Temporary peelable coatings (TPCs) protect military equipment surfaces against chemical warfare agents (CWAs) by absorbing liquid contamination, thereby reducing the contact and vapor hazards to personnel. An understanding of the liquid CWA mass-transport mechanisms governing sorption is critical toward optimizing coating properties for reducing these hazards. We applied Nuclear Magnetic Resonance profiling to resolve mass-transport mechanisms of the CWA bis(2-chloroethyl) sulfide (sulfur mustard) simulant, methyl salicylate (MS), through a two-layered polyurethane TPC, where each layer absorbs liquids using different mechanisms (passive diffusion through pores and solubilization with the liquid). Depth profiles obtained at increasing time-points post-contamination demonstrated (a) dynamics of MS volume spread through the coating, (b) polymer swelling by a significant increase in the thickness of one of the layers and its relationship with overall coating thickness and contamination mass, and (c) preferential sites within the bulk for MS localization. Information of the type obtained from this exemplar system can be correlated to the physiochemical properties of the liquid contaminant as well as contact hazard and vapor hazard measurements to facilitate next generation coating development. Moreover, time-resolved determination of multiple liquid mass-transport mechanisms in an optically opaque multilayered coating were demonstrated noninvasively.
Gazi, E., Mitchell, S.J. Nuclear magnetic resonance profiling of chemical warfare agent simulant mass-transport through a multilayered polymeric coating. J Coat Technol Res9, 735–743 (2012). (open access) https://doi.org/10.1007/s11998-012-9416-8