Gelation of spontaneously formed catanionic vesicles by water soluble polymers

Abstract

The gelation of two spontaneously formed charged catanionic vesicles by four water soluble polymers was systematically studied by tube inversion method and rheology. Eight phase maps were successfully documented for the catanionic vesicle–polymer mixtures. The experimental results, as represented by the relaxation time and the storage modulus at 1 Hz, revealed that the catanionic vesicle–polymer interactions at play were of electrostatic and hydrophobic origin. Firstly, no association between charged catanionic vesicles and the polymer without charge/hydrophobic modification was observed due to lack of both electrostatic and hydrophobic effects. Secondly, hydrophobic interactions accounted for the association between the hydrophobically modified polymer without charge and charged catanionic vesicles with hydrophobic grafts of the polymer inserting in the catanionic vesicle bilayer. Thirdly, the positively charged polymer without hydrophobic modification could interact with negatively charged catanionic vesicles through electrostatic force on one hand but could not interact with positively charged catanionic vesicles on the other hand. Finally, the positively charged polymer with hydrophobic modification could interact both electrostatically and hydrophobically with negatively charged catanionic vesicles, resulting in the formation of strong gels. The hydrophobic interaction might even overcome the unfavorable electrostatic interaction between the positively charged vesicles and the polymer with positive charge/hydrophobic modification.