A relative study on the micellization behavior of 12–2–12 Gemini surfactant with lactose and maltodextrin in aqueous medium: Spectroscopic and conductometric analysis

Article abstract of DOI:10.1016/j.molliq.2017.07.104

The present work reports the micellization mechanism and physico–chemical properties of synthesized 12–2–12 Gemini surfactant in aqueous solution of carbohydrates (lactose and maltodextrin) (0.0, 0.5, 1.0) % (w/v) at varying temperatures in the range (293.15–313.15) K. For this purpose, conductometric as well as spectroscopic measurements have been engaged to analyze the micellar modulation of Gemini surfactant in terms of its critical micelle concentration (CMC). The carbohydrates (lactose/maltodextrin) have been found to decrease the CMC of 12-2-12 Gemini surfactant, however, the effect is much more pronounced in maltodextrin as compared to lactose which is in compliance with the hydrophobic region present in the molecules. Further, temperature dependence of CMC has been employed to compute thermodynamic parameters of micellization in order to procure a better knowledge about the behavior of surfactant and intermolecular interactions present in such systems. The study of aqueous Gemini–carbohydrate systems may be helpful in working towards a healthier world from both personal as well as environmental aspects of life.

Full text of DOI:10.1016/j.molliq.2017.07.104

Accepted Manuscript
A relative study on the micellization behavior of 12–2–12 Gemini
surfactant with lactose and maltodextrin in aqueous medium:
Spectroscopic and conductometric analysis
S. Chauhan, Kailash Singh Atika, Kuldeep Singh, Maninder Kaur,
M.S. Chauhan
PII:
S0167-7322(17)32885-4
doi: 10.1016/j.molliq.2017.07.104
MOLLIQ 7683
DOI:
Reference:
To appear in:
Journal of Molecular Liquids
Received date:
Revised date:
Accepted date:
30 June 2017
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18 July 2017
Please cite this article as: S. Chauhan, Kailash Singh Atika, Kuldeep Singh, Maninder
Kaur, M.S. Chauhan , A relative study on the micellization behavior of 12–2–12 Gemini
surfactant with lactose and maltodextrin in aqueous medium: Spectroscopic and
conductometric analysis, Journal of Molecular Liquids (2017), doi: 10.1016/
j.molliq.2017.07.104
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ACCEPTED MANUSCRIPT
A relative Study on the Micellization Behavior of 12–2–12 Gemini Surfactant
with Lactose and Maltodextrin in Aqueous Medium: Spectroscopic and
Conductometric Analysis
*
S. Chauhan , Atika, Kailash Singh, Kuldeep Singh, Maninder Kaur and M.S. Chauhan
Department of Chemistry, Himachal Pradesh University, Summer Hill, Shimla–171005
*
Corresponding author. Tel.: +91 177 2830803; fax: +91 177 2830775
E-mail address: scschauhan19@gmail.com
Abstract
The present work reports the micellization mechanism and physico–chemical properties of
synthesized 12–2–12 Gemini surfactant in aqueous solution of carbohydrates (lactose and
maltodextrin) (0.0, 0.5, 1.0) % (w/v) at varying temperatures in the range (293.15-313.15) K. For
this purpose, conductometric as well as spectroscopic measurements have been engaged to
analyze the micellar modulation of Gemini surfactant in terms of its critical micelle
concentration (CMC ). The carbohydrates (lactose/maltodextrin) have been found to decrease
the CMC of 12-2-12 Gemini surfactant, however, the effect is much more pronounced in
maltodextrin as compared to lactose which is in compliance with the hydrophobic region present
in the molecules. Further, temperature dependence of CMC has been employed to compute
thermodynamic parameters of micellization in order to procure a better knowledge about the
behavior of surfactant and intermolecular interactions present in such systems. The study of
aqueous Gemini–carbohydrate systems may be helpful in working towards a healthier world
from both personal as well as environmental aspects of life.
Keywords: Conductivity; Critical micelle concentration; 12–2–12 Gemini surfactant;
thermodynamics of micellization; spectroscopic technique.

