Aggregation number of alkanediyl-alpha,omega-bis(dimethylalkylammonium bromide) surfactants determined by static light scattering

Aggregation number of alkanediyl-alpha,omega-bis(dimethyl alkylammonium bro mide) surfactants in aqueous solutions has been determined at different num ber of carbon atoms in the alkyl tail 'm' and in spacer 's' by using static light scattering. Values of aggregation number at different spacer numbers s = 2-10 lie between 17 and 33 and between 18 and 55 for alkyl tail length s m = 9-16, respectively. Data for variable parameter s correspond to resul ts obtained by neutron scattering technique. In all cases but s = 2 and m = 16, the slopes of Debye plots were found to be increasing and the value of the second virial coefficient B was found to be in the range 1.3 x 10(-3)- 13 x 10(-3) cm(3) mol g(-2) indicating the spherical shape of micelles. Inc reased aggregation number and negative B of surfactant with the shortest sp acer s = 2 indicates the rod-like micelle shape. Aggregation number of surf actant with the longest alkyl tail m = 16 is too small to predict the rod-l ike shape of the micelle. (C) 2000 Elsevier Science B.V. All rights reserve d.