Salt-Induced Aggregation of Polystyrene Latex Particles in Aqueous Solutions of a Hydrophobically Modified Nonionic Cellulose Derivative and Its Unmodified Analogue

The structure and kinetics of clusters formed in the salt-induced (0.7 M NaCl) aggregation processes of polystyrene latex particles in the presence of various amounts of ethyl(hydroxyethyl)cellulose (EHEC) or the hydrophobically modified analogue (HM-EHEC) have been investigated with the aid of light scattering measurements. Under all conditions, both with and without polymer, the aggregating clusters are well described by a fractal geometry with a fractal dimension of 2.1. Three stages can be discerned in the salt-induced aggregation process of bare latex particles. In the early stage, the time evolution of the hydrodynamic radius R h can be described by a power law R h ∝ t 0.04, followed by a steep transition zone and an exponential growth at long times. In the presence of polymer, the slow cluster size growth can be described by the above power law over the whole considered time domain. The value of the power law exponent is independent of polymer concentration and hydrophobicity of the polymer. The results show that only a small amount of adsorbed polymer is needed to slow the rate of the aggregation process. The results show that both polymers adsorb to the latex particles, but the adsorption is more pronounced for the hydrophobically modified polymer.