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1
. Introduction
Surfactants (surface active agents) are imperative components in biological systems as well as
pharmaceutical processes, thereby, account for large consumption in industrial and commercial
applications [3-6]. Their biocompatible, biodegradable and non-toxic formulations have greater
potential in food preparation and processing [7-8]. In recent years, a new class of surfactants
called Gemini surfactants emerged as promising substitutes for conventional surfactants [9-12].
They have superiority in terms of surface activity i.e aggregation behavior (micellization),
solubility and efficiency in lowering interfacial tension [13]. These in turn, lead to recurrent
appearance of surfactants in diverse fields ranging from routine commercial products to the high
technology products thereby motivating us to pursue their synthesis and study their aggregation
behavior in aqueous solution. The interactions of surfactants (conventional or Gemini) with
carbohydrates account for the structural organization of bio–active molecules in living systems
and is a subject matter of extensive research in the field of material synthesis, green chemistry,
chemical engineering, biochemistry (gene therapy) etc. [1, 2].
The micellization process and micro-environment of surfactants are largely affected by
the presence of additives such as carbohydrates, amino acids, drugs, electrolytes, etc. as well as
with change in experimental conditions [14-17]. Surfactants have the ability to modify the
conformation of carbohydrates in aqueous solutions, thereby, lead to the change in the
appearance, functionality, stability or rheology of the solution. Range of possible functional
modifications depends upon the nature of surfactant-additive interactions, which might favor or
counter the self-association process and consequently, influence the micellar morphology and its
environment [18-21]. Therefore, it would be beneficial to study the micellization behavior of
Gemini surfactants in the presence of biologically important compounds like carbohydrates,
which can promote our understanding about the interaction mechanism of Gemini–aqueous
carbohydrate system. In addition, this may encourage the scientific community towards the
development of materials with improved functional attributes or bulk physico–chemical
properties.
Thus, in the present work, we have studied the aggregation modulation of synthesized
cationic 12–2–12 Gemini surfactant i.e. ethanediyl–1,2–bis(dimethyldodecylammonium
bromide) in aqueous solutions of carbohydrates (lactose and maltodextrin) by making use of
electrical conductometry. The thermodynamic parameters have been calculated and analyzed to
get better understanding of unique behavior of Gemini surfactants in aqueous medium of

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carbohydrates and their chemical–biological relationships. Additive (carbohydrate) association
with surfactant has also been monitored spectrophotometrically by employing fluorescence and
UV–visible spectrophotometric techniques. For conductivity measurements, a spectrum of
temperature ranging from 293.15 K to 313.15 K at a regular interval of 5 K has been selected to
study the temperature dependence as well. However, the spectroscopic studies have been carried
out at room temperature (i.e. 298.15 K).
2
. Experimental
2
.1 Materials
–
6
–1
Double distilled water with conductivity of 23×10 S∙cm and pH of 6.8 7.0 (at 298.15 K)
obtained from Millipore distillation unit was used for all the studies. Gemini surfactant i.e.
ethanediyl–1,2–bis(dimethyldodecylammonium bromide) was synthesized in the laboratory
using ethyl acetate, 1-bromododecane and N, N, N, N–tetramethyl ethylenediamine (TEMED)
which were obtained from Merck, Sisco Research Laboratory and Himedia respectively.
Maltodextrin from the Loba Chemie Pvt. Ltd. and

–Lactose monohydrate from SD Fine–
Chem. Ltd. Both Carbohydrates were recrystallized twice in distilled water and dried in vacuum
o
oven for 24 hrs at ~ 50–60 C [22]. Pyrene of purity > 96% obtained from Merck was used as
spectrophotometric probe. The provenance and purity of chemicals used have also been provided
in Table 1.
Table 1: Specification of Chemicals Used.
Purification
method
–
Mass Fraction
Chemical Name
Source
a
Purity
ethyl acetate (C H O )
Merck
0.99
4
8
2
Sisco Research
Laboratory
1-bromododecane
–
0.98
N,N,N,N–tetramethyl
ethylenediamine (TEMED)
Himedia
–
0.99
(
C H N )
6 16 2
Maltodextrin
Loba Chemie Pvt. Ltd. Recrystallisation
0.98
0.95
0.96
Lactose (C H O ∙H O)
SD Fine–Chem. Ltd. Recrystallisation
1
2
22 11
2
Merck
–
Pyrene(C H )
1
6
10
a
Declared by Supplier

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2
.2 Instrumentation
The following instruments have been used for characterization and to procure information on
micellization behavior of synthesized 12–2–12 Gemini surfactant in aqueous solution of
carbohydrates (lactose and maltodextrin).
2
.2.1 Characterization of 12–2–12 Gemini surfactant:
1
13

H and C NMR analysis were carried out in D O solvent using JNM–ECS400
2
spectrometer with field strength 400 MHz.

