- Email: [email protected]
Expansion of mixed anionic—non-ionic micelles caused by solubilization of organic solutes
Co1lnifl.s ~cl SWjices. 67 ( 1992) 37-43 Elscvicr Scicncc Publishers B.V., Amsterdam
37
Expansion of mixed anionic-non-ionic by solubilization of organic solutes
micelles caused
Masahiko Abe”*b, Yoshikazu Tokuoka”.‘, Hirotaka Uchiyama”, Keizo Ogino”sb, John F. Scamehorn’ and Shed D. Christian” a Faculty o~Scicwce ami Technology, Scierm University of Tokyo, 2641 Yamazaki, Noda, Chiba 278, Japarl blmtit~~te of Colloid and Interfme Science, Scietlce University of Tokyo, I-3 Kagurazaka, Shinjuku-ku, Tokyo 162, Japau clmtittrtefor Applied
(Received 5 December
Strrfhctant
Research,
The University
of Oklaimxa,
Norman,
OK 73019. USA
1991; accepted 25 June 1992)
Abstract micellcs containing solubilizcd The miccllr size was dctcrmincd by dynamic light scartcrinc fcr mixed anionic -non-ionic organics. The surfactnnts used were sodium dodccyl sulfate and hcxadccyl polyoxycthylcnc ethers (C,,POE, whcrc II = IO, 20. 30 or 40). For pure or mixed surfactant systems, the diameters of micclla which contain solubilizcd n-octane arc almost indcpendcnt of solute concentration, while micetlcs containing solubilizcd I-octanol increase in size with increasing solute content. The change in miccllar size for systems containing I-ocranol is influenced by hydrophilic group interactions bctwcen anionic and non-ionic surfpctants in the mixed system. K~_wwY/,s: Anionic-non-ionic solubilization.
mixed miccllcs; hcxadccyl
polyoxycthylcnc
Introduction
The solution properties of mixtures of some surfactants are often superior to those of the individual surfactant involved C1,2]. Therefore, mixed surfactant sys!ems are used in many practical applications, and arc also of great theoretical interest. Solubilization by surfactant solutions is closely related to detergency and is important in various industrial fields such as cosmetics, foods, medical supplies and surfactant-based separations. A number of papers dealing with the solubilization of organic% in micelIes have been published; Corrcspurrtiellcc to: M. Abe. Faculty of Scicncc and Tcchnology. Scicncc University of Tokyo, 2641 Yamaznki. Noda, Chiba 278, Japan. ’ Present address: Products Research Dcvclopmc:?t. S.T. Chemical Co. Ltd.. 4-10, I -chome. Shimoochiai. Shinjuku-ku, Tokyo 161, Japan. 0 I66-6622/92/P05.00
#:) 1992 -
Elscvicr
Science
Publishers
ethers; miccllar
expansion;
sodium
dodccyl
sulfate;
a few examples are given in Refs [3- 131. Published papers have generally discussed aqueous solutions containing a single surfactant, but relatively few papers have discussed solubilization in mixed surfactants. We have studied ihe solubilization in anionic-non-ionic [4, I I]? cationic-non-ionic [4], amphoteric-anionic [ 121 and amphoteric-nonionic [12] mixed surfactant systems. In anionicnon-ionic mixed surfactant systems, the solubility of azobenzene (an oil-soluble dye) is greater than predicted from a linear additivity rule applied to solubilization in the single surfactants involved [ 131. However, 1-hexanol exhibits less solubilization than that predicted by the linear mixing rule in anionic-non-ionic and in cationic-non-ionic sr- ^:tctant systems [4]. in this paper, we report the diameters of micelles which contain solubilized octane (a non-polar B.V. All rights
reserved.
38
solute) and I-octanol solutions of single surfactants. Experimental
(a polar solutr) in aqueous surfactants and of mixed
section
Mciterinls
Sodium dodecyl sulfate (SDS), purest grade (more than 99.7% purity), was a product of Tokyo Kasei Kogyo Co. Ltd., Tokyo. It was recrystallized from ethanol and was extracted with ether. Hcxadecyl polyoxycthylcnc ethers (C Ih HJ3 O(CHzCH20),,H abbreviated to C16POE,,, where II= IO, 20, 30 and 40) were supplied by Nihon Surfactant Industries Co. Ltd., Tokyo. They have a narrow molecular weight distribution. The purities of these surfactants were ascertained by both surface tension mcasurcmcnts and differential scanning calorimetry (DSC). No minimum was observed in the surface tension curve and no peak caused by impurities was recognized in the DSC mcasuremcnts.
