This work presents the new approach to the investigation of mass transport process in polymers. The Fiber Optic Evanescent Wave Spectroscopy has been used for the real time investigation of diffusion processes in glassy polymers. Unclad AgClBr fibers of 0.9 mm diameter were dip coated by polystyrene layers of 1 - 30 micrometers thickness. The transmission of the fibers in the mid-IR was measured using a Fourier Transform Infrared spectrometer. The penetration of liquids into these layers gave rise to significant changes in the measured spectrum. These changes were used for diffusion studies in situ. The mathematical model, which allows realizing the quantitative treatment of experimental data, was developed. The model details with processes which take place at two interfaces: polymer/liquid and polymer/optical fiber. It was established that the initial stage of diffusion is of the strictly Fickian character. The model permitted us to calculate the coefficient of diffusion of water in polystyrene with a high accuracy. The huge amount of experimental points, which could be obtained by our method, allows calculation of the equilibrium concentration of penetrating liquid with an extremely high precision. This advantage of FEWS procedure offers a high accuracy of calculations of parameters of diffusion. It must be emphasized that the thickness of the film that could be defined with the least precision doesn't affect on final results. The final stage of diffusion is non-Fickian.
|Number of pages||9|
|Journal||Proceedings of SPIE - The International Society for Optical Engineering|
|State||Published - 2000|
- Real time