BIBECHANA A Multidisciplinary Journal of Science, Technology and Mathematics ISSN 2091-0762 (Print), 2382-5340 (0nline) Journal homepage: http://nepjol.info/index.php/BIBECHANA Publisher: Research Council of Science and Technology, Biratnagar, Nepal Micellisation behavior on the dodecyltrimethylammonium bromide in the presence of Brij-35 in pure water by conductivity measurement Neelam Shahi, Ajaya Bhattarai* Department of Chemistry, M.M.A.M.C., Tribhuvan University, Biratnagar, Nepal. *E-mail: bkajaya@yahoo.com Article history: Accepted 28 November, 2017 DOI: http://dx.doi.org/10.3126/bibechana.v15i0.18443 This work is licensed under the Creative Commons CC BY-NC License. https://creativecommons.org/licenses/by- nc/4.0/ Abstract Conductivity measurement of dodecyltrimethylammonium bromide in the presence of Brij-35 in aqueous media at 289.15 K is performed. The result showed a sharp increase in conductivity with increase in the concentration of dodecyltrimethylammonium bromide in the presence of Brij-35. The graph of specific conductivity versus concentration is used in determining the critical micelle concentration (CMC). There is the decrease in CMC of dodecyltrimethylammonium bromide in the presence of Brij-35 in comparison with the CMC of dodecyltrimethyl ammonium bromide [DTAB]. Gibbs free energy of micellisation has also been evaluated. Keywords: Dodecyltrimethylammonium bromide; Brij-35; Conductivity; Critical micelle concentration. 1. Introduction Critical micelle concentrations have been experimentally determined using a number of different methodologies [1,2]. The critical micellar concentration of surfactant in pure water is determined by conductometry method by plotting specific conductance versus surfactant concentration. The data points above and below the inflation were fitted to two linear equation and the curves were obtained from the common intersection. The resolution of CMC indicates self-aggregation of amphiphilic molecules in aqueous media. The idea of CMC plays the significant role during scientific research [3-5]. DTAB is a quaternary ammonium cationic surfactant. It has been used in a study assess the distribution of binary mixed counter ions in surfactant adsorbed films. Brij-35 is a non-ionic surfactant which is beneficial in UV monitoring of solubilized proteins due to their low UV absorbance. It is a polyglycol ether which functions as a detergent for the isolation of functional cell membrane complexes. Different investigation clarifies that Brij-35 acts as a surfactant in Micellar electrokinetic Chromatography(MEKC). Neelam Shahi and Ajaya Bhattarai / BIBECHANA 15 (2018) 85-89: RCOST p.85 http://nepjol.info/index.php/BIBECHANA mailto:bkajaya@yahoo.com http://dx.doi.org/10.3126/bibechana.v15i0.18 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ It is beneficial in slowing down electroosmotic pump which allows users to change pH values without drastically altering the flow rate. The optimization of mixtures of surfactants in aqueous solution is an important part of the formulation of many commercial cleaning products [6]. The mixture of ionic and non-ionic surfactants in pure water exhibit the highly non-ideal behaviour and their behaviour can be complementary to the mixed micelle causing the CMC to decrease [7]. There are many examples in the literature showing that binary mixtures of different types of surfactant are non-ideal in such a way that important properties of the mixture are quite different from those of the individual species [10-12]. In the literature, it is possible to find data concerning the anionic/non-ionic mixtures of two surfaces rather than those of cationic/non-ionic surfactants [2]. 2. Experimental Thus, the graph was plotted taking specific conductance vs concentration of the surfactant so that CMC was determined. 