J. Phys. Chem. 1994,98, 6167-6171
6167
Solubilization of Some Synthetic Perfumes by Anionic-Nonionic Mixed Surfactant Systems. 2 Yoshikazu Tokuoka,'*+** Hirotaka Uchiyama? and Masahiko Abetvll Faculty of Science and Technology. Science University of Tokyo, 2641, Yamazaki, Noda, Chiba 278, Japan, Institute for Applied Surfactant Research, The University of Oklahoma, Norman, Oklahoma 73019, and Institute of Colloid and Interface Science, Science University of Tokyo, 1-3, Kagurazaka, Shinjuku-ku, Tokyo 162, Japan Received: December 21, 1993"
The solubilization of synthetic perfumes, eugenol (EL) and d-limonene (LN), by mixed surfactants of sodium dodecyl sulfate (SDS) and hexadecyl poly(oxyethy1ene) ethers (C16POE,, n = 20 and 40) has been studied from measurements of the maximum additive concentration (MAC) and the distribution coefficient between the micellar and bulk phases (K). The MAC of the hydrophilic perfume, EL, in the mixed systems is smaller than the MAC predicted according to an ideal mixing rule. On the other hand, the MAC of the hydrophobic perfume, LN, is larger than the predicted value. The mixing effect of the surfactants on the MAC is larger in the S D S - C ~ ~ P O Esystem ~ O than in the S D S - C ~ ~ P O E system. ~ ~ J In addition, the mixture of the anionic and nonionic surfactants causes the K value for each perfume to be smaller than the ideal K value. The difference between the experimental and the ideal K values for EL is larger in the S D S - C ~ ~ P O Esystem ~ O than in the S D S - C ~ ~ P O Esystem. ~O In contrast, the difference in Kvalues for LN is more pronounced in S D S - C ~ ~ P O E ~ O than in S D S - C ~ ~ P O E ~The O . results imply that the change in K upon mixing the surfactants may be attributed to surfactant-surfactant interactions in the mixed micelle for the hydrophilic perfume and to the effect of the Laplace pressure on the micelle-bulk interface for the hydrophobic perfume.
Introduction Mixed surfactants are used as solubilizers in many industrial applications since solubilization by surfactant mixtures is often superior to solubilizationby the individual surfa~tants.l-~ It can be postulated that the tendency to form a micellar structure in mixed surfactant solutionswould be substantially different from that in pure surfactant solutions. Since solubilizationis directly related to micelle formation, it is difficult to predict the solubilizationbehavior of a mixed surfactant based upon properties of single-surfactant systems. Of the literally hundreds of solubilizationstudies of organic compounds by mixed surfactant micelles,413most involve measurements with normal alkanes, alcohols, and oil-soluble dyes, but few studies have been made with synthetic perfume compounds. Synthetic perfumes are often used in industrial products such as cosmetics,foods, detergents, pesticides, and coating materials. The synthetic perfumes are used in various forms with other materials such as emulsifiers or solubilizers, depending on the properties of the medium, the solubility of the perfume in the solvent, the stability of the perfume, etc. In the particular fields of cosmetic and food science, surfactants are used to solubilize oily synthetic perfumes. The aqueous solution solubilizing the perfumes becomes transparent, and the perfumes are stabilized. Hence, understanding how the perfume interacts with the surfactant in an aqueous solution is essential for the many industrial applications of perfumes. We reported the solubilizationof some synthetic perfumes by anionic and/or nonionic single surfactants in aqueous solution in previous papers.14J5 The results suggested that the hydrophilic property of the synthetic perfume compounds can affect the solubilization. In the present study, we report the solubilization of some typical synthetic perfumes (eugenol and d-limonene) by
* To whom correspondence should be addressed.
Faculty of Science and Technology, Science University of Tokyo.
t Current address: Research and Development Division, S.T. Chemical Co., Ltd., 4-10, 1-chome, Shimo-ochiai, Shinjuku-ku,Tokyo 161, Japan.
8 The University of Oklahoma. I Institute of Colloid and Interface Science, Science University of Tokyo. Abstract published in Advance ACS Abstracrs, May 15, 1994.
