Heating-induced micelle to vesicle transition in the cationic-anionic surfactant systems: Comprehensive study and understanding

Article abstract of DOI:10.1021/jp045158a

Heating-induced micelle to vesicle transition (MVT), which has been rarely reported in surfactant systems, was systemically studied in a number of mixed cationic-anionic surfactant systems. According to the turbidity measurements, the investigated systems can be divided into two classes: Class A and B. Heating-induced MVT was observed in Class A at certain total surfactant concentrations and mixed surfactant ratios, while no such transition was found in Class B. Further investigations revealed that the heating-induced MVT is more likely to take place in the cationic-anionic surfactant systems with relatively stronger molecule interaction and larger micelle aggregation number. The effects of several physicochemical factors, such as the variation of mixed surfactant ratios and the addition of n-decanol on the heating-induced MVT, were also studied. ? 2005 American Chemical Society.

Full text of DOI:10.1021/jp045158a

4104
J. Phys. Chem. B 2005, 109, 4104-4110
Heating-Induced Micelle to Vesicle Transition in the Cationic-Anionic Surfactant Systems:
Comprehensive Study and Understanding
†
,†
†
†
†
Haiqing Yin, Jianbin Huang,* Yiyang Lin, Yongyi Zhang, Shunchen Qiu, and
Jianping Ye‡
State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and
Molecular Engineering, Peking UniVersity, Beijing, 100871, People’s Republic of China and Institute of
Chemistry, Chinese Academy of Science, Beijing, People’s Republic of China
ReceiVed: October 23, 2004; In Final Form: January 6, 2005
Heating-induced micelle to vesicle transition (MVT), which has been rarely reported in surfactant systems,
was systemically studied in a number of mixed cationic-anionic surfactant systems. According to the turbidity
measurements, the investigated systems can be divided into two classes: Class A and B. Heating-induced
MVT was observed in Class A at certain total surfactant concentrations and mixed surfactant ratios, while no
such transition was found in Class B. Further investigations revealed that the heating-induced MVT is more
likely to take place in the cationic-anionic surfactant systems with relatively stronger molecule interaction
and larger micelle aggregation number. The effects of several physicochemical factors, such as the variation
of mixed surfactant ratios and the addition of n-decanol on the heating-induced MVT, were also studied.
9
Introduction
ionic surfactant/cosurfactant systems, which was attributed to
the dehydration of the surfactant headgroup. Recently, heating-
Amphiphilic molecules have the ability to form various
organized assemblies in solutions such as spherical micelles,
cylindrical micelles, vesicles, or more complex structures, i.e.,
bicontinuous phases and lyotropic liquid crystals, etc. These self-
assemblies have been widely exploited in diverse areas such as
catalysis, biochemistry, and material synthesis as well as
induced MVT was also studied in mixed lipid/ionic surfactant
10
systems. The decreasing solubilization ability of surfactants
in lipid vesicles upon heating was considered to account for
the transition. In our previous study we reported a heating-
induced MVT in the mixed cationic-anionic surfactant system
of sodium n-dodecyl sulfate (SDS)/n-dodecyltriethylammonium
1
petroleum, chemical, and pharmaceutical industries. In the past
11
bromide (DTEAB). Afterward, we also observed similar
few decades research on the formations and transformations of
different self-assemblies has been investigated in numerous
transitions in some other cationic-anionic surfactant systems.
Nevertheless, the transitions in our cases cannot be simply
explained with the interpretations for the systems mentioned
above and may have a more complex origin. Hence, it is
necessary to perform comprehensive studies on the heating-
induced MVT in the cationic-anionic surfactant systems.
In this work heating-induced MVT was investigated exten-
sively in a number of cationic-anionic surfactant systems. It
was revealed this transition may be a general phenomenon in
the cationic-anionic surfactant systems with relatively stronger
molecule interaction and larger micelle aggregation number. On
this basis the transition was adjusted by several physicochemical
factors, such as the mixed surfactant ratio and addition of
n-decanol.
2
works, especially on the effect of cosurfactants’ addition, pH,
temperature, salts, force fields, etc.
Compared with other methods, temperature variation can
provide a quite simple way in tailoring assemblies, which has
attracted special attention of scientists.3 The temperature-
sensitive systems are convenient for studying the individual stage
of the aggregate transition since the transition can be cycled or
stopped at any required step in measurements. Kinetic aspects
can also be examined by controlling the heating and cooling
rates.
