Liquid-Solid Transitions with Applications to Self-Assembly.

Self-assembly;Supercooled Liquid;Glass Transition;Quasicrystal;Shape Matching;Order Parameter;Chemical Engineering;Engineering;Chemical Engineering

Keys, Aaron S.Ziff, Robert M. ;

University of Michigan

关键词: Self-assembly;    Supercooled Liquid;    Glass Transition;    Quasicrystal;    Shape Matching;    Order Parameter;    Chemical Engineering;    Engineering;    Chemical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/78931/askeys_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

We study the thermodynamic and kinetic pathways by which liquids transform into solids, and their relation to the metastable states that commonly arise in self-assembly applications.As a case study in the formation of ordered metastable solids, we investigate the atomistic mechanism by which quasicrystals form.We show that the aperiodic growth of quasicrystals is controlled by the ability of the growing quasicrystal ;;nucleus;; to incorporate kinetically trapped atoms into the solid phase with minimal rearrangement.In a related study, we propose a two-part mechanism for forming 3d dodecagonal quasicrystals by self-assembly.Our mechanism involves (1) attaching small mobile particles to the surface of spherical particles to encourage icosahedral packing and (2) allowing a subset of particles to deviate from the ideal spherical shape, to discourage close-packing.In addition to studying metastable ordered solids, we investigate the phenomenology and mechanism of the glass transition.We report measurements of spatially heterogeneous dynamics in a system of air-driven granular beads approaching a jamming transition, and show that the dynamics in our granular system are quantitatively indistinguishable from those for a supercooled liquid approaching a glass transition.In a second study of the glass transition, we use transition path sampling to study the structure, statistics and dynamics of localized excitations for several model glass formers.We show that the excitations are sparse and localized, and their size is temperature-independent.We show that their equilibrium concentration is proportional to exp[-Ja(1/T-1/To)], where ;;Ja;; is the energy scale for irreversible particle displacements of length ;;a,;; and ;;To;; is an onset temperature.We show that excitation dynamics is facilitated by the presence of other excitations, causing dynamics to slow in a hierarchical way as temperature is lowered.To supplement our studies of liquid-solid transitions, we introduce a shape matching framework for characterizing structural transitions in systems with complex particle shapes or morphologies.We provide an overview of shape matching methods, explore a particular class of metrics known as ;;harmonic descriptors,;; and show that shape matching methods can be applied to a wide range of nanoscale and microscale assembly applications.