Interactions of cationic micelles and polyester hyperbranched dendrimers by estimating degree of micelle ionization from Krafft temperature measurements

Krafft temperature (K-T) measurements of hexadecyltrimethylammonium bromide (HTAB), hexadecylpyridinium bromide (HPyBr), and hexadecylpyridinium chloride (HPyCl) in pure water as well as in the presence of aliphatic polyester (AL-PE) dendrimer and salt have been carried out with the help of conductivity (kappa) measurements. The KT of all surfactants decreases with the increase in the amount of AL-PE, which is explained on the basis of cationic surfactant-AL-PE favorable electrostatic interactions. The quantification of such interactions has been carried out by determining the degree of micelle ionization (a) of HTAB and HPyBr by using the pseudophase thermodynamic model [J. Phys. Chem. B 106 (2002) 9033; 107 (2003) 5398]. it has been found that the alpha value for HTAB and HPyBr is much higher in the presence of AL-PE than that in pure water and effect is much pronounced in the case of second generation (2G) AL-PE and HTAB. (C) 2004 Elsevier B.V. All rights reserved.