Dissolution and mutual diffusion of poly( N ‐vinyl pyrrolidone) in short‐chain poly(ethylene glycol) as observed by optical wedge microinterferometry

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, D V . Thermal activation of diffusion was studied in terms of an Arrhenius‐type relation, with concentration dependent activation energy E a . Values of D V and E a 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. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1128–1136, 2002