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Vol. 2(1), pp.10-17, November 2013 Available online at http://www.accessinterjournals.org/ajps

ISSN 2354-2438 Copyright ©2013 Access International Journals

Full Length Research Paper

Micellization behaviour of cetyltrimethylammonium bromide in methanol-water mixed solvent media in

absence and in the presence of a salt at (308.15, 318.15 and 323.15) K by conductometry

Sujit K. Shah, Sujeet K. Chatterjee and Ajaya Bhattarai

Department of Chemistry, M.M.A.M.C (Tribhuvan University), Biratnagar, Nepal.

Corresponding author. E-mail: bkajaya@yahoo.com

Accepted 11 November, 2013

Accurate measurements on the specific conductivity of solutions of cetyltrimethylammonium bromide in absence and in the presence of potassium chloride in methanol-water mixed solvent media containing 0.10, 0.20, 0.30 and 0.40 volume fractions of methanol at 308.15, 318.15 and 323.15 K are reported. The concentrations of cetyltrimethylammonium bromide are varied from 4.0×10

-5 to 1.2×10

-2

mol.l-1

..The conductance of cetyltrimethylammonium bromide decreases with addition of methanol. It has been observed that the conductance of cetyltrimethylammonium bromide increases with increase in concentration as well as with addition of salt (KCl). The concentrations of KCl are taken 0.0001, 0.001 and 0.01 M during the experiments. The result shows that critical micelle concentration of cetyltrimethylammonium bromide increases with addition of methanol and with rise of temperature. Also, the critical micelle concentration of cetyltrimethylammonium bromide decreases with addition of potassium chloride.

Key words: Cetyltrimethylammonium bromide, methanol-water mixed solvent media, potassium chloride, critical micelle concentration, conductivity.

INTRODUCTION Surfactants are class of compounds having applications in different fields (Schramm et al., 2003). The quaternary ammonium salts are known for their germicidal and

antifungal properties (Zhao and Sun, 2008; Chlebicki et al., 2005); there is also a possibility of employing cationic amphiphiles as vectors in gene delivery (Joestor et al.,

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2003; Srinivas et al., 2009). The critical micelle concentration (cmc) appears to be the most important property in the study of micellization of surfactants and the two models commonly employed in the theoretical thermodynamic treatment of micelles, namely the mass action model and the phase separation model both required the knowledge of the critical micelle concentration (cmc) which is often obtained from the abrupt change in the physical property-concentration curve (Tanford, 1980). Surfactants are used in the presence of additives in order to improve their properties. Among the very large number of additives revealed by a literature survey, alcohols hold a special place, being by far the most, frequently used. This has been especially so in recent years because alcohols are the most common cosurfuctants which are added to surfactant + oil systems to generate microemulsions (Zana, 1995). Comprehensive studies have been done on physicochemical behaviour cetyltrimethylammonium bromide (CTAB) in aqueous polyethylene glycol media (Manna and Panda, 2011) and other alcohols (Li et al., 2006; Akbas and Kartal, 2006). The gradual replacement with water and other polar solvents allows one to explore a wide bulk phase polarity range and its influence on micellization. Addition of small amount of an organic solvent has been known to produce marked changes, in the critical micelle concentration (cmc) of ionic surfactants due to tendency of added organic solvent either to break or make the water structure through solvation of the hydrophobic tail of the surfactant by the hydrocarbon part of the organic solvent (Palepu et al. 1993; Ruiz, 1999). Akbas and Kartal (2006) carried out an investigation on the effect of ethanol and ethylene glycol on the critical micelle concentration (cmc) of CTAB. They observed that cmc decreases upon the addition of ethanol and ethylene glycol. In spite of these literatures, the effect of methanol is not seen so far.

Interactions of foreign ions with the chromophoric groups of amphiphilic compounds are of interest in several areas of chemistry and biochemistry, where it has been established that neutral salts can influence the conformation of proteins and other macromolecules by affecting the prevalent of hydrophobic or ionic interactions. Such processes can usually be explained by invoking the breaking up of the water structure around the amphiphilic compounds due to lyophilic electrolytes (Vijlder, 1985). Comprehensive studies on the effect of electrolytes on ionic surfactants in n-Butanol, n-Pentanol and n-Hexanol are found in literature (Singh et al., 1979). Many techniques have been used in order to investigate the effect of added salt on the micellization of ionic surfactants solution (Aswal and Goyal, 2002; Simmonic and Span, 1998).