It is known that temperature has great effect on the nonionic
surfactant systems. Usually such systems have cloud point
4
properties i.e., heating-induced phase separations, which are
attributed to the dehydration of the hydrophilic groups of
surfactants upon heating. In contrast, in ionic surfactant systems
the aggregate size normally decreases when the temperature
Experimental Section
Materials. Quaternary ammonium bromides including
n-dodecylmethyldiethylammonium bromide (DME2AB),
n-dodecyltriethylammonium bromide (DTEAB), n-dodecyl-
tripropylammonium bromide (DTPAB), and n-decyltriethylam-
monium bromide (DeTEAB) were prepared by reaction of
5
6
increases. In fact, in most vesicular systems phase transitions
7
or transitions from vesicle to micelle usually take place with
increasing temperature. However, the reverse process, such as
heating-induced micelle to vesicle transition (MVT), has been
rarely been reported in surfactant systems. It was once observed
1-bromododecane and the corresponding trialkylamine. Sodium
laurate (SL) was prepared by neutralizing lauric acid with NaOH
in ethanol. Sodium n-decyl sulfate (SDeS), sodium n-octylsul-
fonate (SOS), and sodium n-dodecylsulfonate (SDSO3) were
products of Beijing Chemical Co. Sodium n-dodecyl sulfate
(SDS) and sodium n-dodecylbenzenesulfonate (SDBS) were
bought from ACROS ORGANICS Co. All the surfactants were
8
by H. Hoffmann in some nonionic surfactant systems and mixed
*
To whom correspondence should be addressed. Phone:
8
6-10-62753557. Fax: 86-10-62751708. E-mail: JBHuang@pku.edu.cn.
†
‡
Peking University.
Chinese Academy of Science.
1
0.1021/jp045158a CCC: $30.25 © 2005 American Chemical Society
Published on Web 02/12/2005

Cationic-Anionic Surfactant Systems
J. Phys. Chem. B, Vol. 109, No. 9, 2005 4105
Figure 1. Turbidity heating curves for some Class A (a) and Class B (b) systems.
recrystallized five times from mixed solvents of ethanol-acetone
or ether-acetone. The purity of the surfactant was examined,
and no surface tension minimum was found in the surface
tension curve. The water used was redistilled from potassium
permanganate. The other reagents were products of A. R. Grade.
Turbidity Measurements. Turbidity measurements were
carried out with a Shimadzu UV-250 spectrophotometer at
where C is the total surfactant concentration, cmc is the critical
micelle concentration, and [Q] is the concentration of quencher.
Critical Micelle Concentration Measurements. The critical
micelle concentrations of surfactants in aqueous solutions were
obtained from the surface tension vs concentration curves by
the drop volume method. The ionic strength of the system was
-
1
adjusted to 0.1 mol kg with NaBr all through the measure-
5
14.5 nm.
ments.
DLS Measurements. Dynamic light scattering measurements
were performed with a spectrometer (ALV-5000/E/WIN Mul-
tiple Tau Digital Correlator) and a Spectra-Physics 2017
â Parameter. On the basis of the regular solution theory,
interaction parameters between surfactant molecules in micelles
of mixed systems (named as â ) are obtained from critical
m
1
3
2
00 mW Ar laser (514.5 nm wavelength). The scattering angle
micelle concentration data using eqs 4 and 5
was 90°. The intensity autocorrelation functions were analyzed
using the Contin method, and the apparent hydrodynamic radius
M 2
M
1 12
M
M
(
M 2
X1 ) ln(R C /X1 C1 )
<
Rh> was deduced from the diffusion coefficient D by the
) 1 (4)
M
M
M
Stokes-Einstein formula Rh ) kBT/(6πηD).
(1 - X1 ) ln[(1 - R )C /(1 - X1 )C2 ]
1 12
Transmission Electron Microscopy. Samples for TEM were
prepared by negative-staining technique with uranyl acetate
water solution. A JEM-100CX electron microscope was em-
ployed in the microscopic observation.
M
12
M
M
ln(R C /X1 C1
)
1
âm )
(5)
M 2
(
1 - X1
)
Rheology Measurements. The rheological properties of
samples were measured with a ThermoHaake RS300 rheometer.
A double-gap cylinder sensor system was used with an outside
gap of 0.30 mm and an inside gap of 0.25 mm.
DSC Measurements. Differential canning calorimetry mea-
surements were carried out (1 °C/min) using a Micro DCS III
where X1M is the mole fraction of surfactant 1 of the total
M
M
M
surfactants in the mixed micelle. C1 , C2 , and C12 are the
critical micelle concentrations for surfactant 1, surfactant 2, and
their mixture, respectively, at the mole fraction R1. The ionic
strength of the system was kept constant to avoid the electrical
effect.
(Setaram-France) instrument.
