Cationic surfactant–poly(amido amine) dendrimer interactions studied by Krafft temperature measurements

The Krafft temperatures, TK, of three cationic surfactants, hexadecylpyridinium bromide (HPyBr), hexadecylpyridinium chloride (HPyCl), and hexadecyltrimethyl ammonium bromide (HTAB) at 0.05 M were studied by adding different concentrations of water-soluble poly(amido amine) (PAMAM) dendrimers of 0G–2.5G generations from conductance measurements. The TK of cationic surfactants decreases in the presence of all generations of PAMAM. The decrease in TK was maximum in aqueous 1.5G followed by 0.5G, which are ester-terminated dendrimers. It demonstrated that ester-terminated PAMAM interacted more strongly with cationic surfactants than amine-terminated PAMAM. HPyBr showed minimum while HPyCl maximum interactions with PAMAM, the fact attributed to the tightly associated Br− counterions in the former case.