R C O S T N Chom Nath Adhikari et al./ BIBECHANA 14 (2017) 77-85 : RCOST p.77 (Online Publication: Dec., 2016) BIBECHANA A Multidisciplinary Journal of Science, Technology and Mathematics ISSN 2091-0762 (online) Journal homepage: http://nepjol.info/index.php/BIBECHANA Micellization Behavior of Cetyltrimethylammonium bromide in Presence and Absence of Na2SO4 and MgSO4 in Aqueous media Chom Nath Adhikari, G.S. Shrivastav, Ajaya Bhattarai* *Department of Chemistry, M.M.A.M.C., Tribhuvan University, Biratnagar, Nepal * E-mail: bkajaya@yahoo.com Article history: Received 1 April, 2016; Accepted 1 October, 2016 DOI: http://dx.doi.org/10.3126/bibechana.v14i0.15871 This work is licensed under the Creative Commons CC BY-NC License. https://creativecommons.org/licenses/by-nc/4.0/ Abstract Viscosity and surface tension measurements of cetyltrimethylammonium bromide (CTAB) in presence and absence of Na2SO4 and MgSO4 in aqueous media are reported. The results showed an increase in viscosity with increase in concentration of cetyltrimethylammonium bromide in presence and absence of salts where as the decrease in surface tension with increase in concentration of cetyltrimethylammonium bromide in presence and absence of salts. The viscosity of CTAB was observed lowest in pure water and increases in presence of MgSO4 and then more increases in presence of Na2SO4 where as the surface tension of CTAB was observed highest in pure water and decreases in presence of Na2SO4 and then more decreases in presence of MgSO4.The critical micelle concentration (cmc) of CTAB decreases in presence of salts in both viscosity and surface tension measurements. The decreasing cmc of CTAB are found to be more in the presence of Na2SO4 in comparison with the presence of MgSO4 for both measurements. The graphs of viscosity versus log[C] and the surface tension versus log[C] are used in determining the critical micelle concentration (cmc). Keywords: Critical micelle concentration; Cetyltrimethylammonium bromide; Viscosity; Surface tension. 1. Introduction Cationic surfactants do show antibacterial properties and are used as cationic softeners, lubricants, retarding agents and antistatic agents and in some cases consumer use also. Hence, cationic surfactants offer some additional advantages over other class of surfactants [1-4]. Like all other surfactants CTAB also shows a rapid change in viscosity when the physical and chemical compositions of the solution are changed [5]. In viscometric determination of CMC of pure surfactant in presence and absence of Na2SO4, MgSO4, the viscosities (η) are plotted as a function of the logarithm of the surfactant. The surface tension of a solution is lowered when surfactants are present [6]. The limiting value of surfactant concentration that produces a surface tension decrease is the critical micelle Chom Nath Adhikari et al./ BIBECHANA 14 (2017) 77-85 : RCOST p.78 (Online Publication: Dec., 2016) concentration [7]. In tensiometric determination of the cmc of pure surfactants, the surface tensions (γ ) are plotted as a function of logarithm of the surfactant concentration. The two fitted lines meet in the curve at the particular point. That point of intersection is known as cmc of the solution.The effective factors, such as the addition of electrolytes, buffer pH, temperature, addition of organic modifiers, ionic strength of the aqueous solution, and presence of additives can change the cmc value from that determined in pure water[8-10]. Addition of electrolyte in the surfactant solution decreases the cmc value [11]. In this paper, we report a study of the aggregation process of CTAB at room temperature in the absence and in the presence of Na2SO4 and MgSO4 in aqueous media at room temperature by viscometric and surface tension method. 2. Experimental Cetyltrimethylammonium bromide (CTAB), Na2SO4 and MgSO4 were used as purchased from Loba Chemical, India. The water used in the solutions prepared at room temperature experiments was doubly distilled. The viscometric measurements were performed at room temperature using an Ostwald viscometer. Several independent solutions were prepared, and runs were performed to ensure the reproducibility of the results. To check whether the reduced viscosities depend on the shear rate in the concentration range investigated. This did not lead to different values of the reduced viscosity. Solvent medium from those of the surfactant solutions in presence and absence of salt was taken. The viscometer was always suspended vertically at room temperature. The viscometer was cleaned and dried every time before each measurement. The flow time for constant volume of solution through the capillary was measured with a calibrated stop watch. The coefficient of viscosity of a given liquid can be calculated according to the following equation: 2 2 1 2 1 1 t t d d              (1) 1 = coefficient of viscosity