Investigation of Water Penetration in Polystyrene by Use of Polymer Coated AgCiBr Fibers and Development of New Sensor Intended for the FEWS Spectroscopy of Organic Compounds in Water

摘要

This work presents the new approach tot he 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 mu m thickness. The transmission of the fibers in the mid - IR was measured using a Fourier Transform Infrared (FTIR) 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 deals 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 permittec us to calculate the coefficient of diffusion of water in polysttyrene with a high accuracy. The huge amount of experimental point,s which could be obtained by our method, allows calculationof 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.