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Anisotropic Solvation of Rod-Shaped Nanostructures in Liquid Crystalline SolventsLiquid crystal devices (LCDs) have revolutionized modern display technologies. Exploring the properties of composite materials consisting of a guest molecule or nanostructure in the liquid crystal is motivated by the need to make displays brighter while consuming less battery power. As a physical chemistry group, our interest in liquid crystals is centered around the understanding of how solutes, and in particular rod-shaped polymers, align in an anisotropic medium such as a liquid crystal. We are studying the orientation and degree of alignment of conductive light emitting polymers in thermotropic liquid crystals by using single molecule polarization spectroscopy. Because of the much larger size of a polymer solute compared to the liquid crystalline molecules, the solute is aligned to a much greater extent. This is in agreement with Onsager’s prediction that, in a binary nematic mixture of short and long rods, the long rods experience an enhanced alignment.
The aim of this project is to gain a deeper understanding of how molecular solvent-solute interactions govern
short and long range orientation, alignment and diffusion of solutes in liquid crystalline solvents. We will
examine the anisotropic solvation and diffusion of macro-molecules as a function of size, shape, liquid
crystalline phase, and solvent order. By using a combination of ensemble and single molecule polarization
spectroscopy we are able to extract solute order parameters, which give us detailed information about anisotropic
solvation in liquid crystals.
The figure above shows a typical fluorescence transient (left) of polymer molecules diffusing in a liquid crystal. Each burst corresponds to a single molecule passing through the laser excitation spot. The fluorescence is split into two orthogonally polarized components (blue and red trace), which allows us to calculate the polarization anisotropy of each molecule and then generate a histogram of polarization anisotropy values (right). Modeling of the polarization anisotropy distribution allows us to extract the degree of orientational alignment of the solute in the liquid crystal. Group members involved: Publications:
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