The hydrodynamic size of the micclles was dctermined by carrying out dynamic light scattering measurements using a Model 4700 type submicron particle analyzer (Malvern Instruments Ltd., U.K.) at 30°C. The optical source of the light scattering apparatus is an argon laser operating at 488.0 nm (Mode1 Innova 90 of Coherent Corp., Palo Alto, U.S. -:ith a maximum power output of 5000 mW). The average scattercsd intensity and the time-dependent correlation function of the scattered intensity were measured at a constant scattering angle (90”). From these data. the translational diffusion coefficient D of the particle was determined and the hydrodynamic sizes tl of the particles wcrc obtained from the Stokes-Einstein equation
kT " = 3nrlD where rl is the viscosity of the solvent, /< is the Boltzmann constant and T is the absolute tcmpcrature. Before measurement, the sample solution was passed through a membrane filter (PTFE; 100 nm) for optical purification. Results and discussion
rl-Octane and I-octanol, purest grade, wcrc products of Tokyo Kasei Co. Ltd., Tokyo, and were used without further purilication. Water for injection JP (Japanese Pharmacopoeia) was obtained from Ohtsuka Pharmacy Co., Tokyo, and was used as received.
Samples containing a given concentration of surfactant solution were placed in several 100 ml glass-stoppered Erlenmeyer flasks. Varying amounts of organic solutes were added and the mixtures were stirred for 24 h at 30°C. After equilibrium had been established, the turbidity of I’ J solutions was measured by recording the transmittance at 700 nm with a double-beam spectrophotometer (MPS-2000 of Shimadzu Co. Ltd., Japan) equipped with a quartz cell (10mm x 10 mm).
Figure I shows the change in transmittance of SDS solutions (1.O-IO- ’ mol I - ’ ) with increasing total concentration of solute at 30°C. The transmittance begins to decrease when emulsion droplets appear. Extrapolation of the transmittance to 100% gives the maximum additivit, concentration (MAC) values for II-octane and 1-octanol as shown in Fig. 1. The MAC is the concentration of solute in the surfactant solution at saturation. The values of the MAC for the pure and mixed surfactant systems studied are shown in Tables I and 2.
In this surfactant
paper, d indicates the diameter micclle with solubilizcd organic
of the solute,
111. Ahc er ai./Colloi&
Sltrfaces
67 (1992) 37-43
39 2.-o
g 8 2 = ._ E 2 2 t-
90
$
80
1.5
70
1.0 0.5
1.0
Organic Fig. I. Transmittance tration of solubilizatc
TABLE
1.5
2.0
solute (mol/L> x 10e2
of SDS solutions at 30 ‘C.
0.5
n-Octane
with increasing
1.0 (mol/J_) x low’
Fig. 2. The ratio d/d, for miccllcs of sin@ with increasing concentration of n-octnnc concentration is 1.0. IO-” mol I-‘).
conccn-
surfactant solutions at 30°C (surTactant
I
Values of the maximum additive concentration n-octane and I-octanol for pure surfactant systems
(MAC)
Surfactunl”
n-Oclanc (niol I-‘)
I-Octanol (mall-‘)
SDS C,,PGE,o C,,PO& C,,PGE31, C,,POE,”
4.0.10-3 9.0. 10-3 9.5. 10-J 9.5.10-3 9.4. 10-3
8.9. 10-J 8.2.10-~ I.1 . 10-z 9.4.10-3 9.4. lo-3
~Conccntration,
TABLE
1.0. IO-‘mol
of
I-‘.
and de that of the surfactant micelle without the solute. Figure 2 represents cl/d, for pure SDS and pure Ci6POEn solutions (1.0. IO-’ mall-‘) with changing concentration of dissolved n-octane at 30°C. As can be seen in Fig. 2, the values of d/d,-, are always above 1.0 in the presence of ,I-octane, and are independent of the concentration of dissolved n-octane for the range of solute concentrations studied. Figure 3 illustrates d/do for pure SDS and C,,POE,, solutions (1.0. 10-2mol 1-l) as a func3.0
2
Values of the maximum additive concentration (MAC) rl-octane and I-oct:rnol ;or mixed surktant systems Mixed ratio
0.0
molar
Maximum
additive
n-Octane SDS-CI(, 8:2 6:4 4:6 2:8
POE,,”
SDS-CIh X:2 6:4 4:6 2:8
POEJo”
“Concentration,
of
(mol I- ’ )
concentration I-Oclanol
2.0 g CI 1.5
6.1 * IO-3 5.8. lO-3 6.0 * 10-J 7.3.10-3
7.4. 8.0. 7.2. 7.4.
!O_J
6.9 - IO-’ 8.1 . IO-’ 8.3. IO-3 7.9 * 10-3
9.7. 8.6. 8.3. 8.0.
10-3 to-3 1O-3 10-3
1O-3
10-J 10-3
1.o
1.0. IO-’ mol I-‘.
0.0
1.0
0.5 1-Octanol
(molL)
x 10”
Fig. 3. The ratio d/t/, for miccllcs of single surfactant solutions with increasing concentration of I-octanol at 30°C (surkctaktt concentration is 1.0. 10~‘moll-l).
