Synthesis, characterization and evaluation of the surface active properties of novel cationic imidazolium gemini surfactants

Article abstract of DOI:10.1007/s11743-013-1472-2

New imidazolium gemini surfactants were synthesized by reaction of epichlorohydrin with long chain fatty alcohols furnishing products 2-(alkoxymethyl)oxirane followed by their subsequent treatment with imidazole resulting in the formation of 1-(1H-imidazol-1-yl-3 alkoxy)propane-2-ol which on subsequent treatment with 1,2-dibromoethane and 1,3-dibromopropane resulted in the formation of title gemini surfactants:1,2-bis(1(3-alkoxy-2-hydroxypropyl)- 1H-imidazol-3-ium)ethane bromide (7), 1,3-bis(1(3-alkoxy-2-hydroxypropyl)-1H- imidazol-3-ium)propane bromide (8), 1,2-bis(1(3-alkoxy-2-hydroxypropyl)-1H- imidazol-3-ium)ethane bromide (9), 1,3-bis(1(3-alkoxy-2-hydroxypropyl)-1H- imidazol-3-ium)propane bromide (10), 1,2-bis (1(3-alkoxy-2-hydroxypropyl)-1H- imidazol-3-ium)ethane bromide (11) and 1,3-bis (1(3-alkoxy-2-hydroxypropyl)-1H- imidazol-3-ium)propane bromide (12). Their identification was based on IR, ¹H-, ¹³C-NMR, DEPT, COSY and mass spectral studies. Their surface active properties were also evaluated on the basis of surface tension and conductivity measurements.

Full text of DOI:10.1007/s11743-013-1472-2

J Surfact Deterg (2014) 17:253–260
DOI 10.1007/s11743-013-1472-2
ORIGINAL ARTICLE
Synthesis, Characterization and Evaluation of the Surface Active
Properties of Novel Cationic Imidazolium Gemini Surfactants
•
Pankaj Patial Arifa Shaheen Ishtiaque Ahmad
•
Received: 15 October 2012 / Accepted: 26 March 2013 / Published online: 25 April 2013
Ó AOCS 2013
Abstract New imidazolium gemini surfactants were
synthesized by reaction of epichlorohydrin with long chain
fatty alcohols furnishing products 2-(alkoxymethyl)oxirane
followed by their subsequent treatment with imidazole
resulting in the formation of 1-(1H-imidazol-1-yl-3 alk-
oxy)propane-2-ol which on subsequent treatment with 1,2-
dibromoethane and 1,3-dibromopropane resulted in the
formation of title gemini surfactants:1,2-bis(1(3-alkoxy-2-
hydroxypropyl)-1H-imidazol-3-ium)ethane bromide (7),
1,3-bis(1(3-alkoxy-2-hydroxypropyl)-1H-imidazol-3-ium)
propane bromide (8), 1,2-bis(1(3-alkoxy-2-hydroxypro-
pyl)-1H-imidazol-3-ium)ethane bromide (9), 1,3-bis(1(3-
alkoxy-2-hydroxypropyl)-1H-imidazol-3-ium)propane
bromide (10), 1,2-bis (1(3-alkoxy-2-hydroxypropyl)-1H-
imidazol-3-ium)ethane bromide (11) and 1,3-bis (1(3-alk-
oxy-2-hydroxypropyl)-1H-imidazol-3-ium)propane bromide
Keywords Gemini surfactants ꢀ Synthesis ꢀ Conductivity
and surface tension
Introduction
The development of modern surfactants has been in
rapid progress over the last two decades. Much research
has dealt with how the properties of gemini surfactants
change with the structure of molecules [1–3]. Gemini
surfactants are a new generation of surfactants composed
of two monomeric surfactants molecules chemically
bonded together by a spacer at or near their head groups.
The birth of gemini surfactants was due to the search for
novel surfactants with higher efficiency and effective-
ness. They are more surface active and have much lower
CMC value than their monomeric counterpart [4, 5].
Because of the vast number of their applications, gemini
surfactants continue to gain widespread interest in
modern research and for various applications [6, 7].
Consumption of cationic surfactants is around 700,000
tons per year [8]. They have many applications such as
fabric softeners, asphalt additives, corrosion inhibitors,
biocides, textile auxiliaries and so forth. On adsorbing onto
various surfaces they change the surface properties [9–11].
