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Chapter 5
Interactions between Bisphosphate
Geminis and Sodium Lauryl Ether
Sulphate
110
5.1 Introduction
The physiochemical and surface active properties of mixed surfactants are of more inter-
est and useful than pure surfactants, for industrial applications. By virtue of differences
in the tail and head groups of the surfactants, mixed surfactants may show composi-
tion dependent micellization, mutual interaction, solvation, micellar shape, etc. For
the mixture of two surfactants undergoing micelle formation above a critical micelles
concentration (CMC), the solution properties fall either between or outside the solution
properties of the two-single surfactant solutions. This is also the case for the CMC of a
binary surfactant solution. Clint [Clint, 1975] has given the relation between mole frac-
tion and CMC of the ith component for ideal mixtures, and Rubingh [Rubingh, 1979]
has made a comprehensive theoretical attempt to deal with non-ideal mixture on the ba-
sis of the regular solution theory (RST). In solution containing two or more surfactants,
the tendency of aggregated structures to form is substantially different from that in so-
lutions having only pure water [Tikariha et al. , 2011]. Such different tendency results
in dramatic change in properties and behavior of mixed surfactants compared to that of
a single surfactant. Practical formulations often requires the addition of surfactants to
help in regulating the physical properties of the product or improve it’s stability. The
stability of the mixed micelles depends on two factors (i) coulombic interaction between
ionic head groups and (ii) chain length of the surfactant tail groups. In many practical
applications, the properties of surfactants are important and attractive [Rosen, 1989]. A
mixed micellar solution is a representation of a mixed micelle, mixed monolayer at the
air/water interface and mixed bilayer aggregate at the solid interface [Tikariha et al. ,
2011].
In the present work mixed micellization of anionic bisphosphate gemini surfactants
with sodium lauryl ether sulphate (SLES) was studied. Gemini surfactants were used as
an additive. The purpose of the present study is to investigate the interactions between
a mixed surfactant system (anionic monomeric surfactants with sulphate and anionic
gemini surfactant system with phosphate head group). To our knowledge there hasn’t
been any report published on the mixed micellization of the surfactant system consisting
111
of a phosphate gemini and SLES. SLES is a very important surfactant in many surfac-
tant based formulations, owing to it’s very good foaming power. The present study is an
attempt to find out the compatibility of phosphate gemini surfactants with SLES. This
study has been carried out by surface tension measurements, dynamic surface tension
analysis and foamability of the mixed surfactant systems (SLES + m− 3−m geminis
and SLES + m−5−m geminis). The effect of chain length of the gemini surfactant on
the interaction parameter was studied.
5.2 Materials and Methods
The as synthesized six bisphosphate gemini surfactants (m−3−m and m−5−m gem-
inis), described in chapter 2, were used. Commercial sample of sodium lauryl ether
sulfate (SLES) was obtained from M/s Galaxy Surfactants Pvt. Ltd., India. SLES com-
prised of 60% C12 chain and 40% C14 chain surfactant and the ethoxylation was 2 mol
per mol carbon chain. Distilled water was used for preparing all the surfactant solutions.
The equilibrium surface tension, dynamic surface tension and foamability measure-
ments were carried out using the same procedures discussed in earlier chapters. Hori-
zontal Impinging Jet, foaming apparatus was used for foamability studies.
O
S
O
NaO O
O
R2
R = C12H25
sodium lauryl ether sulphate
Figure 5.1: Structure of SLES
112
5.3 Results and Discussion
5.3.1 Critical Micelle Concentration (CMC)
The CMC of mixed micellar systems of SLES and anionic phosphate gemini surfactants
(m−3−m and m−5−m) in aqueous solutions was investigated, using surface tension
measurements. The surface tension was measured using Wilhelmy plate method on
Kruss K-11 tensiometer, at temperature 25 ± 10C. The CMC value of SLES was found
to be 0.99 mM , Amin value found to be 61 A2. The CMCs and interfacial properties
of the mixture of SLES/geminis was reported in Table 5.1 -5.2. The surface tension
plots were shown in figures 5.2- 5.8. The surface tension results were accurate within
the range of ±0.2 mN/m. It was observed that with increasing mole fraction of gem-
ini surfactants the CMC values decreases, this was observed for both m− 3−m and
m− 5−m geminis. The Amin values were changed drastically for the mixtures, more
than that of individual surfactants, which indicates that the adsorption of the mixed sur-
factants at air/water interface is less than compared to that of the individual surfactants.
Authors Rosen and Zhou [Rosen, 1982; Zhu et al. , 1991] also observed the same ex-
pansion behavior which was attributed to the dissimilarity in the nature of interaction
among hydrophobic groups and hydrophilic groups in the mixed adsorbed layer. In
case of structurally similar hydrocarbon tails, hydrophobic interactions occur at small
distances, whereas ion–dipole interactions among anisotropic head groups are effective
at relatively larger distances. In the case of SLES/m−3−m and SLES/m−5−m sys-
tems, larger Amin values were found because of the repulsive interactions instead of the
attractive forces between the hydrophobic as well as hydrophilic head groups of SLES
and gemini surfactants.
5.3.2 Interactions between mixed anionic surfactants
The commercial products are always comprised of a mixed surfactant system, because
economically synthesis of each component is not viable option. A mixed surfactant
system is often superior in performance to individual surfactants. There is a substantial
113
difference in the micellization tendency of mixtures of two or more surfactants as com-
pared to a single surfactant. This results in a dramatic change in properties and behavior
of mixed surfactants as compared to any single surfactant. Hence it is necessary to in-
vestigate the nature of interactions (synergistic/antagonistic) and the factors affecting
the interactions [Suradkar and Bhagwat, 2006]. A lower CMC of mixture than indi-
vidual surfactants is considered as synergy. The synergistic interactions between the
mixed surfactants is useful from the application point of view. The interaction between
the surfactants can be determined using models for mixed micellization. These mod-
els are based on an equilibrium thermodynamic approach [Ogino and Abe, 1993]. The
pseudo-phase separation model assumes that that the mixed micelle can be treated as
a separate phase. The pseudo-phase separation approach is a very useful tool for the
description of micelle formation [Hassan et al. , 1995]. Clint [Clint, 1975] proposed an
equation , for the CMC of the ideal mixture of two surfactants:
1Cmix
=x′1
C1+
(1− x′1)
C2(5.1)
Where x′1 is the bulk solution mole fraction of surfactant 1 in the mixture; C1, C2
and Cmix are the CMCs of the pure surfactant 1, 2 and mixed system, respectively.