40
tion of the concentration of dissolved I-octanol at 30°C. The solubilization of I-octanol results in an concentration increase in d/tie as the solute increases. and d/d,, is always greater than unity in of the I-octanol. The SDS and the presence C,,POElo solutions show a dramatic increase in diameter as the solute concentration increases, reaching a value of almost 3. Solutions containing ClhPOE30 and C,, POEjo do not C,(, POELO, show the abnormal enlargement observed for C,,POEIo and SDS. It is well known that a non-polar substance is solubilizcd into the hydrocarbon core of the micelle and a polar substance is solubilized into the palisade layer [ 14,151. The solubilization of h-octane in the anionic or non-ionic micelles causes only a slight increase in miceile diameter. consistent with 2. slight swelling of the micclle ccre in which the octane is located. However, I -octanol solubilizes in the palisade layer and the subsequent interactions between the hydroxyl group of the alcohol and the hydrophilic groups of the surfactants can lead to substantial micellc structural rearrangements, specifically, in this case, causing an increase in size. The diffusion coefficients of the micclles are examined as a function of the scattering vector in order to discuss the micellar shape of Ci6POElo in the presence of I-octanol. The reciprocal of the diffusion coefficient of Cr6POElo micelles was not constant and was not independent of the scattering vector either [16]. This result suggests that C,,POEio micclles would not be in the spherical form. In an SDS system, we have previously observed an increase in miccllar size upon solubilization of I -octanol [ 171, consistent with the results reported here. Ishiguro et al. [ 181 have reported that the size of micellcs containing solubilized benzene is slightly larger than that of a solute-free micelle. Benzene is probably solubilized predominantly in the hydrocarbon core of the micelIes.
2.0
g
1.5
1.o 0.5
0.0
Fig. 4. The
ratio
d/d0 for miccllcs
irt rttised
Figures 4 and SDS-CiG POE,,
mixed at
30 C
systems (the total surfactant concentration was 1.0. IO-’ mol I-‘) at 30°C respectively. The value of d/do is almost independent of the It-octane concentration (in systems containing h-octane) for the solute concentrations studied, as is also shown for the pure surfactant systems in Fig. 2. The dependence of (//do on the mixed micellar composition is shown in Fig. 6 for the two anionic-nonionic systems shown in Figs 4 and 5 in the presence of n-octane. AI1 mixed micelles with jr-octane present exhibit a larger diameter than in the absence of n-octane. The relative diameter reaches a maximum at a high mole fraction of non-ionic surfactant in the micelle (between 0.6 and 1.0, with a maxi2.0
g
1.5
1.0 0.5
sw-fcrctcutt s~~stenrs
5 depict d/~lo for /t-octane in and SDS-C,, POE,, mixed
of SDS-C,,,POE,,,
solutions with increasing conccntrztion of woctanc (surfactant conccntralion is 1.0. IO-’ mol 1-l).
0.0
Solrtbilimriort
1.0
n-Octane (mol/L) x 10.’
n-Octane Fig. 5. The
ratio
cl/d,
for
1.o (mol/L) x 10”
miccllcs of SDS-C,,POEJO
solutions with increasing concentration of u-octane (surfactant concentration is 1.0. IO- 2 mol I- ’ ).
mixed at 30°C
AI. Ahr et crl./Colloids
S~$aces
67 (1992) 37-43
41
2.0
2
1.5
1.0
0.0 Fig. 6. The containing composition.
0.2
ratio d/d, for SDS-Cr,PUE, rr-octane as a function of
I -0ctanol
mixed solutions micellar surfactant
mum near 0.8). It is not obvious why this mixed micellar composition range yields the greatest increase in micellar diameter. .The change of d/do for the solubilization of I-octanol in SDS-C16POE,, and SDSC,, POE,, mixed surfactant systems (total concentration, 1.0 - 10e2 mol l- ‘) is shown in Figs 7 and S, respectively. The value of d/do increases considerably with an increase in the concentration of solubilized I-octanol. The dependence of d/do on the mixed micellar composition is shown in Fig. 9 for the two anionic-non-ionic systems shown in Figs 7 and 8 in the presence of 1.0 10m3 mol I - ’ l
(molL> = 1O-’ mixed at 30°C
of I-octanol. All mixed micelles with I-octanol present exhibit a larger diameter than in the absence of l-octanol. The expansion coefficient A(d/d,) is defined by the following equation
where C is the concentration of dissolved I-octanol. This expansion coefficient, corresponding to the slopes of the lines in Figs 7 and 8, will be related to the char;ge of expansion with I-octanol concentrations greater than about 1 - 10e3 mall-’ Figure IO shows the expansion c,oefficients Ifi )r 2.0
0 1.5
1.o
Fig. 8. The ratio d/d, for miccllcs of SDS-C,hPOE,o solutions with increasing concentration of n-octane (surfactant concentration is 1.0. IO-’ mol I-‘).
2.0
$
0.5
0.0
I.0
0.4 0.6 0.8 Mole fraction of ClaPOEn
8
1.5
1
0
1.0
1.0 0.5 I-Octanol
1 .o
0.0
(mol/L) x 10’
Fig. 7. The ratio d/d, for micclles of SDS-C,,POE,O solutions with incrca
B
9
7
I
0.2
0.4
0.6
0.8
Mole mixed at 30°C
fraction
of
1.0
Cr6POEn
Fig. 9. The ratio d/d,, for SDS-C,6 POE, mixed solutions containing 1.0. 10e3 mall-r I-octanol as 3 function of micellar surfactant composition.