On the other hand, environmental problems may be an
important concern during the development of new kinds of
surfactants. Owing to increasing legislative pressure and
requirements with regard to environmental protection, the
design of environmentally benign products to replace con-
ventional surfactant may be the main trend. Different
approaches have been taken to overcome this problem. One
approach is to introduce an easily cleavable bond into the
surfactant structure. The search for novel surfactants with
higher efficiency and effectiveness gave birth to the
1
(12). Their identification was based on IR, H-, 13C-NMR,
DEPT, COSY and mass spectral studies. Their surface active
properties were also evaluated on the basis of surface tension
and conductivity measurements.
Electronic supplementary material The online version of this
article (doi:10.1007/s11743-013-1472-2) contains supplementary
material, which is available to authorized users.
P. Patial ꢀ I. Ahmad (&)
Department of Chemistry, Guru Nanak Dev University,
Amritsar 143005, India
e-mail: chemi_ahmad@yahoo.co.in
A. Shaheen (&)
University College of Engineering, Punjabi University,
Patiala 147002, India
e-mail: chemarifa@gmail.com
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J Surfact Deterg (2014) 17:253–260
concept of gemini surfactants. The gemini surfactants are
made up of two monomeric surfactant molecules with their
head groups chemically bonded together by a spacer [12–
14]. It was found that the surfactant properties of gemini-
type surfactants, such as a low critical micelle concentra-
tion (CMC) values and lower surface tension, were superior
to those of the corresponding single-type surfactants [15].
They are highly efficient in lowering interfacial tension and
form micelles at very low critical micellar concentrations
[16, 17]. Because of these unique properties, they have
great potential to be used as effective emulsifiers, bacteri-
cidal agents, dispersants, anti-foaming agents, detergents
etc. They are also applicable in the solubilization of dyes
and pigments in the textile industry and in gene therapy
[18].
solution in CDCl3, using tetramethylsilane (TMS) as an
internal standard.
Synthesis
Synthesis of 2-(Alkoxymethyl)oxirane (1–3)
The preparation of compounds (1–3) were prepared by
reacting fatty alcohols (hexadecyl, tetradecyl and dodecyl)
with epichlorohydrin in 1:1.5 using tetrabutylammonium
iodide as a catalyst and sodium hydroxide (1:2) ratio. The
resulting products were characterized as 2-alkoxy methy-
loxirane (1–3).The synthesis of the compounds (1–3) was
reported in parenthesis [19].
Keeping in view the past work and interest centered on
cationic gemini surfactants, we have attempted to synthe-
size a series of gemini surfactants from renewable raw
materials such as fatty alcohols and epichlorohydrin. Here,
we have chosen the greener approach to make the process
environmentally friendly and cost effective, too. The pur-
pose of this work was to prepare and characterize the
imidazole-based cationic gemini surfactants from renew-
able raw materials and to evaluate their surface active
properties.
Synthesis of 1-(1H-Imidazol-1-yl-3-alkoxy)propane-
2-ol (4–6)
The resulting products (1–3) on further overnight stirring
with imidazole in 1:1.2 ratio at 60 °C. The resulting
compounds (4–6) were obtained as oily liquids [20]. The
purification of these resulting compounds was done by
washing with hot water. TLC-homogenous products (4–6)
1
were characterized by IR, H-, 13C-NMR, DEPT, COSY
and mass spectral studies as 1-(1H-imidazol-1-yl 3-alk-
oxy)propane-2-ol (4–6).
Materials and Measurements
Chemicals: epichlorohydrin and tetrabutyl ammonium
iodide were purchased from Sigma-Aldrich Chemical Co.
USA. Lauryl alcohol (dodecyl alcohol), myristyl alcohol
(tetradecyl alcohol), cetyl alcohol (hexadecyl alcohol)
and silica gel for TLC were purchased from S. D. Fine
Chemicals Ltd; Mumbai India. 1,2-Dibromo ethane, 1,3-
dibromo propane, imidazole and sodium hydroxide were
purchased from Merck, Germany.
