Phase and Rheological Behavior of Cetyldimethylbenzylammonium Salicylate (CDBAS) and Water.pdf
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Journal of Surfactants andDetergents ISSN 1097-3958Volume 14Number 2 J Surfact Deterg (2011)14:269-279DOI 10.1007/s11743-010-1223-6
Phase and Rheological Behavior ofCetyldimethylbenzylammonium Salicylate(CDBAS) and Water
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ORIGINAL ARTICLE
Phase and Rheological Behaviorof Cetyldimethylbenzylammonium Salicylate (CDBAS) and Water
Francisco Carvajal-Ramos • Alejandro Gonzalez-Alvarez • J. Roger Vega-Acosta •
Donato Valdez-Perez • Vıctor Vladimir Amilcar Fernandez Escamilla •
Emma Rebeca Macıas Balleza • J. Felix Armando Soltero Martınez
Received: 27 May 2010 / Accepted: 6 July 2010 / Published online: 4 August 2010
� AOCS 2010
Abstract The temperature–composition phase diagram in
the diluted region of the cationic surfactant cetyldi-
methylbenzylammonium salicylate/water system was stud-
ied with a battery of techniques. The Krafft temperature
(Tk = 33 ± 1 �C) was measured by differential scanning
calorimetry, polarizing microscopy, conductimetry, viscos-
imetry, and rheometry. The critical vesicle concentration
(cvc, *0.002 wt%) and a vesicle–micellar transition
(cvm, *0.005 wt%) was detected at a temperature of 35 �C.
Below Tk and concentrations B2 wt%, a transparent solution
is formed (I). Above 2–8.5 wt%, a lamellar (L1) phase forms.
At higher concentrations and up to 12 wt%, a second
lamellar phase (L2) is detected. From 12.4 to 15.5 wt%, an
emulsion phase (E) is formed. Rheological dynamic mea-
surements for the I phase indicate that the system exhibits a
predominantly viscous behavior (G0\ G00) for concentra-
tions lower than the overlap or entanglement concentration
(Ce, *0.75 wt%). At higher concentrations, wormlike
micelles form and the elastic behavior predominates
(G0[ G00). The elastic (G0) modulus collapses in a concen-
tration–time master curve in the whole reduced frequencies
range xsc examined, whereas the viscous modulus (G00)collapses only at reduced frequencies lower than 0.1.
Reduced stress plotted as a function of the reduced
shear rate yields a good superposition of the curves at the
different concentrations up to the onset of the non-linear
behavior.
Keywords Phase behavior � Vesicle � Wormlike �Hydrotropic counterion � Rheology � Shear banding flow
Introduction
Surfactants are amphiphile substances that self-organize in
solvents, forming spontaneously a large variety of struc-
tures (micelles, wormlike micelles, liquid crystals, vesicle,
etc.) [1]. These structures are of fundamental interest in
science research and in many technological applications,
such as drug delivery, in medical diagnostics, cosmetic
formulations, and in the food industry [2–11].
The structure transitions in surfactants solution systems
can be induced by using a great variety of parameters, e.g.,
changes in temperature, surfactant concentration, pressure,
ionic strength, pH, additives like alcohol, salts, and hy-
drotropes [12, 13], and by external fields such as shear
deformations, magnetic, and electric fields [14]. Self-
organization behavior of surfactants in solutions is a
spontaneous process that is thermodynamically driven.
This phenomenon can be described based on the packing
parameter, P ¼ vt
ahlc;t
� �; where vt is the volume of the
hydrocarbon tail of the surfactant in the core, ah is the
optimal head group area, and lc,t is the critical chain length
of the tail [14–29]. This parameter is used to predict the
most presumable shapes that a surfactant can form, i.e.,
F. Carvajal-Ramos � A. Gonzalez-Alvarez �E. R. Macıas Balleza � J. Felix Armando Soltero Martınez (&)
Departamento de Ingenierıa Quımica, Universidad de
Guadalajara, Boul. M. Garcıa Barragan #1451, Guadalajara,
Jalisco 44430, Mexico
e-mail: jfasm@hotmail.com; armandosolteros@yahoo.com
J. Roger Vega-Acosta � D. Valdez-Perez
Instituto de Fısica, Universidad Autonoma de San Luis Potosı,
Alvaro Obregon #64, San Luis Potosı, SLP 78000, Mexico
V. V. A. Fernandez Escamilla
Departamento de Ciencias Tecnologicas,
Universidad de Guadalajara, Av. Universidad #1115,
Ocotlan, Jalisco, Mexico
123
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DOI 10.1007/s11743-010-1223-6
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P \ 1/3 for spherical micelles, P = 1/3 - 1/2 for rodlike
micelles, P = 1/2 - 1 for flexible bilayer, vesicles [30,
31].
Many studies have been performed in the past two
decades into understanding the effect of hydrotropes in the
phase behavior of surfactants/water systems [32–34]. Hy-
drotropes are molecules that were described first by Neu-
berg [32]. They have an amphiphilic structure and the
ability of increasing the solubility of scarcely soluble
organic molecules in water [32]. Cationic surfactants are
very sensitive to changes in the molecular structure of
aromatic hydrotropes [35–45], since even small changes in
the organic counterion structure can dramatically modify
the phase and rheological behavior [46]. Hydrotropes cause
profound decreases in critical micelle concentration (cmc)
and induce the formation of viscoelastic wormlike micelle
solutions at lower surfactant concentrations (i.e., salicylate,
tosilate, p-vinylbenzoate) [46–48] compared to that of the
respective halide counterions [36]. Buwalda et al. [49]
studied the influence of aromatic hydrotropes on single-
chain amphiphiles aqueous solutions, observing that hy-
drotropes modify the packing parameter by interacting with
the amphiphiles head, thereby, changing the structure.
The spontaneous formation of vesicles and their appli-
cation in drug delivery and DNA compacting have been
reported in numerous articles [50, 51]. The most interesting
property of vesicles is their capacity to incorporate
hydrophilic and lipophilic substances [14]. Over the last
two decades, mostly natural and synthetic double-chain
amphiphiles have been used for forming vesicles [14].
