Self-diffusion of solvents and solute probes in polymer solutions and gels: the use of a new physical model of diffusion

摘要

We have proposed a new physical model for the interpretation of the diffusion of solvent and other solute molecules in polymer solutions. In this model, the polymer solution is regarded as a network where the diffusing molecules have to overcome periodic energy barriers of equal magnitude, and the distance between the barriers corresponds to the correlation length in polymer solutions. The new diffusion model has been used successfully to describe the effects of polymer concentration, temperature and molecular size of the diffusants on the self-diffusion coefficients of various molecular probes in several polymer systems. It has been shown that this model applies to the diffusion of small molecules in polymer matrices, such as ternary aqueous systems of poly(vinyl alcohol) (PVA) and binary organic solutions of poly(methyl methacrylate). In an effort to link the diffusion solutions of poly(methyl methacrylate). In an effort to link the duffusion properties of small and large molecules in polymer systems, we have measured the self-diffusion coefficients of a series of solute probes, including ethylene glycol and its oligomers and polymers in aqueous solutions and gels of PVA using the pulsed-gradient spin-echo NMR technique. The self-diffusion coefficients of the solute probes decrease with increasing PVA concentrations and with increasing molecular size of the probes. The effect of temeprature on the self-diffusion coefficients has also been studied with selected probe molecules. The dependence of the physical parameters in the diffusion model on the molecular size of the diffusant and on temeprature is also discussed.