The ideal solution theory has been successful in explaining the properties of mixtures
composed of surfactants with similar chemical structures, however deviations occur for
mixtures containing chemically dissimilar surfactants. The non-ideal behavior of mixed
surfactant systems was described by Rubingh [Rubingh, 1979], the model was based on
Regular Solution Theory. The non-ideal form of equation 5.1. can be given as;
1Cmix
=x′1
C1 f1+
(1− x′1)
C2 f2(5.2)
ln( f1) = β (1− x1)2 (5.3)
ln( f2) = β (x1)2 (5.4)
114
where x1 and x2 are the mole fractions of the surfactant 1 and surfactant 2, respec-
tively, in the mixed micelle. β is the interaction parameter that is usually obtained
by fitting the experimental data of mixture CMCs as a function of bulk mole fractions
x′1 of surfactant. Assuming a constant value of interaction parameter β , across the
whole range of mole fractions, it is possible to solve for x1 and hence predict the mixed
CMCs. The interaction parameter is a measure of the extent of net (pairwise) interaction
between the surfactants within the micelles resulting in their deviation from the ideal
behavior. In order to obtain valid interaction parameter β values that do not change sig-
nificantly with change in the ratio of surfactant in the mixture, the following conditions
must be met [Rosen, 2004];
1) The two surfactants must be molecularly homogeneous and free from surface
active impurities.
2) Since the derivation of equation 5.2 and 5.4 are based upon the assumption that
the mixed micelle or monolayer can be considered to contain only surfactants, these
structures are considered to contain no free water, and all the present water can be
considered to bound to the hydrophilic head groups,
3) Since equations 5.2 and 5.4 neglect counterion effects, all solutions containing
ionic surfactants should have the same total ionic strength, with a swamping excess of
any counterion.
The surfactant forms an aggregate or remains as a free monomer in a solution. The
total surfactant concentration is just incrementally larger than Cmix, then the monomer
composition coincides with the overall surfactant composition. This indicates that more
number of free surfactant monomers are present in the solution rather than micelles. The
number of micelles will be increased with an increase in total surfactant concentration.
The mixture CMC, Cmix, is fitted with eq 5.2, which is also known as a Margules one-
constant equation. Such a treatment gives a constant value of interaction parameter at
all bulk solution mole fractions x′1[Suradkar and Bhagwat, 2006].
The value of interaction parameter is then substituted in eq 5.2 to compute the values
of micellar mole fraction x1 at each bulk solution mole fraction x′1. The plots of Cmix
115
against Gemini bulk solution mole fraction x′1 are shown in Figures 5.10- 5.15.
The conditions for synergism or negative synergism in a mixture containing two
surfactants (in the absence of second liquid phase) have been shown mathematically
[Rosen, 1989] to be the following:
(1) For synergism, the interaction parameter must be negative and |β | > |ln(C1/C2)|.
(2) For negative synergism or antagonism, the interaction parameter β must be pos-
itive and |β | > |ln(C1/C2)| where C1 and C2 are the CMCs of individual surfactants.
Interactions between the surfactants in binary mixtures are the result of mainly two
contributions, one associated with interactions between hydrophobic moieties of the
two surfactants in the micellar core and the other with electrostatic interactions between
the head groups of both surfactants at the interface, besides the possibility of hydrogen
bonding cannot be ruled out [Sheikh et al. , 2011].
5.3.2.1 SLES/m-3-m gemini surfactants
The one parameter Margules equation was fit to the experimental data, to obtain single β
value for the entire mole fraction range of gemini surfactants. For the SLES/10−3−10
system, negative deviation was observed from the ideal behavior, except at gemini mole
fraction 0.6. At 0.6 mole fractions of gemini 10-3-10 the Cmix value increased, more
than ideal Cmix. The margules equation was fitted to the experimental Cmix values and
the single negative β value was obtained (-2.82) which means there are attractive in-
teractions or synergistic interactions exists between the mixed surfactants. A negative
interaction parameter means that the attractive interaction between two different sur-
factant monomers is stronger that the attractive interaction between the two individual
surfactant monomers with themselves or that the repulsive interaction between two dif-
ferent surfactant monomers is weaker than the self repulsion of the two individual sur-
factant monomers. However positive β value was obtained for the SLES/12− 3− 12
and SLES/16− 5− 16 (0.13 and 0.69 respectively) which indicates there is negative
synergism, i.e. antagonistic effect was observed. For SLES/12−3−12 system positive
deviation was observed in Cmix, but at 0.8 mole fraction of gemini 12−3−12 the Cmix
116
value was found to be almost similar to ideal Cmix which also suggests that micelliza-
tion is favored by gemini surfactant at higher gemini surfactant concentration. Similarly
the SLES/16−5−16 system also exhibits negative synergism and at mole fractions 0.6
and 0.8, micellization was favored by gemini surfactant. A positive interaction parame-
ter implies that the attractive interaction between the two different surfactant monomers
is weaker than the attractive interactions between the individual surfactant monomers
themselves or the self repulsion between two different surfactant monomers is stronger
than the self repulsion between the individual surfactant monomer themselves.
5.3.2.2 SLES/m-5-m gemini surfactants
A positive β value was obtained for these systems. The positive deviation from ideal
behavior shows antagonistic interactions between mixed surfactant. The β value was
found to be in the order of, 16-5-16 > 12-5-12 > 10-5-10 (1.90 > 0.39 > 0.20 respec-
tively).
Overall in the case of both m−3−m and m−5−m gemini surfactants the β value
increases with the increasing carbon chain length in the tail group of gemini surfactants,
as shown in fig. 5.9. The positive deviations can be attributed to the unfavorable interac-
tions or repulsive interactions between the sulphate head group of SLES and phosphate
head groups of geminis, also similar kind of interactions are possible between the un-
equal chains of SLES/gemini surfactants.