Great effort has been placed into understanding and
controlling the stability of this self-assembled structure
[12]. Kaler et al. [16] reported the spontaneous formation
of vesicles from single-chain mixed cationic and anionic
surfactants. These catanionic surfactants are a cheaper
option compared to lipids for spontaneous vesicles
formation.
Cetyldimethylbenzylammonium chloride (CDBAC) is a
cationic surfactant that forms in water spherical micelles
with low aggregation numbers at low concentrations [52–
54]. The benzyl group can act as a second hydrophobic
chain, which can interact with the hydrocarbon chains and
with the counterions that are around the micelles [54].
In this work, we studied the effect of the hydrotrope
counterion salicylate on the phase and rheological behavior
of the cetyldimethylbenzylammonium ion (CDBA?) in
water from diluted concentrations of up to 15 wt% sur-
factant. Salicylate is a highly hydrophobic counterion that
is able to reduce the effective head-group area (ah) by
shielding the positive charge of the surfactant head.
Besides interacting with the benzyl group as a second
hydrophobic tail, this produces an increase in the packing
parameter value and the possibility of forming lamellar or
vesicular structures. Studies were performed by using a
battery of analytical techniques, such as: differential
scanning calorimetry (DSC), conductimetry, viscosimetry,
polarizing microscopy, transmission electron microscopy
(TEM), and rheometry.
Experimental
Materials
Cetyldimethylbenzylammonium chloride (CDBAC) with a
purity of 97.0 wt% and sodium salicylate (NaSal) with a
purity of 99.5 wt% were purchased from Fluka and used as
received. Two aqueous solutions (100 mL each) of NaSal
(20.2 9 10-3 M) and CDBAC (20.0 9 10-3 M) were
prepared at 40 �C and sonicated for 1 h. The cetyldi-
methylbenzylammonium salicylate (CDBAS) was prepared
by mixing the solutions and standing at 40 �C for 48 h,
when a white precipitate would be observed. The precipi-
tate was filtrated and recrystallized three times from a
water–acetone mixture (10:90 by volume) and the surfac-
tant was dried using phosphorous pentoxide for 1 week.
Methods
The surfactant structure was confirmed by NMR spec-
troscopy (Advance DMX500 Bruker spectrometer). HPLC-
grade water was used.
For phase and rheological studies, samples were prepared
by weighing appropriate amounts of CDBAS and water in
glass vials. For the critical vesicular concentration (cvc), the
vesicular-to-sphere, and sphere-to-rod concentrations tran-
sitions, samples in a range from 5 9 10-4 to 5 9 10-2 wt%
were prepared by dilution from a 0.1 wt% stock solution.
Samples were placed in a water batch at 60 �C for a week,
where they were frequently shaken. Then, the samples were
allowed to reach equilibrium at the examination or mea-
surement temperature. All samples were centrifuged to
remove suspended air bubbles before being tested. Critical
concentrations were determinated by viscosimetry and
conductimetry at 35 �C. Electrical conductivities were
measured with a conductimeter (Oakton Model 510) and an
immersion cell (YSI) with cell constant = 1 cm-1. The cell
was calibrated with standard KCl solutions of known con-
ductivity. Viscosity measurements were performed in an
Anton Paar AMVn microviscometer with a repeatability of
\0.1% for viscosity and 0.01 �C for temperature.
Phase behavior was determinated by visual observa-
tions, polarized light microscopy, differential scanning
calorimetry, and rheometry. In order to discriminate
between isotropic and liquid crystalline phases, samples
were viewed through crossed polarizers.
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To identify the liquid crystalline phases, samples were
examined with an Olympus BX51 optical microscope
equipped with polarizers and a Linkam CSS450 heating-
and-cooling stage, with a digital temperature controller
(±0.1 �C).
Thermograms were obtained with a TA Instruments
Q2000 differential scanning calorimeter that was previ-
ously calibrated with indium, water, and n-octane stan-
dards. All scans were made with heating and cooling rates
of 0.1 �C/min. In order to minimize any loss due to
evaporation, aluminum pans for volatile samples (TA
Instruments) were used. Samples in the sealed pans were
weighed before and after each test. Results from the sam-
ples that lost weight were discarded. Transition tempera-
tures were determined to within 0.5 �C upon heating from
the point where the base line changed slope significantly.
Steady and oscillatory simple-shear experiments were
performed in a strain-controlled TA Instruments Ares-22
rheometer with a cone-and-plate geometry of 0.1 radian
and a diameter of 50 mm. An environmental control unit
was placed around the cone-and-plate fixture to prevent
water evaporation. The temperature was controlled to
within 0.1 �C during the measurements.
Transmission electron microscopy (TEM) was per-
formed following the negative staining technique with
uranyl acetate using a HRTEM FEI TECNAI F30 STWIN
G2. Details of the procedure have been described else-
where [55].
Results and Discussion
Phase Behavior
Figure 1 shows plots of the conductivity and viscosity as a
function of CDBAS concentration measured at 35 �C. At
low surfactant concentrations below the cmc, the viscosity
decreases slightly with increasing concentration and it is
smaller than the viscosity of pure water. There are several
reports about the reduction of water viscosity due to the
addition of surfactants in the premicellar range [56–58].
This behavior was explained in terms of the theory
developed by Nemethy and Scheraga [59, 60]. At around
0.0024 wt% (arrow a), the viscosity begins to increase up
to 0.0050 wt%, where a maximum appears (arrow b). This
slope change is due to the formation of structures larger
than the monomeric ions. From 0.0050 to 0.0085 wt%, the
viscosity decreases as the surfactant concentration aug-
ments and a minimum is observed (arrow c). This decrease
in viscosity indicates a transition to a smaller structure.
After this minimum, the viscosity increases sharply, indi-
cating a third structural transition. The conductivity, on the
other hand, increases linearly with surfactant concentration
up to 0.0024 wt%. At this concentration, the conductivity
decreases steeply (arrow a) and then increases linearly
again up to 0.0050 wt%, where the conductivity increases
steeply (arrow b). At higher surfactant concentrations, the
conductivity increases linearly.
