CONCENTRATION AND TEMPERATURE-DEPENDENCE OF DIFFUSIONAL DEBORAH NUMBER DURING DODECANE TRANSPORT IN CROSS-LINKED POLYSTYRENE

The diffusional Deborah number, De, defined as the ratio of characteri stic relaxation time to characteristic diffusion time was determined a s a function of concentration and temperature in the dodecane transpor t process in polystyrene. The characteristic relaxation time was obtai ned from the viscoelastic properties of dodecane/polystyrene systems m easured by a dynamic mechanical analyzer. The characteristic diffusion time was obtained from the concentration and temperature dependence o f the diffusion coefficient measured by NMR PGSE method. Above the roo m temperature the Deborah number changed significantly during isotherm al transport process; however, the transport mechanism did not deviate from the Fickian transport as the order of De was still greater than 1. Around the room temperature the transport mechanisms represented by the resulting diffusional Deborah number changed significantly as the order of magnitude approached 1 with the temperature decreasing from 50 degrees C to the room temperature. The transport mechanism predicte d from the diffusional Deborah number was verified by the diffusional exponent, n, of an exponential time-dependence of the penetrant uptake .