5.3.3 Dynamic surface tension
Dynamic surface tension measurements were carried out for the SLES (at CMC. 0.99
mM) and SLES (at CMC)/m− 3−m geminis (0.1 and 0.5 mM) and m− 5−m (0.1
and 0.5 mM) gemini surfactants, using Maximum bubble pressure method. The prin-
ciple and procedure of maximum bubble pressure was described in earlier chapters.
The dynamic surface activity parameters were listed in table 5.3. It was found that
with increasing gemini surfactant concentration in the mixture of SLES/m−3−m and
SLES/m− 5−m, the rate of dynamic surface tension reduction decreases, as shown
117
in figures 5.16, 5.18, 5.20, 5.20, 5.22, 5.24, 5.26. The reduced dynamic surface ten-
sion of the mixtures was studied, the plots of RDST versus log t are shown in figures
5.17, 5.19, 5.21, 5.23, 5.25, 5.27. The t∗ values and R1/2, found to decrease for the
SLES/10−3−10 in the order of 10−3−10 (0.1 mM) > 10−3−10 (0.5 mM). Similar
trend was observed for the SLES/12− 3− 12 gemini surfactant, the t∗ values found
to decrease in the order of 12− 3− 12 (0.1 mM) > 12− 3− 12 (0.5 mM). However
the trend was different for the SLES/16− 3− 16, the t∗ values and R1/2 values in-
creased in the order 16− 3− 16 (0.5 mM) > 16− 3− 16 (0.1 mM). The effect of the
increasing chain lengths of the geminis can be seen, as with the increasing chain length,
the R1/2 values decreases which suggests that the increased hydrophobicity, causes de-
crease in the adsorption of the molecules under dynamic condition. It was found that for
SLES/m−5−m system, the SLES/12−5−12 at 0.1 & 0.5 mM gemini concentration
the surface activity was found to increase than SLES (at CMC) alone. The dynamic
surface activity of 16-5-16 at 0.1 mM concentration found to increase by 20 times than
that of SLES. The m− 5−m gemini surfactants found to have good surface activity
under dynamic conditions compared to the m−3−m geminis.
5.3.4 Foamability
An apparatus for measurement of foamability of surfactant solution is recently devel-
oped in our laboratory. The setup generates foam by impacting a stream of liquid on
to a flat horizontal surface of the polydispersed foam generated during the process, the
setup separates the fine bubbles from coarse one. The rate of collection of fine foam
volume gives a measurement of foamability of the test solution. The details of this
method is described in earlier chapter. Experiments were carried out at an ambient tem-
perature (302 ± 2 K). Foam generation of various gemini surfactant solutions and their
monomeric surfactants were investigated by Horizontal Impinging Jet method.
The foamability of SLES (at CMC) and SLES/gemini surfactants aqueous solutions
was studied. The Foamability plots were shown in figures 5.28 - 5.33, and the foam-
ability results was enlisted in table 5.4. Overall it was found that the foamability of
118
SLES in the presence of the gemini surfactants decreases with the increase in gemini
surfactant concentration. This is due to the decreased surfactant availability for ad-
sorption at the interface. Since the newly formed interface must be stabilized by the
adsorption of surfactant to produce foam. The interface creation must be immediately
followed by interface stabilization in order to avoid coalescence of the formed bubbles.
The rate of the stabilization depends on the rate of interface stabilization. The reason
can be correlated to the surface density of the monomers of mixed surfactants present
at the interface. From table 5.1 and 5.2, it was found that the Amin values of the mix-
tures of SLES/gemini, increased significantly, which means the area per molecule at
the interface is larger means very less number of surfactant monomers are available to
adsorb at the interface, this results in the lowering of foamability of SLES. Also the
low foamability can be a attributed to the slow dynamics of SLES/gemini surfactant
mixture. The chain length effect was not observed in the case of m− 5−m gemini
surfactants, however at 0.1 mM m−3−m geminis the foamability increases in the or-
der of 16−3−16 > 12−3−12 > 10−3−10 but less than that of SLES without any
additives.
119
Table 5.1: m− 3−m gemini bulk solution mole fraction x′1, Mixture CMC Cmix ,
Micellar mole fraction x1, and Interaction Parameter β and interfacial properties forSLES/m−3−m gemini surfactant system.
Gemini x′1
CmixmeasuredmM
CmixidealmM β
Γmax1010mol/cm2
Amin
A2
10-3-10 0 0.99 0.990.2 0.13 0.403 0.52 3190.4 0.19 0.254 -2.82 0.52 3190.6 0.22 0.185 0.48 3460.8 0.11 0.146 0.7 2371 0.12 0.12
12-3-12 0 0.99 0.990.2 0.98 0.833 0.16 10380.4 0.64 0.719 0.20 8300.6 0.68 0.633 0.13 0.54 3070.8 0.50 0.565 0.45 3691 0.51 0.51
16-3-16 0 0.99 0.990.2 0.85 0.933 0.11 15090.4 0.54 0.833 0.69 0.17 9760.6 0.34 0.837 0.23 7220.8 0.3 0.797 0.27 6151 0.3 0.76
120
Table 5.2: m− 5−m gemini bulk solution mole fraction x′1, Mixture CMC Cmix ,
Micellar mole fraction x1, and Interaction Parameter β and interfacial properties forSLES/m−5−m gemini surfactant system.
