Glassy Oligomer Sensitivity to Volatile Organic Compounds

The sensitivity of chiral liquid crystals (CLCs) to their surrounding environments enables them to be useful gas sensors. The various CLCs used in this experiment were studied to determine their sensitivity to certain volatile organic compounds (VOCs), namely toluene, cyclohexane, and ethanol. Liquid crystal siloxane oligomers have a high melting point and form a glassy state at room temperature; they were “physically” modified by being blended with low molar mass compounds with a lower melting point. The liquid crystalline blends were placed in a vacuum-sealed container filled with a gaseous VOC for fifteen minutes. The samples were examined by optical and atomic force microscopies (AFM). Responses to VOC treatment were found in all experiments. AFM studies are especially interesting as they point to subtle changes in the very thin surface layer and, therefore, occur during much shorter times of treatment and/or lower concentrations of VOCs. Each solvent was found to have its own impact on surface pattern studied by AFM. The changes observed in AFM are also discussed from theoretical viewpoint.