Dissolution and mutual diffusion of poly(N-vinylpyrrolidone) (PVP) in short-chain poly(ethylene glycol) PEG400 were studied by wedge microinterferometry over the temperature range of 40-100°C. Successive photographs of interference patterns measured at λ = 546 nm with an optical microscope at 130× magnification were used to determine the PVP/PEG concentration-distance profiles. These profiles were found to be highly asymmetric, exhibiting steep concentration gradients near the surface of the glassy polymer sample. The PVP/PEG system is completely miscible, and interdiffusion kinetics are Fickian with a concentration-dependent mutual diffusion coefficient, DV. Thermal activation of diffusion was studied in terms of an Arrheniustype relation, with concentration dependent activation energy Ea. Values of DV and Ea are in accord with the compositional behavior of the glass transition temperature in PVP-PEG blends, indicating that PVP plasticized with PEG behaves like an elastomer.
- Hydrophilic polymers