Design Rules for Chemostrictive Materials as Selective Molecular Barriers

As materials become more advanced, there are opportunities to incorporate multiple engineering functions into them, including chemical sensing coupled to actuation for the control of permeability. Recent interest in chemically responsive materials motivates the question of how to design and optimize such systems to address a specific molecular target. This work formulates an engineering analysis of "chemostrictive materials" that respond to a chemical stimulus by reducing their permeability through constriction of their void volume. The extent to which the material can constrict to reduce chemical diffusivity and the sensitivity of the material to constrict in the presence of a target chemical are explored as parameters which affect the barrier properties of the materials. Further examined are materials that are augmented to also degrade the chemical target by an assumed first-order decomposition reaction in addition. As a case study, the minimum material specifications for chemostrictive personal protective equipment (PPE) designed to reduce exposure to a variety of chemical hazards are presented. Chemostrictive materials possess potential as ideal components for advanced PPE that is highly permeable under safe conditions to allow for comfort and temperature regulation but constricts in the presence of contaminants to protect the wearer.