Time-Resolved Fluorescence Quenching (TRFQ). This
method was applied to determine the micelle aggregation
number (N) of the micellar system using pyrene as a fluores-
cence probe and dodecylpyridinium chloride as a quencher of
the fluorescence probe. Pyrene fluorescence decay curves were
monitored by a Horiba NAES-1100 single-photon counting
spectrophotometer (excitation at 337 nm and emission at
Results and Discussion
Classification of the Cationic-Anionic Surfactant Systems
According to the Turbidity Measurements. Eleven kinds of
cationic-anionic surfactant systems were selected for our studies
(see the Experimental Section for the full names of the individual
surfactants), considering the variation of cationic surfactant
headgroups (SDS/DME2AB, SDS/DTEAB, SDS/DTPAB),
anionic surfactant headgroups (SL/DTEAB at pH ) 9.2
and 13, respectively, SDSO3/DTEAB, SDBS/DTEAB), as
well as the changes of the hydrocarbon chain lengths
3
94 nm).
Calculation of Micelle Aggregation Number. The fluores-
cence decay eqs 1 and 2 in the absence and presence of
12
quencher, respectively, are fitted using a weighted least-squares
procedure by a DECAN 1.0 software
(SDS/DeTEAB, SDeS/DTEAB, SDeS/DeTEAB, SOS/DTEAB).
Turbidity measurements were carried out to monitor the
variations upon increasing temperature in all selected systems.
According to the turbidity curves, these systems can be divided
into two classes which are named as Class A and B. The
SDS/DME2AB, SDS/DTEAB, SDS/DTPAB, SDeS/DTEAB,
SDS/DeTEAB, and SDeS/DeTEAB systems belong to
Class A, while the SL/DTEAB (pH ) 9.2), SL/DTEAB
I(t) ) I(0)exp(-t/τ)
(1)
(2)
I(t) ) I(0)exp{-A t - A [1 - exp(-A t)]}
2
3
4
where I(t) and I(0) are the fluorescence intensities at time t and
time zero, respectively, τ is the pyrene fluorescence lifetime
and A2, A3, and A4 are the time-independent fitting parameters.
The micelle aggregation number N is obtained by eq 3
(
pH ) 13), SDSO3/DTEAB, SDBS/DTEAB, and SOS/DTEAB
systems belong to Class B. For Class A there was an obvious
increase of the turbidity upon increasing temperature
2
N ) A [(C - cmc)/[Q][1 + (A - 1/τ)/A A ]
(3)
3
2
3 4
(
Figure 1a). During this process the original transparent ap-

4106 J. Phys. Chem. B, Vol. 109, No. 9, 2005
Yin et al.
Figure 2. Hydrodynamic radius (R
the Contin method.
h
) distributions of SDS/DME
2
AB (2.7:1, Ctotal ) 10 mM) at 25 (a), 27 (b), 35 (c), and 45 °C (d) calculated by
pearance of the solution turned slightly bluish. In contrast, no
significant increase of the turbidity upon heating was observed
for Class B no matter how the total concentration (Ctotal) or
mixed surfactant molar ratio was varied (Figure 1b). The
increase of the turbidity with increasing temperature in Class
A indicates the size growth or even structural transition of
surfactant aggregates, showing a quite different behavior from
Class B. Further investigations were performed in the
SDS/DME2AB system selected from Class A to confirm our
speculation. In addition, the mixed systems SDSO3/DTEAB and
SL/DTEAB (pH ) 13), in which the individual surfactants have
almost the same hydrocarbon chain length, were also selected
from Class B for comparison.
Microstructure Transition upon Temperature Increasing
in Class A. From Figure 1a it was found that the temperature
interval of obvious turbidity increase for the SDS/DME2AB
system (molar ratio 2.7:1, Ctotal ) 10 mM) was from ca. 27 to
Figure 3. Steady flow curves (apparent relative viscosity ηa,r vs shear
rate) of the system SDS:DME AB (2.7:1, Ctotal ) 10 mM) at different
temperatures (ηa,r ) η/η , where η and η are the viscosities of the
solution and water, respectively).
2
0
0
4
2
5 °C. The average hydrodynamic radius <Rh> was 18 nm at
5 °C measured by DLS (Figure 2a), which is a typical value
for a micellar system. The steady rheology measurements clearly
revealed the non-Newtonian nature of the solution. As shown
in Figure 3, shear-thickening and shear-thinning behaviors took
place successively with the increase of shear rate, suggesting
the existence of asymmetrical aggregates. Similar rheological
behaviors were also reported in some dilute surfactant solutions
14
containing cylindrical micelles. In addition, the average micelle
aggregation number (〈N〉) is about 1100, calculated from the
TRFQ data (see the Experimental Section), showing a typical
value of cylindrical micelles.15 Moreover, TEM results showed
that very few small spherical vesicles exist in this system. Hence,
it may be concluded that cylindrical micelles are the dominating
surfactant aggregates at 25 °C.