The IR spectrum was obtained from RZX (Perkin Elmer) Fourier Transform
-1
Spectrometer (FTIR) at room temperature in the range of 4000–400 cm .
2
.2.2. Micellization Behavior of Synthesized 12–2–12 Gemini Surfactant:

Digital conductivity meter (Cyberscan Con–510) has been employed for conductivity
measurements.

Perkin Elmer LS–55 Fluorescence Spectrophotometer has been used for the fluorescence
probe study.

Genesys 10S UV–Vis spectrophotometer (190–900 nm) supplied by Thermo Scientific
USA, has been used for obtaining UV visible absorption spectrum.
2
.3 Synthesis of 12–2–12 Gemini Surfactant
Gemini surfactant i.e. ethanediyl–1,2–bis(dimethyldodecylammonium bromide) was prepared by
following the well established procedure (Scheme 1) reported in literature [23,24]. Mixture of N,
N, N, N–tetramethyl ethylene diamine (TEMED) and 1–bromododecane (molar ratio of 1:2) in
1
0 ml of ethyl alcohol was taken in round bottom flask then 5 ml of acetone was added to
remove turbidity and get clear solution. This solution was then refluxed at 348.15 K for
approximately 48 hours until the entire volume of TEMED was consumed. After removal of the
solvent by evaporation, the prepared waxy compound was allowed to cool at room temperature

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and washed with mixture of ethyl acetate and acetone in 1:1 ratio. The washing was repeated 6–7
times to eliminate excess of alkyl bromide. The resulting white product was crystallized twice in dry
acetone and dried in vacuum oven at 323.15 K.
Br
N
+
Br
N
TEMED (1 mole)
1
-Bromododecane (2 moles)
under reflux
8h, 348.15 K
Dry acetone
4
N+ Br-
Br-
N+
1
2-2-12 Gemini surfactant (1 mole)
Scheme 1: Systematic scheme for the synthesis of 12–2–12 Gemini surfactant
2
.4 Methods
.4.1 Conductivity Measurements
2
Stock solution of carbohydrates (0.0, 0.5, 1.0) % (w/v) have been prepared in water and has been
used as solvent for the preparation of 12–2–12 Gemini surfactant of different concentrations
-1
(
0.076–1.458 mmol∙kg ). All the solutions have been prepared by using Shimadzu balance with
a precision 0f ±0.0001g. The working principle of conductivity meter has already been
discussed in our earlier publication [3]. However, the conductivity cell has been calibrated before
each measurement by using conductivity standard calibration solution with conductivity 84 and
–
6
–1
1
413×10 S∙cm supplied by Eutech instruments. The temperature of the solution was
maintained to ± 0.1 K by circulating water through the vessel containing the solution with the
help of a high power digital water circulator supplied by Riviera Pvt. Ltd. Mumbai. The

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conductivity, κ for 12–2–12 Gemini surfactant in aqueous solutions of lactose/maltodextrin with
percentage composition (0.0, 0.5, and 1.0) % (w/v) have been measured in temperature range
(293.15–313.15) K at an interval of 5 K.
2
.4.2 Spectroscopic Measurements
Fluorescence probe study has been carried out at room temperature (298.15 K) keeping the
excitation wavelength at 334 nm and recording emission at 373 nm and 384 nm in the
wavelength range (350-450) nm. The working principle of the instrument and the method for the
preparation of Pyrene solution of required concentration has been explained elsewhere [3]. The
excitation and emission slit widths were kept at 8 nm and 2.5 nm respectively. The absorption
spectra have been recorded in (200-400) nm wavelength range and at room temperature (298.15
K) from UV–Vis spectrophotometer using 10 mm path length quartz cuvette.
3
. Result and Discussion
3
.1 Chemical Structure
1
13
The analysis of H NMR, C NMR and FTIR spectra of synthesized 12–2–12 Gemini surfactant
confirms its chemical structure.
1
3
.1.1 H NMR
1
The H NMR spectrum (Fig. 1) of 12–2–12 Gemini surfactant shows resonance at  0.84–0.88
+
+
ppm (t, 6H, alkyl chain, 2 × 1 CH ), 4.79 ppm (s, 4 H, spacer, 1× N CH CH N ), 3.30 ppm (s,
3
2
2
+
1
2H, 2×2 N CH ), 1.31–1.81 ppm (m, 4H, 2× CH attached to each terminal C), 3.53–3.55 ppm
3 2
+
(
m, 4 H, alkyl chain, 2× N –CH ) and 1.81–2.93 ppm (m, 36 H, alkyl chain, 9× 2 CH ).