I
I
I
is consistent with the solubiiization behav%r of 1-octanoi. The expansion coefficient calculated here is a somewhat arbitrary parameter. It is, however, interesting that the expansion coefficient c:I:~ detect such changes with greater sensitivity !c value oft//d, alone (Fig. 9 v; Fig. 10). The ization of I!-octane in the core of the miceile I a poor probe of such a transition from a s;mgie m?eiie type to two coexisting miceiies as is shown in Fig. 6. For a solute, such as 1-octanoi which solubiiizes in the Faiisade layer of the micclie, the interactions between the hydrophilic head groups of the dissimilar SUifaCtalltS in t!Ie miceiie avior. are very important to the solubiiization
I
tem
---_ b< -------
‘.
. .
------
-.
--_
-.
---.
0
.2X
2.
0
0.0 0.2 Mole Fig. IO. Expansion tions as a runclion
a
-.
cl.4 0.6
0.8
1.0
fraction of CKPOE~I cocfficicnt of miccllar
of SDS-C,,POE, mixed surfxtant composition.
solu-
SDS-Cl6 POE,, mixed surfac!ani systems solubilizing l-octanol. If the mixed miceHe soiubiiization varies linearly with t!le mole fraction of a given surfactant in the micelic, the expansion coefficient would correspond to the dashed line in Fig. IO for the two mixed surfactant systems studied. This behavior would also be expected if the dissimilar surfactants form nearly pure component micciies, rather than mixed micelies. For the SDS-C,(,POElo system, the cxp:lnsion coeficient is lower than a linear mixing rui. would predict and reaches the minimum at about an equimoiar surfactant mixture. In the case the expansion coefficient of SDS-Cl6 POE,,, seems to obey the linear mixing rule. ‘,Ve have reported [19-213 that in mixed anionic-non-ionic surfactant systems, the tendency to form two miceiies of different compositions existing simultaneously (one anionic-rich and one non-ionic-rich) increases with decreasing alkyi chain length and/or with increasing poiyoxyethyiene chain length of the non-ionic surfactant. The formation of two coexisting immiscible miceIies in the SDS-C16POE,o system and of one type of mixed miceile in the SDS-C,6POE,, sys-
References 1
K. Ogino and M. AD:: (Eds), Miscd Surfactnnt Systems, Marcc! Dckkcr, New York, in press. J.F. Scztmchorn (Ed.), Phenomena in Mixd Sl;rfactant Systems. Vol. 31 I. ACS Symp. Ser.. Amc+an Chemical Socicry. Washington. DC. 1986. 3 G.A. Smith, S.D. Christian. E.E. Tucker and J.F. Scomchorn, J. Cclloid intcrf::cc Sci., I30 ( IYX9) 254. 4 C.M. Nguyen. J.F. Scamchorn and S.D. Christian, Colloids Surfaces. 30 (I 988) 335. 5 H. Uchiyama. S. Akao. M. Ahc and K. Ogino, Langmuir. 6 (1990) 1763. 6 S. Yiv. R. Zana. W. Ulbricht and H. Hoffmann. J. Colloid Inlcrfacc Sci.. X0 (19x1) 224. 7 E.B. Ahuin and E.A. Lissi. J. Colloid Intcrfclcc Sci., 95 (lYX3) 19x. 8 M. Almgrcn and S. Swarup. J. Colloid Intcrfxc Sci.. 91 (1983) 2.56. 9 K. Haynsc. S. Hayano and H. Tsubotn. J. Colloid intcfx:: Sci., IOI (1984) 336. 10 A.M. Blokhus. H. Hoiland and S. Bncklund. J. Co:loid lntcrface Sci., I I3 (1086) 9. II H. Uchiyama, M. Abe and K. O.cino, J. Jpn. Gii Chcm. Sac., 35 (19x6) 1031. and K. Ogino, C:l!loid I2 M. Abe. T. Kubota. H. Uchiyama Folym. Sci., X7 (1989) 365. I3 H. Uchiyamn, Y. Tokuoka, M. Abe nnd K. Ogino. J. Colloid Intcrfacc Sci., 132 (1989) 88. I4 D. Attwood and A.T. Florcncc. Surfactai:t Systems Ttxir Chcrristry. Pharmacy and Biology. Chapman and Hull. Londtin. l9R5. and Intcr~~cial Phcnomcna. Surfactants 15 M.J. Rosen, Wi!cy-Intcrscicncc, New York. :9R9. p. 170. I6 M. Ab;. Y. Tokuokn, H. Uchiyamn and K. Ogino, unpub:ishcd results. 1990. I7 M. Abe and K. Ogino, J. Jpn. Oil Chcm. Sot. Z! (19Y2) 569.
18 T. Ishiguro, T. Ogushi. Y. Iqhiwada n;xl T. As~hara. Kogyo Kagaku Zasshi, 68 (1965) 2 idi). 19 M. Abe, N. Tsubaki and K. Oginu. f. c’e!!oid lntcrface sci., 107 (19S5) 50.1.
20 21
K. Ogino, N. Tsubaki and M. Abe. J. Colloid Interfact: Sci., 107 (1985) 339. K. Ogino. T. Kakihara, H. Uchiynma and M. Abe. J. Am. Oil Chem. SOL, 65 (1988) 405.
