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

Krafft temperature (KT) 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 (κ) 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 (α) 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 α 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.