Transport phenomena through polymeric systems

Glass Transition Temperatures of Polymers

Comparative study of sorption and permeation techniques for the determination of heptane and toluene transport in polyethylene membranes

The systematic study of small molecule transport in polymers has received increasing attention since the classic paper by Graham in 1866 presented the qualitative features of fixed gas diffusion in polymer membranes.1 Most of the published research, until about 1950, focused on diffusion of small molecules in rubbery polymers. In this regard, a rather consistent transport mechanism involving solution of penetrant in the polymer followed by diffusion through the membrane characterised virtually all of the many polymer-penetrant systems studied. Small deviations from this diffusion model were encountered for rubbery systems complicated by crystalline regions susceptible to reordering by an interacting or plasticising vapour or liquid penetrant. The more recent study of transport of penetrants in organic glasses revealed that transport in the glassy state is characterised more accurately by anomalous or complicated behaviour than it is by a simple, unifying mathematical or conceptual model. These complications include dual sorption modes for even the most noble of gases in organic glasses, time dependent boundary conditions for vapour transport, diffusion coefficients characterised by an apparent time dependence, polymer relaxations providing the rate determining transport step (rather than diffusion), polymer fracture and microfracture (crazing) accompanying transport, and a significant change in the transport mechanism as the glass transition temperature is traversed. These nonideal or anomalous behavioural features will be treated explicitly and in detail for it is these independent, seemingly unrelated observations that describe the diffusion and sorption of gases and vapours in glassy polymers.

R. Mallinder

Papers

Solution and diffusion of gases in poly(vinylchloride)