0022-3654/94/2098-6167$04.50/0
anioniononionic mixed surfactant systems (sodium dodecyl sulfate-hexadecyl poly(oxyethy1ene) ethers) utilizing measurements of the maximum additive concentration (MAC) and the distribution coefficient between micellar and bulk phases ( K ) of each synthetic perfume compound. We also discuss the relationship between the poly(oxyethy1ene) chain length of the nonionic surfactant and the synergistic effect on the maximum additive concentration and/or the distribution coefficient.
Experimental Section
Materials. The anionic surfactant, sodium dodecyl sulfate
(SDS),was the purest grade product (>99.7% purity) of Tokyo Kasei Kogyo Co., Ltd., Tokyo, Japan. It was recrystallized from ethanol and extracted with ether. The nonionic surfactant, hexadecyl poly(oxyethy1ene) ethers (ClaPOE,, C & ~ ~ ~ ( C H Z C H n~ =~20 ) ~and H 40), ; was supplied by Nihon Surfactant Industries Co., Ltd., Tokyo, Japan. The ethers havea narrow molecular weight distribution. Their purities were confirmedby surface tension measurements and differential scanning calorimetry. Synthetic perfumes, eugenol (EL) and d-limonene(LN), were supplied by Hasegawa Kouryo Co., Ltd., Tokyo, Japan, and were used without further purification. Chemicalstructures, molecular weights, hydrophilic-lipophilic balance (HLB), and purities are shown in Table 1. The HLB values were calculated using the method of F ~ j i t a . ' ~ .As ' ~ can be seen in Table 1, EL is much more hydrophilic than LN, according to the HLB values. Water used in the experimentswas twice distilled and deionized with an ion exchanger (NAN0 pure D-1791 of Barnstead Co., Ltd.) and distilled again prior to use. The resistivity of the water was about 18.0 MQ-cm,and the pH was 6.7;the surface tension was 72.1 dyn/cm at 30 OC. Preparation of Surfactant Solutions and Aqueous Solutions Including Synthetic Perfume. 20-mL portions of a given concentration of water and/or surfactant solution were placed into several 100-mL glass-stopperedErlenmeyer flasks, and varying amounts of a synthetic perfume were added. The mixtures were stirred by a shaker (Model SS-82D Type of Tokyo Rikakikai Q 1994 American Chemical Society
6168
Tokuoka et al.
The Journal of Physical Chemistry, Vol. 98, No. 24, 1994
TABLE 1: Chemical Structure, Abbreviation, Molecular Weight, HLB, and Purity of Synthetic Perfumes Used in This Study synthetic perfume eugenol
6chemstruct
abbrev EL
molwt
164.21
HLB 6.9
purity >988
P
W
u a
CH&H=CH2
d-limonene
s
LN
136.24
0.7
>95%
Co., Tokyo, Japan) for 12 h and allowed to stand for 12 h to establish a solubilization equilibrium at 30 "C. Determination of Maximum Additive Concentration and Solubility in Water. After equilibrium has been established in the solutions, turbidities can be determined by measuring the transmittance at 700 nm with a double-beam spectrophotometer (Model MPS-2000 of Shimadzu Co., Ltd., Tokyo, Japan) with a quartz cell ( 10mm light pass length) as describedin the previous paper. 14 The solubilities of perfumes in water were measured by using a total organic carbon analyzer (Model TOC-5000 of Shimadzu Co., Ltd.), which determined the amount of total organic carbon in the aqueoussolution. Samples for the solubility measurements were prepared by placing excess perfume in aqueous solution and stirring for 12 h. The undissolved organic phase was removed before the measurement by utilizing a glass filter (Glass Microfibre Filter of Whatman Ltd., England) when necessary to separate the small particles from the aqueous solution. DeterminationofMicellar Compositiom. A micellar surfactant mole fraction ( X M )is not always equal to the stoichiometric surfactant mole fraction in the aqueous solution ( X ) at high concentrations of surfactant.I2J8 Turro et al. determined X Mby using a pyrene probing method.Ig The ratio between the intensities of the first and third peaks of the pyrene fluorescence spectrum is proportional to the permittivity of the localized pyrene environment. The permittivity obtained from the fluorescence peaks of pyrene solubilized in the mixed micelle (CM) can be equated to
where t l and €2 correspond to the perimittivities in, the pure surfactant micelles. The micellar mole fraction,&, in the SDSC16POEnsystem was determined by using eq 1 and by measuring the fluorescence spectrum of pyrene solubilized in single- and mixed-surfactant micelles according to the method described in a previous paper.14 Results
Figure 1 depicts the relationship between the maximum additive concentration (MAC) of EL and the mole fraction of C16POEn in the solution. The MACs of each system initially decrease with an increase in the mole fraction of Cl,$OE,,, reaching a minimum at approximately equimolar surfactant mixture concentration. Although the MAC for the C16POE2o single-surfactant system is much larger than that for the Cl(,POE40 system, substantial difference in the MACs in the mixed-surfactant system are not observed. Figure 2 shows the MAC of LN as a function of the mole fraction O f C16POEnin SDS-CI~POE,mixed-surfactant solution. The MACs of LN in both surfactant solutions increase as the mole fraction of CI~POE,,increases. The MAC for the SDS-
E
XC16POEn
Figure 1. Maximum additive concentration of EL as a function of mole fraction of ClsPOE,, at 30 OC (total conc, 1.0 x 10-2 mol/L).