2
2

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1
Fig. 1: H–NMR spectrum of 12–2–12 Gemini surfactant
13
3
.1.2 C NMR
1
3
The C NMR spectrum of synthesized 12–2–12 Gemini surfactant is shown in Fig. 2.The
resonance at –64.32 ppm (C–atom of –CH group as spacer), 63.28 ppm ( –C of –CH group

2
2
of the alkyl chain length), 13.9 ppm (C–atom of terminal –CH groups of hydrophobic tail),
3
6
0.18, 52.71, 44.69, 32.00, 30.16, 29.88, 29.83, 29.72, 29.52, 22.69 (10 C–atoms of –CH group
2
of alkyl chain).The two C–atoms of –CH groups directly attached to N–atom are expected to
3
give same chemical shift but they resonate at  – 51.48 ppm and 51.29 ppm. The small difference
in these values may be due to some rotation in the molecule which makes the two carbon atoms
to reside in different environments..

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1
3
Fig. 2: C–NMR spectrum of 12–2–12 Gemini surfactant
.1.3 FTIR Spectrum
3
-1
The spectrum of pure 12–2–12 Gemini surfactant (Fig. 3) showing peaks at 2858 cm and 2959
-1
-1
cm (symmetric and asymmetric stretching, methylene group of alkyl chain), 1465 cm
-1
(
scissoring, C–H bending), 1380 cm (bending, –CH groups which is attached directly to the
3
-
1
-1
-1
-1
nitrogen), 2780 cm (stretching, –CH of terminal –CH group), 1160 cm and 978 cm
3
+
-1
(
stretching, C–N ), 2925 cm (asymmetric stretching, methylene group of spacer) and 720 cm
(
rocking, –CH bending).
2

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100
1
160
90
80
70
60
50
2780
1
380
2
959
978 720
1
465
2
858
2
925
4000
3500
3000
2500
2000
1500
1000
-1
wavenumber (cm )
Fig. 3: Infrared spectrum of 12–2–12 Gemini surfactant
3
.2 Critical Micelle Concentration (CMC) Determination
3
.2.1 Conductivity Measurements
The Conductivity values of 12–2–12 Gemini surfactant in (0.0, 0.5, 1.0) % (w/v)
lactose/maltodextrin have been shown in Table S1 and S2 of supplementary data. In each
experimental set,

varies linearly with [Gemini surfactant] in pre–micellar and post–micellar
region, the intersection of the slopes corresponds to a particular point, referred to as critical
micelle concentration ( CMC ). The conductivity values have been found to increase sharply
before CMC but, vary slowly afterCMC . At low concentration, mobility plays an important role
as ions are relatively far apart and therefore have larger contribution towards

(sharp increase) ,
but at higher concentrations, presence of micelles inhibit the movement of ionic species as a
result conductivity increases slowly [25].

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240
220
200
180
160
140
120
100
(a)
CMC
80
60
40
20
0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
-1
[
Gemini surfactant] (mmol·kg
)
300
250
200
150
100
CMC
50
0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
-1
[
Gemini surfactant] (mmol·kg
)
Fig. 4: Representative plots of
Lactose and (b) Maltodextrin at 293.15 K (■), 298.15 K (●), 303.15 K (▲), 308.15 K (▼), and 313.15 K
◄).

, versus [Gemini surfactant] in 1.0 % (w/v) aqueous solution of (a)
(
The conductivity values of 12–2–12 Gemini surfactant in pure water (electrolyte) are higher in
comparison to the aqueous solutions of carbohydrates (non electrolytes). Comparatively, the

values of lactose are lower than that of maltodextrin, as it, being smaller molecule, is largely
hydrated which leads to the inhibition in movement of species. The CMC values of 12-2-12
Gemini surfactant in aqueous solutions of lactose and maltodextrin are documented in Table 2
and the values follow the order: no additive > lactose > maltodextrin. It has been assumed that