Figure 4. Micrographs of the system SDS/DME
2
AB (2.7:1,
Ctotal ) 10 mM) at 27 (a) and 45 °C (b) by negative-staining technique.
However, the situation was different as the temperature
increased to 27 °C. DLS plot (Figure 2b) showed that at 27 °C
the peak corresponding to the cylindrical micelles shrank
compared with that of 25 °C whereas another peak appeared
(R ≈ 100 nm). Correspondingly, the formation of spherical
h
vesicles with a diameter of ca. 100-200 nm was observed by
TEM (Figure 4a), which coincided with the new peak in the
DLS plot. Moreover, there was an obvious decrease of the

Cationic-Anionic Surfactant Systems
J. Phys. Chem. B, Vol. 109, No. 9, 2005 4107
Figure 5. DSC curves of the systems: SDS/DME
2
AB system (2.7:1, Ctotal ) 10 mM) (a) and SDS/DTPAB (2:1, Ctotal ) 10 mM) (b).
Figure 6. Turbidity heating curves of SDS/DME
c) with different mixed surfactant molar ratios.
2
AB (Ctotal ) 10 mM) (a), SDS/DTEAB (Ctotal ) 10 mM) (b), and SDS/DTPAB (Ctotal ) 10 mM)
(
TABLE 1: List of TMVT for Several Class A Systems
TABLE 3: Average Aggregation Numbers 〈N〉 of Class A
and Class B Systems at 25 °C
systems
TMVT (°C)
systems
〈N〉
SDS/DME
2
AB (2.7:1,Ctotal ) 10 mM)
27
30
37
43
20
SDS/DTPAB (2:1, Ctotal ) 10 mM)
SDeS/DeTEAB (2.1:1, Ctotal ) 15 mM)
SDeS/DTEAB (3.2:1, Ctotal ) 20 mM)
SDS/DeTEAB (1.6:1, Ctotal ) 5 mM)
Class A
AB (2.7:1,Ctotal ) 10 mM)
SDS/DTEAB (2:1, Ctotal ) 10 mM)
SDS/DTPAB (2:1, Ctotal ) 10 mM)
SDS/DME
2
1100
850
430
Class B
TABLE 2: â Parameters in Micelle (â
and Class B Systems
m
) of Several Class A
SDSO
3
/DTEAB (2:1, Ctotal ) 10 mM)
188
187
134
SL/DTEAB (2:1, Ctotal ) 10 mM, pH ) 13)
SL/DTEAB (2:1, Ctotal ) 10 mM, pH ) 9.2)
systemsa
â
m
Class A
AB (molar ratio 2.7:1)
SDS/DTEAB (molar ratio 2:1)
SDS/DTPAB (molar ratio 2:1)
with the TEM observation (Figure 4b) it may be concluded that
spherical vesicles became the dominating aggregates at 45 °C.
Thus, the micelle to vesicle transition upon temperature increas-
ing from 27 to 45°C was demonstrated in the SDS/DME2AB
system (2.7:1, Ctotal ) 10 mM), which is coincident with the
turbidity measurement result (Figure 1a).
SDS/DME
2
-15.0
-13.3
-15.0
Class B
/DTEAB (molar ratio 1:1)
SDBS/DEAB (molar ratio 1:1)
SL/DTEAB (molar ratio 1:1, pH ) 13)
SL/DTEAB (molar ratio 1:1, pH ) 9.2)
b
SDSO
3
-9.6
-8.9
-8.9
-6.2
Similar rheology, DLS, and TEM results were also obtained
in the SDS/DTPAB system (see Figures 1 and 2 in the
Supporting Information) and other Class A systems. Referring
to our previous work in the SDS/DTEAB system,11 it can be
concluded that the increase of the turbidity upon heating for
Class A (Figure 1a) is attributed to the temperature-induced
MVT in this kind of systems.
a
-1
T ) 25 °C, I (ionic strength) ) 0.1 mol.kg for all systems if
without further notation. cmc of SDSO
limit of the Krafft point.
b
3
at 40 °C was used due to the
apparent relative viscosity ηa,r of the solution at low shear rate
Figure 3), indicating that the shape of aggregates turned from
(
asymmetric to symmetric. All these results suggest the transition
from cylindrical micelles to spherical vesicles in the system.