0.010 o ;SDS/Ci#OEu,
;SDS/C16POEm
E
u a
W
0.005
E n.nnn -.---
0.0
0.2
0.4
0.6 0.8 1.0
X C I6POE
Figure 2. Maximum additive concentration of L N as a function of mole fraction of C I ~ P O E ,at 30 OC (total conc, 1.0 x 10-2 mol/L).
Cl6POE2o system is always greater than that for the SDS-C16POEM system at any mole fraction. The MACs of both perfume compounds in the SDS-C16POE,, mixed system are compared with those of the individual singlesurfactant systems in Figures 3 and 4. In both figures, the relationship between the MAC and the mole fraction of c16POEM is depicted for the S D S - C I ~ P O Emixed ~ ~ system (filled right circle). In the pure surfactant systems (empty and filled circles), the concentrations of the single surfactants correspond to their concentrations in the mixed-surfactant solution. In other words, the concentration ratio of each surfactant is equal to its molar ratio in the mixed-surfactant solution. Moreover, the dashed line in the figure represents the estimated MAC (Ccal)for the mixed system based on an ideal mixing rule (eq 2) using the MAC of the pure surfactant solution, ccal
= sLSDScSDS + SL16nC16n + SLwatcr
(2)
where SLSDSand are the moles of the synthetic perfume solubilized per unit mole of SDS and C16POEn, CSWand Cl6n are the concentrations of SDS and ClaPOE,, in the mixed-surfactant solution, and SL,(, is the solubility of the perfume in water. If the dissimilar surfactants form nearly pure component micelles rather than mixed micelles, the MAC would be expected to be comparable to the calculated MAC (C-1). As the results plotted in Figures 3 and 4 indicate, the experimental MAC of EL in SDS-Cl6POE40 solution is obviously smaller than the estimated MAC (C=I, dashed line). In contrast, the MAC of LN in the
The Journal of Physical Chemistry, Vol. 98, No. 24, 1994 6169
Solubilization of Synthetic Perfumes 0
;Cone. of C I W E a (moV1)
o.Oo0 0.002 0.004 0.006 0.00s 0.010 I
o.04
I
0.010 0.00s 0.006 0.004 0.002 o.Oo0
0;Cone. of SDS (mom) I
'
I
'
I
'
I
.
0.03
s 8
v
0.02
-"'1
tt
O.O1
, /
0.00 0.0
0.2
0.4
0.6
0.8
1.0
XCdOEm Figure 3. Maximum additive concentration of EL with mole fraction of C16POEa in the SDS-'&,POEa mixed system (total conc, 1.0 x 10-2 mol/L) and concentration of pure surfactant at 30 ' C . 0 ;COnC. Of C16POE40 (mOM) O.Oo0 0.002 0.004 0.006 0.008 0.010 4
I
0.010 0.008 0.006 0.004 0.002 O.Oo0
o ;Cone. of SDS (mom)
0.004
0.0
0.2
0.4
0.6
0.8
1.0
X C I6 POE 40 Figure 4. Maximum additiveconcentration of LN with mole fraction of Cl6POEa in the S D S - C I ~ P O mixed E ~ system (total conc, 1.0 X 1k2 mol/L) and concentration of pure surfactant at 30 'C.