Gemini x′1
CmixmeasuredmM
CmixidealmM β
Γmax1010mol/cm2
Amin
A2
10-5-10 0 0.990.2 1 0.933 0.20 8300.4 0.91 0.833 0.20 0.27 6150.6 0.87 0.837 0.24 6920.8 0.82 0.797 0.22 7541 0.76
12-5-12 0 0.9900.2 0.69 0.634 0.19 8740.4 0.49 0.466 0.25 6640.6 0.47 0.369 0.39 0.25 6640.8 0.29 0.305 0.33 5031 0.26
16-5-16 0 0.990.2 0.75 0.381 0.19 8740.4 0.84 0.236 1.90 0.15 11070.6 0.30 0.171 0.32 5190.8 0.10 0.134 0.37 4481 0.11
121
Table 5.3: Dynamic surface activity parameters of SLES and SLES/geminis
Surfactant Conc. n t∗ γm R1/2
(mM) (mN/s)SLES 0.99 0.37 0.263 28.9 5.67
10−3−10 0.1 0.218 0.03 35.2 0.620.5 0.263 0.02 32.7 0.45
12−3−12 0.1 0.243 0.16 36. 3.020.5 0.214 0.06 37.5 1.05
16−3−16 0.1 0.161 0.30 36.8 5.340.5 0.12 0.65 32.1 12.93
10−5−10 0.1 0.285 0.24 33 4.750.5 0.073 – 35.2 –
12−5−12 0.1 0.30 0.47 36.7 8.370.5 0.29 0.88 37.9 15.09
16−5−16 0.1 0.203 5.28 32.1 105.20.5 0.187 0.14 27.5 3.29
Table 5.4: Foamability of SLES and SLES/m−3−m and SLES/m−5−m geminis
Surfactant system Conc. (mM) Foamability (ml/s)SLES at CMC, 0.99 0.45
SLES/10−3−10 0.1 0.160.5 0.14
SLES/12−3−12 0.1 0.180.5 0.11
SLES/16−3−16 0.1 0.310.5 0.10
SLES/10−5−10 0.1 0.110.5 0.10
SLES/12−5−12 0.1 0.110.5 0.08
SLES/16−5−16 0.1 0.100.5 0.07
122
0.01 0.1 1 10Concentration (mM)
20
30
40
50
60
Surf
ace
tens
ion
(mN
/m)
Figure 5.2: Surface tension plot of SLES
123
0.01 0.1 120
30
40
50
60
70
0.01 0.1 120
30
40
50
60
70
0.01 0.1 120
30
40
50
60
70
0.01 0.1 120
30
40
50
60
70
Concentration (mM)
Surf
ace
tens
ion
(mN
/m)
x1’ = 0.8 x
1’ = 0.6
x1’ = 0.4 x
1’ = 0.2
Figure 5.3: Surface tension plots of SLES with 10−3−10 gemini surfactants
124
0.01 0.1 120
30
40
50
60
70
0.01 0.1 120
30
40
50
60
70
0.01 0.1 120
30
40
50
60
70
0.01 0.1 120
30
40
50
60
70
Surf
ace
tens
ion
(mN
/m)
Concentration (mM)
x1’ = 0.8 x
1’ = 0.6
x1’ = 0.4 x
1’ = 0.2
Figure 5.4: Surface tension plots of SLES with 12−3−12 gemini surfactants
125
0.001 0.01 0.1 120
30
40
50
60
70
0.01 0.1 120
30
40
50
60
70
0.01 0.1 120
30
40
50
60
70
0.01 0.1 120
30
40
50
60
Surf
ace
tens
ion
(mN
/m)
Concentration (mM)
x1’ = 0.8 x
1’ = 0.6
x1’ = 0.4 x
1’ = 0.2
Figure 5.5: Surface tension plots of SLES with 16−3−16 gemini surfactants
126
0.01 0.1 120
30
40
50
60
70
0.01 0.1 120
30
40
50
60
70
0.01 0.1 120
30
40
50
60
70
0.01 0.1 120
30
40
50
60
70
Surf
ace
tens
ion
(mN
/m)
Concentration (mM)
x1’ = 0.8 x
1’ = 0.6
x1’ = 0.4 x
1’ = 0.2
Figure 5.6: Surface tension plots of SLES with 10−5−10 gemini surfactants
127
0.01 0.1 110
20
30
40
50
60
70
0.01 0.1 110
20
30
40
50
60
70
0.01 0.1 110
20
30
40
50
60
70
0.01 0.1 110
20
30
40
50
60
70
Surf
ace
tens
ion
(mN
/m)
Concentration (mM)
α = 0.8 α = 0.6
α = 0.4 α = 0.2
Figure 5.7: Surface tension plots of SLES with 12−5−12 gemini surfactants
128
0.01 0.1 110
20
30
40
50
60
70
0.01 0.1 110
20
30
40
50
60
70
0.01 0.1 110
20
30
40
50
60
70
0.01 0.1 110
20
30
40
50
60
70
Surf
ace
tens
ion
(mN
/m)
Concentration (mM)
x1’= 0.8 x
1’= 0.6
x1’ = 0.4 x
1’ = 0.2
Figure 5.8: Surface tension plots of SLES with 16−5−16 gemini surfactants
129
8 10 12 14 16 18Carbon chain length of gemini surfactants
-3
-2
-1
0
1
2
3m-3-m geminism-5-m geminis
β
Figure 5.9: Plot of interaction parameter (β ) between SLES and geminis versus chainlength
130
0 0.2 0.4 0.6 0.8 1Mole fraction of gemini 10-3-10
0
0.2
0.4
0.6
0.8
1
CM
C (
mM
)
Cmix measured
Margules equation fitC
mix ideal
β = −2.87
Figure 5.10: Plot of Cmix against mole fraction of gemini 10-3-10
0 0.2 0.4 0.6 0.8 1Mole fraction of gemini 12-3-12
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
CM
C (
mM
)
Cmix measured
Margules equation fitC
mix ideal
β = 0.13
Figure 5.11: Plot of Cmix against mole fraction of gemini 12-3-12
131
0 0.2 0.4 0.6 0.8 1Mole fraction of gemini 16-3-16
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
CM
C (
mM
)
