Investigation of water penetration in polystyrene by use of polymer coated AgClBr fibers and development of new sensor intended for the FEWS spectroscopy of organic compounds in water

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 mum 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 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 him that could be defined with the least precision doesn't affect on final results. The final stage of diffusion is non-Fickian. The sensitivity of the method was sufficient for studying the penetration of small concentrations (up to 5 ppm) of organic liquids through polymer layers. This fact allows using the polymer coated AgBrCl fibers as sensor elements for identifying organic liquids in water. It must be emphasized that the cylindrical symmetry of our fibers renders them especially suitable for the diffusion study and allows us to obviate the difficulties caused by end effects.