Colloidal Dynamics in Fluids with Spatiotemporally Modulated Nematic Order

Johns Hopkins University, Baltimore MD

Investigators

Abstract

Non-technical abstract Liquid crystals are fluids composed of rod-shaped molecules. The molecules arrange themselves to be more ordered than in an ordinary liquid but less so than in a crystalline solid. Nematic liquid crystal are an important example of this. The molecules in nematics all orient along a common direction. Impurities, like small particles, can disrupt this order and introduce important new effects. These can include important new optical and magnetic properties that potentially enable new technologies. The behavior becomes even richer when the order in the fluid is spatially patterned or changes with time. This project will investigate experimentally several classes of spatially or temporally varying nematic liquid crystals. They include 'active' nematics that undergo internally driven perpetual flow and that are seeded with magnetic particles and nematics with a striped pattern of ordering that should cause particles to sort themselves spontaneously by size. Among the broader impacts of the project will be research training and education for graduate and undergraduate students. The project will also enable a partnership with a local majority-minority magnet science high school to provide talented Baltimore City students with opportunities for research internships. Technical Abstract The study of inclusions suspended in liquid crystals can lead to important new insight about the viscoelastic and interfacial properties of these materials and can further create novel platforms for manipulation of colloids through unique anisotropic interactions engendered by the fluids. Further, particle-dispersed liquid crystals hold technological promise as composite materials with enhanced properties deriving from coupling of the particles to the liquid crystalline order. This work will seek to advance substantially the understanding of the nature of dynamics in liquid crystalline materials and how the dynamics relates to colloidal transport. The particular goal will be to interrogate fluids with nematic order that are driven from equilibrium, either by internally generated flows in the case of active nematics or by externally imposed electric or stress fields, and to investigate how the spatiotemporal response to this driving couples to the particle motion. The research will focus on three thematically linked projects: (i) active nematic films containing magnetically actuated nano- and micro-particles that will provide new insights into the viscoelastic and hydrodynamic properties of active matter on key intrinsic lengthscales and timescales; (ii) colloidal dynamics in patterned and dynamically modulated liquid crystals configured to test striking predictions for colloidal transport in such environments; and (iii) nanoparticle dynamics in fluids with shear-induced nematic order, where new x-ray scattering techniques can enable novel microscopic perspectives on the structural dynamics of such out-of-equilibrium, driven systems. Broader impacts of the work will include research training for graduate and undergraduate students in physics that will prepare them for careers in academia and industry. The project will also enable a partnership with a local majority-minority magnet science high school to provide talented Baltimore City students with opportunities for research internships.