3. Results and Discussion The CMC determined using conductivity method is the most reliable and easy method for the investigation. The CMC value obtained for the mixed surfactant (cationic and non-ionic surfactant) in pure water has the significant influence on the CMC value in contrast to the single cationic surfactant. The size and type of structure of the polar head region of the surfactant molecule play a significant role in surfactant’s CMC under different conditions. Small ionic heads typically form micelles at higher molar concentrations than surfactants with large non- ionic compounds. Thus the mixed cationic and non-ionic surfactant have decreased CMC value than single cationic surfactant due to their non-ideal behaviour. Thus, the CMC of mixed surfactants in pure water was determined using conductivity method at temperature 289.15 K. The CMC determined is 12.42 mmol/lt obtained from the break in the conductance-concentration profile (Fig.1). There is the intersection of two lines having different slopes is identified as CMC. The ratio of slopes i.e., post-micellar slope (S2) to the pre-micellar slope (S1) gives the degree of ionization (α). α = S2/ S1 (1) Neelam Shahi and Ajaya Bhattarai / BIBECHANA 15 (2018) 85-89: RCOST p.86 Further reading of specific conductance was measured by the process of internal dilution [25 ml DTAB – 2 ml DTAB = 23 ml DTAB and adding 2 ml Brij-35 solution making 25 ml DTAB + Brij-35 solution] repeating a process no. of times till the constant reading appeared. The specific conductance of DTAB in the presence of Brij -35 solution at different concentrations was mentioned in table 1. DTAB and Brij-35 (Merck Specialties Pvt. Ltd., Mumbai, India) were dried in an electric oven below their melting points for 1 h and 0.00124 M Brij-35 solution was prepared by dissolving 0.3715 gm in 250 ml volumetric flask. 0.0748 M DTAB solution was prepared by dissolving 2.3051 gm in 100 ml volumetric flask by using Brij 35 solution and 25 ml DTAB solution in the presence of Brij-35 was taken in a small beaker and specific conductance was measured using conductivity meter (LT-17 E.I. an ISO 9001-2000 certified company). Cationic surfactants are used as antifungal, antibacterial and antiseptic agents and have attracted recently more attention with reference to their DNA and lipids whereas non-ionic surfactants are useful as detergents, solubilizers and emulsifiers [8,9]. S.No. Volume of (DTAB+Brij 35) ml Specific Conductance(ms/cm) Concentration(mol/lt) 1 25 1.46 0.0322 2 25 1.39 0.0298 3 25 1.32 0.0274 4 25 1.26 0.0254 5 25 1.20 0.0234 6 25 1.14 0.0213 7 25 1.08 0.0197 8 25 1.04 0.0181 9 25 1.00 0.0167 10 25 0.97 0.0153 11 25 0.93 0.0141 12 25 0.89 0.0130 13 25 0.85 0.0119 14 25 0.81 0.0110 15 25 0.77 0.0101 16 25 0.73 0.0092 17 25 0.67 0.0081 18 25 0.63 0.0072 19 25 0.57 0.0060 20 25 0.53 0.0052 The CMC value has been calculated for DTAB in pure water is 12.68 mmol/lt. It is seen that the CMC value has been decreased in the mixture of cationic and non-ionic surfactant in pure water than the CMC value of cationic surfactant in pure water. On the basis of pseudo-phase separation model [13], standard Gibb’s free energy of micellization (∆𝐺m o ) is calculated from the relation ∆𝐺m o = (2 − 𝛼)𝑅𝑇 ln𝑋CMC (2) where R is universal gas constant, T is the temperature and 𝑋CMC is mole fraction of surfactant at CMC. The critical micelle concentration (CMC) of a surfactant is an important physical parameter. When surfactants are present at the concentration above the CMC they can act as emulsifiers, allowing normally immiscible compounds to dissolve in the solvent [1]. Neelam Shahi and Ajaya Bhattarai / BIBECHANA 15 (2018) 85-89: RCOST p.87 Fig1:Variation of specific conductivity versus concentration of DTAB in the presence of Brij-35. Table 1: Variation of specific conductance versus concentration of DTAB in the presence of Brij-35. The normally insoluble compound is sequestered in the micelle core, while the head group interacts with the solvent. The CMC value of the mixed surfactants is significantly necessary for further utilization in different modern methods. Among them, conductometry method has been adopted for CMC determination for the mixed surfactants. 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 post-micellar regions which allowed us to draw two unambiguous straight lines above and below the CMC. It is the matter of great concern for further investigation under such mixed surfactant in characterized solvent media for better utilization. The Gibbs free energy of micellisation of dodecyltrimethylammonium bromide in the presence of Brij-35 is found to be -28.96 kJ/mol. According to Sharma et.al [2], ∆𝐺m 4. Conclusion Acknowledgment One of the authors (Neelam Shahi) is very grateful to Associate Prof. Sitaram Gupta (Head of the Department of Chemistry), Mahendra Morang Adarsh Multiple Campus for providing research facilities. References [1] M. Prasad, R. Palepu, S. P. 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