Graduate Thesis Or Dissertation
 

Diffusion in silicone polymers

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/4b29b913x

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  • The study of diffusion coefficients of n-alkanes and other organic compounds in silicones is undertaken by gas-liquid chromatography. About 0. 3% of stationary phase is coated on glass bead support so that the only significant source of peak spreading is due to slow liquid phase mass transfer. Diffusion coefficients are higher in higher molecular weight methylsilicones than in lower molecular weight. The anomaly is partially explained by the increase of free volume with increasing molecular weight. Partition coefficients of n-alkanes in the methylsilicones are independent of the molecular weights of the silicones. Chromatographic peaks for n-alkanes in methylsilicones become increasingly skewed as the molecular weight of the n-alkane increases. Diffusion coefficients in phenyl, fluoro and cyanosilicones are strongly dependent on the steric hindrance of the substituent groups of the silicones and the molecular size and shape of the penetrants. Three equations for the dependence of the diffusion coefficients of n-alkanes on the physical properties of the penetrant-polymer system are investigated by linear regression. It is found that the best fit through the 158 data points is obtained when the densities and the percent phenyl content of silicones are included in the regression equation. It suggests the diffusion process is dependent on the free volume and steric hindrance of the silicones studied, and is independent of intermolecular attraction between the polymer and the penetrant.
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