Cmix measured
Margules equation fitC
mix ideal
β = 0.69
Figure 5.12: Plot of Cmix against mole fraction of gemini 16-3-16
0 0.2 0.4 0.6 0.8 1Mole fraction of gemini 10-5-10
0.6
0.7
0.8
0.9
1
CM
C (
mM
)
Cmix measured
Margules equation fitC
mix ideal
β = 0.20
Figure 5.13: Plot of Cmix against mole fraction of gemini 10-5-10
132
0 0.2 0.4 0.6 0.8 1Mole fraction of gemini 12-5-12
0.2
0.4
0.6
0.8
1
CM
C (
mM
)
Cmix measured
Margules equation fitC
mix ideal
β = 0.39
Figure 5.14: Plot of Cmix against mole fraction of gemini 12-5-12
0 0.2 0.4 0.6 0.8 1Mole fraction of gemini 16-5-16
0
0.2
0.4
0.6
0.8
1
CM
C (
mM
)
Cmix measured
Margules equation fitC
mix ideal
β = 1.90
Figure 5.15: Plot of Cmix against mole fraction of gemini 16-5-16
133
0.1 1 10 100Time (s)
25
30
35
40
45
50
Dyn
amic
Sur
face
tens
ion
(mN
/m)
SLES at cmc without additivesSLES at cmc + 0.1 mM 10-3-10SLES at cmc + 0.5 mM 10-3-10
Figure 5.16: Dynamic surface tension plot of SLES / 10-3-10 gemini
1 2 31/ sqrt t
25
30
35
40
45
50
55
Dyn
amic
sur
face
tens
ion
(mN
/m)
10-3-10 (0.1 mM)10-3-10 (0.5 mM)
0.1 1 10t
1
10
RD
ST
10-3-10 (0.1 mM)10-3-10 (0.5 mM)
SLES (at cmc) + 10-3-10
Figure 5.17: Plots of dynamic surface tension versus t−1/2 and RDST versus t of SLES/ 10-3-10 gemini
134
0.1 1 10 100Time (sec)
25
30
35
40
45
50
55
Dyn
amic
Sur
face
tens
ion
(mN
/m)
SLES at cmc without additivesSLES + 0.1 mM 12-3-12SLES + 0.5 mM 12-3-12
Figure 5.18: Dynamic surface tension plot of SLES / 12-3-12 gemini surfactant
0 0.5 1 1.5 2 2.5
t-1/2
34
36
38
40
42
44
46
48
50
Dyn
amic
sur
face
tens
ion
(mN
/m)
12-3-12 (0.1 mM)12-3-12 (0.5 mM)
SLES + 12-3-12
0.1 1 10 100t
1
10
RD
ST
12-3-12 (0.1 mM)12-3-12 (0.5 mM)
SLES + 12-3-12
Figure 5.19: Plots of dynamic surface tension versus t−1/2 and RDST versus t of SLES/ 12-3-12 gemini
135
0.1 1 10 100Time (s)
30
35
40
45
50
55
60
Dyn
amic
Sur
face
tens
ion
(mN
/m)
SLES at cmc, without additivesSLES + 0.1 mM 16-3-16SLES + 0.5 mM 16-3-16
Figure 5.20: Dynamic surface tension plot of SLES / 16-3-16 gemini
0 0.5 1 1.5 2
t-1/2
20
25
30
35
40
45
50
55
60
Dyn
amic
Sur
face
tens
ion
(mN
/m)
16-3-16 (0.1 mM)16-3-16 (0.5 mM)
SLES + 16-3-16
0.01 0.1 1 10 100t
0.1
1
10
RD
ST
16-3-16 (0.1 mM)16-3-16 (0.5 mM)
SLES + 16-3-16
Figure 5.21: Plots of dynamic surface tension versus t−1/2 and RDST versus t of SLES/ 16-3-16 gemini
136
0.1 1 10 100Time (s)
25
30
35
40
45
50
55
Dyn
amic
sur
face
tens
ion
(mN
/m)
SLES at cmc, without additivesSLES + 0.1 mM 10-5-10 SLES + 0.5 mM 10-5-10
Figure 5.22: Dynamic surface tension plot of SLES / 10-5-10 gemini
0 1 21/sqrt t
30
35
40
45
50
55
Dyn
amic
sur
face
tens
ion
(mN
/m)
10-5-10 (0.1 mM)10-5-10 (0.5 mM)
0.1 1 10 100t
1
10
RD
ST
10-5-10 (0.1 mM)10-5-10 (0.5 mM)
SLES + 10-5-10
Figure 5.23: Plots of dynamic surface tension versus t−1/2 and RDST versus t of SLES/ 10-5-10 gemini
137
0.1 1 10t (sec)
30
35
40
45
50
55
60
Dyn
amic
Sur
face
tens
ion
(mN
/m)
SLES + 12-5-12(0.1mM)SLES + 12-5-12 (0.5mM)
Figure 5.24: Dynamic surface tension plot of SLES / 12-5-12 gemini surfactant
0 0.5 1 1.5 2 2.5
t-1/2
25
30
35
40
45
50
55
60
Dyn
amic
sur
face
tens
ion
(mN
/m)
12-5-12 (0.1 mM)12-5-12 (0.5 mM)
SLES + 12-5-12
1 10 100t
1
10
RD
ST
12-5-12 (0.1 mM)12-5-12 (0.5 mM)
SLES + 12-5-12
Figure 5.25: Plots of dynamic surface tension versus t−1/2 and RDST versus t of SLES/ 12-5-12 gemini
138
0.1 1 10 100Time (s)
30
35
40
45
50
55
60
Dyn
amic
sur
face
tens
ion
(mN
/m)
SLES at cmc without additivesSLES + 0.1 mM 16-5-16SLES + 0.5 mM 16-5-16
Figure 5.26: Dynamic surface tension plot of SLES / 16-5-16 gemini surfactant
0 0.5 1 1.5 2
t-1/2
25
30
35
40
45
50
55
60
Dyn
amic
sur
face
tens
ion
(mN
/m)
16-5-16 (0.1 mM)16-5-16 (0.5 mM)
SLES + 16-5-16
0.1 1 10t
0.1
1
10
RD
ST
16-5-16 (0.1 mM)16-5-16 (0.5 mM)
SLES + 16-5-16