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in the presence of carbohydrates, water–water interactions are replaced by water–sugar
interactions cause the dehydration of hydrophilic group and results in decrease in CMC
.
Moreover, carbohydrates have the tendency to promote the formation of water matrix which
lower degree of hydrophilic hydration reinforcing the micellization and thus lowers theCMC
values [26-28].
Table 2: CMC of 12–2–12 Gemini surfactant in aqueous solutions of lactose and maltodextrin
a
(
m = 0.0, 0.5 and 1.0% (w/v)) at different temperatures (T/K).
3
-1
CMC ·10 (mol·kg )
T
(
K)
Lactose
Maltodextrin
a
a
a
a
a
m (0.0%)
m (0.5%)
m (1.0%)
m (0.5%)
m (1.0%)
0.66
2
93.15
98.15
0.80
0.75
0.72
0.69
0.76
a
0
.85 (0.88)
0.81
0.78
0.72
c
c
c
c
c
2
(0.86)
(0.80)
(0.78)
(0.77)
(0.77)
0.84
(0.74)
d
d
d
d
d
(
0.85)
(0.81)
(0.79)
(0.73)
b
3
3
3
03.15
08.15
13.15
0.92(0.95)
0.99
0.87
0.96
1.02
0.85
0.90
0.98
0.81
0.88
0.97
0.90
b
1.06 (1.11)
0.99
a
m is the percentage of lactose and maltodextrin(w/v) in water. Standard uncertainties, u, are u(T) =
.01 K and u(CMC ) = 0.01·10 mol·kg , (level of confidence = 0.68).
−
3
−1
0
a
b
c
d
Ref 30 Ref 29 Fluorescence study UV–Visible study.
3
.2.2 Fluoroscence Pyrene Probe Measurements
Fluorescence probe technique is one of the powerful tools in investigating the association of
surfactant in the presence of carbohydrates. In order to determine the CMC values of 12–2–12
Gemini surfactant in aqueous solutions of lactose/maltodextrin with percentage composition (0.0,
0
.5, and 1.0) % (w/v) at room temperature, we have amplified the pyrene probe fluorescence
spectra for aqueous 12–2–12 Gemini surfactant.
Pyrene has been used as a probe in this study and there were five emission peaks at 373,
–
6
–1
3
79, 383, 389 and 393 nm for pyrene (2×10 mol∙kg ) fluorescence spectra [31,32]. Pyrene

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fluorescence spectrum depends on the vibronic fine structure and relative peak intensity is
strongly dependent on the microenvironment polarity. The polarity–induced changes in
photophysical properties of pyrene can be determined by measuring the ratio of emission
intensities between first and third bands (I /I ) [32]. Lower value of I /I indicates apolar
1
3
1 3
environment and vice varsa [33]. With increasing polarity, the intensity of first band is increased
I ) but on the other hand, there is no effect on the intensity of third band (I ) [34]. Since pyrene,
(
1
3
–
7
–1
being hydrophobic molecule, has a much lower aqueous solubility (about 10 mol∙kg ) than in
–
1
hydrophobic solvent (0.075 mol∙kg ), it is very strongly distributed into micelles as soon as they
form, and the transfer is accompanied by abrupt decrease in the I /I ratio indicating micelle
1
3
formation (apolar environment), when a surfactant is added to aqueous solution containing
pyrene [35].
The change of I /I with the concentration of 12–2–12 Gemini surfactant in pure water and
1
3
in presence of aqueous lactose and maltodextrin has been plotted in Fig. 5. Pyrene senses the
polar environment of water molecules before CMC and results in higher I /I values. However,
1
3
above theCMC where micelles are present; there is solubilization of pyrene molecules in the
interior of micellar phase owing to their high hydrophobicity. Micelles act as hydrophobic–like
solvent and thus the environment sensed by pyrene is less polar, thereby resulting in the
decrease of I /I values.
1
3
The CMC values (Table 2) have been calculated by fitting the plots of I /I versus
1
3
concentration of surfactants to the Sigmoidal Boltzman equation (SBE) [31], as all plots were of
sigmoidal nature.

