Measurement of diffusion coefficients of additive molecules in colloidal polymer particles by electron paramagnetic resonance

Abstract.

Nonpolar paramagnetic additives mixed into the aqueous serum of colloidal polymer dispersions are absorbed by the polymer particles with a rate that depends on the diffusion coefficient of the additive in the polymer. The absorption leads to an immobilization of the additive which can be detected in the electron paramagnetic resonance spectrum. By fitting the time dependence of the immobilized fraction to the appropriate diffusion model, it is possible to determine the diffusion coefficient of the additive in the polymer if the polymer particles are approximately uniform in size. This opens up a new way to determine diffusion coefficients in the range between 10^–14 and 10^–17 cm²s^–1, as are expected for low-molecular-weight additives in polymers below their glass-transition temperature.