mixed-surfactant system is much larger than the calculated MAC. A similar tendency is obtained in the SDS-CI~POEZO system. A mole fractional distribution coefficient ( K ) can be defined as follows:
where the superscripts "mic" and "aq" denote the micellar and the aqueous bulk phase, respectively. X,, is the mole fraction of the perfume in the micellar or the aqueous solution phase, n,, and nsurfare the numbers of moles of synthetic perfume and surfactant, and nHIO is the number of moles of water in the bulk phase. Since n H 2 0 is always much greater than the sum of I$,and nt!rf, the (n:, nZf) term in eq 3 is negligible, and eq 3 can be rearranged to give
+
where CM and CW refer to the MAC and the solubility of the perfume in water, respectively. CS is the total surfactant concentration, and CMC is the total monomeric surfactant concentration. However, the CMC under solubilization conditions is generally different from that in the pure surfactant solution.20-21 The CMC of SDS solutions with each perfume was measured:14 EL, 8.0 X 10-4 mol/L; LN, 4.9 X mol/L. The CMC values are employed to calculate the K values in the SDS solution. In the cases of nonionic single- and anionic-nonionic mixedsurfactant systems, the CMCs in the presence of the perfume are unknown. But the CMCs are most likely much smaller than the total surfactant solution concentration (1.0 X mol/L) in the given experimental conditions.22 The CMC in eq 4 can therefore be neglected in the calculation of the K values in the nonionic and in the mixed-surfactant system. These values are listed, along with X and XM,in Table 2.
Discussion Effect of Poly(oxyethy1ene) Chain Length on MAC in the Mixed-Surfactant System. As shown in Figures 1 and 2, no substantial differences in the MACs of EL in the SDS-C16POE, mixed-surfactant solutions are observed, although a large differenceis observed between the pure nonionic surfactant solutions. However, the MACs of L N are larger in the SDS-CI~POEZO system than in the SDS-Cl6POEa system at any mole fraction of nonionic surfactant. We previously reported the solubilization of the perfumes in SDS and in Cl6POE, single-surfactant solution^.^^^^^ The solubilizing capacities of EL and LN by SDS and ClaPOE, solutions are listed in Table 3. The solubilizing capacities of each perfume by SDS are smaller than those by the nonionic surfactants. In addition, the solubilizing capacities of C16POE20 are larger than those of C16POEa. However, the MAC of the S D S - C ~ ~ P O Esystem ~ O is almost the same as that of the SDS solution. The comparison between Figures 1 and 2 indicates that the mixing effect of anionic and nonionic surfactants on the MAC of perfumes is closely related to the hydrophilicity of the perfumes. The solubilization location of the perfume changes with the hydrophilicity of the perfume in the micelle; the perfume molecule is presumably transferred from near the micellar surface to near the hydrocarbon core of the micelle as its hydrophilicity is reduced. The differential ratio (R) between the experimental MAC and the calculated MAC for the perfumes studied can be calculated from the equation
where Ccxpis the experimental value of the MAC of a synthetic perfume in a mixed-surfactant solution, and C,l is the calculated MAC from eq 2. When the R value is equal to zero, this implies that there is no mixing effect of the surfactants on the solubilization. The differential ratios as a function of the mole fraction of the nonionic surfactant in the mixed solution are plotted in Figures 5 and 6. The R values of EL in both mixed-surfactant solutions are smaller than zero, and the R values in the SDSC16POE20mixedsystemaremorenegativethan thosein theSDSClaPOEa mixed system for mole fractions greater than 0.4. The R values for L N in both mixed surfactant systems are much larger than zero at any mole fraction Of C16POEn. Moreover, the differential ratiovalues for the S D S - C ~ ~ P O Esystem ~ O are larger than the values for the SDS-ClaPOEa system. We have reported that in anionic-nonionic mixed-surfactant systems the mixed micelle is formed more easily by nonionic surfactants having shorter POE chains than by nonionic sur-
6170 The Journal of Physical Chemistry, Vol. 98, No. 24, 1994
Tokuoka et al. TABLE 4
Characteristic Parameters of the Distribution
EqUtiO"
In K = XMIn K,,,
+ (1 - X M ) hKsDs + BXM( 1 - XM)
SDs-cl6POEm Mixed System EL: InK=X&31 + ( l - X ~ ) 8 . 2 4 - 0 . 4 o X ~ ( l - x ~ ) LN: In K = X ~ 1 0 . 2 7+ ( 1 - Xd9.36 - 0 . 0 2 X ~ ( l XM) ;SDS/C ,,POEM -0.2 0.0
I
.