The formation of structures larger than monomer ions is
indicated by the viscosity increase and the conductivity
drop detected at 0.0024 wt% (arrow a). The second tran-
sition observed from 0.0050 to 0.0085 wt%, where the
viscosity decreases and the conductivity increases with
surfactant concentration, suggests that there is a transition
from larger to smaller structures. We believe that the first
transition is due to the formation of vesicles and the second
one is a vesicles-to-micelle transition. On the other hand,
the third slope change in conductivity, detected at con-
centrations higher than 0.0085 wt%, is probably due to the
micelle-to-rod transition.
Measurements of TEM were performed in order to
discriminate the structures that are formed in these transi-
tions. Figure 2 shows the negative-staining TEM photo-
graph for the sample with a concentration of 0.005 wt%.
This micrograph affirmably proved the existence of vesi-
cles. In this picture, it is evident that vesicles coexist with
spherical micelles.
CDBAS is quite soluble in water above 33 ± 1 �C. At
temperatures lower than 33 �C, CDBAS/water samples
exhibit a white, granular appearance due to the presence of
CDBAS crystals dispersed in an isotropic saturated sur-
factant solution. At 35 �C and for surfactant concentrations
lower than 0.75 wt%, the solutions are isotropic and
transparent, with viscosities similar to that of water. At
higher concentrations and up to around 2.3 wt%, the vis-
cosity increases as the concentration augments. Samples
are transparent and isotropic when viewed through crossed
polarizers, but they show streaming birefringence that
increases in intensity upon increasing concentration and
decreases as temperature increases. This behavior is similar
to that exhibited by wormlike micellar solutions of single-Fig. 1 Electrical conductivity (filled squares) and viscosity (opensquares) as a function of CDBAS measured at 35 �C
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tail surfactants with aromatic hydrotropes, e.g., cetyltri-
methylammonium tosilate (CTAT)/water system [47], but
the streaming birefringence intensity and viscosity values
for solutions with the same concentration are much lower
for CDBAS/water than those of the CTAT/water system
[47]. At concentrations higher than 2.3 wt% and up to
12 wt%, samples are birefringent, with textures typical of
lamellar liquid crystals. To the naked eye, samples with
concentrations from 2.3 to 8.5 wt% are milky and opales-
cent; at higher concentrations, the samples turned bluish
and turbid. Figure 3a depicts photograph of a 7 wt%
CDBAS sample taken through crossed polarizers in the
polarizing microscope at 35 �C. In this picture, a cloudy
texture, positive, and negative spherulites are detected;
these textures are consistent with the lamellar phase [61].
For a 9 wt% CDBAS sample (Fig. 3b), the micrographs
show changes in textures, oily streaks are observed, neg-
ative spherulites are predominant, and only a few positive
spherulites are observed. With increasing temperature, the
lamellar phase texture disappears slowly in the polarizing
microscopy at around 80 �C for a 6 wt% CDBAS sample,
indicating a transition into an isotropic phase. At concen-
trations higher than 12 wt% and up to 15 wt%, the samples
are completely milky and isotropic. When samples are
observed in the polarizing microscopy with parallel
polarizers, a suspension of small and isotropic droplets
dispersed in an isotropic solution is detected. We noted this
phase as emulsion (E). When diluted samples
(C \ 12 wt%) are cooled at temperatures lower than Tk,
they do not crystallize for months, up to around 23 �C;
these solutions are named pseudo-solutions by Ravin et al.
[62]. Recently, Benedini et al. [63] reported this behavior
in the amiodarone/water system. For pure surfactant, three
transitions were detected in the polarizing microscopy with
crossed polarizers. At temperatures lower than 35 �C,
hydrated crystals of surfactant (Ch) are observed. From 35
and up to 45 �C, waxy crystals (Cw) are detected, and for
higher temperatures, an isotropic solution is formed.
Figure 4 shows DSC thermograms at different CDBAS
concentrations. For concentrations lower than 2 wt% (see
thermogram for 0.5 wt%), only two peaks are detected, the
large peak (peak a) that appears at 0 �C is due to the
melting of free water, the peak area of which diminishes
with surfactant concentration, as expected. The second
smaller peak (peak b) begins at around 33 �C and increases
in intensity with surfactant concentration; this temperature
coincides with that observed visually when the surfactant
begins to be soluble in water. This confirms that this
temperature corresponds to the Krafft temperature
(Tk = 33 �C), which is bigger than that observed in sur-
factants with the same length tail and with different hy-
drotropes, such as tosilate [47] and p-vinylbenzoate [48].
At concentrations higher than 2 wt% and up to 12 wt%
(see thermogram for 4 wt% sample), a third peak (peak c)
is detected at 73 �C, which coincides with the transition L1
to I, observed by temperature sweeps in the polarizing
Fig. 2 Negative-staining TEM photograph for 0.005 wt% CDBAS
concentration
Fig. 3 Photograph of CDBAS/water samples taken at 35 �C through
crossed polarizers in a polarizing microscope: a 7 wt%, b 9 wt%
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microscopy. For more concentrated solutions (see ther-
mogram for 15 wt% sample), only both the melting (a) and
Tk (b) peaks are observed. When the pure surfactant is
heated, two peaks are detected. The first one (peak d)
appears at 35 �C and is due to the surfactant hydrocarbons
chain melting when waxy crystals are formed, which was
observed by polarizing light microscopy, and a second
sharp peak (peak e) is seen at ca. 43 �C, which is associated
to the waxy crystal-to-isotropic transition seen at 45 �C in
the polarizing microscopy.
Rheological Behavior
Figure 5 depicts G0 and G00 as a function of temperature for
selected CDBAS concentrations, 1 (c), 3 (b), and 6 (c) wt%
samples. Measurements were performed at a frequency of
10 rad/s and a deformation of 20% for the (a) and (b)
samples and 0.1% for the (c) sample, which are within the
linear viscoelastic regime (LVR). The 1 wt% sample
(Fig. 5a) exhibits a slightly predominant viscous behavior,
that is, G00[ G0 for temperatures lower than 15 �C; in this
temperature range, both moduli diminish gradually with
increasing temperature. Above 15 �C, G0 and G00 cross over
(arrow a) and a predominantly elastic response is observed
(G0[ G00); both moduli increase with temperature up to
around 23 �C, where a maximum is observed (arrow b).
