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TRANSPORT OF SMALL MOLECULES IN POLYMER BLENDS: TRANSPORT-MORPHOLOGY RELATIONSHIPS (SORPTION, MICROSCOPY, GASES)

JAMES E SAX, University of Massachusetts Amherst

Abstract

This thesis concerns itself with the influence of morphology on transport processes, specifically the prediction of effective diffusion coefficients of small penetrants (gases) in binary polymer blends of varying degrees of miscibility and microstructural order. Experimental results, modeling studies, and image analysis results are presented and compared. Several models are developed and critically evaluated with the help of previously published experimental data and new data obtained in this work. Completely random two-phase media are modeled in terms of Effective Medium Theory and a simple network based percolation model. Effective Medium Theory is found to predict experimental data satisfactorily, except near the percolation threshold. Another simple model is presented for systems exhibiting microscale order and macroscale disorder. A sorption apparatus was used to study the transport properties of mechanically interspersed blends of polystyrene and polybutadiene. Also, a digital image analysis package was developed for the quantitative characterization of the morphology of the blends, allowing such quantities as inferfacial area density, cluster size distributions, orientation, and accessible and inaccessible area fractions to be calculated from transmission electron micrographs. Experimental data indicates that the overall transport process in blends appears "non-Fickian", even though both pure components exhibit Fickian behavior. An explanation based solely on morphological effects, is presented. Examination of the morphology of the systems via transmission electron microscopy and digital image analysis indicates that this system is not truly random. A significant finding is that for this system the maximum in the interfacial area density occurs near 15.0 volume percent polybutadiene. Experimental studies of more ordered systems, such as blends of poly(methyl methacrylate) spheres in a poly dimethyl siloxane matrix, and star-branched copolymers of polystyrene and polyisoprene also exhibit "non-Fickian" transport processes of varying degrees. An important conclusion of this study is that the different methods usually taken as equivalent, to compute the effective diffusion coefficient from sorption data, can give significantly different results.

Subject Area

Chemical engineering

Recommended Citation

SAX, JAMES E, "TRANSPORT OF SMALL MOLECULES IN POLYMER BLENDS: TRANSPORT-MORPHOLOGY RELATIONSHIPS (SORPTION, MICROSCOPY, GASES)" (1985). Doctoral Dissertations Available from Proquest. AAI8509601.
https://scholarworks.umass.edu/dissertations/AAI8509601

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