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1
1
1
1
1
1
1
1
1
.40
.35
.30
.25
.20
.15
.10
.05
.00
water
0
1
0
1
.5% lactose
.0% lactose
.5% maltodextrin
.0 % maltodextrin
CMC
0
.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 0.22
-
1
[
Gemini surfactant] (mmol·kg )
Fig. 5: Plot of I /I vs. [Gemini surfactant] in aqueous solution of (0.0, 0.5 and 1.0) % (w/v)
1
3
lactose/maltodextrin at room temperature (298.15 K).
.2.3 UV–Visible Measurements
3
The UV spectral manifestation of pyrene in aqueous surfactant solution is equally important for
the estimation of CMC of surfactants. Consequently, we have elaborated the potential of pyrene
absorption spectrum for the determination of CMC of 12–2–12 Gemini surfactant in the
absence and presence of carbohydrate in aqueous solutions at room temperature.
Further, pyrene absorption spectrum has evidenced eight strong (s) and weak (w) peaks, at
2
32w, 242s, 252w, 260w, 272s, 308w, 320s and 336s nm, [36]. It has been shown that the
absorbance at 242 nm increases, while above 315 nm, absorbance decreases with the solvent
polarity [37]. The micellar interior is non–polar and pyrene, being hydrophobic, is naturally
attracted to reside in the non–polar interior as there is no hydrophilic functionality of pyrene.
After micellization there is small increase in the UV absorbance which is due to the formation of
micelles and incorporation of more pyrene monomers into them [38]. The sum of absorbances of
all the four strong peaks (A ) against the concentration of Gemini surfactant in pure water and in
T
aqueous solution of lactose and maltodextrin has been illustrated in Fig. 6. It has been revealed

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that in all profiles A exhibits sigmoidal increase with the surfactant concentration and therefore,
T
fitting them to the Sigmoidal–Boltzmann equation (SBE).
0
0
0
0
0
0
0
0
0
0
0
.28
.26
.24
.22
.20
.18
.16
.14
.12
.10
.08
CMC
water
0
.5% lactose
1
0
1
.0% lactose
.5% maltodextrin
.0% maltodextrin
0
.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 0.22
-
1
[
Gemini surfactant] (mmol·kg )
Fig. 6: Plot of A vs. [Gemini surfactant] in aqueous solution of (0.0, 0.5 and 1.0) % (w/v)
T
lactose/maltodextrin at room temperature (T=298.15 K).
3
.3 Temperature dependence of CMC
The effect of temperature on CMC or XCMC values of 12–2–12 Gemini surfactant in aqueous
solutions of lactose/maltodextrin (0.0, 0.5, and 1.0) % (w/v) have been graphically represented in
Fig. 7. It has been noticed that CMC or XCMC values increase with rise in temperature. The
effect of temperature on CMC of Gemini surfactant in studied solvent system depends on two
opposing factors [39, 26]:
i) The de–solvation of the ionic head groups of Gemini surfactant/carbohydrates by water
molecules at lower temperatures (hydrophilic hydration), which favors the micellization
and decrease the CMC values.
ii) The interruption of the structured water molecules surrounding the non–polar parts of
Gemini surfactant/carbohydrates and breaking up of the hydrogen bonds present
between different species in the system which oppose micelle formation.

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Therefore, the variation of CMC depends on the competition of above two factors. In case of
1
2–2–12 Gemini surfactant, second factor predominates in the temperature range studied
which results in the increment of CMC values with temperature. Moreover, thermal motion of
surfactant and solvent molecules also increases with rise in temperature as a result the
formation of ordered micellar structure becomes difficult. This leads to decrease in the
aggregation of surfactant monomers and hence increase in CMC of the solute.
(
a)
0.019
0.018
0.017
0.016
0.015
0.014
0.013
[lactose](w/v)
0
0
1
.0 %
.5%
.0%
290
295
300
305
310
315
T(K)
(
b)
0.019
0.018
0.017
0.016
0.015
0.014
0.013
0.012
0.011
[
maltodextrin](w/v)
.0 %
0.5%
0
1
.0%
2
90
295
300
305
310
315
T(K)

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Fig. 7: Plot of XCMC versus temperature for 12–2–12 Gemini surfactant in aqueous solution of
(0.0, 0.5 and 1.0) % (w/v) (a) lactose and (b) maltodextrin.
3
.4 Thermodynamics of Micellization
Using pseudo phase separation model [40], the standard thermodynamic parameters of
micellization for 12–2–12 Gemini surfactant in pure water and aqueous solutions of
carbohydrates have been calculated using the XCMC data.
o
m
The standard enthalpy of micellization, H for ionic surfactants is given by the equation [41,
4
2]:
o
m
2

H  2RT (1.5)[d(ln X ) dT]
(1)
CMC
where d(ln XCMC dT) is the slope of the curve plotted between ln XCMC vs. T and the data so
obtained was subjected to least–squares treatment. Here,

is the degree of counter–ion
dissociation, which was calculated from equation [42].
S2


(2)
S1
where, S1 and S are the slopes in pre–and post–micellar regions determined from the
2
conductivity graphs with correlation coefficient always greater than 0.990. The standard free
o
m
o
m
energy of micellization, G and entropy of micellization, S have been estimated from the
following equations [41,42];
o
m

G  2(1.5)RT ln

XCMC

(
3)
o
m
o
m
o
m
H  G

S 
(4)
T
o
m
o
m
o
m
The values of H
,
G and S for 12–2–12 Gemini surfactant in aqueous solutions of
lactose/maltodextrin have been summarized in Table 3.