I
.
0.4
0.2
1
.
1
.
0.8
0.6
1.0
X C lhPOEn
Figure 5. Relationship between R for EL and mole fraction of ClsPOE,.
3.0
1
'
1
'
1
.
1
.
o ;SDS/C16POEu,
.
$DS/C16POE~
-
&
0
0.0
0.2
0.4
0.6
0.8
1.0
XClsPOE.
Figure 6. Relationshipbetween R for LN and mole fraction of Cl6POE..
TABLE 2 Distribution Coefficients of the Perfume (XlOj) in the SDS-C16pOEuMixed System with Stoichiometric Mole of C16pOE. Fraction ( X ) and Micellar Mole Fraction (XM) A. S D S - C ~ ~ OSystem E~O
X XM K
EL LN
0.00 0.00
0.20 0.38
0.40 0.62
0.60 0.69
0.80 0.71
1.00 1.00
3.80 11.57
3.57 13.38
3.59 20.52
3.58 22.15
3.77 25.28
4.08 28.90
B. SDS-CI~POE~ System X XM K
EL LL
0.00 0.00
0.20 0.69
0.40 0.72
0.60 0.72
0.80 0.88
1.00 1.00
3.80 11.57
3.63 7.33
3.65 9.40
3.66 9.39
3.61 11.40
3.81 16.14
TABLE 3 Solubilizing Capacity in a Single Surfactant for EL and LN surfactant EL LN 1.94 0.11 SDS CisPOE2o 2.85 0.41 CisPOEa 2.10 0.20 ~~
factants with longer POE chains.22-2' We have also reported that interactions between the hydrophilic head groups of the surfactants are stronger in the S D S - C I ~ P O Esystem ~ O than in the SDS-Cl6POEm ~ y s t e m . ~Moreover, *-~~ in a solubilizationstudy of azobenzene, solubilized in the hydrocarbon core of micelle, it was shown that the MAC in the anionienonionic mixed system was larger than the sum of the MACs of the individualsurfactant solutions.10 For the hydrophobicorganiccompounds, the effective solubilization area in the mixed micelles becomes larger than that of the pure surfactant micelles as a result of an increase in the radius of the mixed micelle including the electric double layer.22.27 Although the mixed micelle is easily formed in the SDS-Cl6POE20 system, the strong hydrophiliohydrophilic interactions between the head groups of SDS and ClaPOE20 may cause the
SDS-CI~POEU Mixed System EL: In K = X ~ 8 . 2 5+ (1 - Xd8.24 - 0 . 2 9 X ~1( - X M ) LN: In K = X ~ 9 . 6 9+ (1 - Xd9.36 - 2.64Xd 1 - X M ) is the mole fraction of nonionic surfactant in micellar phase. K,. and K s are ~ mole fractional distribution coefficients in nonionic surfactant and SDS, respectively. hydrophilic part of the mixed micelle to be more rigid than that of single-surfactant micelles. The total effective area for the solubilizationof EL into the hydrophilic region near the micellar surface may become less than that of single surfactant micelles; therefore, it is reasonable that the R values of EL are smaller than zero. On the contrary, the solubilization of LN, which is incorporatedinto the hydrophobic part of the mixed micelle rather than near the surface, may be influenced less by hydrophilichydrophilic interactions. The effect of an increase in the radius of the mixed micelle is greater for the solubilizationof hydrophobic perfume compounds. Since the radius of the mixed micelle is larger than that of a single surfactant micelle, causing expansion of the effective solubilizationregion where LN is solubilized, the R values of LN are positive as is shown in Figure 6. In the SDS-ClaPOEm system, however, the two dissimilar surfactants form nearly pure surfactant rich micelle rather than mixed micelles. The deviation of the R values from zero in the SDSC16POEa system is smaller than that in the S D S - C ~ ~ P O E ~ O system as shown in Figure 5 and 6. Mixing Effect of Surfactants on Distribution Coefficient (K). Treiner et aL8J2have suggested that the distribution coefficient of a neutral organic solute between micellar and bulk phases in a mixed-surfactant system follows the relationship shown in eq 6,
In K = XMIn K,+ (1 - XM)ln K2 + BXM(l-XM) (6)