Hence, the first turning point of the turbidity heating curve may
be considered as the beginning of obvious MVT, and the
corresponding temperature will be called TMVT. The TMVTs of
several Class A systems are listed in Table 1.
DSC measurements were employed to study the heat effect
of the temperature-induced MVT in the Class A systems (Figure
5). Endothermic peaks can be obviously observed in the DSC
heating curves. The temperatures for the corresponding peaks
coincided with the temperature intervals of MVT obtained from
the turbidity measurements. Considering the spontaneity of the
transition in these systems, it is demonstrated that the temper-
ature-induced MVT in Class A is accompanied by an increase
of entropy.
The transition from micelle to vesicle continued as the
temperature continued increasing. At 45 °C the system became
a complete Newtonian fluid (Figure 3) and the peak assigned
to cylindrical micelles almost disappeared in the DLS plot,
leaving the peak assigned to vesicles (Figure 2d). Combined
Turbidity variations of Class A systems during a heating-
cooling circulation were also studied (see Figure 3 in the

4108 J. Phys. Chem. B, Vol. 109, No. 9, 2005
Yin et al.
Figure 7. Turbidity variations as a function of temperature for the systems: SDS/DTEAB (2:1, Ctotal ) 10 mM) (a) and SDSO
2:1, Ctotal ) 10 mM) (b) upon addition of n-decanol.
3
/DTEAB
(
h 3
Figure 8. R distributions of SDSO /DTEAB (2:1, Ctotal ) 10 mM) upon addition of 1.4 mM n-decanol at 25 (a), 30 (b), 35 (c), and 50 °C (d).
Supporting Information). The shapes of the cooling curves are
similar to the heating curves, although they do not overlap
completely. In addition, all systems can recover their original
states after the heating-cooling circulation, suggesting the
temperature-induced MVT in these systems may be considered
as a reversible process.
an easy and effective way to find temperature-induced MVT in
the cationic-anionic surfactant systems.
Differences of Molecule Interaction and Micelle Aggrega-
tion Number between Class A and B. The nature of formation
or transformation of self-assemblies in solutions is to satisfy
the corresponding requirements of energy and geometry.
Therefore, the interaction between the surfactant molecules in
the organized assemblies should play an important role for the
heating-induced MVT in our systems. On the basis of regular
solution theory, the â parameter is utilized to estimate the
Effect of Temperature on Class B. As mentioned above,
no increase of turbidity upon heating was observed for Class
B. From the results of DLS, the size of micelles of Class B
always decreased with increasing temperature (see Figure 4 in
the Supporting Information), which is similar to the behavior
of a single ionic surfactant system. The results of DLS and TEM
also showed no vesicle formation upon heating in these systems.
Additionally, no obvious heat effect was detected by DSC
measurements.
1
3
molecule interaction in mixed systems. The â parameters in
micelles (âm) of several Class A and B systems have been
calculated (see Experimental Section) and listed in Table 2.
From Table 2 it is found that âm parameters of all the studied
systems are negative, indicating the existence of an attractive
interaction between the surfactant molecules. Among these
systems the absolute value of the âm parameter of Class
A is above 13 while that of Class B is below 10. It is worth
noting that âm parameters of Class A are generally more
In conclusion, heating-induced MVT was demonstrated in
Class A while no such transition was found in Class B.
Considering the complexity of rheology, DLS, as well as TEM
and the coincidence of these results with the turbidity measure-
ments, the increase of turbidity upon heating may be used as

Cationic-Anionic Surfactant Systems
J. Phys. Chem. B, Vol. 109, No. 9, 2005 4109
negative than those of Class B, indicating stronger interaction
between the surfactant molecules in Class A.13
of medium chained alcohols may facilitate heating-induced
MVT and reduce the TMVT of Class A systems. In fact, the
addition of a tiny amount of n-decanol effectively lowered the
TMVT of the SDS/DTEAB system (Figure 7a).
Furthermore, it is interesting to find that as n-decanol was
added into some Class B systems such as SDSO3/DTEAB
The average micelle aggregation numbers (〈N〉) of several
Class A and B systems have been also measured and listed in
Table 3. It is clearly shown that Class A has a larger 〈N〉 than
Class B. Combined with the results of DLS, it may be concluded
that surfactant molecules pack more closely and aggregate into
larger micelles in Class A.
(2:1, Ctotal ) 10 mM), the micelles of the system were
transformed into vesicles upon increasing temperature, which
was demonstrated by the turbidity (Figure 7b) and DLS (Figure
8) measurements. TRFQ data also revealed that 〈N〉 of the
system SDSO3/DTEAB (2:1, Ctotal ) 10 mM) increased from
188 to 432 at 25 °C (close to the case of Class A) after addition
of 1.4 mM n-decanol, indicating a notable increase of the p
value of the system. Hence, addition of n-decanol may promote
the occurrence of heating-induced MVT in this case.
