PGSE-NMR STUDIES OF SOLVENT DIFFUSION IN POLY(N-ISOPROPYLACRYLAMIDE) COLLOIDAL MICROGELS

The solvent self-diffusion coefficient has been studied in thermoshrin king poly(N-isopropyl acrylamide) microgel dispersions by the pulsed-g radient spin-echo PGSE-NMR technique, as a function of temperature and mass fraction. After suitable corrections for the temperature, the H2 O/D2O ratio and the relative volume fractions, all the self-diffusion data obtained over a temperature range of approximately 40 degrees C a nd mass fraction (2-12 % wt/wt) could be superimposed with the volume fraction as the universal factor. The observed reduction in the solven t self-diffusion coefficient with volume fraction was greater than tha t predicted by simple obstruction theory. After correction for-, and t he subsequent removal of the obstruction effect, the diffusion of the solvent through the core of the particle is elucidated. As found for o ther polymer-solvent systems, there were no specific binding effects. The diffusion of the solvent in these dispersions over such temperatur e and mass fraction ranges could be rationalised assuming a constant s olvent self-diffusion coefficient in the core of the particles.