Polymer-polymer nanocomposite membranes as breathable barriers with electro-sensitive permeability

In this study, a new class of membranes has been developed, which is based on a polymer-polymer nanocomposite that consists of nanodomains of hydrophilic polyelectrolyte gels within a hydrophobic polymer host matrix. The hydrophobic host matrix provides a mechanically strong, durable, flexible barrier, while the polyelectrolyte provides a highly water permeable (breathable) membrane. A co-continuous morphology ensures transport across the membrane in the ionic phase. Two membrane concepts have been developed: (1) nanopore-filled membranes and (2) nanofiber encapsulated membranes. Nanopore-filled membranes entail the synthesis of nanoporous polymers that are subsequently filled (via graft polymerization) with polyelectrolyte gels, while nanofiber encapsulated membranes consist of fabricating polyelectrolyte nanofiber meshes (via electrospinning) that are subsequently encapsulated in a durable barrier material. A key feature in these membranes is responsiveness, where the nanoscale cocontinuous phase of ionic gel can contract and expand in response to electrical stimuli providing "tunable" permeability valves - maximum water permeability in non-threat situations and reduced agent permeability in situations when a chemical threat is imminent. This responsive behavior (electro-sensitive permeability) was demonstrated in the nanopore-filled membranes, where the membranes were nearly impermeable to dimethyl methylphosphonate (DMMP; a simulant of the nerve agent Sarin) with the application of a low voltage and selectively permeable with the removal of voltage. In addition to responsive behavior, nanopore-filled membranes showed intriguing properties, such as a 10 times higher selectivity (water/agent permeability) compared to current standard materials used in chemical protective clothing with a high water vapor transmission rate (breathable) and mechanical strength similar to the matrix membrane in both dry and hydrated state, unlike the bulk ionic gel, which was many orders of magnitude lower in strength in the hydrated state. Also, successful synthesis of nanofiber encapsulated membranes was demonstrated.