Studies on the micellization behavior of surfactants in selected solvent media

Abstract

The present thesis entitled, Studies on the Micellization Behaviour of Surfactants in Selected Solvent Media , consists a total of six chapters. In Chapter 1, a general introduction to the subject is given and the newlinescope of the work is described. In Chapter 2, a brief description of the experimental techniques used to carry out the work has been given. Chapter 3 deals with the study on the aggregation and counterion binding characteristics of sodium dioctylsulfosuccinate (AOT) in aqueous newlinesodium chloride medium. Critical micelle concentrations (cmc) of AOT in presence of NaCl and NaSa (sodium salicylate) have been determined from surface tension measurements at 40 C. The aggregation process in AOT + newlineaqueous NaCl / NaSa is endothermic. The special counterion binding behaviour of AOT has been found to be independent of the temperature. The greater condensation of counterions to AOT micelles has also been confirmed by zeta potential measurements at 40 C for AOT + NaCl, while for NaSa no newlinesuch observation was made. Small-angle neutron scattering (SANS) profiles of AOT in the presence of NaCl clearly reveal a change in the shape of AOT micelle near the NaCl concentration where a two-fold increase in its and#946; value occurs. From the SANS data analysis this shape change has been shown to be from prolate spheroid to rod-like shape. On the other hand, SANS profiles of AOT in the presence of NaSa do not indicate any shape change of AOT micelle and interestingly in NaSa solution no abrupt change in the value of and#946; also occurs. Therefore, it is concluded that counterion binding constant of newlineionic micelle is a micellar shape dependent parameter. From the present study it is proposed that and#946; of prolate ellipsoidal shaped micelle is less than that of rod-like shaped micelle. This is consistent with the proposition made by Fujio et al. that the value of and#946; follow the order, spherical lt oblate ellipsoidal lt rodlike micelle. Generally, the counterion binding is thought to be one of the factors determining size and shape of ionic micelles.