Rheological Properties of Disperse Systems of Photosensitive Particles: II. The Influence of Particle Aggregation on Slow Relaxation Process

Abstract

Rheological properties of disperse systems of photosensitive particles were studied in relation to the degree of aggregation of dispersing particles. Photosensitive particles were prepared by introducing cinnamoyl groups to styrenedivinylbenzene copolymer spherical particles. The degree of aggregation (total number of primary particles forming an aggregate) was controlled by irradiation of light to the disperse system and was estimated from light scattering by assuming a hexagonal close‐packed aggregate model. Viscoelastic properties of the disperse systems of the photosensitive particles in diethylphthalate were measured by means of a cone‐plate type rheometer. Terminal zone of the modulus shifts progressively to lower frequency with increasing the irradiation time, i.e., with increasing the degree of aggregation. It is strongly suggested that the aggregate is a cause of the long‐time relaxation and that the maximum relaxation time of the disperse system can be directly related to the rotational diffusion of the aggregate.