Braun Group People
Weon-Sik Chae,
Former Post-Doctoral Researcher
Ph D. Yonsei University, 2003. 8
Post-Doc. Yonsei University, 2003. 9-2005. 4
Post-Doc. MSE in UIUC, 4/2005-12/2007
One of my research interests is on confinement effects of mesophased materials within nanospaces. Generally, in bulk systems, the structure of mesophased material varies according to the concentration of surfactant and inorganic precursor, the solvent, and temperature, as all these parameters modify the lyotropic mesophases responsible for the formation of the mesoporous material [1]. When the precursors to the mesostructured materials are introduced into a confined environment, additional factors including structural frustration, interfacial interactions, and confinement-induced entropy loss work can strongly modulate the structure of the mesophase [2]. As an example, 3D assembled silica colloids are possible to be prepared through a templating route by using a polymer inverse opal. Each component silica particle has mesoporosity, and the internal mesostructures of the confinement-induced component colloidal particles can be controlled by the surface chemical properties of, diameter of, and number of interconnecting windows between the spherical voids (Figure 1). It is hopefully expected that the 3D assembled mesoporous silica particles may provide unique optical and photonic properties.
Figure 1. 3-dimentionally (3D) assembled mesoporous silica colloids and their different internal structures.
The other one of my research is on patterning of dielectric colloidal particles within an opal. A dielectric colloidal particle with a high refractive index, such as ZnS semiconductor, can be used as a component particle, as shown in Figure 2. An optical tweezers, which can make and hold a specific pattern, is a decent tool to move a pattern of dielectric particle to inside of an opal. I hopefully expect the specific pattern written in the opal provides a unique waveguide structure as a defect pattern within the synthetic opal [3].
Figure 2. Synthesized ZnS colloid (d = 200 nm) and their patterning in index matched solvent and opal.
References
1) Raman, N. K.; Anderson, M. T.; Brinker, C. J. Chem. Mater. 1996, 8, 1682.
2) Wu, Y.; Cheng, G.; Katsov, K.; Sides, S. W.; Wang, J.; Tang, J.; Fredrickson, G. H.; Moskovits, M.; Stucky, G. D. Nature Mater. 2004, 3, 816.
3) Lee, W. S.; Pruzinsky, A.; Braun, P. V. Adv. Mater.2002, 14, 271.
Professor Paul Braun • Phone: +1.217.244.7293 • Fax: +1.217.333.2736 • Email: pbraun@illinois.edu
Department of Materials Science and Engineering • University of Illinois at Urbana-Champaign