Synthesis of Gemini Surfactants (7–12)
The above compounds (4–6) were subsequently treated
with 1,2-dibromo ethane and 1,3-dibromo propane (2:1)
separately at 60 °C for 1 h. In each case the resulting crude
product was crystallized with diethylether and then re-
crystallized with cold acetone to give the pure compounds
1
(7–12) which were characterized on the basis of IR, H-,
13C-NMR, DEPT, COSY and mass spectral analysis as
1,2-bis (1(3-alkoxy 2-hydroxypropyl)-1H-imidazol-3-ium)
ethane bromide (7),1,3-bis(1(3-alkoxy-2-hydroxypropyl)-
1H-imidazol-3-ium)propane bromide (8), 1,2-bis (1(3-alk-
oxy 2-hydroxypropyl)-1H-imidazol-3-ium)ethane bromide
(9),1,3-bis (1(3-alkoxy-2-hydroxypropyl)-1H-imidazol-3-
ium)propane bromide (10), 1,2-bis(1(3-alkoxy-2-hydroxy-
propyl)-1H-imidazol-3-ium)ethane bromide (11) and 1,3-bis
(1(3-alkoxy 2-hydroxypropyl)-1H-imidazol-3-ium)propane
bromide (12).
Instrumentation
IR spectra were recorded as a thin film on a KBr Pellet on a
Shimadzu 8400 s FT-IR (Kyoto, Japan) instrument. Mass
spectra were recorded on a Waters Q-T of micro mass
using ESI as an ion source at the sophisticated analytical
instrumentation facility (SAIF), Panjab University, Chan-
digarh. 1H-, DEPT, COSY and 13C-NMR spectra were
recorded on a JEOL AL-300(JEOL, Japan) system as a
The schemes of the reactions are shown below.
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J Surfact Deterg (2014) 17:253–260
255
Where R = CH3(CH2)11-; CH3(CH2)13-and CH3(CH2)15-.
Where n = 2 and 3.
Surface Tension Measurements [21]
Measurements
Surface tension values were used to calculate CMC using a
CSC Du Nouy tensiometer (Central scientific Co., Inc.)
equipped with platinum-iridium ring (circumference
5.992 cm) at 25 °C. The tensiometer was calibrated using
triple distilled water. For the determination of CMC and
surface tension, adequate quantities of a concentrated stock
solution were used. The data of this determination is pre-
sented in Table 1.
Conductivity Measurements [21]
The critical micelle concentrations (CMC) of these sur-
factants (7–12) were determined by the conductivity
method. The conductance as a function of surfactant con-
centration was measured at 25 °C. Measurements were
performed with an Equiptronic Conductometer (Auto
temperature conductivity meter model E.Q.661) with stir-
ring to control the temperature. The solutions were
thermostated in the cell at 25 °C. For each series of mea-
surements, an exact volume of 25 ml Millipore water
(resistivity 18 MX) was introduced into the vessel, and the
specific conductivity of the water was measured. For the
determination of CMC, adequate quantities of concentrated
stock surfactant solutions were added in order to change
the surfactant concentration from concentrations well
below the CMC and repeated to verify our results. The
break in the curve of specific conductivity versus surfactant
concentration was taken as the CMC (Fig. 1a). The degree
of counterion binding (b) was calculated as (1–a), where
a = Smicellar/Spremicellar, i.e., Dispersion of micelles in
solvent/the existence of surfactant molecules below CMC.
Thermal stability measurements. The thermal stability of
the present gemini surfactants was measured with SDT Q600
Thermal Gravimetric Analyzer (TGA), using a nitrogen
atmosphere. All samples were in aluminum pans under a
nitrogen atmosphere at a heating rate of 10 °C per minute.
Results and Discussion
Spectral Results
The structures of ether based gemini imidazolium surfac-
tants (7–12) were established by IR, 1H-, 13C-NMR, DEPT,
COSY and mass spectral data. The IR spectra of the
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1,126–1,130 cm-1 were well established, the presence of
aromatic C–N group of all products. The two terminal
methyl protons of these gemini surfactants (7–12) are
observed as a distorted triplet at d 0.80–0.88 in their
1H-NMR spectra. Broad singlets in (7–12) are observed at
d 1.18–1.87 accountable for methylene protons of chain.