of the solution 2 = coefficient of viscosity of the solvent t1 = time flow of the solution t2 = time flow of the solvent d1 = density of the solution d2 = density of the solvent The density of any one solution must be known which is calculated by using the expression: 2 2 1 1 d w w d        (2) d1 = density of liquid d2 = density of water w1= weight of liquid w2= weight of water Before using the stalagmometer was first carefully washed with a solution of chromic acid and then with doubled distilled water. Finally it was washed with acetone and water and dried. The surface tension of CTAB in absence and presence of Na2SO4 and MgSO4 was measured by drop count method using a stalagmometer. In this process, first the stalagmometer was filled with Chom Nath Adhikari et al./ BIBECHANA 14 (2017) 77-85 : RCOST p.79 (Online Publication: Dec., 2016) distilled water as above without changing the pressure. Then the drop count was started. By following the same process all the solutions of varied strength of CTAB in presence and absence of salts (Na2SO4 and MgSO4) was measured. The following equation is used to calculate the surface tension of required solution: solv solv lnso lnso solv lnso d d n n              (3) where, γ soln = surface tension of solution γ solv = surface tension of solvent nsoln = number of drops of solution nsolv = number of drops of solvent dsoln = density of solution dsolv = density of solvent If the surface tension of one of the liquids is known then that of the other can be easily calculated from the equation (3). 3. Results and Discussion The specific viscosity decreases with decrease of concentration of CTAB and there is a pronounced break and then remains constant. The breaking point is known as critical micelle concentration, cmc (Fig. 1-3). Our results indicate that there is increase in viscosity with increase in concentration of salt added. The viscosity of CTAB in presence of Na2SO4 is more than in presence of MgSO4 (Table1), this is because while MgSO4 is absorbed on the surface of the micelle, Na2SO4 remains in the bulk of the solution. Addition of salt is known to decrease cmc of the solution [12]. Increasing the salt concentration reduces the electrostatic Debye screening length around the surfactant, which encourages the formation of longer micelles at equilibrium. This, in turn contributes to the changes in cmc. Fujio (1998) [13] found that spherical micelles associated to form into rod-like micelles when salt concentration exceeded a threshold concentration. Salts decrease the cmc in the order: MgSO4< Na2SO4. Here Mg+ + is least effective in decreasing the cmc due to small size and large hydrated radius and would act as a water-structure promoter decreasing the availability of water to the micelles. Therefore, upon addition of MgSO4 and Na2SO4 in CTAB, Na2SO4 is more effective in reducing the cmc of CTAB. Hence in our case Na2SO4 decreases the cmc of CTAB more than MgSO4 (Table 2). The surface tension of CTAB in the presence and absence of Na2SO4 and MgSO4 were calculated from equation (3) and were tabulated in Table 3. The graphical representations of the surface tension of CTAB in the presence and absence of Na2SO4 and MgSO4 with log [CTAB] are shown in Figs. 4- 6. Since, there was sharp decrease of surface tension on increase of surfactant concentrations. According to the experimental calculations and determinations, the surface tension was found to be decreased in presence of salts .i.e. Na2SO4 and MgSO4.The surface tension value was high in case of water because of absence of externally added salts. Since, on the addition of inorganic salts, affect surfactant aggregation mainly through reducing the electrostatic interaction among the surfactant head groups and consequently decrease the surface tension of the surfactant molecules. Chom Nath Adhikari et al./ BIBECHANA 14 (2017) 77-85 : RCOST p.80 (Online Publication: Dec., 2016) Table 1: Viscosity of CTAB in absence and presence of MgSO4 and Na2SO4 at room temperature Solvent Concentration(mol/l) Viscosity(cp) Distilled water 0.00315 0.91643 0.00271 0.90422 0.00235 0.89231 0.00204 0.88256 0.00176 0.87561 0.00153 0.86825 0.00133 0.85967 0.00116 0.85272 0.00103 0.84782 0.00086 0.84921 0.00074 0.84920 0.00065 0.84919 0.00056 0.84919 0.00048 0.84918 Solvent Concentration(mol/l) Viscosity(cp) MgSO4-Water 0.00210 0.89079 0.00181 0.88780 0.00157 0.88380 0.00136 0.88050 0.00118 0.87800 0.00100 0.87500 0.00085 0.86900 0.00077 0.86500 0.00066 0.85100 0.00057 0.85100 0.00050 0.85100 0.00043 0.85100 Solvent Concentration(mol/l) Viscosity(cp) Na2SO4-Water 0.00170 0.92019 0.00156 0.91475 0.00135 0.90722 0.00118 0.89900 0.00104 0.89433 0.00074 0.88079 0.00052 0.86689 0.00040 0.86025 0.00031 0.85300 0.00025 0.85300 0.00020 0.85300 0.83 0.85 0.87 0.89 0.91 0.93 0.0001 0.001 0.01 cmc=1.0mM log[CTAB] v is c o s it y (c p ) 0.87 0.91 0.0001 0.001 0.01 cmc=0.63m M log[CTAB] v is c o s it y (C p ) 0.85 0.87 0.89 0.91 0.93 0.0001 0.001 0.01 cmc=0.31m M log[CTAB] vi sc o si ty (C p ) 30 35 40 45 50 -3.208 -3.108 -3.008 -2.908 -2.808 -2.708 -2.608 -2.508 Cmc = 1.04 mM log[CTAB] su rf a ce te n si o n ( , d yn e /c m ) Chom Nath Adhikari et al./ BIBECHANA 14 (2017) 77-85 : RCOST p.81 (Online Publication: Dec., 2016) Fig. 1: Variation of Viscosity with log[CTAB] in distilled water at room temperature. Fig. 2: Variation of Viscosity with log[CTAB] in MgSO4-Water at room temperature. Fig.3: Variation of Viscosity with log[CTAB] in Na2SO4-Water at room temperature. Fig. 4: Variation of surface tension with log[CTAB] in distilled water at room temperature. 