(14a) Casting Solvent Effects on Block Ionomer Morphology and Corresponding Property Changes

The role of casting solvent has been shown to play an important role in the microstructure of block copolymers that have not been, or are not able to be, annealed. Casting solvent plays a stronger influence in block ionomer ordering because these materials can possess strongly incompatible blocks that are easily templated in various solvent environments. Here, this principle is utilized to produce different morphologies from a sulfonated pentablock ionomer. The judicious selection of polar and nonpolar solvents, and their mixtures, translates to different solution structures that in turn create different solid film morphologies. Transmission electron micrographs and tomograms provide morphological information amongst samples varying in sulfonate concentration and casting solvent(s). The obtained data shows that casting solvent identity does, in fact, alter the ordering of the pentablock copolymer into vastly different morphologies. Following identification, the effect of the produced morphologies on swelling (water uptake), water vapor transmission rate (WVTR), and water-based semi-permanent deformation will be presented. Preliminary results indicate that geometric restriction of the sulfonated, hydrophilic phases reduces water uptake. Additionally, systems that exhibit more long range order have a lower apparent sulfonate-domain percolation threshold that results in maintained, high WVTR at low sulfonate concentration. Lastly, more disordered sulfonate domains translate to more easily deformed microstructures under the stress of liquid water and heat.