37
Expansion of mixed anionic-non-ionic by solubilization of organic solutes
micelles caused
Masahiko Abe”*b, Yoshikazu Tokuoka”.‘, Hirotaka Uchiyama”, Keizo Ogino”sb, John F. Scamehorn’ and Shed D. Christian” a Faculty o~Scicwce ami Technology, Scierm University of Tokyo, 2641 Yamazaki, Noda, Chiba 278, Japarl blmtit~~te of Colloid and Interfme Science, Scietlce University of Tokyo, I-3 Kagurazaka, Shinjuku-ku, Tokyo 162, Japau clmtittrtefor Applied
(Received 5 December
Strrfhctant
Research,
The University
of Oklaimxa,
Norman,
OK 73019. USA
1991; accepted 25 June 1992)
Abstract micellcs containing solubilizcd The miccllr size was dctcrmincd by dynamic light scartcrinc fcr mixed anionic -non-ionic organics. The surfactnnts used were sodium dodccyl sulfate and hcxadccyl polyoxycthylcnc ethers (C,,POE, whcrc II = IO, 20. 30 or 40). For pure or mixed surfactant systems, the diameters of micclla which contain solubilizcd n-octane arc almost indcpendcnt of solute concentration, while micetlcs containing solubilizcd I-octanol increase in size with increasing solute content. The change in miccllar size for systems containing I-ocranol is influenced by hydrophilic group interactions bctwcen anionic and non-ionic surfpctants in the mixed system. K~_wwY/,s: Anionic-non-ionic solubilization.
mixed miccllcs; hcxadccyl
polyoxycthylcnc
Introduction
The solution properties of mixtures of some surfactants are often superior to those of the individual surfactant involved C1,2]. Therefore, mixed surfactant sys!ems are used in many practical applications, and arc also of great theoretical interest. Solubilization by surfactant solutions is closely related to detergency and is important in various industrial fields such as cosmetics, foods, medical supplies and surfactant-based separations. A number of papers dealing with the solubilization of organic% in micelIes have been published; Corrcspurrtiellcc to: M. Abe. Faculty of Scicncc and Tcchnology. Scicncc University of Tokyo, 2641 Yamaznki. Noda, Chiba 278, Japan. ’ Present address: Products Research Dcvclopmc:?t. S.T. Chemical Co. Ltd.. 4-10, I -chome. Shimoochiai. Shinjuku-ku, Tokyo 161, Japan. 0 I66-6622/92/P05.00
#:) 1992 -
Elscvicr
Science
Publishers
ethers; miccllar
expansion;
sodium
dodccyl
sulfate;
a few examples are given in Refs [3- 131. Published papers have generally discussed aqueous solutions containing a single surfactant, but relatively few papers have discussed solubilization in mixed surfactants. We have studied ihe solubilization in anionic-non-ionic [4, I I]? cationic-non-ionic [4], amphoteric-anionic [ 121 and amphoteric-nonionic [12] mixed surfactant systems. In anionicnon-ionic mixed surfactant systems, the solubility of azobenzene (an oil-soluble dye) is greater than predicted from a linear additivity rule applied to solubilization in the single surfactants involved [ 131. However, 1-hexanol exhibits less solubilization than that predicted by the linear mixing rule in anionic-non-ionic and in cationic-non-ionic sr- ^:tctant systems [4]. in this paper, we report the diameters of micelles which contain solubilized octane (a non-polar B.V. All rights
reserved.
38
solute) and I-octanol solutions of single surfactants. Experimental
(a polar solutr) in aqueous surfactants and of mixed
section
Mciterinls
Sodium dodecyl sulfate (SDS), purest grade (more than 99.7% purity), was a product of Tokyo Kasei Kogyo Co. Ltd., Tokyo. It was recrystallized from ethanol and was extracted with ether. Hcxadecyl polyoxycthylcnc ethers (C Ih HJ3 O(CHzCH20),,H abbreviated to C16POE,,, where II= IO, 20, 30 and 40) were supplied by Nihon Surfactant Industries Co. Ltd., Tokyo. They have a narrow molecular weight distribution. The purities of these surfactants were ascertained by both surface tension mcasurcmcnts and differential scanning calorimetry (DSC). No minimum was observed in the surface tension curve and no peak caused by impurities was recognized in the DSC mcasuremcnts.
The hydrodynamic size of the micclles was dctermined by carrying out dynamic light scattering measurements using a Model 4700 type submicron particle analyzer (Malvern Instruments Ltd., U.K.) at 30°C. The optical source of the light scattering apparatus is an argon laser operating at 488.0 nm (Mode1 Innova 90 of Coherent Corp., Palo Alto, U.S. -:ith a maximum power output of 5000 mW). The average scattercsd intensity and the time-dependent correlation function of the scattered intensity were measured at a constant scattering angle (90”). From these data. the translational diffusion coefficient D of the particle was determined and the hydrodynamic sizes tl of the particles wcrc obtained from the Stokes-Einstein equation
kT " = 3nrlD where rl is the viscosity of the solvent, /< is the Boltzmann constant and T is the absolute tcmpcrature. Before measurement, the sample solution was passed through a membrane filter (PTFE; 100 nm) for optical purification. Results and discussion
rl-Octane and I-octanol, purest grade, wcrc products of Tokyo Kasei Co. Ltd., Tokyo, and were used without further purilication. Water for injection JP (Japanese Pharmacopoeia) was obtained from Ohtsuka Pharmacy Co., Tokyo, and was used as received.