The critical packing parameter p proposed by Israelachvili
et al.16 has been widely used to explain the formation and
transformation of self-assemblies in dilute surfactant solutions:
1
7
0
e p e 1/3 for sphere micelle, 1/3 e p e 1/2 for cylinder
micelle, and 1/2 e p e 1 for bilayer structure (p is defined as
V/a0lc, where V is the surfactant tail volume, lc is the tail length,
and a0 is the equilibrium area per molecule at the aggregate
surface). Considering the fact that the individual surfactant
molecules of the Class A and B systems in Table 3 have the
same length of hydrocarbon chain, V/lc is almost the same and
the variation of a0 will significantly influence the p values of
these systems. The results of âm and 〈N〉 suggest that Class A
systems have relatively larger p values than Class B systems,
which may be closer to the case of vesicle formation. Thus, the
micelles of Class A are more easily transformed into vesicles
than those of Class B. Furthermore, the strong attraction between
oppositely charged surfactant headgroups of Class A systems
may also impart some nonionic character to the mixed mi-
Conclusion
Heating-induced MVT was systemically investigated in a
number of cationic-anionic surfactant systems. Turbidity
measurements can be used as an easy and effective way to
determine the occurrence of MVT in the cationic-anionic
surfactant systems. It is predicted that heating-induced MVT
will take place more easily in the cationic-anionic surfactant
systems with relatively stronger molecule interactions and larger
micelle aggregation numbers. On this basis TMVT can be
efficiently adjusted by variation of the mixed surfactant ratios
or addition of n-decanol. It is also noteworthy that the addition
of n-decanol can promote the occurrence of heating-induced
MVT in some cationic-anionic systems in which no such
transition is observed before addition of n-decanol. We hope
this work may advance the understanding of the temperature-
induced self-assembly transitions and promote its applications
in related fields.
1
8
celles, which will cause a0 to be effectively decreased upon
heating due to dehydration of headgroups. Hence, the transfor-
mation from micelles to vesicles may occur as the temperature
increases beyond a certain value (TMVT). As for Class B, the
size of micelles will generally decrease upon heating no matter
how the total concentration or mixed surfactant ratio is varied,
showing similar behavior in ionic surfactant systems. Thus, it
can be concluded that heating-induced MVT is more likely to
take place in the cationic-anionic surfactant systems with a
relatively stronger molecule interaction and larger micelle
aggregation number. On this basis the effects of several
physicochemical factors on the heating-induced MVT, such as
variation of mixed surfactant ratios and addition of n-decanol,
were further studied.
Acknowledgment. This work was supported by National
Natural Science Foundation of China (20233010, 20373003,
20425310).
Supporting Information Available: Rheology, DLS, and
TEM results for the SDS/DTPAB system (Figures 1, and 2),
turbidity variations of Class A systems (Figure 3), rheology
variations for the SDSO3/DTEAB and SL/DTEAB systems, and
rheology variations for the SDS/DTEAB and SDS/DTPAB
systems. This material is available free of charge via the Internet
at http://pubs.acs.org.
Variation of the Mixed Surfactant Molar Ratio in Class
A. Figure 6 reveals that the heating-induced MVT in Class A
has a strong dependence on the mixed surfactant molar ratio.
TMVT decreased obviously with the mixed ratio approaching 1:1.
It is known that the electrostatic attraction between the head-
groups of oppositely charged surfactants in cationic-anionic
surfactant systems becomes stronger as the mixed ratio ap-
proaches equimolar, which will make the surfactant molecules
pack closer in the aggregates. Correspondingly, the p value of
the system will increase and be closer to the case of vesicle
References and Notes
(1) (a) Evans, D. F.; Wennerstrom, H. The Colloidal Domain, Where
Physics, Chemistry, Biology, and Technology Meet, 2nd ed.; John Wiley:
New York, 1999. (b) Birdi, K. S. Surface and Colloid Chemistry; CRC
Press: New York, 1997. (c) Fendler, J. H. Membrane Mimetic Chemistry;
John Wiley: New York, 1982. (d) Rosoff, M. Vesicles; Marcel Dekker:
New York, 1996. (e) Makai, A.; Csanyi, E.; Nemeth, Z.; Palinkas, J.; Eros,
I. Int. J. Pharm. 2003, 256, 95-107. (f) Kresge, C. T.; Leonowicz, M. E.;
Roth, W. J.; Vartuli, J. C.; Beck, J. S. Nature 1992, 359, 710-712.
