Penetrant transport in glassy polymers
Abstract
The recently developed framework built upon the rational thermodynamics covering various types of mass transport phenomena in penetrant/polymer systems was investigated through a series of experiments. Penetrant transport phenomena in crosslinked polystyrenes were studied. The penetrant transport rate, equilibrium penetrant uptake, and degree of penetrant overshoot were affected by several parameters such as sample crosslinking ratio, penetrant size and temperature of experimentation. Penetrant transport behavior was analyzed with a simple non-Fickian transport equation. Dodecane/polystyrene samples were investigated with respect to their viscoelastic properties. The temperature and frequency dependence of the shear moduli was studied for various samples containing different amounts of dodecane from the dynamic mechanical analysis. The temperature and concentration dependence of the shift functions determined by time-temperature and time-concentration superpositions was analyzed with both entropy model and free volume model. The frequency dependent complex moduli master curves experimentally determined were converted to discrete relaxation time spectra; subsequently, the time dependent material function was determined from the relaxation spectra. The temperature and time dependent bulk moduli from ultrasonic measurement were also studied. The pressure-volume-temperature (PVT) behavior of dodecane/polystyrene systems was studied. The Tait equation was used to describe the PVT behavior of systems. The concentration dependent equilibrium bulk modulus was described by the Tait equation. The volume additivity applied not only in the rubbery region but in the glassy region at an appropriate pressure, when the glass transition temperature of the polymer phase was adjusted to the glass transition temperature of the swollen polymer. Self diffusion coefficient was measured using pulsed gradient spin echo NMR spectroscopy. The temperature and concentration dependence of the mutual diffusion coefficient converted from self diffusion coefficient was analyzed by a couple of free volume models. The applicability of the new transport framework was evaluated by the numerical analysis with the known material parameters determined from several studies mentioned above. Time dependent concentration and polymer stress profiles within polymeric systems illustrate different transport characteristics for varying temperatures. The fractional mass uptake behavior predicted from the model agreed well with that observed from experiments.
Degree
Ph.D.
Advisors
Peppas, Purdue University.
Subject Area
Chemical engineering|Polymers|Plastics
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