Samples containing a given concentration of surfactant solution were placed in several 100 ml glass-stoppered Erlenmeyer flasks. Varying amounts of organic solutes were added and the mixtures were stirred for 24 h at 30°C. After equilibrium had been established, the turbidity of I’ J solutions was measured by recording the transmittance at 700 nm with a double-beam spectrophotometer (MPS-2000 of Shimadzu Co. Ltd., Japan) equipped with a quartz cell (10mm x 10 mm).
Figure I shows the change in transmittance of SDS solutions (1.O-IO- ’ mol I - ’ ) with increasing total concentration of solute at 30°C. The transmittance begins to decrease when emulsion droplets appear. Extrapolation of the transmittance to 100% gives the maximum additivit, concentration (MAC) values for II-octane and 1-octanol as shown in Fig. 1. The MAC is the concentration of solute in the surfactant solution at saturation. The values of the MAC for the pure and mixed surfactant systems studied are shown in Tables I and 2.
In this surfactant
paper, d indicates the diameter micclle with solubilizcd organic
of the solute,
111. Ahc er ai./Colloi&
Sltrfaces
67 (1992) 37-43
39 2.-o
g 8 2 = ._ E 2 2 t-
90
$
80
1.5
70
1.0 0.5
1.0
Organic Fig. I. Transmittance tration of solubilizatc
TABLE
1.5
2.0
solute (mol/L> x 10e2
of SDS solutions at 30 ‘C.
0.5
n-Octane
with increasing
1.0 (mol/J_) x low’
Fig. 2. The ratio d/d, for miccllcs of sin@ with increasing concentration of n-octnnc concentration is 1.0. IO-” mol I-‘).
conccn-
surfactant solutions at 30°C (surTactant
I
Values of the maximum additive concentration n-octane and I-octanol for pure surfactant systems
(MAC)
Surfactunl”
n-Oclanc (niol I-‘)
I-Octanol (mall-‘)
SDS C,,PGE,o C,,PO& C,,PGE31, C,,POE,”
4.0.10-3 9.0. 10-3 9.5. 10-J 9.5.10-3 9.4. 10-3
8.9. 10-J 8.2.10-~ I.1 . 10-z 9.4.10-3 9.4. lo-3
~Conccntration,
TABLE
1.0. IO-‘mol
of
I-‘.
and de that of the surfactant micelle without the solute. Figure 2 represents cl/d, for pure SDS and pure Ci6POEn solutions (1.0. IO-’ mall-‘) with changing concentration of dissolved n-octane at 30°C. As can be seen in Fig. 2, the values of d/d,-, are always above 1.0 in the presence of ,I-octane, and are independent of the concentration of dissolved n-octane for the range of solute concentrations studied. Figure 3 illustrates d/do for pure SDS and C,,POE,, solutions (1.0. 10-2mol 1-l) as a func3.0
2
Values of the maximum additive concentration (MAC) rl-octane and I-oct:rnol ;or mixed surktant systems Mixed ratio
0.0
molar
Maximum
additive
n-Octane SDS-CI(, 8:2 6:4 4:6 2:8
POE,,”
SDS-CIh X:2 6:4 4:6 2:8
POEJo”
“Concentration,
of
(mol I- ’ )
concentration I-Oclanol
2.0 g CI 1.5
6.1 * IO-3 5.8. lO-3 6.0 * 10-J 7.3.10-3
7.4. 8.0. 7.2. 7.4.
!O_J
6.9 - IO-’ 8.1 . IO-’ 8.3. IO-3 7.9 * 10-3
9.7. 8.6. 8.3. 8.0.
10-3 to-3 1O-3 10-3
1O-3
10-J 10-3
1.o
1.0. IO-’ mol I-‘.
0.0
1.0
0.5 1-Octanol
(molL)
x 10”
Fig. 3. The ratio d/t/, for miccllcs of single surfactant solutions with increasing concentration of I-octanol at 30°C (surkctaktt concentration is 1.0. 10~‘moll-l).
