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ACS Appl Mater Interfaces

Title:		Structural and Optical Response of Polymer-Stabilized Blue Phase Liquid Crystal Films to Volatile Organic Compounds
Author(s):		Yang Y; Kim YK; Wang X; Tsuei M; Abbott NL;
Address:		"Smith School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853, United States. Department of Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States"
Journal Title:		ACS Appl Mater Interfaces
Year:		2020
Volume:		20200908
Issue:		37
Page Number:		42099 - 42108
DOI:		10.1021/acsami.0c11138
ISSN/ISBN:		1944-8252 (Electronic) 1944-8244 (Linking)
Abstract:		"Engineering useful mechanical properties into stimuli-responsive soft materials without compromising their responsiveness is, in many cases, an unresolved challenge. For example, polymer networks formed within blue-phase liquid crystals (BPs) have been shown to form mechanically robust films, but the impact of polymer networks on the response of these soft materials to chemical stimuli has not been explored. Here, we report on the response of polymer-stabilized BPs (PSBPs) to volatile organic compounds (VOCs, using toluene as a model compound) and compare the response to BPs without polymer stabilization and to polymerized nematic and cholesteric phases. We find that PSBPs generate an optical response to toluene vapor (change in reflection intensity under crossed polars) that is sixfold greater in sensitivity than the polymerized nematic or cholesteric phases and with a limit of detection (140 +/- 10 ppm at 25 degrees C) that is relevant to the measurement of permissible exposure limits for humans. Additionally, when compared to BPs that have not been polymerized, PSBPs respond to a broader range of toluene vapor concentrations (5000 vs <1000 ppm) over a wider temperature interval (25-45 vs 45-53 degrees C). We place these experimental observations into the context of a simple thermodynamic model to explore how the PSBP response reflects the effect of toluene on competing contributions of double-twisted LC cylinders, disclinations, and polymer network to the free energy that controls the PSBP lattice spacing. Overall, we conclude that the mechanical and thermal stability of PSBPs, when combined with their optical responsiveness to toluene, make this class of self-supporting LCs a promising one as the basis of passive and compact (e.g., wearable) sensors for VOCs"
Keywords:		blue phase liquid crystal optical and structural response polymer network sensor volatile organic compound;
Notes:		"PubMed-not-MEDLINEYang, Yu Kim, Young-Ki Wang, Xin Tsuei, Michael Abbott, Nicholas L eng 2020/08/17 ACS Appl Mater Interfaces. 2020 Sep 16; 12(37):42099-42108. doi: 10.1021/acsami.0c11138. Epub 2020 Sep 8"