Shah et al. 11 The effect of inorganic salt is explained in terms of the shielding of the electrostatic repulsion by the counterions (Miyagishi, 1974; Chung et al., 1991). The effect of KCl and alcohol on the cmc of cetylpyridinium chloride (CPC) was studied by Chung et al. (1991). They observed the decrease in cmc with the addition of electrolyte and vice versa. In this paper, we report a study of the aggregation process of CTAB at three different temperatures in absence and in the presence of KCl by conductivity method in methanol water mixed solvent media. MATERIALS AND METHODS Methanol (E. Merck, India, 99% pure) was distilled with phosphorous pentoxide and then redistilled over calcium hydride. The purified solvent had a density of 0.7772 g.cm

-3 and a co-efficient of viscosity of 0.4742 mPa.s at

308.15 K; these values are in good agreement with the literature values (Apelblat, 2011).

Triply distilled water

with a specific conductance less than 10-6

S.cm-1

at 308.15 K was used for the preparation of the mixed solvents. The physical properties of methanol-water mixed solvents used in this study at 308.15, 318.15, and 323.15 K are reported in Table 1 have been taken from the published papers(Bhattarai et al. 2006, 2011; Chatterjee and Das, 2006). The relative permittivity of methanol-water mixtures at the experimental temperatures were obtained by regressing the relative permittivity data as function of solvent composition from the literatures (Albright and Gasting, 1946; Yilmaz and Guler, 1998) and are included in Table 1.

Cetyltrimethylammonium bromide was purchased from Loba Chemical Private Limited India and it was recrystallised several times until no minimum in the surface tension-concentration plot was observed and its critical micellar concentration (cmc) agreed with the literature value (Chakraborty et al., 2006).

Potassium chloride (KCl) was purchased from Loba chemical, India and dried before use.

The conductivity values of CTAB in methanol-water in absence and in presence of KCl were determined by conductometric method using digital conductivity meter from Systronics India Ltd with dip type conductivity cell having cell constant 1.002 cm

-1 and having an uncertainty

of 0.01%. The cell was calibrated by the method of Lind et al. (1959) using aqueous potassium chloride solution.

The measurements were made in a water bath

maintained within 0.01 K of the desired temperature. Several independent solutions were prepared and runs were performed to ensure the reproducibility of the results.

The solutions were prepared by weight using analytical

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Adv. J. Phys. Sci. 12

Table 1. Properties of methanol-water mixtures containing 0.10, 0.20, 0.30 and 0.40 volume fraction of methanol at (308.15, 318.15, and 323.15) K.

T/K 0 /g.cm-3

0 / mPa.s D

0.10 volume fraction of methanol

308.15 0.97973 0.8665 71.57

318.15 0.97604 0.7017 68.18

323.15 0.97438 0.6375 66.45

0.20 volume fraction of methanol

308.15 0.96632 1.0217 68.14

318.15 0.96162 0.8075 64.80

323.15 0.95875 0.7300 63.15

0.30 volume fraction of methanol

308.15 0.95160 1.1418 64.25

318.15 0.94626 0.8957 60.99

323.15 0.94331 0.8052 59.41

0.40 volume fraction of methanol

308.15 0.93364 1.2034 60.34

318.15 0.93140 0.9309 57.18

323.15 0.92800 0.8288 55.62

balance with the accuracy of ± 1 × 10

-4 g.

RESULTS AND DISCUSSION Conductivity technique has been found to be highly useful for studying the association behaviour of various systems (Fujiwara et al., 1997; Moulik et al., 1996; Gonzalez-Perez et al., 2002, 2003). Specific conductivities of surfactant solutions were measured as a function of concentrations of CTAB in methanol-water mixed solvent media containing 0.10, 0.20, 0.30 and 0.40 volume fractions of methanol in absence and in the presence of KCl at (308.15, 318.15 and 323.15) K. The cmcs were obtained from the inflections in the plots of specific conductivity versus surfactant concentration. The data points above and below the inflection were fitted to two linear equations, and the cmcs were obtained from the common intersection. This method is found to be reliable and convenient for the present system because of the significant variations of specific conductivity with surfactant concentration in the pre- and postmicellar regions which allowed us to draw two unambiguous straight lines above and below the cmc. A typical plot of specific conductivity (κ) vs. concentration of CTAB in 0.1

volume fraction of methanol at 308.15 K is presented in Figure 1.

