. Three-dimensionalprofile of AH,,n&,+,, and n,,/ ne+, at 25 OC. Points 1-8 represent74% ,70%,68%, 64% ,60% , 59%,58%, and 56% oil (w/w).The lengths of the vertical lines designateAHBvalues as per the ordinate scale expressed in joules
Qmi
(27) Gupta, S.; Dae, A. R.; Moulik,5. P. Can. J. Chem. 1989,67,356.
+ Qhyd + Qorg
(2)
Both Q,, and QdW are difficult to estimate so that they are lumped together to give
per mole.
mixtures; the values are also considerably lower. The presence of oil has entirely changed the pattern and direction of the associatedheaG the variation is fairly linear. In the mixed state, both TX 100 and Bu can undergo dipolar interactions, forming associated species which are solvated by water molecules and also by dipolar interactions. It is known that in the form of amicelle polyethylene oxide can be considerably hydrated.27 With addition of water, the overall enthalpy comprises (1)the endothermic enthalpy of dissociation of the molecular aggregates present in the TX 100and Bu mixture, (2) the exothermic enthalpy of hydration of TX 100 and Bu, and (3) the enthalpy of interfacial adsorption and orientation of amphiphiles or the enthalpy of organization. The resultant AH,is negative. The enthalpy of solution of water in the binary TX 1001Bu system at different compoeitions of n,dlzs+ca presented in Figure 6 reveals that the AHH, continuously increases with increasing with a leveling effect. At a ratio of 1:1, the resultant AH,is nearly
Qdagg
Qsi= (Qdagg
+ QorJ + Qhyd
(3)
Evaluation of Qhyd can thus help to estimate Qw+ Qoq from Qml.The Qhyd has resulted from the hydration of both TX 100 and Bu. TX 100 has on the average 9.5 enthylene oxide (EO) residues and 10.5 oxygen centers in the molecule. According to recent literature each EO group in a polyethylene oxide moiety can accept 1-4 molecules of water. A hydration nutnber of 5 or more was also reported in the past.32 It has been recently r e p ~ r t e d that ~ ' ~while ~~ polyethylene glycols (PEG)of lower molar masses accept nearly two molecules of water per EO group of oxygen center, each oxygen center of TX 100 in the form of a micelle is associated with four molecules of water. The (28) N k n , P. G.; Lindman, B. J. Phys. Chem. 1983,87,4766. (29) Guveli, D.E.; Davis, S. S.;Kayee, J. B. J. Colloid Znterfoce Sci. 1983,91, 1. (30) Michael, J. H.; Stephen, M.I. J. Chem. SOC.,Faraday Dane 1 1991,87, 3671.
(31) M i y d , Y.;hfataura, H. Bull. Chem. Soc. Jpn. 1991,154, 288. (32) Kaatze, U.; Gottman, 0.;Podbieleki, R.; Pottel, R.; Terveer, U. J. Phys. Chem. 1978,82,112. (33) Bisal, S.; Moulik, S. P. J. Phys. Chem. 1990,94, 4212.
Thermodynamics of Microemulsion Formation
Langmuir, Vol. 8, No. 9, 1992 2139
Table 111. Different Thermal Terms for the Solution of Water in Hp/TX lOO/Bu, Forming Microemulsions at 298 K nwX1103
eamule’ 1 3 4 6 7
9 10 12
added 4.04 12.46 16.62 25.45 25.90 34.90 44.14 50.90
resdb(TX1OO) - Q d J 73.1 (22.8) 81.7 (27.2) 86.9 (29.00) 97.4 (32.50) 110.5 (36.80) 111.8 (37.30) 113.0 (37.70) 122.0 (39.30)
14.9 39.7 53.6 72.4 75.9 95.3 104.7 108.9
-&dJ 12.1 37.4 50.0 76.4 77.7 104.7 132.4 152.7
(QQ, + QA/J -2.8 -2.3 -3.7 4.0 1.8 9.4 27.7 43.8
oSample numbers as in Table I. bn&eqd) = moles of water required to solvate all of TX 100 and Bu. The share of TX 100 is given in parentheses.
hydration of free EO groups (asin PEG)is therefore lower than when it is organized (asin a TX 100 micelle). In this study with the formation of a microemulsion, the TX 100 molecules become organized at the wlo interface along with butanol. The hydration of the oxygen centers in the organized interfacial refion is considered comparable with that of TX 100 micelles. A 1:l (w/w) mixture of TX 100 and Bu corresponds to a 1:8.4mole ratio which in turn (at the rate of four molecules of water attachedto each oxygen center in the mixture) corresponds to 8 mol of water/mol of the mixture. Taking 24 kJ/mol-l of the mixed solute as the enthalpy of hydration (equivalent to 3 kJ mol-’ of
bound water), the Qh,d of a TX 100 and Bu mixture has been calculated and expressed in joules (Table 111). It is to be noted that the amount of water added has been lower than even the hydration capacity of TX 100 in most of the mixtures except the last two cases. The Qhyd values have been used in eq 3 to obtain Qdwg + Qorg, which is found to be initially negative and afterward positive. The initial exothermicity supports the prominence of Qorg over Above 0.017 mol of water addition, QdFg overrides QoF and the resultant event is endothermic. The analysis herein presented is a simplified version; further experimentations are required for better interpretation of the energetic pattern of the studied four-componentsystem. In Figure 6, the three-dimensional profiie of AHa, %I ns+cs,and ndns+csis presented. Ita base has a triangular column-like appearance with a curved front arm. The top has more or less a regular twisted fold; the variation of AHBis on the whole systematic. The depth of the twist shows the spread by the interaction of water and oil with surfactant and cosurfactant.
Acknowledgment. M.L.D.thanks Jadavpur University for laboratory facilities. We are thankful to the reviewers for stimulating criticism and suggestions. %&StwNO.TX 100,9002-93-1;
HzO, 7732-18-5.
Bu,71-36-3; Hp, 142-82-6;
