Master curve captures the effect of domain morphology on ethanol pervaporation through block copolymer membranes

We report on the effect of changing nanoscale morphology on pervaporation of ethanol/water mixtures through block copolymer membranes. Experiments were conducted using polystyrene-b-polybutadiene-b-polystyrene (SBS) copolymers with polybutadiene (PB) as the ethanol transporting block, using an 8 wt% ethanol/water mixture as the feed. The volume fraction of the transporting PB microphase, ϕPB, was varied from 0.63 to 0.93, and the overall molecular weight of the copolymer, Mn, was varied from 34 to 207 kg mol−1. The normalized ethanol permeability through the membrane, PE/ϕPB, and the ethanol selectivity, αEW, increase with increasing Mn. In the case of ϕPB = 0.73 and 0.80 systems (cylindrical morphologies), PE/ϕPB and αEW appear to reach a plateau in the high Mn limit. Master curves are obtained when all of the permeation data are plotted in the PE/ϕPB and PW/ϕPB versus αEW format. The performance of the SBS membrane with Mn = 207 kg mol−1 and ϕPB = 0.80 is tested using a fermentation broth mixture.