CAREER: Colloidal Sedimentation and Colloidal Clusters: Exploring New Ways for Making Microstructured Materials with Novel Optical Properties

Ohio State University, The, Columbus OH

Investigators

Abstract

This is a CAREER experimental research project that will explore colloidal sedimentation and colloidal cluster formation as a basis for generating new materials with important optical properties, such as photonic band gaps. Monodisperse colloids show great promise as building blocks for tomorrow's photonic materials since they self assemble into crystals with lattice repeats that are of the order of the wavelength of visible light. Two shortcomings, however, are low index of refraction for currently available monodisperse (crystallizable) spheres and crystal structures only moderately favorable for photonic bandgaps. To address the first issue this project will explore fluidization of colloidal materials as an effective means of particle size segregation. The final goal of this phase of the project is to narrow the size distribution of high index polydisperse particles, such as Titania, so they can be crystallized. The other research phase of the project will seek new colloidal crystal structures which have large predicted photonic bandgaps. Current colloidal crystals are nearly all grown from particles with spherically symmetric interaction potentials. Small clusters of spherical particles will have more complex inter-cluster interaction potentials and promise new crystal structures with potentially larger band gaps. Techniques for monodisperse colloidal cluster formation and crystallization will therefore be explored. The educational portion of the project will involve public outreach and collaboration with science museums. Exhibits based on giant soap films will be developed and new soap film physics experiments will be developed for high schools and colleges. Graduate and undergraduate students will participate in all phases of the proposed research. A graduate course on soft condensed matter physics will also be developed, enhancing the physics curriculum at the Ohio State University. %%% This is a CAREER project that investigates colloidal crystalline materials that have interesting and technologically relevant optical properties. Opal is a naturally occurring gemstone gemstones that is a colloidal crystal built up of identical microscopic sand grains. Its iridescent properties show the profound influence that colloid lattices can have on light rays. Calculations show that colloidal crystalline materials, not unlike opal gems, called photonic bandgap materials, can be used to bend light rays around very sharp curves, much sharper than can be achieved by bending a glass fiber optic material. Further, by altering the properties of the sand grains and their structure, colloidal crystals can be synthesized that will reflect, but not transmit, a particular range of colors, no matter what the position of the light source. When such materials are used to encase optical fibers the light cannot leak out, no matter how tight the turns. . Unfortunately the current state of the art in synthesizing colloidal crystals can not produce the right size particles nor arrange colloid particles in the crystal structures required by theory. This project addresses both these issues as it proposes ways to isolate new colloids and from them build new colloid crystals. This research in soft condensed matter physics may facilitate next generation computing and communications technologies. The educational portion of the project will involve public outreach and collaboration with science museums. Exhibits based on giant soap films will be developed and new soap film physics experiments will be developed for high schools and colleges. The project also provides an excellent means of educating students in this relatively new branch of physics through museum exhibits, high school and college laboratory experiments, and an advanced graduate course.