Figure 5.27: Plots of dynamic surface tension versus t−1/2 and RDST versus t of SLES/ 16-5-16 gemini
139
0 50 100 150Time (min)
0
5
10
15
20
25
30
Foam
Vol
ume
(ml)
SLES + 0.1 mM 10-3-10SLES + 0.5mM 10-3-10SLES without additive
Figure 5.28: Foamability of SLES / 10-3-10 gemini
0 100 200 300 400 500Time (min)
0
5
10
15
20
25
30
Foam
Vol
ume
(ml)
SLES + 0.1 mM 12-3-12SLES + 0.5 mM 12-3-12 SLES without additive
Figure 5.29: Foamability of SLES / 12-3-12 gemini
140
0 50 100 150 200 250 300Time (min)
0
5
10
15
20
25
30
Foam
vol
ume
(ml)
SLES without additivesSLES + 0.1 mM 16-3-16SLES + 0.5 mM 16-3-16
Figure 5.30: Foamability of SLES / 16-3-16 gemini
0 50 100 150 200 250 300Time (min)
0
5
10
15
20
25
30
Foam
Vol
ume
(ml)
SLES + 0.1 mM gemini 10-5-10SLES + 0.5 mM gemini 10-5-10
Figure 5.31: Foamability of SLES / 10-5-10 gemini
141
0 100 200 300 400Time (min)
0
5
10
15
20
25
30
Foam
Vol
ume
(ml)
SLES + 0.1 mM 12-5-12SLES + 0.5 mM 12-5-12
Figure 5.32: Foamability of SLES/12-5-12 gemini
0 100 200 300 400Time (min)
0
5
10
15
20
25
30
Foam
Vol
ume
(ml)
SLES + 0.1 mM 16-5-16 SLES + 0.5 mM 16-5-16
Figure 5.33: Foamability of SLES/16-5-16 gemini
142
Table 5.5: Equilibrium surface tension data for SLES/10-3-10 gemini mixture
α = 0.2 α = 0.4 α = 0.6 α = 0.8Conc. γ Conc. γ Conc. γ Conc. γ
(mM) (mN/m) (mM) (mN/m) (mM) (mN/m) (mM) (mN/m)0.01 64.94 0.01 67.08 0.01 68.28 0.03 67.300.03 54.68 0.03 62.3 0.03 66.67 0.05 55.110.05 45.32 0.05 57.72 0.05 63.93 0.07 47.710.07 41.84 0.07 49.56 0.07 51.74 0.09 42.380.09 39.66 0.09 43.85 0.09 48.15 0.1 37.960.1 34.87 0.1 41.12 0.1 44.77 0.2 33.570.2 30.08 0.2 34.05 0.2 37.42 0.3 33.130.3 29.65 0.3 33.02 0.3 36.29 0.5 32.370.5 29.87 0.5 32.37 0.5 34.54 0.7 32.910.7 29.32 0.7 31.26 0.7 33.89 1 32.481 29.43 1 32.31 1 33.46 1.3 32.37
1.3 28.78 1.3 31.93 1.3 33.24 1.5 32.691.5 28.56 1.5 31.61 1.5 33.35 1.7 32.262 28.23 1.7 32.15 2 32.64 2 31.72
2 32.48
Table 5.6: Equilibrium surface tension data for SLES/12-3-12 gemini mixture
α = 0.2 α = 0.4 α = 0.6 α = 0.8Conc. γ Conc. γ Conc. γ Conc. γ
(mM) (mN/m) (mM) (mN/m) (mM) (mN/m) (mM) (mN/m)0.01 56.61 0.01 60.32 0.01 68.75 0.01 66.380.03 51.27 0.03 53.79 0.03 59.37 0.02 61.630.05 47.15 0.05 49.05 0.05 54.63 0.03 57.710.07 44.40 0.07 45.48 0.07 51.78 0.05 54.150.09 43.57 0.09 44.18 0.09 49.16 0.07 50.230.1 42.07 0.1 42.75 0.1 47.15 0.09 47.860.3 35.59 0.2 35.51 0.2 41.01 0.1 46.080.5 32.96 0.3 32.78 0.3 39.79 0.2 41.800.7 30.61 0.5 30.41 0.5 39.61 0.3 38.830.9 28.25 0.7 29.44 0.7 30.41 0.5 35.271 26.90 0.9 29.51 0.9 30.10 0.7 34.05
1.5 26.54 1 29.95 1 30.03 0.8 33.582 26.49 1.5 29.85 1.5 30.69 0.9 33.81
2 30.67 1 33.13
143
Table 5.7: Equilibrium surface tension data for SLES/16-3-16 gemini mixture
α = 0.2 α = 0.4 α = 0.6 α = 0.8Conc. γ Conc. γ Conc. γ Conc. γ
(mM) (mN/m) (mM) (mN/m) (mM) (mN/m) (mM) (mN/m)0.01 49.86 0.01 59.29 0.01 59.83 0.001 68.630.03 45.33 0.02 52.88 0.02 55.90 0.003 66.970.05 43.31 0.03 51.73 0.03 51.23 0.005 64.950.07 41.75 0.05 47.74 0.05 49.05 0.007 63.410.09 39.55 0.07 43.58 0.07 46.23 0.01 62.750.1 38.41 0.09 41.43 0.09 43.16 0.02 59.020.2 36.04 0.1 39.51 0.1 41.72 0.03 55.220.3 33.66 0.3 32.90 0.2 34.48 0.05 50.110.5 31.83 0.5 31 0.3 31.95 0.07 46.200.7 30.05 0.7 29.93 0.5 30.69 0.09 42.990.9 29.10 0.9 29.44 0.7 29.63 0.1 41.821 29.46 1 29.51 0.9 29.15 02 33.732 29.81 1.5 29.58 1 29.79 0.3 31
2 29.81 1.5 29.44 0.5 30.410.7 30.05
Table 5.8: Equilibrium surface tension data for SLES/10-5-10 gemini mixture
α = 0.2 α = 0.4 α = 0.6 α = 0.8Conc. γ Conc. γ Conc. γ Conc. γ
(mM) (mN/m) (mM) (mN/m) (mM) (mN/m) (mM) (mN/m)0.01 59.61 0.01 60.32 0.01 68.75 0.001 68.630.03 54.27 0.03 53.79 0.03 59.37 0.003 66.970.05 47.15 0.05 51.05 0.05 54.63 0.005 64.950.07 43.40 0.07 48.48 0.07 51.78 0.007 63.410.09 42.57 0.09 45.18 0.09 49.16 0.01 62.750.1 41.07 0.1 44.84 0.1 47.15 0.02 59.020.3 35.59 0.2 41.51 0.2 43.19 0.03 55.220.5 30.96 0.3 39.78 0.3 39.79 0.05 50.110.9 26.25 0.5 35.41 0.5 33.61 0.07 46.201 25.90 0.7 30.44 0.7 30.41 0.09 42.99