Above 23 �C and up to 34 �C, the moduli decrease by more
than one magnitude order. The slope change detected at
15 �C is due to the transition from hydrated crystals (Ch) to
a mixture of waxy crystal (Cw) and isotropic phase (I), as
confirmed by polarizing light microscopy. The reduction
exhibited for the moduli from 23 to 34 �C is due to the
melting of waxy crystals into a transparent, isotropic phase
that exhibits streaming birefringence; this transition was
seen by the naked eye. At temperatures higher than 34 �C
(arrow c), both G0 and G00 increase sharply by around two
magnitude orders. This sharp increase in moduli with
temperature is a sign of the Krafft temperature. This
increase in the elastic modulus is due to the formation,
growth, and entanglement of wormlike micelles. Above Tk
and up to the temperature of the G0 and G00 crossover (Ts),
the sample response is dominantly elastic. For temperatures
higher than Ts, the sample becomes viscous again. This
response is observed for concentrations up to 2 wt%
CDBAS. The sample with 3 wt% concentration (Fig. 5b)
and for temperatures lower than Tk (arrow c) exhibits a
similar behavior, and two transitions were detected (arrows
a and b). For temperatures above Tk, the rheological
behavior is predominantly viscous, where both moduli
decrease with temperature and around 70 �C, a slope
change is detected. At this temperature, a transition from a
milky and opalescent solution to an isotropic non-bire-
fringent solution was visually detected. For concentrations
in the range where the lamellar phase was detected, the
rheological behavior at temperatures lower than Tk is
similar to that shown for 1 and 3 wt% samples. The
moduli–temperature dependence for a 6 wt% sample is
depicted in Fig. 5c. At temperatures higher than Tk, both G0
Fig. 4 DSC thermograms of CDBAS/water samples as a function of
CDBAS concentration. The heating rate was 0.1 �C/min
Fig. 5 Storage G0 (filled squares) and loss G00 (open squares) moduli
at 10 rad/s within the linear viscoelastic region as a function of
temperature for CDBAS concentrations of: a 1, b 3, and c 6 wt%
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and G00 decrease by almost two magnitude orders and a
predominantly elastic response is observed. It is evident
that, from 34 to 70 �C, the moduli are temperature-inde-
pendent; above 70 �C, both G0 and G00 diminish up to
80 �C, where the moduli cross over (Ts) and a predomi-
nantly viscous behavior is observed. Figure 6 depicts
moduli temperature dependence performed in the heating
and cooling modes for the sample with 3 wt% in surfactant.
It is evident in this figure that, for temperatures higher than
Tk, the data for both experiments have the same tendency.
For temperatures lower than Tk, in the cooling mode data,
the Krafft temperature is not observed and it is possible to
measure moduli data even up to 15 �C lower than Tk
(18 �C, arrow a) without the sample crystallizing. In the
temperature range from 18 to 33 �C, G0 and G00 crossover is
observed at Ts = 28 �C.
With the data collected visually, by DSC, rheometry,
and optical microscopy, the temperature–concentration
phase diagram was generated (Fig. 7). At temperatures
below 0 �C, ice and surfactant crystals coexist. Between 0
and ca. 15 �C, an aqueous solution (I) and hydrated sur-
factant crystals are present. From 15 up to 23 �C, waxy
crystals in an aqueous solution are formed. For
concentrations between the cvc and ca. 15 wt% (shaded
area), a pseudo-solution is formed. For temperatures higher
than the Krafft temperature (ca. 33–34 �C) and concen-
trations between the cvc and up to around 2 wt%, a
micellar solution (I) forms; this phase is transparent,
streaming-birefringent, and viscoelastic. Two lamellar
phases, L1 and L2, span from 2 to 12 wt%; the boundary
between phase the L1 and L2 phases is around 8.5 wt%.
The phase behavior of the CDBAS/water system is very
different from that reported for surfactants with the same
length tail, with different head (–(CH3)3N? instead of –
(CH3)2–CH2C5H6N?) and aromatic counterions, e.g., tos-
ilate [47] and p-vinylbenzoate [48]. The phase diagram of
the surfactant with the cetyltrimethylammonium tosilate
(CTAT) in water [47] exhibits a larger micellar phase (I)
that extends to 25 wt% at 25 �C and to higher concentra-
tions at higher temperatures; in fact, at 80 �C, the isotropic
micellar phase extends to 90 wt% CTAT. At room tem-
perature and in a concentration range between 27 and
47 wt% CTAT, a hexagonal phase forms, but the extent of
this region diminishes with increasing temperature. At even
higher concentration, the hexagonal phase (H-phase)
coexists with a viscous–isotropic phase (V1) [47]. Inter-
estingly, no lamellar phase was reported for the CTAT/
water system [47], in contrast to the system reported here.
However, the lamellar phase was reported in CTAT/water
by adding some electrolytes [64]. Hassan et al. have
observed the formation of vesicles and lamellar phase by
substituting the counterion in CTAT by 3-hydroxy-naph-
thalene 2-carboxylate (HNC). They suggested that the
hydrophobicity of the counterion plays an important role in
controlling the curvature of the interface and, thus, in set-
ting the structure of the supramolecular assemblies [65,
66]. In the case of cetyltrimethylammonium p-vinyl-
benzoate (CTAVB), a micellar solution (I) is formed for
temperatures higher than the Krafft temperature (ca.
17–18 �C) and concentrations between the cmc and ca.
23 wt%, a H-phase is detected from 30 to 70 wt%, and a
lamellar phase is detected at high concentrations from 80 to
near 100 wt% [48]. The lamellar phase formed by the
CDBAS in water at relatively lower concentrations is due
to the benzyl group that acts as a second hydrophobic
chain. Besides, the salicylate counterion that is highly
hydrophobic reduces the effective head-group area (ah), by
shielding the positive charge of the surfactant head and by
interacting with the benzyl group that produces an increase
in the packing parameter value, inducing the forming of
lamellar or vesicular structures.
Figure 8 shows the elastic (G0) and viscous (G00) moduli
measured at 35 �C as a function of CDBAS concentration.
