Self-Diffusion of Small Hydrophobic Molecules in Aqueous Poly(n-Butylacrylate/Acrylic Acid) Latex Dispersions

The self-diffusion of relatively small amounts of various organic solvents both in water and in a colloidal dispersion of poly(butylacrylate) in water was studied by pulsed field gradient NMR. On the timescale studied (45 ms) self-diffusion was found to be dominated by exchange of solvent molecules among the colloidal particles. A pronounced dependence on the latex volume fraction was found. A conceptually simple cell model proposed by Jönnson et al. (Colloid Polym. Sci.264, 77 (1986)) was shown to be in excellent agreement with the experimental data. The partition of organic solvent between the colloidal particle and the water phase can be accurately determined solely from the self-diffusion experiment. In this manner the dynamics of the system provide an important static quantity which would otherwise be difficult to obtain experimentally.