2, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
New materials are required for the fabrication of advanced multifunctional garments that allow high moisture vapor transport rates (MVTR) while blocking toxic chemicals and biothreats. In particular, for in-the-field personnel protection from chemical and biological (CB) agents, smart dynamic materials are highly desirable that exhibit a reversible, CB-triggered, rapid transition from a breathable state to a protective state. High breathability is a critical requirement for protective clothing to prevent heat-stress and exhaustion. Current protective military ensembles cannot meet the critical demand of simultaneous high comfort and protection, and provide a passive rather than active response to the environmental threat.
Toward the realization of this new paradigm of adaptive protection, we are developing a chemical threat responsive material based on a surface-functionalized carbon-nanotube (CNT)-membrane, in which vertically-aligned CNTs function as the only pores in an otherwise impermeable, polymeric film. Response to the threat is designed to be triggered by direct chemical warfare agent (CWA) attack to the functional groups at the membrane surface, upon which the membrane switches from a highly breathable state in no-threat environment to a protective state by closing the CNT pore entrance to CWA permeation.
To demonstrate this concept, we first fabricated membranes with sub 5-nm CNT pores and quantified their breathability and rejection properties before functionalization with CWA-responsive polymers. Our results show that these membranes provide MVTR up to 11,000 gr/m2day, thus exceeding state-of-art breathable fabrics (eVent, GoreTex, etc.) even if the moisture conductive pores are only a few nm wide. Complete rejection of 3-nm charged dyes, 5-nm uncharged gold nanoparticles, and ~40-60-nm Dengue virus from aqueous solutions during filtration tests demonstrates that our CNT membranes provide a high degree of protection from bio-threats by size exclusion .
Then, we covalently grafted actuating polymers responsive to G-agent simulants to the surface of these CNT membranes. Upon exposure to simulants, these membranes switch from a breathable state with MVTR> 4,000 gr/m2day to a protective state with MVTR> 1,000 gr/m2day. Initial permeation tests reveal that simulant transport is also reduced by 90% in the protective state. Finally, we demonstrated that a simple liquid base treatment reopens the CNT pores effectively and that regenerated membranes can be re-used for multiple cycles without performance loss.
These results suggest that CNT membranes functionalized with CWA-responsive, actuating polymers could indeed combine on-demand protection with high breathability in a single multifunctional material, and achieve the goal of a lighter, cooler, smarter protection of military and civilian personnel in CB contaminated environments.