K Iand K2 are the mole fractional distribution coefficients of a solute by the single surfactants constituting the mixed micelle; B is an experimental parameter including both the surfactantsurfactant interactions and the surfactant-solute interactions. When there is no synergistic effect on the partitioning of the solute, the B coefficient is expected to be zero. Table 4 lists the analytical functions which represent the experimental data with the average B value at any XM. As can be seen from Table 4, the B coefficient for EL is more negative in the SDS-CI~POE~O system than in the SDS-C18OEm system. However, the B coefficient of LN in SD!?&16POEm is more negative than that in the S D S - C I ~ P O Esystem. ~O When a surfactant-solute interaction is constant, the B coefficient for a polar solute is closely related to the binary surfactants interaction parameter (a)from the so-called regular solution theory. Supposing that the surfactant-perfume interactions in both the mixed system are almost the same as a result of the homologous structure of the nonionic surfactants, the B coefficient is dependent on the a value. The a coefficients in the SDS-C16POEnmixed systems were determined from the measurements using the so-called regular solution theory.22 The interaction parameter (a)at an equimolar surfactant mixture in the S D S - C ~ ~ P O system E ~ O was -6.1 8, whereas the a value in the SD%c#OEmmixed systemcould not bedetermined as a result of little interaction between SDS and c16PoEm. Thus, the B coefficientdeviates more from zero in the SDS-CI~POE~O mixed system than in the S D W I ~ P O E mixed Q system. In the case of
Solubilization of Synthetic Perfumes
The Journal of Physical Chemistry, Vol. 98, No. 24, 1994 6171
solubilization of hydrophilic perfumes, the synergistic effect of surfactants on the distribution coefficient seems to depend largely on surfactant-surfactant head group interactions. In the case of mixtures forming with large negative values of a,one will normally expect a greater reduction in the extent of solubilization of a polar solute in the mixed micellar system. However, values of the B coefficients must depend both on surfactant-surfactant interactions and on surfactant-solute interactions in the mixed micelle. In systems where surfactantsolute interactions are not particularly strong, the B coefficient will be determined primarily by the a value. However, if there are strong surfactant-solute interactions in the mixed micelle, B may be less negative than expected, even if CY is quite large and negative. Thus, a hydrophilic perfume may be attracted to the ether and sulfate head groups of the surfactants in the mixed micelle more strongly than a hydrophobic perfume. The progression of Bvalues for EL in Table 4 indicatesthat hydrophilic groups of the perfume molecules tend to interact strongly with the head groups as the POE chain length increases. On the other hand, the B value for LN in the S D S - C I ~ P O E ~ O system is nearly zero and the B coefficient for the SDS-C16POEu system is more negative than that for the SDS-CI~POEZO system, indicating that solubilizationof LN in the mixed systems is greatly enhanced compared to the solubilization of EL. This may result from a reduction in the Laplace pressure across the micelle-bulk interface, owing to an increase in the aggregation number (and micellar radius) upon mixing the surfactants.'* Since LN is practically nonpolar, its solubilization in the binary surfactant mixture be influenced more by the increase in size of the surfactant than are the hydrophilic perfumes.
Conclusion The solubilization of perfumes in anionic-nonionic mixedsurfactant solution has been investigated using maximum additive concentration measurements and determinations of the distribution coefficient between micellar and bulk phases ( K ) . The difference between the experimental and the calculated MAC based on the ideal mixing rule increases with a decrease in the poly(oxyethy1ene) chain length of C16POEe. Thus the mixed micelle is formed more easily in the S D S - C ~ ~ P O Esystem ~ O than in the SDS-C16POE~system. The negativesynergisticeffect on the K value of the hydrophilic perfume, EL, increases with a decrease in the poly(oxyethy1ene) chain length. Examination of the values of the distribution coefficients, however, indicates a reduction in the tendency of the perfume components to be solubilized by the surfactant mixture, compared to the solubilization by the individual surfactants. This effect becomes greater as the solutesbecome less hydrophilicand the nonionic surfactant
has shorter POE chains, although the negative effect practically disappears in the case of the most hydrophobic (least polar) perfume in the SDS-C16POE20 systems.