40
tion of the concentration of dissolved I-octanol at 30°C. The solubilization of I-octanol results in an concentration increase in d/tie as the solute increases. and d/d,, is always greater than unity in of the I-octanol. The SDS and the presence C,,POElo solutions show a dramatic increase in diameter as the solute concentration increases, reaching a value of almost 3. Solutions containing ClhPOE30 and C,, POEjo do not C,(, POELO, show the abnormal enlargement observed for C,,POEIo and SDS. It is well known that a non-polar substance is solubilizcd into the hydrocarbon core of the micelle and a polar substance is solubilized into the palisade layer [ 14,151. The solubilization of h-octane in the anionic or non-ionic micelles causes only a slight increase in miceile diameter. consistent with 2. slight swelling of the micclle ccre in which the octane is located. However, I -octanol solubilizes in the palisade layer and the subsequent interactions between the hydroxyl group of the alcohol and the hydrophilic groups of the surfactants can lead to substantial micellc structural rearrangements, specifically, in this case, causing an increase in size. The diffusion coefficients of the micclles are examined as a function of the scattering vector in order to discuss the micellar shape of Ci6POElo in the presence of I-octanol. The reciprocal of the diffusion coefficient of Cr6POElo micelles was not constant and was not independent of the scattering vector either [16]. This result suggests that C,,POEio micclles would not be in the spherical form. In an SDS system, we have previously observed an increase in miccllar size upon solubilization of I -octanol [ 171, consistent with the results reported here. Ishiguro et al. [ 181 have reported that the size of micellcs containing solubilized benzene is slightly larger than that of a solute-free micelle. Benzene is probably solubilized predominantly in the hydrocarbon core of the micelIes.
2.0
g
1.5
1.o 0.5
0.0
Fig. 4. The
ratio
d/d0 for miccllcs
irt rttised
Figures 4 and SDS-CiG POE,,
mixed at
30 C
systems (the total surfactant concentration was 1.0. IO-’ mol I-‘) at 30°C respectively. The value of d/do is almost independent of the It-octane concentration (in systems containing h-octane) for the solute concentrations studied, as is also shown for the pure surfactant systems in Fig. 2. The dependence of (//do on the mixed micellar composition is shown in Fig. 6 for the two anionic-nonionic systems shown in Figs 4 and 5 in the presence of n-octane. AI1 mixed micelles with jr-octane present exhibit a larger diameter than in the absence of n-octane. The relative diameter reaches a maximum at a high mole fraction of non-ionic surfactant in the micelle (between 0.6 and 1.0, with a maxi2.0
g
1.5
1.0 0.5
sw-fcrctcutt s~~stenrs
5 depict d/~lo for /t-octane in and SDS-C,, POE,, mixed
of SDS-C,,,POE,,,
solutions with increasing conccntrztion of woctanc (surfactant conccntralion is 1.0. IO-’ mol 1-l).
0.0
Solrtbilimriort
1.0
n-Octane (mol/L) x 10.’
n-Octane Fig. 5. The
ratio
cl/d,
for
1.o (mol/L) x 10”
miccllcs of SDS-C,,POEJO
solutions with increasing concentration of u-octane (surfactant concentration is 1.0. IO- 2 mol I- ’ ).
mixed at 30°C
AI. Ahr et crl./Colloids
S~$aces
67 (1992) 37-43
41
2.0
2
1.5
1.0
0.0 Fig. 6. The containing composition.
0.2
ratio d/d, for SDS-Cr,PUE, rr-octane as a function of
I -0ctanol
mixed solutions micellar surfactant
mum near 0.8). It is not obvious why this mixed micellar composition range yields the greatest increase in micellar diameter. .The change of d/do for the solubilization of I-octanol in SDS-C16POE,, and SDSC,, POE,, mixed surfactant systems (total concentration, 1.0 - 10e2 mol l- ‘) is shown in Figs 7 and S, respectively. The value of d/do increases considerably with an increase in the concentration of solubilized I-octanol. The dependence of d/do on the mixed micellar composition is shown in Fig. 9 for the two anionic-non-ionic systems shown in Figs 7 and 8 in the presence of 1.0 10m3 mol I - ’ l
(molL> = 1O-’ mixed at 30°C
of I-octanol. All mixed micelles with I-octanol present exhibit a larger diameter than in the absence of l-octanol. The expansion coefficient A(d/d,) is defined by the following equation
where C is the concentration of dissolved I-octanol. This expansion coefficient, corresponding to the slopes of the lines in Figs 7 and 8, will be related to the char;ge of expansion with I-octanol concentrations greater than about 1 - 10e3 mall-’ Figure IO shows the expansion c,oefficients Ifi )r 2.0
0 1.5
1.o
Fig. 8. The ratio d/d, for miccllcs of SDS-C,hPOE,o solutions with increasing concentration of n-octane (surfactant concentration is 1.0. IO-’ mol I-‘).
2.0
$
0.5
0.0
I.0
0.4 0.6 0.8 Mole fraction of ClaPOEn
8
1.5
1
0
1.0
1.0 0.5 I-Octanol
1 .o
0.0
(mol/L) x 10’
Fig. 7. The ratio d/d, for micclles of SDS-C,,POE,O solutions with incrca
B
9
7
I
0.2
0.4
0.6
0.8
Mole mixed at 30°C
fraction
of
1.0
Cr6POEn
Fig. 9. The ratio d/d,, for SDS-C,6 POE, mixed solutions containing 1.0. 10e3 mall-r I-octanol as 3 function of micellar surfactant composition.
