• [2012-07-13]

  Date posted: April 23, 2012 Mechanics of Unidirectional Packing of Microbeads in Water

 Title：Mechanics of Unidirectional Packing of Microbeads in Water Lecturer：Li Tan Time： 10:00 am Date:  April 24，2012.   Venue：Conference Room 434, Mechanics Building Host：Prof. Guo-Xin Cao   Abstract：     Direct observation of crystallization dynamics in real space is of special interests to scientists in various disciplines. Although direct observation of transient structural transformation in a nanocrystalline system has been recently achieved using the start-of-the-art aberration-corrected transmission electron microscopy (AC-TEM), the small length scales of individual species in molecular systems still preclude routine observation of crystallization dynamics.  Unidirectional packing of microbeads can serve as experimental model system as their dynamics can be observed and recorded readily in laboratory due to their larger size and slower time scale.  In this seminar, I will present direct observation of a two-dimensional (2D) crystallization process enabled by such a packing process (J. Phys. Chem. B, 2012, ASAP online).  The direct imaging approach not only allows observation of the dynamics in a bead-by-bead fashion (see figure above), but also reveals intriguing phenomena, such as the formation of grain boundaries, disorder-order transitions, and the Moiré patterns which arise when two periodic monolayers are overlaid at certain angles.  In addition, the imaging afforded by confocal microscopy facilities a structural analysis of height-dependent polygonal tiling of the top monolayer, which has implication to the formation of 2D quasicrystals.   About the speaker：
    Li Tan received his PHD from the University of Michigan in 2002. He is an associate professor of Mechanical Engineering at the University of Nebraska-Lincoln (UNL). His main research interests are about Material Design, Self-Assembly and Nanomanufacturing; Mechanics of Nanomaterials and Nanostructures. He got the Multi-Disciplinary Research Award of University of Nebraska at 2009 and the Harold Edgerton Innovation Award of University of Nebraska at 2008.