Past studies have reported that confinement of liquid crystals (LCs) within micrometer-sized droplets dispersed in aqueous phases (e.g., LC-in-water emulsions) provides a versatile platform for the design of droplet-based LC sensors that can respond sensitively to the presence of amphiphilic analytes in aqueous environments. Here, we report a novel approach to design responsive materials based on LC emulsions with improved colloidal stability. Our approach makes use of surfactant-nanoparticle complexes (CnTAB/SiO2, n=8,12,16) that adsorb to the LC droplet interface to stabilize LC emulsions for extended periods. The LC droplet size remains largely unchanged over time (e.g., droplet diameter ≤ 4 μm over 2 months), and droplets that sediment over this time period can be readily dispersed, demonstrating the remarkable colloidal stability of the system. Moreover, the addition of amphiphiles (e.g., SDS) to these CnTAB/SiO2-stabilized LC emulsions triggers bipolar-to-radial changes in LC droplet configurations similar to those observed in bare LC emulsions that can be readily observed using polarized light. Our results also show that bipolar-to-radial ordering transitions induced by SDS depend upon the carbon chain length of the CnTAB surfactant used to form the CnTAB/SiO2 stabilizing complex, suggesting the possibility of using this particle adsorption strategy to tune both droplet stability and the sensitivity/selectivity of response. Overall, our observations suggest that LC emulsions stabilized by CnTAB/SiO2 complexes provide a potential approach to design liquid-droplet sensors with improved colloidal stability for the detection of aqueous analytes.

Liquid crystal emulsions stabilized by nanoparticle-surfactant complexes

ACS Spring Meeting 2021

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