Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session W1: Direct Imaging of Crystal Nucleation |
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Sponsoring Units: DCMP Chair: Arjun Yodh, University of Pennsylvania Room: Oregon Ballroom 201 |
Thursday, March 18, 2010 11:15AM - 11:51AM |
W1.00001: Nucleation of Hard Sphere Colloidal Crystals Invited Speaker: Colloids, micron-sized particles suspended in a molecular solvent, are much larger than atoms or molecules, such that confocal microscopy allows to track individual particles in a dense three dimensional system, in real time. The colloids minimize their free energy, mimicking atoms and molecules; thus, colloidal suspension is a perfect model system, where both the collective behavior and the behavior of individual particles are experimentally accessible. Hard sphere colloids are among the simplest systems which exhibit crystal nucleation; therefore, this system provides an important insight onto the basics of nucleation, which are very poorly understood. I will present our recent studies of the three-dimensional morphology of crystal nuclei in a system of hard sphere colloids. The nuclei, observed by direct confocal imaging, are not compact or spherical, as most theories of nucleation assume. Instead, the nuclei adopt a wide range of somewhat ramified morphologies; the existence of these morphologies modifies the free energy of the nuclei and results into an enormous increase in the rates of crystal nucleation. The applicability of these results to a wider range of atomic and molecular systems will be discussed. [Preview Abstract] |
Thursday, March 18, 2010 11:51AM - 12:27PM |
W1.00002: The initial stages of template-controlled CaCO3 formation revealed by Cryo-TEM Invited Speaker: |
Thursday, March 18, 2010 12:27PM - 1:03PM |
W1.00003: Nanocrystal Formation and Cation Ordering in Li-Intercalation Metal Phosphate. Invited Speaker: The control of the nucleation and growth behavior of crystals from solutions or melts in inorganic compounds is scientifically and technologically of great importance for fabricating crystalline particles of optimum size and shape as well as with a narrow size distribution. Here, we show the formation of metal phosphate nanocrystals at a high temperature using high-resolution transmission electron microscopy (HRTEM), of which new developments allow one to determine the structural variation in real time in a variety of nanoscale materials. Lithium iron phosphate (LiFePO4) was selected as a multi-component model system for this atomic-level in situ observation. Since the report of the impressive lithium intercalation reaction in LiFePO4 (S.-Y. Chung et al., Nature Mater., 1, 123 (2002)), a great deal of attention has been paid to the phosphate as an alternative cathode material in lithium-ion batteries due to its outstanding thermochemical stability and environmental benignity. Our present study will be able to suggest practical approaches to the effective synthesis of metal phosphate nanocrystals, as well as to elucidate the fundamental mechanism for nucleation and growth during crystallization of complex inorganic materials. And also in this presentation the observations of a variety of lattice defects in ordered olivine LiFePO4 crystals after rapid phase transformation during crystallization will be presented, showing notable distribution behaviors of the defects. For this direct observation, in siu and ex situ high-resolution transmission electron microscopy is utilized. This analysis suggests that the lattice defects in LiFePO4 can be adjusted for improved Li ion transport. [Preview Abstract] |
Thursday, March 18, 2010 1:03PM - 1:39PM |
W1.00004: A Fast Response Mechanism for Insulin Storage in Crystals May Involve a Novel Mode of Kink Generation Invited Speaker: Crystals, likely rhombohedral, of Zn-insulin hexamers form in the islets of Langerhans in the pancreases of many mammals. The suggested function of crystal formation is to protect the insulin from proteases and increase the degree of conversion of soluble proinsulin. To accomplish this, crystal growth should be fast and adaptable to rate fluctuations in the conversion reaction. Zn-insulin crystals grow layer-by-layer. Each layer spreads by the attachment of molecules to kinks located at the layers' edges, also called steps. The kinks are thought to be generated either by thermal fluctuations, as postulated by Gibbs, or by one-dimensional nucleation of new crystalline rows. The kink density determines the rate at which steps advance, and these two kink-generation mechanisms lead to weak near-linear responses of the growth rate to concentration variations. We demonstrate for the crystallization of Zn-insulin a novel mechanism of kink generation, whereby 2D clusters of several insulin molecules pre-formed on the terraces between steps associate to the steps. This mechanism results in several-fold higher kink density, faster rate of crystallization, and a high sensitivity of the kinetics to small increases of the solute concentration. If the found mechanism operates during insulin crystallization \textit{in vivo}, it could be a part of the biological regulation of insulin production and function. For other crystallizing materials in biological and non-biological systems, this mechanism provides an understanding of the often seen non-linear acceleration of the kinetics. [Preview Abstract] |
Thursday, March 18, 2010 1:39PM - 2:15PM |
W1.00005: Computer simulation of structure and dynamics of liquids Invited Speaker: In this talk, I will discuss some of what recent computer simulation studies have taught us about the relationship between the real-space structure and dynamics of model equilibrium and supercooled fluids. Specifically, I will discuss which experimentally measurable aspects of static structure reliably track the dynamical trends of homogeneous and confined equilibrium fluids, and which do not. I will also explain how some of the well-known ``dynamic anomalies'' of supercooled water and concentrated suspensions of particles with short-range attractions, reflect corresponding anomalies in the underlying static structure. Finally, I will explore how dynamic heterogeneities of deeply supercooled fluids connect to dynamic aspects of their local structure. [Preview Abstract] |
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