UC Berkeley

Motivated by the need for developing membranes for biofuel purification, we made pervaporation membranes by casting a polystyrene-b-polydimethylsiloxane-b-polystyrene (SDS) triblock copolymer using toluene, cyclohexane, and hexane as casting solvents. The three solvents have different affinities for each of the blocks of the SDS, which enables the creation of membranes with different nano-morphologies using the same block copolymer. These membranes were used in pervaporation experiments with butanol/water mixtures as the feed solution. We quantify the effect of morphology on butanol and water permeabilities. Poorly-ordered granular morphology, obtained from hexane-cast membranes, is optimal for selective butanol transport. Butanol permeability was a more sensitive function of morphology than water permeability. Butanol uptake measurements showed that morphology had negligible effects on solubility. Therefore, we attribute the dependence of permeability on morphology to differences in diffusivities.