30 35 40 45 50 55 -3.4 -3.2 -3.0 -2.8 -2.6 -2.4 Cmc = 0. 4 m M log[CTAB] s u rf a c e te n s io n ( , d y n e /c m ) 33 35 37 39 41 -3.408 -3.308 -3.208 -3.108 -3.008 -2.908 -2.808 -2.708 Cmc = 0.64 mM log[CTAB] s u rf a c e te n s io n ( , d y n e /c m ) Chom Nath Adhikari et al./ BIBECHANA 14 (2017) 77-85 : RCOST p.82 (Online Publication: Dec., 2016) Fig. 5 : Variation of surface tension with log[CTAB] in Na2SO4-Water at room temperature. Fig. 6: Variation of surface tension with log[CTAB] in MgSO4- water at room temperature. Table 2. Critical micellar Concentration (Cmc) obtained from Viscometry of CTAB in presence and in absence of Na2SO4 and MgSO4 in aqueous media at room temperature Distilled water cmc (mM) Na2SO4-Water cmc (mM) MgSO4-Water cmc (mM) 1.08 0.31 0.63 In the case of Na2SO4 and MgSO4, the sodium ion (Na+) is larger than the Magnesium ion (Mg2+) because the Magnesium cation, Mg2+ has a greater cationic charge than the Na+ cation. The surface tension of CTAB in presence of Na2SO4 is more than in presence of MgSO4 because the smaller ions are strongly hydrated, so they need to pull more water molecules with them which make them less mobile. Thus, due to Magnesium ions (Mg2+) .i.e. counter ions reduced largely the electrostatic interaction among the surfactant molecules and decreased surface tension largely. When surface tension of a solution is plotted against log[C], where C is the concentration of surfactant. The results showed a sharp decrease in surface tension with increase in concentration of cetyltrimethylammonium bromide in presence and absence of Na2SO4 and MgSO4 and then minimum surface tension has been observed and again the small increase in surface tension has been noticed and finally the almost flat curves were obtained. The intersection between two curves gives the critical Chom Nath Adhikari et al./ BIBECHANA 14 (2017) 77-85 : RCOST p.83 (Online Publication: Dec., 2016) micelle concentration. The critical micelle concentration of the surfactant decreased in presence of Na2SO4 and MgSO4, the decrease in cmc depended upon the concentration of added salts. Our calculation of cmc of CTAB in distilled water at room temperature found to be 1.04 mM which is almost matching with 1.102 mM by surface tension method [14]. When surfactant and salt are mixed in solution, salting-out phenomenon often happens [15-18]. According to hydration theory [19] salting-out is the result of preferential movement of water molecules, which immobilize and quench their role as solvents, from coordination shells of surfactant molecules to those of salts. The effects of halide salts on the growth of micelles in ionic surfactant solutions have been systematically studied [20-21]. With the addition of inorganic salts, the reduced electrostatic repulsion among the surfactant head groups is a key factor to influence the morphology of aggregates in ionic surfactant solutions. For conventional single-chain cationic surfactants, micelles may change from global to rod like or wormlike with the addition of inorganic salts [22-23 ]. Salts decrease the cmc in the order: MgSO4< Na2SO4 as like viscosity measurements. (Table 4). Table 3: The surface tension of CTAB in presence and absence of Na2SO4 and MgSO4 . Solvent Concentration(mol/l) Surface tension(dyne/cm) Distilled water 0.00253 33.43 0.00203 33.77 0.00162 34.11 0.00130 34.47 0.00104 34.83 0.00095 37.79 0.00087 40.52 0.00078 43.73 0.00070 46.46 0.00066 48.31 0.00063 49.40 Na2SO4-Water 0.00073 40.70 0.00066 40.70 0.00060 40.60 0.00040 40.10 0.00030 41.00 0.00020 42.00 0.00010 43.00 0.00009 43.50 MgSO4-Water 0.00161 33.55 0.00127 33.54 0.00091 33.78 0.00077 34.03 0.00064 33.44 0.00057 38.02 0.00053 39.11 0.00050 39.38 0.00047 39.55 0.00044 40.14 Chom Nath Adhikari et al./ BIBECHANA 14 (2017) 77-85 : RCOST p.84 (Online Publication: Dec., 2016) Table 4: Critical micellar Concentration (Cmc) obtained from Tensiometry of CTAB in presence and in absence of Na2SO4 and MgSO4 Distilled water Na2SO4-Water MgSO4-Water cmc cmc cmc (mM) (mM) (mM) 1.04 0.40 0.64 4. Conclusions The following conclusions have been drawn from above results and discussion. 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