Solid State Sensing of Nonpolar VOCs Using the Bistable Expansion and Contraction of Helical Polycarbodiimides

Abstract

A molecular switch that operates from the discrete expansion and contraction of helical polymer chain segments in response to chemical environment is studied and applied to volatile organic compound (VOC) sensing. Populations of expanded/contracted segments of poly(N-(1-naphthyl)-N′-(n-octadecyl)carbodiimide (polyNOC) are found to be sensitive to solvent composition yet can be retained and modulated in the solid state. Previous studies have established that the two discrete local conformations of polyNOC can be measured in solution using infrared spectroscopy. Infrared spectroscopy, differential scanning calorimetry, and grazing incidence X-ray diffraction are used to study polyNOC in the solid state at various conformation populations. Results provide insight into the role of the core-dual shell structure of polyNOC on the mechanism of reversible switching between expanded/contracted, helical-rod conformations. Solid-state switching is applied to sensing VOC’s using infrared spectroscopy for transduction with the ability to distinguish between similar chemical compositions/structures, both polar and nonpolar—even between n-hydrocarbons.