The effect of water-alcohol mixed solvent media can be found to play important roles in different research fields (Prasad and Singh, 1990; Akbas and Kartal, 2006; Li et al. 2005; Manna and Panda, 2011; Gutmann and Kertes, 1974; Zana et al., 1980). There has been less work done particularly in methanol-water system. When methanol is mixed with water, several physical properties such as density, viscosity, surface tension, relative permittivity are changed due to molecular interactions (Carr and Riddick, 1951; Mikhail and Kimel, 1961). The cmc values of CTAB in methanol-water mixed solvent media containing 0.10, 0.20, 0.30 and 0.40 volume fractions of methanol in absence and in the presence of KCl at 308.15, 318.15 and 323.15 K are listed in Table 2.

Figure 2 shows that increase in volume fraction of methanol in water results in increase in cmc values. The alcohol added to a micellar surfactant solution is distributed between the micelles and the bulk solvent, forming mixed micelles with the surfactant. When the alcohol concentration increases the dielectric constant of the mixture becomes lower and lower as a result of the electrostatic interaction of the ionic head groups in micelles. This is due to co-solvent effects on the

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Shah et al. 13

0

100

200

300

400

500

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2

CONCENTRATION OF CTAB X10-2

M

SP

EC

IFIC

CO

ND

UC

TA

NC

E / c

m-1

Figure 1. Plot of specific conductivity vs. concentraion of CTAB in 0.1 volume fraction of methanol at 308.15 K.

1

3

5

7

9

0 0.1 0.2 0.3 0.4 0.5

323.15 K318.15 K308.15 K

Volume Fractions of Methanol-Water

CM

C (

mM

)

Figure 2. Variation of cmc with different volume fractions of methanol-water at (308.15, 318.15 and 323.15) K.

interactions and on the property of solvent. The addition of cosolvent changes the dielectric constant of solvent and the degree of structuring. The more cosolvent is

added, the lower is the dielectric constant of the mixtures and the micelles expand. The cosolvent molecules at the micelle/solution interface lower the repulsion between

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Adv. J. Phys. Sci. 14

Table 2. The critical micellar concentration (cmc) values of cetyltrimethylammonium bromide in absence and in the presence of KCl from conductometry in methanol-water mixed solvent media containing 0.10, 0.20, 0.30 and 0.40 volume fraction of methanol at (308.15, 318.15, and 323.15) K.

Methanol % Concentration

KCl /M

Critical Micellar Concentration(cmc)/mM

308.15 K 318.15 K 323.15 K

0.10 volume fraction of methanol

0.0000 1.37 1.68 1.79

0.0001 1.32 1.54 1.70

0.0010 1.10 1.22 1.40

0.0100 0.89 0.94 1.18

0.20 volume fraction of methanol

0.0000 1.80 2.63 2.81

0.0001 1.75 2.53 2.68

0.0010 1.13 2.48 2.58

0.0100 1.07 1.98 2.03

0.30 volume fraction of methanol

0.0000 4.60 5.75 5.81

0.0001 4.50 5.47 5.61

0.0010 4.19 5.42 5.56

0.0100 3.14 5.04 5.23

0.40 volume fraction of methanol

0.0000 7.21 7.49 7.71

0.0001 6.42 7.18 7.20

0.0010 6.19 6.87 6.97

0.0100 4.73 6.78 6.87

CTA

+ head groups due to an increase in the ionic

strength of the bulk phase (Vijlder, 1985). Furthermore, with the increase in cosolvent concentration, the hydrophobic interaction between hydrophobic groups of surfactants is gradually reduced (Ray, 1971), that is, the micellization potential decreases.

An increase in the volume fraction methanol results in increase in the viscosity of the medium which eventually results in the increase in the hydrophobic hydration of the CTAB; hence the surfactant monomer would prefer to remain in the bulk than to form the micelle. Moreover, it is illustrated that presence of methanol decreases the number of hydrogen bonds between the water molecules (Farhadian and Shariaty-Niassar, 2009) due to which the hydrophobic repulsion decreases. Li et al. (2005) studied the effect of ethanol-water mixed solvent media and concluded that there is significant increase in the cmc of CTAB with increase in volume fraction ethanol. Ghosh and Baghel (2008) carried out investigation on the micellar properties of benzyldimethyldodecylammonium bromide in aquo-organic solvent media and discussed that the addition of organic solvent to water decrease the dielectric constant and increase the cmc value with increase in volume fraction of methanol.