1.5 25.45 0.9 28.51 0.9 29.10 0.1 41.822 26.49 1 27.95 1 29.03 0.2 33.73
1.5 26.85 1.5 29.69 0.3 312 26.25 2 30.67 0.5 30.413 26.38 0.7 30.05
144
Table 5.9: Equilibrium surface tension data for SLES/12-5-12 gemini mixture
α = 0.2 α = 0.4 α = 0.6 α = 0.8Conc. γ Conc. γ Conc. γ Conc. γ
(mM) (mN/m) (mM) (mN/m) (mM) (mN/m) (mM) (mN/m)0.01 56.41 0.01 64.72 0.01 64.48 0.01 61.870.03 49.40 0.02 61.27 0.02 60.09 0.02 58.540.05 45.84 0.03 55.10 0.03 56.05 0.03 54.030.07 42.16 0.05 49.52 0.05 50.11 0.05 46.910.09 38.72 0.07 46.31 0.07 46.08 0.07 43.230.1 36.54 0.09 41.80 0.09 42.28 0.09 39.310.3 29.58 0.1 39.90 0.1 40.61 0.1 38.120.5 26.73 0.3 31 0.3 34.56 0.2 32.660.7 24.59 0.5 27.91 0.5 29.69 0.3 25.060.9 23.88 0.7 26.85 0.7 28.39 0.5 24.471 24.55 0.9 27.44 0.9 26.96 0.7 23.28
1.5 24.71 1 28.15 1 26.73 0.9 23.052 25.66 1.5 28.98 1.5 26.51 1 24.11
2 28.51 2 26.13 1.5 23.162 24.59
Table 5.10: Equilibrium surface tension data for SLES/16-5-16 gemini mixture
α = 0.2 α = 0.4 α = 0.6 α = 0.8Conc. γ Conc. γ Conc. γ Conc. γ
(mM) (mN/m) (mM) (mN/m) (mM) (mN/m) (mM) (mN/m)0.01 60.68 0.01 56.41 0.01 62.58 0.01 61.630.02 54.27 0.02 50.59 0.02 58.54 0.02 52.730.03 52.37 0.03 46.08 0.03 53.79 0.03 48.450.05 48.33 0.05 42.50 0.05 47.15 0.05 42.400.07 45.96 0.07 40.47 0.07 43.35 0.07 38.240.09 43.94 0.09 38.84 0.09 39.16 0.09 34.880.1 42.63 0.1 38.12 0.1 36.82 0.1 33.730.2 36.46 0.3 35.27 0.2 32.31 0.2 31.360.3 33.85 0.5 32.66 0.3 26.73 0.3 30.640.5 30.86 0.7 29.34 0.5 25.66 0.5 30.050.7 28.27 0.9 28.47 0.7 27.32 0.7 29.580.9 28.15 1 29.58 0.9 27.20 0.9 29.101 28.63 1.5 29.69 1 27.68 1 28.98
1.5 27.91 2 30.88 1.5 28.152 29.10 2 28.39
145
Table 5.11: Dynamic surface tension data of SLES at CMC and SLES/10-3-10 geminisurfactant
SLES (at CMC) 10-3-10 (0.1 mM) 10-3-10 (0.5 mM)t (sec) γ (mN/m) t (sec) γ (mN/m) t (sec) γ (mN/m)11.2 38.4 0.15 46.2 0.4 42.40.27 46.4 0.25 46.2 0.44 42.40.56 44.8 0.32 45.6 1.04 40.61.37 43.2 0.35 45.6 1.52 40.24.08 41.6 0.39 44.6 1.58 40.25.32 40 0.42 44.6 2.21 38.26.63 38.4 0.94 42.4 4.16 38.2
7 38.4 1.52 42.4 5.62 36.67.83 38.4 1.84 40.8 10.15 34.410.05 38.4 2 40.8 18.7 30.4
15 38.4 3.08 40.2 20.2 30.420 38.4 4.04 40.2 31.2 30.425 38.4 6.96 39.630 38.4 13.66 38.6
16.9 38.220 36.225 3630 36
146
Table 5.12: Dynamic surface tension data of SLES at CMC and SLES/12-3-12 geminisurfactant
12-3-12 (0.1 mM) 12-3-12 (0.5 mM)t (sec) γ (mN/m) t (sec) γ (mN/m)0.55 46.6 0.21 45.40.9 45.8 0.28 45.4
1.74 44.4 0.57 44.81.91 44.4 0.77 44.82.92 43.6 0.86 44.83.7 42.8 0.98 44.8
4.12 42.6 1.08 42.26.7 42 1.19 44.2
7.06 42 1.64 42.87.92 41.8 1.84 42.89.15 41.8 2.09 42.2
10.25 40.2 3.05 41.610.6 39.6 3.81 41.610.8 39.6 6.1 40.824.2 38.2 6.12 40.830 34.2 10.05 39.6
15 38.820 36.225 34.830 34.8
147
Table 5.13: Dynamic surface tension data of SLES at CMC and SLES/16-3-16 geminisurfactant
16-3-16 (0.1 mM) 16-3-16 (0.5 mM)t (sec) γ (mN/m) t (sec) γ (mN/m)0.13 51.2 0.27 51.20.26 51.2 0.36 51.20.42 49.6 0.43 51.20.58 49.6 0.53 51.20.84 49.6 0.88 51.21.09 48 1.12 49.61.18 48 1.88 49.61.31 48 2.23 481.47 48 2.63 481.6 48 3.3 48
1.72 48 3.5 481.81 46.4 5.32 482.36 46.4 5.5 482.84 46.4 13.1 46.46.8 43.2 15.1 46.4
11.6 43.2 16 46.414.4 41.6 19.3 44.815.6 41.6 21.4 43.216.2 40 22.6 43.217.8 40 35.6 38.418.5 40 37.4 38.420 40 45.6 38.430 40 46.2 38.4
31.4 4032.4 40
148
Table 5.14: Dynamic surface tension data of SLES at CMC and SLES/10-5-10 geminisurfactant
10-5-10 (0.1 mM) 10-5-10 (0.5 mM)t (sec) γ (mN/m) t (sec) γ (mN/m)
0.1 49.2 0.12 45.60.25 49.2 0.33 45.60.33 48.2 0.5 45.20.47 48.2 1 44.80.5 48.2 2 44.2
0.76 47.6 3.8 43.61 45.8 4.2 43.6
1.22 45.2 5 43.61.31 44.8 5.75 42.21.53 44.8 6.5 41.6
