Nanostructured Block Copolymer Membranes for Biofuel Production

We report on the effect of changing nanoscale morphology on pervaporation of alcohol/water mixtures through block copolymer membranes.  Experiments were conducted using polystyrene-b-polybutadiene-b-polystyrene (SBS) and polystyrene-b-polydimethylsiloxane-b-polystyrene copolymers with polybutadiene (PB) and polydimethylsiloxane (PDMS) as the alcohol transporting blocks.  The morphology of the membranes is governed by the composition of the block copolymer while the size of the domains is governed by the molecular weight of the block copolymer.  The volume fraction of the transporting PB and PDMS microphases was varied from 0.63 to 0.93 and 0.59 to 0.83 for PB (f_PB) and PDMS (f_PDMS) microphases, respectively.  The overall molecular weight of the copolymers, M_n, was varied from 34 to 207 kg mol^-1.  Normalized ethanol permeability through the membrane, P_E /f_PB  , and the ethanol selectivity, a_EW, increase with increasing M_n for SBS, but P_E /f_PDMS  and a_EW are not a strong function of M_n for SDS based membranes. Master curves are obtained when all of the permeation data are plotted in the P_E /f_transporting, P_W/f_transporting, versus a_EW format.