Fundamental studies of liquid crystal nanodroplets

University Of Chicago, Chicago IL

Investigators

Abstract

NONTECHNICAL SUMMARY Liquid crystals consist of elongated molecules that can pack into ordered structures, reminiscent of those assumed by atoms in solid crystals, while remaining fluid. Such ordered structures can be used to manipulate light - a property that is exploited in liquid crystal displays. An interesting feature of liquid crystals is that their structure can be altered through small perturbations at an interface; the liquid crystal can therefore serve as an amplifier, capable of transmitting molecular events over relatively long distances. This property has been used to develop sensors for specific molecules, including toxins, in which adsorption at a liquid interface triggers a series of molecular transformations that result in macroscopic color changes, which can be detected reliably and inexpensively. In this project, the PI will use theory and computation to advance understanding of the series of events, from the moment a molecule or a nanoscopic particle is adsorbed at a liquid crystal-water or at a liquid crystal-vapor interface, to the ensuing structural changes that lead to measurable optical responses. The knowledge gained from this project will contribute to the development of liquid crystal sensing technologies that could augment or surpass those available today, particularly in the realm of biological toxins, thereby leading to important societal benefits. The PI aims to integrate science and computational aspects of this project in part into a summer workshop for high school students and an outreach activity aimed to introduce computation to minority students in inner city Chicago public schools. TECHNICAL SUMMARY This award supports theoretical and computational research and education to advance the fundamental understanding of liquid crystal interfaces. The PI aims to develop predictive molecular models capable of describing atomistic, mesoscale, and macroscopic length scales. The primary physical geometry considered here will consist of liquid crystal droplets, whose interfaces will be in contact with water or air. At the atomistic level, molecular simulations will be used to predict material properties, such as molecular conformation at an interface, that are difficult to measure experimentally and are often unavailable. At slightly longer length scales, coarse-grained models of the molecules will be used to predict and examine the defects that arise in nanoparticle-laden LC systems, thereby providing a direct description of how different morphologies respond to foreign bodies and external stimuli. At even longer length scales, continuum models will be used to understand the arrangement or segregation of surface-active molecules or nanoscopic particles in distinct regions of the droplets and their interfaces, and the formation of ordered structures within such systems. Such models will rely on the material properties and insights generated on the basis of finer, atomistic and coarse-grained levels of description. The theoretical and computational formalism for study of LC systems that will emerge from this project will offer a number of attractive features, including the ability to describe large, fully three-dimensional realizations of the inhomogeneous materials of interest and their structural and thermodynamic properties. That formalism will serve to identify new physical phenomena governed by the coupling of a three-dimensional LC system to a two-dimensional, decorated interface, and will serve as a screening tool for promising materials combinations and for demonstration of the concepts put forth in this proposal. The PI aims to integrate science and computational aspects of this project in part into a summer workshop for high school students and an outreach activity aimed to introduce computation to minority students in inner city Chicago public schools.