ACCEPTED MANUSCRIPT
o
o
o
Table 3: Standard thermodynamic parameters H , G and S of micellization for
m
m
m
a
1
2–2–12 Gemini surfactant in aqueous solutions of ( m = 0.0, 0.5, 1.0) % (w/v) lactose and
maltodextrin at different temperatures (T/K).
Lactose
Maltodextrin
Conc.
0
.0 %
0.5 %
1.0 %
0.5 %
1.0 %
T (K)
o
m
-1
H
(kJ·mol )
2
93.15
-25.73
-25.99
-26.31
-26.64
-26.89
-27.74
-28.02
-28.26
-28.56
-28.81
-27.56
-27.78
-28.12
-28.46
-28.79
-31.65
-31.83
-32.16
-32.37
-32.57
-35.62
-35.86
-36.15
-36.45
-36.68
2
3
3
3
98.15
03.15
08.15
13.15
o
m
-1
G
(kJ·mol )
2
2
3
3
3
93.15
98.15
03.15
08.15
13.15
-69.89
-69.05
-68.26
-67.52
-66.66
-70.73
-69.79
-68.77
-67.77
-70.55
-69.42
-68.59
-67.94
-67.09
-71.35
-70.41
-69.27
-68.17
-66.91
-72.53
-71.25
-69.89
-68.82
-67.55
-66.90
o
m
-1
-1
S
(kJ·mol ·K )
2
2
3
3
3
93.15
98.15
03.15
08.15
13.15
0.151
0.144
0.138
0.133
0.127
0.147
0.140
0.134
0.127
0.122
0.147
0.140
0.133
0.128
0.122
0.137
0.129
0.122
0.116
0.110
0.126
0.119
0.111
0.105
0.099
a
m is the percentage of lactose and maltodextrin(w/v) in water. Standard uncertainties, u, are u(T) =
.01 K and u(CMC ) = 0.01·10 mol·kg , (level of confidence = 0.68).
−
3
−1
0
o
m
It can be visualized from Table 3 that the G values for 12–2–12 Gemini surfactant are
negative in pure water and in aqueous solutions of lactose/maltodextrin indicating micellization
to be a spontaneous process and micelles are thermodynamically stable in all studied systems. It

ACCEPTED MANUSCRIPT
o
m
has been observed that G values increase i.e. become less negative with temperature. This
may be attributed to the fact that as temperature increases, enhancement of molecular motions
and promotion of repulsions between head groups takes place resulting in disaggregation of
o
m
surfactant monomers which inhibits micellization process [42]. The G values are more
negative in case of maltodextrin as compared to lactose indicating higher steadiness of the
system which may be due to stronger driving forces for micellization. This enhanced stability in
case of maltodextrin may be due to the structural modification in the system as we move from
lactose to maltodextrin i.e. presence of additional hydrophobic region.
o
m
Negative values of H in present case depicts that process of micellization is exothermic in
nature which may be the consequence of possible interactions between surfactant–solvent and
solvent–solvent molecules resulting into release of water molecules surrounded by a
hydrophobic tail during their transformation from bulk phase to micelle. Moreover, the negative
values of enthalpy indicate that the London dispersion forces also play an important role in the
micellization process for Gemini surfactant–carbohydrate system. It can be seen from the Table
o
m
3
that H values becomes more negative with temperature because of increased contribution
o
m
of H towards free energy as a result of reduction of hydrogen bonds between solvent
molecules and therefore lesser energy required to break up the water cluster [42]. However, the
values further decrease with the rising concentration of carbohydrates which may be due to the
decreased energy requirements to break up the ice–berg structure surrounding the hydrophobic
part of the mixture [43, 44].
o
m
The values for S have been found to be positive for 12–2–12 Gemini surfactant in the
absence and presence of both additives i.e. aqueous solution of lactose/maltodextrin. This may be
attributable to the melting of “ice–bergs” or flickering structures around hydrocarbon tails of
surfactant monomers and increased randomness of the hydrocarbon chains in the micellar core
o
m
[
16]. Also S values decrease with rise in temperature. This can be explained by taking two
opposing processes into account [45, 46]:
i) disruption of three–dimensional water matrix around the hydrocarbon tails of
surfactant monomers due to their incorporation into micelles resulting into increase in
randomness and hence entropy.
ii) arrangement of disordered monomers into more ordered surfactant aggregates leading to
negative change in entropy.