Multiplet signals are observed at d 1.47–1.57 due to pro-
tons next to terminal methyl groups. The two middle pro-
tons of (8, 10 and 12) ImCH2CH2CH2Im are observed as
triplets at d 2.70–2.72. A doublet is observed at d 3.29–3.45
due to hydroxyl groups. A triplet is observed at d 3.36–3.47
due to methylene protons attached to ether linkage. Other
doublets are observed at d 3.51–3.58 due to methylene
protons next to secondary carbon. Other doublets are
observed at d 3.60–4.22 due to methylene protons attached
to nitrogen of imidazole. Other multiplets are observed at
d 4.18–4.35 due to two protons of secondary carbons.
Another type of multiplet is observed at d 4.30–5.10 due to
ImCH2CH2Im or ImCH2CH2CH2Im protons. The three sets
of ring protons of imidazole ring are observed as a singlet at
d 7.27–7.33, d 7.92–8.17 and d 9.56–9.67. 13C/DEPT NMR
spectra displayed sp3 carbon of terminal methyl group at d
13.49–14.06. The carbons next to terminal methyl groups
are observed in the range of d 22.26–22.75. The carbons
(OCH2CH2CH2) are observed at d 25.87–26.28. The chain
carbons are observed at d 29.05–29.32. The methylene
carbons i.e. (CH2CH2CH3) are observed at d 31.35–31.95.
The middle carbon of spacer in (8, 10 and 12)
ImCH2CH2CH2Im are observed at d 31.70–31.86. The
methylene carbons of spacer i.e. (ImCH2CH2Im) are
observed at d 46.77–48.92. The a methylene carbons
(a)
15
10
5
cmc
0.04
0
0
0.02
0.06
0.08
0.1
0.12
0.14
Concentration in mM
(b)
70
60
50
40
30
20
cmc
-2
-3
-2.5
-1.5
-1
Log C
Fig. 1 a Specific conductivity versus concentration plot of gemini
surfactant 7, b Surface tension versus concentration plot of gemini
surfactant 7
attached to imidazole nitrogen are observed at
d
50.02–53.42. Other signals are observed at d 67.38–67.67
due to secondary carbons and at d 71.0–71.90 due to
methylene carbon attached to ether linkage. A signal is
observed at d 71.84–72.17 due to (CH2O). Other structure
revealing signals are observed at d 103.90–123.85 due to
(NCHCHN) and at d 123.05–137.21 due to NCHN. On all
these accounts the structures of (7–12) are deduced to be
1,2-bis(1(3-alkoxy-2-hydroxypropyl)-1H-imidazol-3-ium)
imidazolium gemini surfactants (7–12) showed the
absorption bands in the region at 3,340–3,345 cm-1 indi-
cating the presence of hydroxyl groups. The absorptions at
2,950–2,930 cm-1 indicate the presence of C–H stretching
whereas other absorptions at 3,047–3,030 cm-1 indicate
the presence of C–H in an aromatic ring. The band at
1,570–1,540 cm-1 was very well established, the presence
of aromatic C = C of all products (7–12) and the band at
Table 1 Surface, thermodynamic and thermal properties of the synthesized surfactants (7–12)
S. CMC
no (mM)
a (%) b (%) CMC
(mM)
c PCMC
(mN/m) (mN/m)
C20
CMC/ 106Tmax
c20
Amin
(nm2)
DGmic
KJ/mol
DGads
(KJ/mol) (°C)
TONSET TSTART
(°C)
(Mol/m2)
(M)
7
8
9
0.021
0.020
0.232
48
49
32
34
33
38
52
51
68
66
67
62
0.022
0.020
0.234
0.073
0.429
0.415
30.04
36.08
43.51
44.51
48.07
50.06
42.36
36.32
28.89
27.81
24.33
21.84
0.010 2.21
0.008 2.54
0.035 2.01
0.117 2.08
0.299 1.43
0.350 1.48
4.53
3.48
3.22
2.99
2.71
2.01
0.036 -36.49 -45.84
0.047 -36.75 -47.15
0.051 -20.87 -29.84
0.055 -23.81 -33.13
0.061 -20.99 -29.96
0.082 -22.90 -33.76
279.5
285.3
270.6
281.9
253.3
270.4
235.8
248.4
230.0
240.7
221.6
232.1
10 0.071
11 0.421
12 0.411
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257
ethane bromide (7), 1,3-bis(1(3-alkoxy-2-hydroxy propyl)-
1H-imidazol-3-ium)propane bromide (8), 1,2-bis (1(3-alk-
oxy-2-hydroxypropyl)-1H-imidazol-3-ium)ethane bromide
(9), 1,3-bis(1(3-alkoxy-2-hydroxypropyl)-1H-imidazol-3-ium)
propane bromide (10), 1,2-bis(1(3-alkoxy-2-hydroxypropyl)-
1H-imidazol-3-ium)ethane bromide (11) and 1,3-bis
(1(3-alkoxy-2-hydroxypropyl)-1H-imidazol-3-ium)propane
bromide (12). The structures of these gemini surfactants
(7–12) are further consolidated by ESI–MS (positive ion)
mass spectral data. Important peaks in these spectra are
found at m/z 761.2, 762.2, 773.8, 774.7, 704.5, 705.7, 717.7,
718.7, 648.5, 649.5, 662.7, 663.7. These ion peaks account
for the loss of proton and two bromide ions from the mole-
cule leading to the formation of positively charged parent ion
{M- 2Br)-1)}? and the direct loss of two bromide ions from
the molecule leading to formation of (M-2Br)? positively
charged ions. All the spectral results of the synthesized
compounds are provided in the supplementary material file.