The frequency sweeps are made at oscillatory strain
deformation within the linear viscoelastic region. All
samples except the 0.5 wt% sample exhibit a crossover of
Fig. 6 Temperature sweeps made at 10 rad/s within the linear
viscoelastic (20%) region for 3 wt% CDBAS concentration: (filledsquares, open squares) heating mode; (filled circles, open circles)
cooling mode
Fig. 7 Temperature–composition phase diagram of binary mixtures
of CDBAS and water. I isotropic micellar solution, L1 lamellar phase,
L2 lamellar phase, E emulsion, Cw waxy crystals, Ch hydrated crystals
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G0 and G00 at a characteristic frequency (xc), the reciprocal
of which corresponds to the main relaxation time (or dis-
entanglement time) of the system sc. For concentrations up
to 1.5 wt%, xc shifts to lower values; however, above this
concentration, xc shifts to higher values. It is evident that,
for CCDBAS B 0.5 wt%, the rheological behavior is pre-
dominantly viscous for all frequencies. For higher con-
centrations, the wormlike micelles begin to overlap and
entangle, and, hence, a predominantly elastic behavior is
observed. This characteristic concentration is the critical
entanglement concentration (Ce) [67]. A value of
Ce & 0.7 wt% is determined [on the basis of the observed
onset of the elastic plateau (G0)]. The predominantly elastic
behavior region increases with concentration. From
CCDBAS = 1 wt% to the highest concentration studied
(2 wt%), the elastic modulus (G0) increases with frequency,
but its slope decreases with concentration. However, the
plateau modulus (G0) is not detected in the frequencies
range studied.
The G0 and G00 frequency dependence performed in the
linear viscoelastic zone (c = 0.1%) for 6 and 10 wt%
samples is shown in Fig. 9. The moduli for both samples
exhibit a predominantly elastic response and are frequency
independent; this gel-like behavior is characteristic of
lamellar phase structures [68].
Figure 10 shows the concentration dependencies of G0
(estimated as G0 ¼ scg�0), the main relaxation time (sc), the
zero shear viscosity (g0, obtained under steady shear rate
experiments), and the complex zero shear viscosity (g0*) at
35 �C. G0 follows a power law concentration dependence
of the form: G0 / C2:5surf (Fig. 10a) from 0.75 up to 2.3 wt%.
This concentration dependence of G0 has been reported
for a variety of micellar and polymer solutions with a
similar exponent [40, 41, 69, 70]. Around 2.3 wt%, G0
exhibits a slope change, which coincides with that of the
isotropic-to-lamellar transition (see Fig. 7). Figure 10b
shows the main relaxation time as a function of concen-
tration. It is clear that sc increases with concentration and at
around 1.4 wt%, a maximum is exhibited and it then
decreases up to a concentration of 2.3 wt%, where a
departure from the tendency is observed. The same
behavior is depicted by g0 and g0* (Fig. 10c); the departing
from the tendency is due to the I-to-L1 transition.
Figure 11 depicts the time–concentration master curves
of G0/G0 and G00/G0 for CDBAS concentrations from 0.75
to 2.25 wt% at 35 �C. G0 collapses in all of the dimen-
sionless frequencies (scx) that were studied. On the other
hand, G00 collapses only at scx B 1 values, where the effect
of the entanglements is not important (terminal zone). At
higher scx, where the effects of the entanglements become
important, G00 data departs from the master curve.
Fig. 8 Storage G0 (filled symbols) and loss G00 (open symbols) moduli
versus frequency measured at 35 �C for various CDBAS aqueous
solutions (wt%): (filled squares) 0.50; (filled circles) 0.75; (filledtriangles) 1; (filled inverted triangles) 1.25; (filled left pointingtriangles) 2
Fig. 9 Storage G0 (filled symbols) and loss G00 (open symbols) moduli
versus frequency measured at 35 �C for CDBAS aqueous solutions of
(wt%): (filled circles) 6; (filled squares) 10
Fig. 10 Dependence on CDBAS concentration with a plateau elastic
modulus (G0), b relaxation time (sc = 1/xc), and c zero-frequency
complex viscosity (filled squares) and zero-shear viscosity (opensquares) measured at 35 �C
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Figure 12 shows the steady-shear master dynamic
r=G0 vs: _cscð Þ diagram proposed by Berret et al. [71] for
samples with concentrations from 0.75 to 2.25 wt% at
35 �C. At _csc\0:3 where the behavior is Newtonian, all
the data collapse in a single line. For _csc� 0:3; where a
shear thinning behavior develops, the data depart from the
master diagram. However, two different patterns can be
discerned; at lower concentrations, the stress continuously
increases with the shear rate, whereas at higher concen-
trations, a stress plateau or a sigmoid behavior in the stress
versus shear rate is observed. The inflexion in the shear
stress–shear rate curve has been observed in several sur-
factant systems, which has been associated with the
appearance of an unstable region in a critical shear rate
value [72–74]. Reduced logarithmic shear stress increases
again linearly at higher logarithmic reduced shear rates
values, indicating a second Newtonian behavior (g?). The
stress plateau has been associated with the appearance of
the shear banding flow, in which two phases coexist, sup-
porting different shear rates. The reduced stress plateau
occurs at r=G0 � 0:62; which is slightly lower than that
predicted by the Cates and Fielding’s model [75].
In conclusion, the Krafft temperature for the cetyldi-
methylbenzylammonium salicylate (CDBAS) in water is
33 ± 1 �C. This value is higher than that measured for
surfactants with the same tail length, trimethylammonium
head, and different aromatic counterions, e.g., tosilate
(Tk = 23 �C) and p-vinylbenzoate (Tk = 18 �C). The
CDBAS/water system forms vesicles at 0.002 wt% and a
vesicle–micellar transition at 0.005 wt% is detected at a
temperature of 35 �C. The formation of vesicles is proba-
bly due to the salicylate counterion, which is highly
hydrophobic. This reduces the effective head-group area
(ah) by shielding the positive charge of the surfactant head
and by interacting with the benzyl group, producing an
increase in the packing parameter value. This kind of
surfactant is a cheap alternative for spontaneous vesicle
formation instead of catanionic surfactants, double-tail
surfactants, or lipids.
Acknowledgments This work was supported by a project of the
National Council of Science and Technology of Mexico (CONACYT
grant no. 25463). FC-R acknowledges the scholarship from the
CONACYT.