(2) (a) Hao, J. C.; Hoffmann, H.; Horbaschek, K. J. Phys. Chem. B
2000, 104, 10144-10153. (b) Hassan, P. A.; Raghavan, S. R.; Kaler, E.
W. Langmuir 2002, 18, 2543-2548. (c) Mao, M.; Huang, J. B.; Zhu, B.
Y.; Ye, J. P. J. Phys. Chem. B 2002, 106, 219-225. (d) Wang, C. Z.; Huang,
J. B.; Tang, S. H.; Zhu, B. Y. Langmuir 2001, 17, 6389-6392.
1
9
formation. DLS results also demonstrated the formation of
larger aggregates in Class A systems as the mixed ratio
approached 1:1 (see Figure 5 in the Supporting Information).
Therefore, MVT will take place at a lower temperature as the
mixed ratio approaches equimolar.
Addition of n-Decanol. Recently, much interest has been
focused upon the addition of cosurfactants such as medium-
chained alcohols in surfactant solutions for their great impact
on the formation and transformation of surfactant self-as-
semblies.2 Due to the poor solubility in water, medium-chained
(
3) (a) Bott, R.; Wolff, T.; Zierold, K. Langmuir 2002, 18, 2004-
2
012. (b) Gorski, N.; Kalus, J. Langmuir 2001, 17, 4211-4215. (c) Kumar,
S.; Sharma, D.; Khan, Z. A.; Din, K. U. Langmuir 2001, 17, 5813-5816.
(d) Forster, S.; Plantenberg, T. Angew. Chem., Int. Ed. 2002, 41, 688-
714.
0
alcohols are considered to solubilize into the palisade of micelles
with the hydroxyl groups toward the surface,21 which can cause
(4) (a) Robson, R. J.; Dennis, E. A. J. Phys. Chem. 1977, 81, 1075.
b) Corti, M.; Minero, C.; Degiorgio, V. J. Phys. Chem. 1984, 88, 309.
c) Ravey, J. C. J. Colloid Interface Sci. 1983, 94, 289. (d) Hayter, J. B.;
(
(
an increase of the p value and growth of micelles. Combined
with our previous discussion, it can be expected that the addition
Zulauf, M. Colloid Polym. Sci. 1982, 260, 1023.

4110 J. Phys. Chem. B, Vol. 109, No. 9, 2005
Yin et al.
(
5) (a) Mazer, N. A.; Benedek, G. B.; Carey, M. C. J. Phys. Chem.
(c) Hofmann, S.; Hoffmann, H. J. Phys. Chem. B 1998, 102, 5614-5624.
(d) Oelschlaeger, Cl.; Waton, G.; Candau, S. J.; Cates, M. E. Langmuir
2002, 18, 7265-7271.
1
8
4
980, 84, 3105. (b) Porte, G.; Appell, J.; Poggl, Y. J. Phys. Chem. 1980,
4, 3105. (c) Yu, Z. J.; Zhao, G. X. J. Colloid Interface Sci. 1989, 414-
20. (d) Rohde, A.; Sackmann, E. J. Colloid Interface Sci. 1979, 70, 494.
(
15) Lianos, P.; Lang, J.; Strazlelle, C.; Zana, R. J. Phys. Chem. 1982,
(
6) (a) Ueno, M.; Katoh, S.; Kobayashi, S.; Tomoyama, S.; Obata, R.;
Nakao, H.; Ohsawa, S.; Koyama, N.; Morita, Y. Langmuir 1991, 7, 918-
22. (b) Chapman, D.; Williams, R. M.; Ladbrooke, B. D. Chem. Phys.
8
6, 1019-1025.
(16) (a) Israelachvili, J. N.; Mitchell, D. J.; Ninham, B. W. J. Chem.
9
Soc., Faraday Trans. 2 1976, 72, 1525. (b) Israelachvili, J. N.; Mitchell,
D. J.; Ninham, B. W. Biochim. Biophys. Acta 1977, 470, 185.
(c) Israelachvili, J. N.; Marcelja, S.; Horn, R. G. Q. ReV. Biophys. 1980,
13, 121.
Lipids 1967, 1, 445. (c) Chapman, D. Form and Function of Phospholipids;
Ansell, G. B., Hawthorne, J. N., Eds.; Elsevier: Amsterdam, 1973; p 117.
(
d) Wikinson, D. A.; Nagle, J. F. Liposomes; Knight, C. G., Ed.; Elsevier:
Amsterdam, 1981; p 273.
