55 J. Indian Chem. Soc., Vol. 95, January 2018, pp. 55-63 Analysis of CMC of polyoxyethylene(20)sorbitan monopalmitate (Tween-40) and cetyltrimethylammoniumbromide (CTAB) in aqueous medium T. B. Sinha a,b , H. S. Das b , R. K. Dubey b , R. Das b , G. Roymahapatra b and P. K. Khatua* a,b a ICARE School of Research & Development, University of Mysore, ICARE Complex, Haldia-721 657, West Bengal, India b Department of Applied Science, Haldia Institute of Technology, Haldia-721 657, West Bengal, India E-mail : pijuskhatua@gmail.com Manuscript received 01 November 2017, accepted 24 November 2017 Abstract : In aqueous environment of different concentration ratio of CTAB and Tween-40 formed mixed micelles. In this present paper the mixed micelles and their critical micellar concentration (CMC) has been studied by different instrumental techniques like spectrophotometric, spectrofluorometric by using a probe 1-anilinonapthalene-8-sulfonic acid (1,8-ANS) as well as conductometric, tentiometric by using Clint, Motomura, Rosen, Rubingh, Blankschtein et al., and Rubingh and Holland equation for verification of the experimental CMC, composition parameters, quantification of interaction among the mixed micelle components, and esti- mation of their activity coefficients. Keywords : Mixed micelles, CTAB, Tween-40, 1,8-ANS, CMC. Introduction In the field of chemistry, bio-chemistry, drug in- dustry, biotechnology, pharmaceuticals engineering etc. micellar environment have wide range of appli- cation. From the modern study 1–3 it has been implied that micellar environments are more active and have more potential on the view points of fundamental, technological, pharmaceutical, bio-chemical consi- deration. To prepare a mixed micelle, more than one surfactant is necessary in the form of any one mode i.e. ionic-ionic and ionic-nonionic, nonionic-nonionic 4–9 . More than one surface active agent when mixed in definite proportion form mixed micelles which are widely used in industrial preparation as well as phar- maceuticals and medical applications. In mixed surfactant environment with increase in concentration of surfactant system they aggregate and formed micelle at a particular concentration called CMC. The formation of CMC does not only concen- tration depended; it also depends other factors like temperature, additives, pressure and pH of the envi- ronment. Mixed micelles have some special charac- teristics 10–17 than the individual micelle formed only from one surfactant. So the characterization of CMC for mixed surfactant is very much important in the field of medicine, pharmaceuticals, dyeing cloths etc. The present study is associated with two surfac- tants Tween-40 and CTAB. The physical and chemi- cal properties of both surfactants are very much de- pendent on their different concentration ratio. We have studied CMC and other properties like thermodynamics of micellization and interfacial adsorption, polarity, composition and interaction, counter ion binding of the mixed micellar system, have been determined by using the theory of Clint 18 , Motomura 19 , Rubingh 20 and Blankschtein 21,22 to better understand the behav- ior of binary combination of surfactants having dif- ferent characteristics. Experimental The dye 1,8-ANS was crystallized thrice from an ethanol-water mixture 23,24 . The amphiphiles, polyoxyethylene(20)sorbitan monopalmitate (Tween- 40) and CTAB were of E. Merck (Germany) prod- JICS-8