First Principles Design Of Liquid Crystalline Based Chemoresponsive Materials

Computational chemistry calculations can be used to elucidate how organic molecules orientate at interfaces and respond to an external stimuli, but this capability is not widely leveraged in the design of soft material interfaces. One promising platform to study these interactions is chemoresponsive liquid crystals (LCs). LCs are fluid phases within which molecules exhibit preferred orientations in the bulk. The orientations of LCs can be manipulated by molecular interactions occurring at interfaces. Therefore, LCs are capable of providing insight into molecular events at solid-liquid crystal interfaces by amplifying changes at the surface into the macroscopic-scale, which can be transduced optically. These chemoresponsive LCs can also act as gas sensors because a desired analyte can bind or react at an interface to disrupt the LC ordering causing an optical transition. This also provides a unique opportunity to study how interfacial properties can change depending on reaction thermochemistry and kinetics.In this dissertation, we utilize first-principles density functional theory (DFT) calculations, transport modeling, microkinetic modeling, and reaction kinetic experiments to elucidate detailed atomic-scale surface structures and reactivity of LC chemoresponsive materials to design new materials with optimal properties such as high sensitivity and selectivity to a desired analyte. This methodology was used to successfully design LC chemoresponsive materials to new analytes (SO2, Cl2, O3, or H2). While these LC chemoresponsive materials typically operate based on disruption of the LC ordering via displacement of the strongly bound LC molecules by the analyte, we also discuss new mechanisms. This includes developing new chemoresponsive LC systems with reactive surfaces (metals, alloys, and metal oxides) and developing of detection mechanisms that either operate on simple elementary reactions (e.g. Cl2 or H2 dissociation), oxidation of the surface (e.g. O3 or Cl2 oxidation of metal salt surfaces), reaction between two analytes at the surface (e.g. SO2 + H2O reaction), or even a more complex reaction (e.g. hydrogenation of the benzonitrile group). Our insights from this study demonstrate a fundamental convergence between principles governing functional interfaces with those governing heterogeneous catalysis.