7) (a) Mendes, E.; Oda, R.; Manohar, C.; Narayanan, J. J. Phys. Chem.
(
(17) (a) Nagarajan, R. Structure-Performance Relationships in Surfact-
B 1998, 102, 338-343. (b) Buwalda, R. T.; Stuart, M. C. A.; Engberts, J.
B. F. N. Langmuir 2000, 16, 6780-6786. (c) Hassan, P. A.; Valaulikar, B.
S.; Manohar, C.; Kern, F.; Bourdieu, L.; Candau, S. J. Langmuir 1996, 12,
ants; Esumi, K., Ueno, M., Eds.; Marcel Dekker: New York, 1997; Chapter
1
, pp 1-89. (b) Dill, K. A.; Flory, P. J. Proc. Natl. Acad. Sci. U.S.A. 1980,
77, 3115. (c) Ben-Shaul, A.; Szleifer, I.; Gelbart, W. M. Proc. Natl. Acad.
4
350-4357. (d) Narayanan, J.; Mendes, E.; Manohar, C. Int. J. Mod. Phys.
B 2002, 16, 375-382.
8) Wanka, G.; Hoffmann, H.; Ulbricht, W. Colloid Polym. Sci. 1990,
Sci. U.S.A. 1984, 81, 4601. (d) Puvvada, S.; Blankschtein, D. J. Phys. Chem.
1
992, 96, 5567-5579.
18) (a) Kumar, S.; Sharma, D.; Din, K. U. Langmuir 2000, 16, 6821-
824. (b) Yu, Z. J.; Neuman, R. D. Langmuir 1994, 10, 377-380. (c) Yu,
(
(
2
68, 101-117.
6
(9) Hoffmann, H.; Horbaschek, K.; Witte, F. J. Colloid Interface Sci.
Z. J.; Xu, G. Z. J. Phys. Chem. 1989, 93, 7441-7445. (d) Srinivasa, R. R.;
Hakan, E.; Kaler, E. W. Langmuir 2002, 18, 1056-1064. (e) Bales, B. L.;
Zana, R. Langmuir 2004, 20, 1579-1581.
2
001, 235, 33-45.
(
(
10) Majhi, P. R.; Blume, A. J. Phys. Chem. B 2002, 106, 10753-10763.
11) Yin, H. Q.; Zhou, Z. K.; Huang, J. B.; Zheng, R.; Zhang, Y. Y.
Angew. Chem., Int. Ed. 2003, 42, 2188-2191.
(19) (a) Brasher, L. L.; Herrington, K. L.; Kaler, E. W. Langmuir 1995,
11, 4267-4277. (b) Yin, H. Q.; Mao, M.; Huang, J. B.; Fu, H. L. Langmuir
2002, 18, 9198-9203.
(
12) (a) Zana, R. In Surfactant Solutions. New Methods of InVestigation;
Zana, R., Ed.; M. Dekker Inc.: New York, 1987; Chapter 5. (b) Miller, D.
D.; Magid, L. J.; Evans, D. F. J. Phys. Chem. 1990, 94, 5921-5930.
(
20) (a) Hoffmann, H.; Ebert, G. Angew. Chem., Int. Ed. Engl. 1988,
(
c) Gehlen, M.; De Schryver, F. C. Chem. ReV. 1993, 93, 199.
2
7, 2-912. (b) Amaral, L. Q.; Santin Filho, O.; Taddei, G.; Vila-Romeu,
(
13) (a) Li, F.; Rosen, M. J.; Sulthana, S. B. Langmuir 2002, 17, 1037-
N. Langmuir 1997, 13, 5016-5021. (c) Filho, O. S.; Itri, R.; Amaral, L. Q.
J. Phys. Chem. B 2000, 104, 959-964. (d) Oda, R.; Bourdieu, L. J. Phys.
Chem. B 1997, 101, 5913-5916.
1
1
042. (b) Zhao, G. X.; Ding, F. X.; Zhu, B. Y. Colloids Surf., A 1998, 132,
. (c) Siddiqui, F. A.; Franses, E. I. Langmuir 1996, 12, 354-362. (d) Zhou,
Q.; Rosen, M. J. Langmuir 2003, 19, 4555-4562.
(14) (a) Bruinsma, R.; Gelbart, W.; Shaul, A. B. J. Chem. Phys. 1992,
(21) Fenandez, Y. D.; Calvo, S. R.; Gramatges, A. P. Phys. Chem. Chem.
Phys. 2002, 4, 5004-5006.
9
6, 7710-7727. (b) Wang, S. Q. J. Phys. Chem. 1990, 94, 8381-8348.