Modelling and scaling of dichroism during relaxation in emulsions and polymer blends

Relaxation after cessation of flow is studied in mixtures of immiscible pol ymer fluids by means of linear conservative dichroism. Depending on the pre vious shear history, relaxation is known to proceed by either droplet retra ction or break-up. Here, scaling relations for the evolution of the dichroi sm for both mechanisms of relaxation are presented. In addition a direct an alysis of the rheo-optical relaxation curves is given. Starting from a suit able model for droplet retraction and applying Rayleigh-Gans-Debye scatteri ng theory, this particular type of dichroism relaxation can be described qu ite accurately. A similar approach has been applied to relaxation by drople t break-up as induced by interfacial instabilities (Rayleigh instabilities) . Tomotika theory is used to model the evolution of the droplet shape. The theoretical result deviates systematically from the experiments which is at tributed to end-pinching. Lacking a suitable model for the latter, it is ta ken into account by an empirical correction similar to that used to describ e the normal stress relaxation. With the rheo-optical technique the evoluti on of the relaxation time as a function of the initial aspect ratio of the droplets can be studied. In addition the effect of concentration on the rel axation time is investigated.