Ackwwledgment. The authors are indebted to Professor Shenil D. Christian, Institute for Applied Surfactant Research, The University of Oklahoma, for valuable discussions. References and Notes (1) Lange, H.; Beck, K. H. Kolloid 2.Z . Polym. 1973, 251, 424. (2) Moroi, Y.;Nishikido, N.; Matsuura, R. J . Colloid Interface Sci. 1977, 50, 344. (3) Moroi, Y.;Akisada, H.; Sato, M.; Matsuura, R.J . Colloid Interface Sci. 1977, 61, 233. (4) Nishikido, N. J. Colloid Interface Sci. 1977, 60, 242. ( 5 ) Uchiyama, H.; Abe, M.; Ogino, K. J . Jpn. Oil Chem. SOC.1986,35, 1031. (6) Nugara, N.; Prapaitrakul, W.; King, A. D., Jr. J. Colloid Interface Sci. 1987, 120, 118. (7) Muto,Y.;Asada,M.;Takasawa,A.;Esumi,K.;Meguro,K.J. Colloid Interface Sci. 1988, 124, 632. (8) Treiner, C.;Nortz, M.; Vaution, C.; Puisietx, F. J . Colloid Interface Sci. 1989, 125, 261. (9) Smith, G.A.; Christian, S.D.; Tucker, E. E.; Scamehorn, J. F.;J . Colloid Interface Sci. 1989, 130, 254. (10) Uchiyama, H.; Tokuoka, Y.;Abe, M.; Ogino, K.J . Colloid Interface Sci. 1989, 132, 88. (1 1) Abe, M.; Kubota, T.; Uchiyama, H.; Ogino, K. Colloid Polym. Sci. 1989, 267, 365. (12) Treiner, C.; Nortz, M.; Vaution, C. Lungmuir 1990, 6, 1211. (13) Zhao, G.; Li, X . J. Colloid Interface Sci. 1991, 144, 185. (14) Abe, M.; Tokuoka, Y.;Uchiyama, H.; Ogino, K. J. Jpn. Oil Chem. SOC.1990,39, 565. (15) Tokuoka, Y.;Uchiyama, H.; Abe, M.; Ogino, K. J . Colloid Interface Sci. 1992, 152, 402. (16) Fujita, A. Kagaku no Ryoiki 1957, 11, 719. (17) Fujimoto,T. New Introduction tosurface Actiw Agents;SanyoChem. Ind. Ltd.: Japan, 1985; p 197. (18) Nishikido, N.; Imura, Y.;Kobayashi. H.: Tanaka. M. J . Colloid Interface Sci. 1983, 91, 125. (19) Turro, N. J.; Kuo,P. L.;Somasundaran,P.; Wory, K.J. Phys. Chem. 1986, 90, 288. (20) Shirahama, K.; Kashiwabara, T. J. Colloid Interface Sci. 1971,36, 65. (21) Manabe, M.; Kawamura,H.; Kamashita, A.;Tokunaga, S . J . Colloid Interface Sci. 1987, 115, 147. (22) Ogino, K.; Kakihara, T.; Uchiyama, H.; Abe, M. J. Am. Oil Chem. SOC.1988, 65, 405. (23) Abe, M.; Tsubaki, N.; Ogino, K. J. Jpn. Oil Chem. Soc. 1983,32, 672. (24) Abe, M.; Tsubaki, N.; Ogino, K. Colloid Polym. Sci. 1984,262,584. (25) Abe, M.; Tsubaki, N.; Ogino, K. J . Colloid Interface Sci. 1985,107, 503. (26) Ogino, K.; Tsubaki, N.; Abe, M. J. Colloid Interface Sci. 1985,107, 509. .. .
(27) Abe, M.; Kakihara, T.; Uchiyama, H.; Ogino, K. J . Jpn. Oil Chem. Soc. 1987, 36, 135. (28) Ogino, K.; Uchiyama, H.; Ohsato, M.; Abe, M. J. Colloid Interface Sci. 1987. 116. 81. (29) Ogino; K.; Uchiyama, H.; Abe, M. Colloid Polym. Sci. 1987, 265, 52.
