Open Access Kent State (OAKS)

Fourier transform infrared spectroscopy is often used to study, liquid crystals and liquid crystal systems. In this work, the factors that influence the IR absorbance of nematic liquid crystals and their consequences on FT-IR imaging are examined. In the IR spectrum of E7, ordering in the nematic phase causes a 28.7% reduction in the nitrile band height relative to the isotropic phase, and the combination of ordering and liquid crystal director alignment causes a 65.0% decrease in the nitrile band height. For a phase-separated blend of E7 and 10% NOA65 polymer, the FT-IR images were found to be concentration-based for the polymer-specific carbonyl band and phase/alignment-based, which masked the concentration dependence, for the liquid crystal-specific nitrile band. These findings were exploited to produce an FT-IR image or the isotropic-to-nematic phase transition of neat E7. This transition image emphasizes the dependence of liquid crystal bands on ordering and alignment and the need for caution in the interpretation of FT-IR images of liquid crystals and liquid crystal systems.

The use of photocrosslinkable polymers and photomasks was proposed as a means of reducing the number of raw materials necessary to create a chemical sensor array. To test this hypothesis, poly(vinyl cinnamate) was crosslinked to various degrees with the use of a photomask, exposed to a binary solvent vapor of benzonitrile and dimethyl formamide, and examined by FT-IR imaging. The results illustrate that FT-IR imaging is effective for visualizing the patterning of the crosslink density of a polymer film as well as the temporal and spatial sorption patterns of different solvent vapors. The FT-IR images show that the decrease in sorption capacity with crosslink density is solvent-specific, which suggests that photocrosslinkable polymers can be used to reduce the number of raw materials needed to create a chemical sensor array. The potential disadvantage of using glassy polymers as chemical sensors is also demonstrated by the temporal FT-IR images of solvent desorption.