(336a) 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.