Journal of Membrane Science, Vol.566, 35-43, 2018
Block copolymer membranes with catecholic bolaamphiphile assemblies
We report the first use of the assemblies of catecholic bolaamphiphilic compound, i.e., bis-(N-alpha-amido-3,4-di-hydroxyphenylalanine) - 1,7-heptane dicarboxylate (DOPA-C7), as an organic filler for gas separation membranes. Specifically, the membranes were prepared by adding the assembly fillers to a block copolymer matrix, i.e., nonpolar polystyrene-b-polybutadiene-b-polystyrene (SBS) or polar poly (ether-b-amide) (PEBAX). The interaction between the filler and matrix was investigated regarding the structure, morphology, and CO2/N-2 separation performance. The strongly interacting PEBAX/DOPA-C7 membranes showed a typical trade-off behavior, i.e., a decrease in CO2 permeability and increase in CO2/N-2 selectivity with the filler contents. In contrast, the weakly interacting SBS/DOPA-C7 interestingly showed an improved CO2/N-2 selectivity, from 14.1 to 21.1, with a slight increase in CO2 permeability (from 347.5 to 349.7 Barrer) owing to the catechol group of DOPA-C7 that can function as a Lewis base. This indicates that very strong interactions between the polymeric matrix and filler could have a negative impact on the gas separation performance. This work not only explores the importance of a polymer matrix, but also opens up the feasibility of using a catecholic compound in gas separation membranes.