Surface Reconstruction of Glass Forming Liquid Crystals s a Tool for Sensing Volatile Organic Compounds*

Glass forming cholesteric liquid crystalline oligomers (CLCO) based on siloxanes are known for their ability to form focal conic domains at temperatures higher than their glass transition temperature. These domains form a peculiar pattern on a surface of CLCOs that looks like double spirals and can be observed by Atomic Force Microscopy (AFM). This research demonstrated that the addition of low molar mass compounds of different polarity blended with oligomers changes the structure of the domains and makes the surface pattern sensitive to volatile organic compounds (VOCs) in the air. It was also demonstrated that this response is selective with respect to the nature of the particular VOC. We also discovered that the double spiral pattern is able to untwist and form less tight spirals. This new and unique behavior demonstrates the importance of mechanical tension in a glassy state and the plasticizing effect of VOCs. Interestingly, this surface reconstruction is reversible and spiral pattern appears after VOC removal. The response of these blends to many VOCs was studied by the AFM and UV-VIS spectroscopy. Each solvent uniquely reconstructs the surface and this provides a way to identify the solvent used.