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Abstract Surface‐supported liquid crystals (LCs) that exhibit orientational and thus optical responses upon exposure to ppb concentrations of Cl2gas are reported. Computations identified Mn cations as candidate surface binding sites that undergo redox‐triggered changes in the strength of binding to nitrogen‐based LCs upon exposure to Cl2gas. Guided by these predictions, μm‐thick films of nitrile‐ or pyridine‐containing LCs were prepared on surfaces decorated with Mn2+binding sites as perchlorate salts. Following exposure to Cl2, formation of Mn4+(in the form of MnO2microparticles) was confirmed and an accompanying change in the orientation and optical appearance of the supported LC films was measured. In unoptimized systems, the LC orientational transitions provided the sensitivity and response times needed for monitoring human exposure to Cl2gas. The response was also selective to Cl2over other oxidizing agents such as air or NO2and other chemical targets such as organophosphonates.
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Designing chemically selective liquid crystalline materials that respond to oxidizing gases
Computational methods can provide first-principles insights into the thermochemistry and kinetics of reactions at interfaces, but this capability has not been widely leveraged to design soft materials that respond selectively to chemical species. Here we address this opportunity by demonstrating the design of micrometer-thick liquid crystalline films supported on metal-perchlorate surfaces that exhibit selective orientational responses to targeted oxidizing gases. Initial electronic structure calculations predicted Mn 2+ , Co 2+ , and Ni 2+ to be promising candidate surface binding sites that (1) coordinate with nitrile-containing mesogens to orient liquid crystal (LC) phases and (2) undergo redox-triggered reactions upon exposure to humid O 3 leading to a change in the strength of binding of the nitrile group to the surface. These initial predictions were validated by experimental observations of orientational transitions of nitrile-containing LCs upon exposure to air containing parts-per-billion concentrations of O 3 . Additional first-principles calculations of reaction free energies of metal salts and oxidizing gases predicted that the same set of metal cations, if patterned on surfaces at distinct spatial locations, would provide LC responses that allow Cl 2 and O 3 to be distinguished while not responding to environmental oxidants such as O 2 and NO 2 . Experimental results are provided to support this prediction, and X-ray diffraction measurements confirmed that the experimentally observed LC responses can be understood in terms of the relative thermodynamic driving force for formation of MnO 2 , CoOOH, or NiOOH from the corresponding metal cation binding sites in the presence of humid O 3 and Cl 2 .
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- PAR ID:
- 10297264
- Date Published:
- Journal Name:
- Journal of Materials Chemistry C
- Volume:
- 9
- Issue:
- 20
- ISSN:
- 2050-7526
- Page Range / eLocation ID:
- 6507 to 6517
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d1tc00544h
