Chapter 8: Heteroflocculation Studies of Colloidal Poly(N-isopropylacrylamide) Microgels with Polystyrene Latex Particles: Effect of Particle Size, Temperature and Surface Charge

The heteroaggregation behaviour of thermosensitive cationic poly(N-isopropylacrylamide) [poly(NIPAM)] microgels and anionic polystyrene (PS) latex particles has been investigated with respect to particle size, surface charge, deformability of the particle, temperature and concentration. Microgels and PS latex particles have been characterised. Turbidimetric analysis and scanning electron microscopy have been employed to determine the state of aggregation of mixtures of the two types of particles.

PS latex particles of varying size (100–800 nm) have been studied in mixtures with two cationic microgels. Results show that the ionic interaction between oppositely charged deformable and non-deformable particles can be manipulated by changing the particle size, concentration and temperature of the particles in the mixture. It has been found that aggregation is induced in the mixtures containing the largest of the PS latex particles by the lowest concentration of microgel. It is also reported that the larger the latex the less is the influence of temperature on the stability of the mixed particulate system.

The heteroflocculation/aggregation behaviour is influenced by the relative concentration of the two oppositely charged species. The change from a dispersed to an aggregated system is most likely continuous and the relative concentration at which aggregation begins to occur is somewhere between a 1 : 1 ratio and 10 : 1 excess of the cationic microgel. This concentration effect can be used to initiate aggregation at temperatures below the volume phase transition temperature of the poly(NIPAM) microgels.