decreases with increasing chain length and decrease with
increasing spacer length (Table 1) [22].
Surface Tension Measurements
The CMC of new imidazolium gemini surfactants were
calculated by using surface tension measurements Fig. 1b.
The increase in the surface tension for the series of imi-
dazolium gemini surfactants with increasing hydrophobic
alkyl chain lengths can be explained on the basis of the
CMC/C20 ratio observed for these amphiphiles. The
affinity of a particular surfactant to reduce surface tension
of solvent depends upon CMC/C20 ratio, greater the
observed value greater is the tendency of the amphiphile to
reduce surface tension of the system [23]. Thus, imidazo-
lium surfactants 7 and 8 have maximum ability while
amphiphile 11 and 12 have minimum ability to reduce
surface tension of aqueous system in the series of amphi-
phile being reported. Two important parameters of gemini
surfactants, i.e. the effectiveness of surface tension reduc-
tion (PCMC) and the adsorption efficiency (pC20) were
obtained from the surface tension plots. The former
parameter, PCMC is the surface pressure at the CMC and
is defined as:
Surface Active Properties of Gemini Surfactants (7–12)
Critical Micelle Concentration
Geminis have lower CMC values than the corresponding
single tail surfactants. Only a few reports are available
regarding the syntheses and CMC values of gemini imi-
dazolium surfactants [21]. The CMC and degree of counter
ion binding of these new imidazolium amphiphiles were
determined by the conductivity method. These new gemini
imidazolium amphiphiles have low CMC values. The
values of CMC and degrees of counter ion binding are
given in Table 1. The graph of the concentration versus
conductivity has been plotted Fig. 1a. It was found that the
imidazolium gemini surfactants having short spacer lengths
and short chain lengths have lower CMC values than
gemini surfactants having long spacer lengths and long
chain lengths [21].
PCMC ¼ c0 ꢁ cCMC
ð1Þ
Where c0 is the surface tension of pure solvent and cCMC
is the measured surface tension at CMC. The maximum
reduction in surface tension caused by the dissolution of
amphiphilic molecules has been indicated by PCMC and
as a result PCMC becomes a measure for the effectiveness
of the amphiphile to lower the surface tension of the water
[23]. Imidazolium gemini surfactants synthesized in
present work (7, 8, 9,10, 11 and 12) have greater ability
to reduce surface tension of the aqueous system. The
adsorption efficiency (pC20) is determined by using the
following equation [23]:
pC20 ¼ ꢁlogC20
ð2Þ
The Degree of Counterion Binding (b)
In this equation C is the molar concentration of
surfactant and C20 stands for the concentration required
to reduce the surface tension of the pure solvent by 20
mN m-1 [24]. Thus C20 becomes a measure of adsorption
efficiency of amphiphilic molecules at the air–water
interface. The results from Table 1 indicate that the
compounds 11 and 12 have higher adsorption efficiency
among six long chain gemini surfactants [24]. The values
of these two parameters obtained for the six gemini
surfactants are listed in Table 1 along with their CMC and
c values. The maximum surface excess concentration
(Cmax) was estimated by applying the Gibbs adsorption
isotherm [24] to the surface tension data:
The ratio of the slopes of the conductivity versus concen-
tration curve above and below the CMC gives the degree of
counterion dissociation a (i.e., a = Smicellar/Spremicel-
lar) and (1- a) gives the degree of counterion binding, b. It
is an important parameter because it shows the counterions
that are contained in the Stern layer counterbalance the
electrostatic force that opposes micelle formation. Qua-
gliotto et al. [21] determined the b value for a series of
gemini bis-pyridinium bromides having different spacers
where they showed that a different spacer is responsible for
different b value. The b value signifies the ability of
counter ion to bind micelles. It was found that the b value
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J Surfact Deterg (2014) 17:253–260
standard Gibbs free energy of adsorption (DG0ads) was
obtained from the following relationship [25].