It is clear from the Table 2 and Figure 3 that on increasing the temperature, cmc increases. The effect of temperature on the micellization is usually discussed in terms of two opposite factors. First, as the temperature increases, the degree of hydration of the hydrophilic group decreases, which favors micellization; however, an increase in temperature also causes the disruption of the water structure surrounding the hydrophobic group and this is unfavorable to micellization. It seems from the data in Table 2 that this second effect is predominant in the temperature range studied (Varade et al., 2005). The value of cmc increases with increase in temperature, such behavior is also observed by Dubey (2008).

From the data of Table 2, the cmc of the surfactant CTAB decreases with increasing salt concentration and the decrease of the cmc with increasing salt concentration follows the Shinoda equation (Shinoda, 1953) which represents the total counter ion binding to the micelle at the cmc, that is: log cmc = A – B log(cmc + [KCl]) (1) where A and B are constants. The plot of log cmc against log (cmc +[KCl]) is shown in Figure 4. The results of plot

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Shah et al. 15

3

6

9

305 310 315 320 325

0.4 volume fration of methanol0.3 volume fraction of methanol0.2 volume fraction of methanol0.1 volume fraction of methanol

T / K

CM

C /

mM

Figure 3. Variation of CMC with temperature at different volume fractions of methanol water.

-3.3

-3.0

-2.7

-2.4

-2.1

-1.8

-3.0 -2.7 -2.4 -2.1 -1.8 -1.5

0.4 volume fraction of methanol0.3 volume fraction of methanol0.2 volume fraction of methanol0.1 volume fraction of methanol

Log ( cmc + [KCl] )

Lo

g c

mc

Figure 4. Plot of log (CMC+[KCl]) vs log CMC in different volume fractions of methanol-water at 308.15 K.

in Figure 4 are listed in Table 3. The correlation coefficients of fits (as r

2) are higher than 0.900 numerical

value. Hence, the fitting of the data looks good. It Is seen

that the cmc values of CTAB in 0.1, 0.2, 0.3 and 0.4 volume fractions of methanol solution decreases with increase of KCl concentration. As the salt is added, the

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Adv. J. Phys. Sci. 16 Table 3. Linear Regression Analysis of the cmc: The correlation coefficients of fits (as r2) and A and B are constants in methanol-water mixed solvent media containing 0.10, 0.20, 0.30 and 0.40 volume fraction of methanol at 308.15 K.

Volume fraction of methanol A B r2

0.1 -3.40 0.174 0.913

0.2 -3.25 0.269 0.993

0.3 -3.13 0.331 0.991

0.4 -3.01 0.375 1.000

electrostatic repulsive force between ionic head groups of the surfactant molecules is reduced by shielding of micelle charge, so that spherical micelles are more closely packed by the surfactant ions (Aswal and Goyal, 2002; Shinoda, 1953), hence a decrease in the cmc values after adding 0.0001, 0.001 and 0.01 M concentrations of KCl. CONCLUSIONS The effects of concentration, temperature and solvent composition on the conductance of CTAB in absence and presence of KCl in methanol (1) + water (2) mixed solvent media have been studied by measuring specific conductance through conductometric method. The following conclusions have been drawn from the results and discussion. The specific conductivities are found to increase with increase in concentration over the entire concentration range investigated whereas the specific conductivities of CTAB decrease with increase in volume fraction of methanol. Also, the specific conductivities of CTAB in presence of KCl are found more than in absence of KCl in methanol-water mixed solvent media. The cmc of CTAB increases with increase in temperature and with increase in volume fractions of methanol and cmc decreases with addition of KCl in methanol-water mixed solvent media.

ACKNOWLEDGEMENTS One of the authors (Sujit Kumar Shah) is thankful to University Grants Commission for financial support in order to pursue the Ph.D. work. The authors are thankful to the faculties of Central Department of Chemistry, Tribhuvan University, Kirtipur, Nepal for valuable suggestions during the research works. The authors are also thankful to Associate Professor Ghanashyam Shrivastav, the Head of Department of Chemistry, Mahendra Morang Adarsh Multiple Campus, Tribhuvan

University, Biratnagar, Nepal for providing us the research facilities to conduct this research work. Especially Sujit Kumar Shah is highly obliged of Hon’ble Geeta Didi and her learned team members, Brahma Kumaris Meditation Centre, Biratnagar, Nepal, for inspiration and guidance. REFERENCES Akbas H, Kartal C (2006). Conductometric studies of

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