References
1. Tanford Ch (1985) Monolayers, micelles, lipid vesicles and
biomembranes. In: Degiorgio V, Corti M (eds) Physics of am-
phiphiles: micelles, vesicles and microemulsions. Elsevier,
Bologna, pp 547–554
2. Malmsten M (2002) Liposomes. In: Malmsten M (ed) Surfactants
and polymers in drug delivery. Marcel Dekker Inc., New York,
pp 87–132
3. Woodle MC (1995) Sterically stabilized liposome therapeutics.
Adv Drug Deliv Rev 16:249–265
4. Hagstrom JE, Sebestyen MG, Budker V, Ludtke JJ, Fritz JD,
Wolff JA (1996) Complexes of non-cationic liposomes and his-
tone H1 mediate efficient transfection of DNA without encap-
sulation. Biochim Biophys Acta Biomembr 1284:47–55
5. Lasic DD, Papahadjopoulos D (1996) Liposomes and biopoly-
mers in drug and gene delivery. Curr Opin Solid State Mater Sci
1:392–400
Fig. 11 Time–concentration superposition master curves for a G0 and
b G00 at 35 �C as a function of CDBAS concentration (wt%): (opensquares) 0.75; (open circles) 1; (open triangles) 1.25; (open invertedtriangles) 1.5; (open diamonds) 1.75; (open left pointing triangles) 2;
(open stars) 2.25
Fig. 12 Reduced shear stress versus shear rate measured at 35 �C as
a function of CDBAS concentration (wt%): (open squares) 0.75;
(open circles) 1; (open triangles) 1.25; (open inverted triangles) 1.5;
(open diamonds) 1.75; (open left pointing triangles) 2; (open stars)
2.25
276 J Surfact Deterg (2011) 14:269–279
123
Author's personal copy
6. Tseng WC, Haselton FR, Giorgio TD (1999) Mitosis enhances
transgene expression of plasmid delivered by cationic liposomes.
Biochim Biophys Acta Gene Struct Expression 1445(1):53–64
7. Monkkonen J, Urtti A (1998) Lipid fusion in oligonucleotide and
gene delivery with cationic lipids. Adv Drug Deliv Rev 34:37–49
8. Torchilin VP (2005) Recent advances with liposomes as phar-
maceutical carriers. Nat Rev Drug Discov 4:145–160
9. Betz G, Aeppli A, Menshutina N, Leuenberger H (2005) In vivo
comparison of various liposome formulations for cosmetic
application. Int J Pharm 296:44–54
10. Taylor TM, Davidson PM, Bruce BD, Weiss J (2005) Liposomal
nanocapsules in food science and agriculture. Crit Rev Food Sci
Nutr 45:587–605
11. Smith AM, Jaime-Fonseca MR, Grover LM, Bakalis S (2010)
Alginate-loaded liposomes can protect encapsulated alkaline
phosphatase functionality when exposed to gastric pH. J Agric
Food Chem 58:4719–4724
12. Svenson S (2004) Controlling surfactant self-assembly. Curr
Opin Colloid Interface Sci 9:201–212
13. Schurtenberger P, Bertani R, Kanzig W (1986) Formation of
mixed bile salt–lecithin vesicles: a study of the temperature
dependence. J Colloid Interface Sci 114:82–87
14. Segota S, Tezak D (2006) Spontaneous formation of vesicles.
Adv Colloid Interface Sci 121:51–75
15. Soussan E, Cassel S, Blanzat M, Rico-Lattes I (2009) Drug
delivery by soft matter: matrix and vesicular carriers. Angew
Chem Int Ed Engl 48:274–288
16. Kaler EW, Murthy AK, Rodriguez BE, Zasadzinski JA (1989)
Spontaneous vesicle formation in aqueous mixtures of single-
tailed surfactants. Science 245:1371–1374
17. Herrington KL, Kaler EW, Miller DD, Zasadzinski JA, Chiruvolu
S (1993) Phase behavior of aqueous mixtures of dodecyltri-
methylammonium bromide (DTAB) and sodium dodecyl sulfate
(SDS). J Phys Chem 97:13792–13802
18. Huang JB, Zhao GX (1995) Formation and coexistence of the
micelles and vesicles in mixed solution of cationic and anionic
surfactant. Colloid Polym Sci 273:156–164
19. Yuet PK, Blankschtein D (1996) Molecular-thermodynamic
modeling of mixed cationic/anionic vesicles. Langmuir
12:3802–3818
20. O’Connor AJ, Hatton TA, Bose A (1997) Dynamics of micelle–
vesicle transitions in aqueous anionic/cationic surfactant mix-
tures. Langmuir 13:6931–6940
21. Bergstrom M, Pedersen JS, Schurtenberger P, Egelhaaf SU
(1999) Small-angle neutron scattering (SANS) study of vesicles
and lamellar sheets formed from mixtures of an anionic and a
cationic surfactant. J Phys Chem B 103:9888–9897
22. Jung HT, Coldren B, Zasadzinski JA, Iampietro DJ, Kaler EW
(2001) The origins of stability of spontaneous vesicles. Proc Natl
Acad Sci USA 98:1353–1357
23. Hao JC, Hoffmann H (2004) Self-assembled structures in excess
and salt-free catanionic surfactant solutions. Curr Opin Colloid
Interface Sci 9:279–293
24. Vlachy N, Drechsler M, Verbavatz JM, Touraud D, Kunz W
(2008) Role of the surfactant headgroup on the counterion
specificity in the micelle-to-vesicle transition through salt addi-
tion. J Colloid Interface Sci 319:542–548
25. Aratono M, Onimaru N, Yoshikai Y, Shigehisa M, Koga I,
Wongwailikhit K, Ohta A, Takiue T, Lhoussaine B, Strey R,
Takata Y, Villeneuve M, Matsubara H (2007) Spontaneous ves-
icle formation of single chain and double chain cationic surfac-
tant mixtures. J Phys Chem B 111:107–115
26. Guo X, Li H, Zhang FM, Zheng SY, Guo R (2008) Aggre-
gation of single-chained cationic surfactant molecules into
vesicles induced by oligonucleotide. J Colloid Interface Sci
324:185–191
27. Marques EF, Brito RO, Silva SG, Rodrıguez-Borges JE, do Vale
ML, Gomes P, Araujo MJ, Soderman O (2008) Spontaneous vesicle
formation in catanionic mixtures of amino acid-based surfactants:
chain length symmetry effects. Langmuir 24:11009–11017
28. Bhattacharya S, Acharya SNG (2000) Vesicle and tubular
microstructure formation from synthetic sugar-linked amphi-
philes. Evidence of vesicle formation from single-chain amphi-
philes bearing a disaccharide headgroup. Langmuir 16:87–97
29. Israelachvili JN, Mitchell DJ, Ninham BW (1977) Theory of self-
assembly of lipid bilayers and vesicles. Biochim Biophys Acta
470:185–201
30. Israelachvili JN, Mitchell DJ, Ninham BW (1976) Theory of self-
assembly of hydrocarbon amphiphiles into micelles and bilayers.
