The properties of polyampholyte microgel particles prepared by microemulsion polymerization

Abstract

Polyampholytemicrogels have been synthesized by copolymerizing the anionic monomer sodium 2-acrylamido-2-methylpropanesulfonate (NaAMPS), the cationic monomer (2-(methacryloyloxy)ethyl)trimethylammonium chloride (MADQUAT), and a crosslinking monomer N,N′-methylenebisacrylamide (BA), using an inverse microemulsion route. The swelling properties of so-called ‘balanced’ microgel particles (i.e. containing the same number of positive and negative monomers in the initial mixture), but containing variable amounts of the crosslinking monomer, have been investigated as a function of ionic strength using photon correlation spectroscopy. The microgel particles flocculate below a certain electrolyte concentration. Above this concentration they are stable and the particle size appears to be insensitive to both ionic strength and the crosslinker concentration in the monomer feed. The structure of the microgel particles in pure water has been investigated using transmission electron microscopy. The samples consist of both aggregates and isolated particles. The isolated particles are somewhat ellipsoidal in the collapsed state. In order to monitor the ‘surface charge’ of the particles, under various conditions, electrophoretic mobility measurements have been performed. The swelling behaviour of ‘unbalanced’ 20/80 [anionic/cationic] polyampholyte microgel particles has been examined. Unexpectedly, these microgel particles displayed only a very small decrease in size with increasing electrolyte concentration.