Elasticity, Deformation, Rearrangement & Assembly in Complex Fluids

University Of Pennsylvania, Philadelphia PA

Investigators

Abstract

Non-technical Abstract The proposed experimental research will have impact in two major science and technology arenas: how to make a tougher material and how to adapt ideas of liquid crystal display technology to new water-based liquid crystal systems. Broadly, the program develops new ability to formulate and manipulate micro- and nano-particles and macromolecules in solution. Thus the research enhances the science and technology enterprise that underpins applications efforts for US industries involved with sensing/actuation, microfluidics, drug delivery, photonics, printing, coatings, cosmetics and agriculture. The program will train a new generation of scientists and engineers in soft materials, formulation, advanced optical microscopy, electro-optics, microfluidics, rheology & computation. After finishing, PhD students & post-docs enter the work force and strengthen US technological and economic infrastructure; furthermore, a diverse group of undergraduate and high school participants are typically stimulated every summer in our laboratory to pursue STEM education/career choices. Technical Abstract The proposed program aims to advance knowledge about complex fluids and soft materials, but many findings will also interest the hard condensed matter, chemical engineering and materials science communities. The proposed experiments are unified by their focus on micro-mechanics, broadly defined. One set will measure structural and dynamical properties of colloidal glasses and crystals with goals to identify regions within these materials that are "soft" and exhibit increased propensity to deform or rearrange. A second set will investigate lyotropic chromonic liquid crystals. These liquid crystals are unusual in that they twist very easily which leads to formation of chiral structures from achiral mesogens, they exhibit two levels of assembly hierarchy from molecules to rod-mesogens to LC phases, and they are water soluble. The consequences of these properties will be probed by diffusion experiments which track motions of particles dressed by local LC director fields, by study of the competition between elastic energy and molecular assembly hierarchy in "extreme" confined geometries, and in novel "drying" of multi-phase droplets. Collectively, the experiments use advanced optical microscopies, light scattering and rheometry for sample observation, and they require formulation of novel soft materials via controlled suspension chemistry and physics, microfluidics, etc. For example, colloidal particles with different shapes, interactions and potential for in-situ manipulation are/will-be developed.