The elucidation of elastomeric network properties that affect the pervaporation membrane performance

The focus of this thesis was to investigate the influence of the elastomeric network structure properties on pervaporation performance for the removal of halogenated organics at dilute concentration from water. This involved studies with elastomeric unimodal and bimodal networks as the thin film separating layer on composite pervaporation membranes. Cross-linking end-linking polymers using addition polymerization with a vinyl-hydrosilylation system allowed for the formation of elastomeric networks of known and controlled structure. Poly(dimethylsiloxane) was selected as the chemical backbone for the end-linking and cross-linking agent due to its relatively high affinity for halogenated organics over water.; Statistical experimental designs were applied for the elastomer formation and pervaporation performance studies. An automated pervaporation test apparatus with 3 radial cross-flow test cells permitted testing at specified set point feed temperatures and permeate pressures. The feed and permeate concentrations and permeate mass flows are measured on-line as well; pertinent operating parameters were stored electronically with this apparatus. The author was involved in the design, fabrication, and implementation of this apparatus and performed the subsequent modification to permit feed flow rates in the turbulent regime.; It was concluded from the pervaporation studies with unimodal and bimodal membranes that the elastomeric network structure becomes non-affine or exhibits phantom behaviour selectivity for the organic component decreases. The non-affine behaviour of elastomeric bimodal networks was due to an increase in fluctuations of the shorter chains over their unimodal counterpart. The increase in junction fluctuations results in a decrease in allowable conformations of the chains. The affect of this is a decrease in selectivity for the organic component.; The concept of "Membrane Architecture" is utilized to recommend a blueprint for developing elastomeric pervaporization membranes for particular applications. If the selectively permeating species is the lowest molar volume species then the elastomeric network structure should be in the phantom regime. This will reduce the allowable chain conformations thus increasing mass transfer resistance in the elastomer for the larger molar volume species. When the selectively permeating species is the largest molar volume species, then the elastomeric network structure should be in the affine regime. This will allow for a relatively large number of chain conformations and provide for increased solvent-polymer interactions of the larger molar volume species. The affect is to reduce diffusional resistance of the larger molar volume species.