Surface activity of amphiphilic cationic pH-responsive poly(4-vinylpyridine) microgel at air/water interface

Abstract

Abstract In this study, we report the relation between the surface activity parameters of soft, pH sensitive microgel particles based on cationic poly(4-vinyl pyridine), p(4-VP) for the first time and corroborate the variation of their chemical structures and their concentrations adsorbed at the air–water interface. In this respect, p(4-VP) particles were quaternized by modifying with alkyl bromides of different chain length. Additionally, hydroxyl, amino and nitrile functional group-containing alkyl bromides were used to quaternize the crosslinked p(4-VP) to determine the effect of hydrophilic and hydrophobic groups on the surface activities of the prepared microgels. The chemical structures of the prepared microgel were characterized by Fourier transform infrared spectrometry (FT-IR). The solution behavior was investigated by surface tension technique, scanning electron microscopy (SEM), dynamic light scattering (DLS), and zeta potential measurements. The results indicate that the microgels can spontaneously assemble into spherical-shaped micelle aggregates, with different critical aggregation concentrations (cac), and hydrodynamic diameters from about 500–1000 nm at pH 4, 7 and 9, depending on the microgel chemical structure. For the first time, p(4-VP) microgels quaternized with hydroxyethyl bromide showed reduction of surface tension of water using amphiphilic microgels from 72.1 to 31.1 mN/m.