ACCEPTED MANUSCRIPT
o
m
In studied system, second factor predominates and hence resulted in smaller value of S with
o
m
temperature. It has been further found that values ofS are greater for aqueous 12–2–12 Gemini
surfactant as compared to those in the presence of carbohydrates as ordering of randomly
oriented cationic surfactant from the solvated form to micellar structure dominates over
o
m
destruction of water structure [44, 47]. Comparatively, maltodextrin lowers S values of 12–2–
1
2 Gemini surfactant to a larger magnitude than lactose due to enhanced micellization in former
o
m
case. However, S values of Gemini surfactant in aqueous lactose are almost independent of
concentration, whereas the same shows an observable decrease in case of maltodextrin.
o
m
A curious investigation of Table 3 shows that G values are practically independent of
temperature and nature of carbohydrate as well. This behavior reasonably accounts for the
o
m
o
m
o
m
o
m
compensation between S and H values leaving G almost unaffected. However, as G
is the sum of the enthalpic and entropic contributions, with increase in temperature, the
enthalpic contribution to the free energy increases, whereas the entropic contribution decreases
as can be seen from Fig. 8.
-26
-28
-30
-32
-34
-36
-38
-40
-42
-44
(
a)
o

H
m
o
-
TS
m
290
295
300
305
310
315
T(K)

ACCEPTED MANUSCRIPT
(
b)
-31
-32
-33
-34
-35
-36
-37
o

H
m
o
-
TS
m
290
295
300
305
310
315
T(K)
o
o
o
Fig. 8: Representative Plots of contribution of H and –TS to G versus temperature for
m
m
m
1
2–2–12 Gemini surfactant in 1.0 % (w/v) (a) lactose and (b) maltodextrin.

ACCEPTED MANUSCRIPT
5
. Conclusion
The addition of carbohydrates to aqueous 12–2–12 Gemini surfactant has been found to facilitate
micellar behaviour of surfactant as revealed by the determined CMC order i.e. no additive >
lactose > maltodextrin. This may be attributed to the fact that, the structural modification has
been imparted to the system by these bio-molecules because of presence of more hydrophobic
region. In addition, the temperature has also been found to be decisive factor in the micellization
of the surfactants. With rise in temperature, the CMC increases which may be due to the
interruption of structured water molecules surrounding the non–polar parts of Gemini
surfactant/carbohydrates system. The process of micellization is of spontaneous nature as
shown by thermodynamic parameters and both hydrophobic interactions and London dispersion
forces seem to play an important role for the same. The results obtained from the conductivity
measurements are strongly supported by those obtained from fluorescence and UV-Visible probe
studies. The findings of the study may form the basis for utilizing surfactants in presence of
carbohydrates especially for industrial applications with the eventual aim of producing eco–
friendly and sustainable surface active formulations.
Acknowledgments
Kailash Singh and Maninder Kaur thank UGC, New Delhi for the award of Senior Research
Fellowship (No. F.17-40/2008(SA-1) dated 31.07.2014) and Basic Scientific Research
Fellowship (F.No. 25-1/2013-14(BSR)/7-75/2007 (BSR)) respectively. Kuldeep Singh thanks
Himachal Pradesh University, Shimla for the award of Junior Research Fellowship (No.1-
3
/2016-HPU(DS)). Financial support from UGC-SAP (DRS-I) (No. F.540/3/DRS/2010 (SAP-1))
to Department of Chemistry, HPU is also acknowledged.

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Highlights





Analysis of Micellar modulation of 12–2–12 Gemini surfactant in presence of
carbohydrates by conductometry and spectroscopic studies.
A decrease in the CMC values of 12–2–12 Gemini surfactant has been observed in the
presence of lactose/maltodextrin.
Enhancement of hydrophobic region in case of maltodextrin results in more decrease of
CMC values as compare to lactose.
Temperature dependence of
CMC has been employed to compute standard
thermodynamic parameters of micellization.
The entropy dominance switched to enthalpy dominance around the midpoint of the
temperature range examined.