J Chem Soc Faraday Trans II 72:1525–1568
31. Israelachvili JN (1985) Intermolecular and surface forces, 2nd
edn.: with application to colloidal and biological systems. Aca-
demic Press, London
32. Hodgdon TK, Kaler EW (2007) Hydrotropic solutions. Curr Opin
Colloid Interface Sci 12:121–128
33. Kumar S, Bansal D, Kabir-ud-Din (1999) Micellar growth in the
presence of salts and aromatic hydrocarbons: influence of the
nature of the salt. Langmuir 15:4960–4965
34. Kumar S, Naqvi AZ, Kabir-ud-Din (2000) Micellar morphology
in the presence of salts and organic additives. Langmuir
16:5252–5256
35. Thurn H, Lobl M, Hoffmann H (1985) Viscoelastic detergent
solutions. A quantitative comparison between theory and exper-
iment. J Phys Chem 89:517–522
36. Ohlendorf D, Interthal W, Hoffmann H (1986) Surfactant systems
for drag reduction: physico-chemical properties and rheological
behavior. Rheol Acta 25:468–486
37. Shikata T, Hirata H, Kotaka T (1987) Micelle formation of
detergent molecules in aqueous media: viscoelastic properties of
aqueous cetyltrimethylammonium bromide solutions. Langmuir
3:1081–1086
38. Shikata T, Hirata H, Kotaka T (1988) Micelle formation of
detergent molecules in aqueous media. 2. Role of free salicylate
ions on viscoelastic properties of aqueous cetyltrimethylammo-
nium bromide-sodium salicylate solutions. Langmuir 4:354–359
39. Shikata T, Hirata H, Kotaka T (1989) Micelle formation of
detergent molecules in aqueous media. 3. Viscoelastic properties
of aqueous cetyltrimethylammonium bromide-salicylic acid
solutions. Langmuir 5:398–405
40. Rehage H, Hoffmann H (1988) Rheological properties of visco-
elastic surfactant systems. J Phys Chem 92:4712–4719
41. Shikata T, Hirata H, Takatori E, Osaki K (1988) Nonlinear vis-
coelastic behavior of aqueous detergent solutions. J Non-New-
tonian Fluid Mech 28:171–182
42. Wunderlich AM, Hoffmann H, Rehage H (1987) Flow birefrin-
gence and rheological measurements on shear induced micellar
structures. Rheol Acta 26:532–542
43. Strivens TA (1989) The rheological properties of concentrated
cetyltrimethylammonium bromide-salicylic acid solutions in
water. Colloid Polym Sci 267:269–280
44. Gobel S, Hiltrop K (1991) Influence of organic counterions on the
structure of lyotropic mesophases. Prog Colloid Polym Sci
84:241–242
45. Clausen TM, Vinson PK, Minter JR, Davis HT, Talmon Y, Miller
WG (1992) Viscoelastic micellar solutions: microscopy and
rheology. J Phys Chem 96:474–484
46. Gravsholt S (1976) Viscoelasticity in highly dilute aqueous
solutions of pure cationic detergents. J Colloid Interface Sci
57:575–577
47. Soltero JFA, Puig JE, Manero O, Schulz PC (1995) Rheology of
cetyltrimethylammonium tosylate–water system. 1. Relation to
phase behavior. Langmuir 11:3337–3346
J Surfact Deterg (2011) 14:269–279 277
123
Author's personal copy
48. Soltero JFA, Alvarez-Ramırez JG, Fernandez VVA, Tepale N,
Bautista F, Macıas ER, Perez-Lopez JH, Schulz PC, Manero O,
Solans C, Puig JE (2007) Phase and rheological behavior of the
polymerizable surfactant CTAVB and water. J Colloid Interface
Sci 312:130–138
49. Buwalda RT, Stuart MCA, Engberts JBFN (2000) Wormlike
micellar and vesicular phases in aqueous solutions of single-tailed
surfactants with aromatic counterions. Langmuir 16:6780–6786
50. Cevc G (1996) Transfersomes, liposomes and other lipid sus-
pensions on the skin: permeation enhancement, vesicle penetra-
tion, and transdermal drug delivery. Crit Rev Ther Drug Carrier
Syst 13:257–388
51. Alatorre-Meda M, Taboada P, Sabın J, Krajewska B, Varela LM,
Rodrıguez JR (2009) DNA–chitosan complexation: a dynamic
light scattering study. Colloids Surf A 339:145–152
52. Gonzalez-Perez A, Czapkiewicz J, Del Castillo JL, Rodrıguez JR
(2001) Micellar properties of long-chain alkyldimethylbenzy-
lammonium chlorides in aqueous solutions. Colloid Surf A
193:129–137
53. Del Castillo JL, Czapkiewicz J, Gonzalez Perez A, Rodrıguez JR
(2000) Micellization of decyldimethylbenzylammonium chloride
at various temperatures studied by densitometry and conductivity.