I
I
I
is consistent with the solubiiization behav%r of 1-octanoi. The expansion coefficient calculated here is a somewhat arbitrary parameter. It is, however, interesting that the expansion coefficient c:I:~ detect such changes with greater sensitivity !c value oft//d, alone (Fig. 9 v; Fig. 10). The ization of I!-octane in the core of the miceile I a poor probe of such a transition from a s;mgie m?eiie type to two coexisting miceiies as is shown in Fig. 6. For a solute, such as 1-octanoi which solubiiizes in the Faiisade layer of the micclie, the interactions between the hydrophilic head groups of the dissimilar SUifaCtalltS in t!Ie miceiie avior. are very important to the solubiiization
I
tem
---_ b< -------
‘.
. .
------
-.
--_
-.
---.
0
.2X
2.
0
0.0 0.2 Mole Fig. IO. Expansion tions as a runclion
a
-.
cl.4 0.6
0.8
1.0
fraction of CKPOE~I cocfficicnt of miccllar
of SDS-C,,POE, mixed surfxtant composition.
solu-
SDS-Cl6 POE,, mixed surfac!ani systems solubilizing l-octanol. If the mixed miceHe soiubiiization varies linearly with t!le mole fraction of a given surfactant in the micelic, the expansion coefficient would correspond to the dashed line in Fig. IO for the two mixed surfactant systems studied. This behavior would also be expected if the dissimilar surfactants form nearly pure component micciies, rather than mixed micelies. For the SDS-C,(,POElo system, the cxp:lnsion coeficient is lower than a linear mixing rui. would predict and reaches the minimum at about an equimoiar surfactant mixture. In the case the expansion coefficient of SDS-Cl6 POE,,, seems to obey the linear mixing rule. ‘,Ve have reported [19-213 that in mixed anionic-non-ionic surfactant systems, the tendency to form two miceiies of different compositions existing simultaneously (one anionic-rich and one non-ionic-rich) increases with decreasing alkyi chain length and/or with increasing poiyoxyethyiene chain length of the non-ionic surfactant. The formation of two coexisting immiscible miceIies in the SDS-C16POE,o system and of one type of mixed miceile in the SDS-C,6POE,, sys-
References 1
K. Ogino and M. AD:: (Eds), Miscd Surfactnnt Systems, Marcc! Dckkcr, New York, in press. J.F. Scztmchorn (Ed.), Phenomena in Mixd Sl;rfactant Systems. Vol. 31 I. ACS Symp. Ser.. Amc+an Chemical Socicry. Washington. DC. 1986. 3 G.A. Smith, S.D. Christian. E.E. Tucker and J.F. Scomchorn, J. Cclloid intcrf::cc Sci., I30 ( IYX9) 254. 4 C.M. Nguyen. J.F. Scamchorn and S.D. Christian, Colloids Surfaces. 30 (I 988) 335. 5 H. Uchiyama. S. Akao. M. Ahc and K. Ogino, Langmuir. 6 (1990) 1763. 6 S. Yiv. R. Zana. W. Ulbricht and H. Hoffmann. J. Colloid Inlcrfacc Sci.. X0 (19x1) 224. 7 E.B. Ahuin and E.A. Lissi. J. Colloid Intcrfclcc Sci., 95 (lYX3) 19x. 8 M. Almgrcn and S. Swarup. J. Colloid Intcrfxc Sci.. 91 (1983) 2.56. 9 K. Haynsc. S. Hayano and H. Tsubotn. J. Colloid intcfx:: Sci., IOI (1984) 336. 10 A.M. Blokhus. H. Hoiland and S. Bncklund. J. Co:loid lntcrface Sci., I I3 (1086) 9. II H. Uchiyama, M. Abe and K. O.cino, J. Jpn. Gii Chcm. Sac., 35 (19x6) 1031. and K. Ogino, C:l!loid I2 M. Abe. T. Kubota. H. Uchiyama Folym. Sci., X7 (1989) 365. I3 H. Uchiyamn, Y. Tokuoka, M. Abe nnd K. Ogino. J. Colloid Intcrfacc Sci., 132 (1989) 88. I4 D. Attwood and A.T. Florcncc. Surfactai:t Systems Ttxir Chcrristry. Pharmacy and Biology. Chapman and Hull. Londtin. l9R5. and Intcr~~cial Phcnomcna. Surfactants 15 M.J. Rosen, Wi!cy-Intcrscicncc, New York. :9R9. p. 170. I6 M. Ab;. Y. Tokuokn, H. Uchiyamn and K. Ogino, unpub:ishcd results. 1990. I7 M. Abe and K. Ogino, J. Jpn. Oil Chcm. Sot. Z! (19Y2) 569.
18 T. Ishiguro, T. Ogushi. Y. Iqhiwada n;xl T. As~hara. Kogyo Kagaku Zasshi, 68 (1965) 2 idi). 19 M. Abe, N. Tsubaki and K. Oginu. f. c’e!!oid lntcrface sci., 107 (19S5) 50.1.
20 21
K. Ogino, N. Tsubaki and M. Abe. J. Colloid Interfact: Sci., 107 (1985) 339. K. Ogino. T. Kakihara, H. Uchiynma and M. Abe. J. Am. Oil Chem. SOL, 65 (1988) 405.