Physicochemical testing of free films containing non‐soluble components

Eudragit® L 30D‐55 films containing diclofenac sodium in different concentrations (0%, 1%, and 5%) were studied by conventional physicochemical methods and positron annihilation spectroscopy. Diclofenac sodium was found to change the properties of the film formed significantly. Positron annihilation spectroscopy was applied to track the Eudragit–diclofenac interaction. The presence of diclofenac initially led to significant distortion of the structure of the pure Eudragit film. However, during storage (17°C, 65% relative humidity), the distorted structure relaxed because of water uptake from the air. At the end of the storage period, the free‐volume size was almost the same in all films. Copyright © 2011 John Wiley & Sons, Ltd.