WATER PENETRATION IN GLASSY-POLYMERS - EXPERIMENT AND THEORY

We describe the design and implementation of a method based on infrared monitoring of the OD stretch mode which permits measurement of the diffusion profiles of water permeating glassy polymers for the first time. Results for several glassy polymers are compared with a theory of trapping diffusion which leads to a nonlinear diffusion problem in which the trapped water penetrates the polymer as a sharp front if there is a large amount of trapping. In the case of two of the polymers studied, the trapping model describes the data, very well (much better than a simple diffusion model) and permits determination of parameters related to the free volume and the residence time of the water on traps in the model.