Self-reporting and self-regulating liquid crystals

Abstract

Liquid crystals (LCs) are anisotropic fluids that combine the long-range order of crystals with the mobility of liquids(1,2). This combination of properties has been widely used to create reconfigurable materials that optically report information about their environment, such as changes in electric fields (smart-phone displays)(3), temperature (thermometers)(4) or mechanical shear(5), and the arrival of chemical and biological stimuli (sensors)(6,7). An unmet need exists, however, for responsive materials that not only report their environment but also transform it through self-regulated chemical interactions. Here we show that a range of stimuli can trigger pulsatile (transient) or continuous release of microcargo (aqueous microdroplets or solid microparticles and their chemical contents) that is trapped initially within LCs. The resulting LC materials self-report and self-regulate their chemical response to targeted physical, chemical and biological events in ways that can be preprogrammed through an interplay of elastic, electrical double-layer, buoyant and shear forces in diverse geometries (such as wells, films and emulsion droplets). These LC materials can carry out complex functions that go beyond the capabilities of conventional materials used for controlled microcargo release, such as optically reporting a stimulus (for example, mechanical shear stresses generated by motile bacteria) and then responding in a self-regulated manner via a feedback loop (for example, to release the minimum amount of biocidal agent required to cause bacterial cell death).