Cmax ¼ ꢁ1=2nRT ðoc=oln CÞT
ð3Þ
where, R is the gas constant (8.314 J mol-K-), T is the
absolute temperature, and C is the surfactant concentration.
The value of n is taken as 2 as there is one counter ion
associated with each cationic head group. The minimum
area occupied by a single amphiphilic molecule at the air–
water interface (Amin) was also obtained by applying the
Gibbs adsorption isotherm to the surface tension data:
DG0ads ¼ DG0mic ꢁ PCMC=Cmax
ð6Þ
Here, pCMC denotes the surface pressure at the CMC
(pCMC = c0-cCMC, where c0 and cCMC are the surface
tensions of water and the surfactant solution at the CMC,
respectively). The free energy of adsorption (DG0ads
)
represents the free energy of transfer of 1 mol of
surfactant in solution to the surface, and the free energy
of micellization (DG0mic) represents the work done to
transfer the surfactant molecules from the monomeric form
at the surface to the micellar phase. The standard free
energy of micellization (DG0mic) and adsorption (DG0ads) is
always negative, indicating tendencies to form micelles in
solution and to adsorb at the air/water interface [25]. If the
value of (DG0ads) is more negative and greater than the
difference between (DG0ads) and (DG0mic), then the
adsorption of surfactant molecules at the interface
becomes more favorable because of the greater freedom
of motion of hydrocarbon chains at the planar air/aqueous
solution interface than in the interior of the micelle.
However, if the energy difference is small, then less work
has to be done to transfer surfactant molecules from the
monomeric form at the surface to the micellar phase. When
the difference in the free energies is small, the surfactant
undergoes aggregation more readily than when the
difference in the free energies is large. This is evident
from the results obtained by Yeshimua et al. [26]. The
(DG0mic) and (DG0ads) values of gemini imidazolium
surfactants are summarized in Table 1. The difference in
the free energy gap is small for gemini imidazolium
surfactants, therefore these surfactants have a greater
tendency to aggregate in solution.
À
Á
Amin ¼ 1= NA:Cmax ꢂ1023
ð4Þ
where NA is the Avogadro constant. All imidazolium gemini
surfactants have lower Amin values (Table 1). The lowest
A
min values of imidazolium gemini surfactants (7 and 8) can
be attributed to tighter packing of the longer chains at the
interface [24]. A part from positively charged imidazolium
cation in all these imidazolium gemini surfactants contains
free hydroxyl group. The presence of hydroxyl group in
addition to positively charged center plays important role in
their aggregation behavior. The energy required for the
closer packing of hydrocarbon alkyl chain length at interface
may come from the energy released upon hydrogen bond
formation between the hydroxyl group present close to
positively charged imidazolium center and water molecule
[24]. The Gibbs free energy of the micellization (DG0mic
was calculated by use of following equation.
)
DG0mic ¼ ð2 ꢁ aÞRTlnXCMC
ð5Þ
where XCMC is the mole fraction at the CMC and a is the
extent of counter ion dissociation. The micellization free
energy has a negative sign because thermodynamically
stable micelles are formed spontaneously. The results from
Table 1 indicate that the driving force for micellization
becomes large as DG0mic becomes more negative. The
Fig. 2 The thermal decomposition curve of
surfactant (7) determined by TGA,
indicating the Start (TSTART) and onset
(TONSET) temperature
100
80
60
40
20
0
Tonset
100
200
300
400
500
0
Universal V4.7A TA
Instruments
Temperature (°C)
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J Surfact Deterg (2014) 17:253–260
259
The graph of the surface tension versus concentration is
shown for gemini surfactants (7–12). A clear break is
observed Fig. 1b. It is observed from the graphs that imi-
dazolium gemini surfactants having short spacer length and
short chain length have low CMC values as compared to
the imidazolium gemini surfactants having long spacer
length and long chain length. The CMC values are reported
in Table 1 for all the gemini surfactants. The values for
both the conductivity methods and surface tension method
correspond well with each other.
imidazolium cationic gemini surfactants may show good
antimicrobial properties, DNA binding capability if tested
properly.