Colloid Surf A 166:161–169
54. Rozycka-Roszak B, Cierpicki T (1999) 1H NMR studies of
aqueous micellar solutions of N-dodecyl- N,N-dimethyl-N-ben-
zylammonium chloride. J Colloid Interface Sci 218:529–534
55. Sierra MB, Messina PV, Morini MA, Ruso JM, Prieto G, Schulz
PC, Sarmiento F (2006) The nature of the coacervate formed in
the aqueous dodecyltrimethylammonium bromide–sodium 10-
undecenoate mixtures. Colloids Surf A 277:75–82
56. Kushner LM, Duncan BC, Hoffmann JI (1952) A viscometric
study of the micelles of sodium dodecyl sulfate in dilute solu-
tions. J Res Natl Bur Stan 49:85–90
57. Messina P, Morini MA, Schulz PC, Ferrat G (2002) The aggre-
gation of sodium dehydrocholate in water. Colloid Polym Sci
280:328–335
58. Lopez-Fontan JL, Sarmiento F, Schulz PC (2005) The aggrega-
tion of sodium perfluorooctanoate in water. Colloid Polym Sci
283:862–871
59. Nemethy G, Scheraga HA (1962) Structure of water and hydro-
phobic bonding in proteins. 1. A model for the thermodynamic
properties of liquid water. J Chem Phys 36:3382–3400
60. Nemethy G, Scheraga HA (1962) Structure of water and hydro-
phobic bonding in proteins. 2. Model for the thermodynamic
properties of aqueous solutions of hydrocarbons. J Chem Phys
36:3401–3417
61. Rosevear FBJ (1954) The microscopy of the liquid crystalline
neat and middle phases of soaps and synthetic detergents. J Am
Oil Chem Soc 31:628–639
62. Ravin LJ, Shami EG, Rattie ES (1975) Micelle formation and its
relationship to solubility behavior of 2-butyl-3-benzofuranyl-4-
[2-(diethylamino)ethoxy]-3,5-diiodophenyl ketone hydrochlo-
ride. J Pharm Sci 64:1830–1833
63. Benedini L, Messina PV, Manzo RH, Allemandi DA, Palma SD,
Schulz EP, Frechero MA, Schulz PC (2010) Colloidal properties
of amiodarone in water at low concentration. J Colloid Interface
Sci 342:407–414
64. Monduzzi M, Olsson U, Soderman O (1993) Bicontinuous
micellar solutions. Langmuir 9:2914–2920
65. Hassan PA, Valaulikar BS, Manohar C, Kern F, Bourdieu L,
Candau SJ (1996) Vesicle to micelle transition: rheological
investigations. Langmuir 12:4350–4357
66. Hassan PA, Narayanan J, Menon SVG, Salkar RA, Samant SD,
Manohar C (1996) Aggregates from cetyltrimethylammoniumhy-
droxynaphthalene carboxylate (CTAHNC): a light scattering
study. Colloids Surf A 117:89–94
67. De Gennes PG (1979) Scaling concepts in polymer physics.
Cornell University Press, London
68. Soltero JFA, Robles-Vasquez O, Puig JE, Manero O, Corona GS,
Tripodi SB, Valles E (1995) Thixotropic–antithixotropic behavior
of surfactant-based lamellar liquid crystals under shear flows.
J Rheol 39:235–240
69. Soltero JFA, Puig JE, Manero O (1996) Rheology of the cetyl-
trimethylammonium tosilate–water system. 2. Linear viscoelastic
regime. Langmuir 12:2654–2662
70. Ferry JD (1980) Viscoelastic properties of polymers. Wiley, New
York
71. Berret JF, Porte G, Decruppe JP (1997) Inhomogeneous shear
flows of wormlike micelles: a master dynamic phase diagram.
Phys Rev E 55:1668–1676
72. Bautista F, Soltero JFA, Manero O, Puig JE (2002) Irreversible
thermodynamics approach and modeling of shear-banding flow of
wormlike micelles. J Phys Chem B 106:13018–13026
73. Escalante JI, Macıas ER, Bautista F, Perez-Lopez JH, Soltero
JFA, Puig JE, Manero O (2003) Shear-banded flow and transient
rheology of cationic wormlike micellar solutions. Langmuir
19:6620–6626
74. Bandyopadhyay R, Sood AK (2003) Effect of screening of in-
termicellar interactions on the linear and nonlinear rheology of a
viscoelastic gel. Langmuir 19:3121–3127
75. Cates ME, Fielding S (2007) Theoretical rheology of giant
micelles. In: Zana R, Kaler EW (eds) Giant micelles: properties
and applications. Marcel Dekker, Boca Raton, pp 109–161
Author Biographies
Francisco Carvajal-Ramos received his B.Sc. and M.Sc. and is
studying for his Ph.D. in Chemical Engineering at the University of
Guadalajara, Mexico.
Alejandro Gonzalez-Alvarez received his B.Sc. and M.Sc. in
Chemical Engineering from the University of Guadalajara, Mexico,
and his Ph.D. in Genie des Procedes from the INPG, Grenoble,
France. He is currently Head Professor of the Chemical Engineering
Department of the University of Guadalajara, Mexico.
J. Roger Vega-Acosta received his Ph.D. at the Institute of Physics
of the Universidad Autonoma de San Luis Potosı, Mexico. His
research interests include the application of viruses to nanotechnol-
ogy. He uses viral protein as nanocontainers and studies different
forms of assemblies and techniques of the characterization of
materials.
Donato Valdez-Perez is an invited professor of research at the
Institute of Physics of the Universidad Autonoma de San Luis Potosı,
S.L.P., Mexico. His research interests include the fundamental studies
focused on scanning probe techniques in the interdisciplinary areas of
bio/nanotribology, bio/nanomechanics and bio/nanomaterials charac-
terization, and applications to bio/nanotechnology.
Vıctor Vladimir Amilcar Fernandez Escamilla is a research
professor at Guadalajara University. He received his M.Sc. and
Ph.D. in Chemical Engineering from Guadalajara University, Mexico.
He undertook a stay at the Laboratory of Rheology in Grenoble,
France, in 2006.
Emma Rebeca Macıas Balleza received her B.Sc., M.Sc., and Ph.D.
from the Universidad de Guadalajara in Chemical Engineering. She
also received her Ph.D. in Physics at the Universite Joseph Fourier at
278 J Surfact Deterg (2011) 14:269–279
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Grenoble, France. She is a Professor at the University of Guadalajara
and works in the field of the rheology of complex fluids.
J. Felix Armando Soltero Martınez is chief of the Laboratory of
Rheology in the Chemical Engineering Department of the University
of Guadalajara. He received his B.Sc., M.Sc., and Ph.D. from the
University of Guadalajara, Mexico. He is a research professor in the
Chemical Engineering Department. His interests include ionic and
non-ionic surfactant properties for consumer product formulation in
the food and pharmaceutical industries.
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