4 42.6 7.1 41.24.08 42.6 8 41.24.26 42.6 9 41.2
8 42.6 10 39.89 40.6 15 39.8
10 40.6 19 35.211.05 40.2 25 3212.5 39.6 30 3215 39.6 32.8 32
15.9 39.216.8 38.420 38.425 36.427 36.4
28.4 36.430 36.4
149
Table 5.15: Dynamic surface tension data of SLES at CMC and SLES/12-5-12 geminisurfactant
12-5-12 (0.1 mM) 12-5-12 (0.5 mM)t (sec) γ (mN/m) t (sec) γ (mN/m)0.26 47.2 0.39 48.40.42 46.8 0.61 47.80.64 46.8 0.89 47.80.95 46.2 1.24 47.21.28 46.2 1.88 46.81.71 46.2 3.02 45.81.99 45.8 4.67 45.22.63 44.6 7.34 44.65.42 43 10.3 43.27.95 41.8 14.27 43.29.16 41.8 16.14 41.4
10.53 41.8 21.86 40.615.62 40.6 26.84 39.822.78 38.427.71 38.431.6 38.4
150
Table 5.16: Dynamic surface tension data of SLES at CMC and SLES/16-5-16 geminisurfactant
16-5-16 (0.1 mM) 16-5-16 (0.5 mM)t (sec) γ (mN/m) t (sec) γ (mN/m)0.15 56.8 0.14 49.80.25 56.2 0.19 49.20.56 55.8 0.38 48.60.68 55.8 0.55 48.21.1 54.6 0.86 47.6
2.72 53.8 0.98 47.64.6 51.4 1.16 46.8
5.48 51.4 1.81 45.85.65 51.4 3.11 44.46.31 49.2 4.53 43.86.5 49.2 5.21 43.26.8 49.2 9.25 42
7.16 49.2 14.54 39.87.24 49.2 18.91 38.67.68 49.2 25.79 36.28.04 48.6 30 36.28.52 46.48.68 46.48.8 46.4
9.45 46.412.35 43.4
20 36.230.2 35.432.6 35.433.2 35.435.6 35.4
151
Table 5.17: Foamability data of SLES at CMC and SLES/10-3-10 gemini surfactant
SLES (at CMC) 10-3-10 (0.1 mM) 10-3-10 (0.5 mM)t (min) Foam (ml) t (min) Foam (ml) t (min) Foam (ml)
1.11 1 6.04 1 25.53 12.35 2 12.49 2 40.18 23.2 3 19.2 3 49.36 3
14.43 4 23.05 4 57.43 416.55 5 29.43 5 62.4 519.3 6 33.45 6 69 621.3 7 40.5 7 77.15 7
23.81 8 47.45 8 85.14 826.12 9 51.47 9 91.37 928.28 10 60.27 140 98.24 1031.1 11 66.05 11 104.21 11
33.18 12 75.11 12 114.1 1235.35 13 82.41 13 118.24 1337.56 14 92.2 14 124 1440.06 15 110.44 15 130.34 1542.17 16 139.17 1644.17 1846.42 1950.48 2052.46 2154.55 22
57 2359.08 2460.3 25
152
Table 5.18: Foamability of SLES at CMC and SLES/12-3-12 gemini surfactant
12-3-12 (0.1 mM) 12-3-12 (0.5 mM)t (min) Foam (ml) t (min) Foam (ml)
40 1 19.06 170.46 2 52.56 293.58 3 90.13 3
108.04 4 131.35 4120.13 5 176.52 5133.15 6 219.16 6141.42 7 245.08 7151.12 8 264.1 8158.18 9 280.35 9164.49 10 294.01 10172.17 11 307.22 11179.22 12 317.33 12184.26 13 325.42 13190.26 14 335.02 14198.52 15 343.16 15
200 16 352.51 16204.49 17 361.44 17209.49 18 369.22 18215.08 19 377 19219.38 20 386 20224.14 21 394 21229.18 22 401 22233.49 23 409 23237.55 24 418 24241.58 25 425 25
153
Table 5.19: Foamability of SLES at CMC and SLES/16-3-16 gemini surfactant
16-3-16 (0.1 mM) 16-3-16 (0.5 mM)t (min) Foam (ml) t (min) Foam (ml)14.35 2 36 2
29 4 70 438 6 90 645 8 108 851 10 128 10
58.46 12 147 1265.3 14 166 14
71.33 16 184 1675 18 201 1883 20 219 2089 22 238 2294 24 256 2498 25 275 25
Table 5.20: Foamability of SLES at CMC and SLES/10-5-10 gemini surfactant
10-5-10 (0.1 mM) 10-5-10 (0.5 mM)t (min) Foam (ml) t (min) Foam (ml)11.19 2 36.13 222.47 4 59 4
34 6 82.15 646 8 107.09 8
68.2 10 124.9 1083.54 12 147.47 12109.3 14 165.29 14127.5 16 180.13 16144.2 18 192.6 18161.7 20 206.26 20181 22 232 22
203.8 24 260.6 24224.7 25 274.55 25
154
Table 5.21: Foamability of SLES at CMC and SLES/12-5-12 gemini surfactant
12-5-12 (0.1 mM) 12-5-12 (0.5 mM)t (min) Foam (ml) t (min) Foam (ml)27.58 1 33.58 2
56 2 59.16 4158 7 90 6175 8 120.54 8188 9 135.24 10
202.57 10 151 12216.53 11 165.17 14232.45 12 178 16244.14 13 206 18257.31 14 222 20267.39 15 247.36 22279.14 16 261 24290.7 17
300.13 18310.35 19
319 20331.57 21
342 22355 23
366.48 24375.42 25
Table 5.22: Foamability of SLES at CMC and SLES/16-5-16 gemini surfactant
16-5-16 (0.1 mM) 16-5-16 (0.5 mM)t (min) Foam (ml) t (min) Foam (ml)22.32 2 53.49 247.6 4 105 4
60.56 6 139.12 671.7 8 160 889.3 10 190.25 10
104.6 12 210 12121.25 14 240 14140.37 16 265.49 16
159 18 287.28 18177.36 20 312 20
201 22 337 22231 24 365.25 24
247.21 25 381 25
155