Dielectric relaxation of dilute polystryene lactices

The main aim of the investigations, described in this thesis is to provide data which can be used to test theories of dielectic phenomena in dilute colloid systems.The possibility of preparing homodisperse polystyrene latices with surfaces uncontaminated by emulsifiers, means that dielectric methods can be applied to these colloid dispersions. The equipment used and the latices which where prepared are described in chapters two and three respectively.The experimental results for latex A ₁ , with KCl as the added electrolyte, are particularly relevant. These results, which are characteristic of the dielectric behaviour of dilute polystyrene latices, are used in chapter five for calculations with different theories. Based on the dependence of the static dielectric increment Δε _st on c _b , the concentration of added electrolyte, it appears that until now no theory exists, by which the experimental results obtained are explained conclusively. The best agreement between theory and experiment is obtained both with the theory of Dukhin and Shilov and with that of Schurr. Using the calculated relaxation times, it is impossible to discriminate between these two theories, because in both cases a relaxation time is calculated which is of the right order of magnitude compared with the experimental value.Figure (5-2) demonstrates that Schurr's theory is the best in accordance with the experimental results. However, in Schurr's theory the diffusion fluxes of the ions in the diffuse part of the double layer are not taken Into account. In view of their theoretical starting points the theory of Dukhin and Shilov must be considered as the best one. The larger discrepancy between the theory of Dukhin and Shilov and the experimental results for Ac st as a function of c h may be caused by an overestimation of the influence of radial fluxes in their theory.In conclusion, based on the established discrepancies between theory and experiment It is thought to be pertinent to perform further dielectric measurements on other colloid model systems such as chromium hydroxide sols. Probably, a part of these discrepancies is due to irregularities in the polystyrene latices used. on the other hand, it is necessary to develop the theory further. In this case special attention must be paid to the role played by the diffusion coefficients and diffusion fluxes around the colloid particles.