Acknowledgments Pankaj Patial is thankful to the UGC (Univer-
sity Grant Commission of India) for providing the research grant for
this work and Sophisticated Analytical Instrumentation Facility
(SAIF), Panjab University–Chandigarh, for the mass spectral analyses
of the compounds. We are also thankful to Dr. Satindar Kaur and Ms.
Charanjeet Kaur for their help and helpful discussions.
Thermal Stability Measurements
References
Thermal stability measurement shows that these long chain
gemini surfactants are stable up to 320 °C. Figure 2 shows
a characteristic curve for the decomposition of the gemini
surfactants as measured by thermal gravimetric analyzer.
The onset temperature (TONSET) is the intersection of the
baseline weight, either from the beginning of the experi-
ment and the tangent of the weight versus temperature
curve as decomposition occurs [27]. The start temperature
(TSTART) is the temperature at which the decomposition of
the sample begins. The example of the onset and start
temperatures is shown in figure. The onset and start tem-
peratures for present imidazolium gemini surfactants are
listed in Table 1. Thermal stability measurements desig-
nated that these surfactants have better thermal stability.
Thermal stability of these gemini surfactants increases as
chain length and spacer length increases.
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Conclusion
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In the present study we have described a new protocol for
the synthesis of novel imidazolium gemini surfactants
through an environmental friendly process. All the gemini
cationic surfactants (7–12) were produced in excellent
yields and these surfactants were examined and found to
have good surface active properties. These imidazolium
amphiphiles were investigated for their self-aggregation
properties by surface tension and conductivity methods.
These imidazolium amphiphiles have lower CMC values.
The results show that gemini imidazolium surfactants with
longer hydrophobic chains as well as longer chain lengths
have a lower CMC value. Further results showed that these
gemini surfactants have good thermal properties. The
thermal stability of these gemini surfactants was investi-
gated by TGA analysis. The thermal stability of these
amphiphiles increases with increasing size of the hydro-
phobic alkyl chain length and increasing spacer length.
Owing to their ease of synthesis, superior self-aggregation
and thermal properties, these gemini surfactants may find
use in several industrial applications. In addition, these
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Author Biographies
Pankaj Patial obtained his M.Sc. degree in industrial chemistry in
2008 from Guru Nanak Dev University, Amritsar, India. He is
currently working on his Ph.D. in the field of surfactant chemistry
from Guru Nanak Dev University, Amritsar, India.
22. Song LD, Rosen MJ (1996) Surface properties, micellization and
premicellar aggregation of gemini surfactants with rigid and
flexible spacer. Langmuir 12:1149–1153
23. Verma SK, Gosh KK (2011) Micellar and surface properties of
some monomeric surfactants and a cationic gemini surfactant.
J Surf Deterg 14:347–352
24. Bhadani A, Singh S (2011) Synthesis and properties of thioether
spacer containing gemini imidazolium surfactants. Langmuir
27:14033–14044
Arifa Shaheen obtained her Ph.D. degree in analytical chemistry in
2009 from Guru Nanak Dev University, Amritsar, India. She is
currently working as an assistant professor at the University College
of Engineering, Punjabi University, Patiala, India.
25. Tsubone K, Arakawa Y, Rosen MJ (2003) Structural effects on
surface and micellar properties of alkanediyl-a, x-bis(sodium
N-acyl-b-alaninate) Gemini surfactants. J Colloid Interface Sci
262:516–524
26. Yeshimua T, Bong M, Matsuoka K, Honda C, Endo K (2009)
Surface properties and aggregate morphology of partially
Ishtiaque Ahmad obtained his Ph.D. degree in organic chemistry in
1979 from Aligarh Muslim University, Aligarh, India. He retired in
2010 as a professor in chemistry from Guru Nanak Dev University,
Amritsar, India.
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