Materials science. Melting colloidal crystals from the inside out (original) (raw)
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We propose a theory of shear-induced melting of colloidal crystals based on a nonequilibrium generalization of first-order freezing theory. The results agree qualitatively with experiment.
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A melting transition for a system of hard spheres interacting by a repulsive Yukawa potential of DLVO form is studied. To find the location of the phase boundary, we propose a simple theory to calculate the free energies for the coexisting liquid and solid. The free energy for the liquid phase is approximated by a virial expansion. The free energy of the crystalline phase is calculated in the spirit of the Lenard-Jonnes and Devonshire (LJD) theory. The phase boundary is found by equating the pressures and chemical potentials of the coexisting phases. When the approximation leading to the equation of state for the liquid breakes down, the first order transition line is also obtained by applying the Lindemann criterion to the solid phase. Our results are then compared with the Monte Carlo simulations.
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Physical Review B, 1990
An ensemble of particles with repulsive Yukawa-type interaction is solved at high dimension. The fluid exhibits a new static singularity at density (p/T)", which characterizes the supercooledfluid branch and the glass transition; at equilibrium the system crystalhzes at p(p". Thus, a unified picture of crystallization, supercooled fluid, glass formation, and melting is discovered. The theory remains exact for arbitrary potential as p~p"and agrees qualitatively with experiments.
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Scripta Materialia - SCRIPTA MATER, 2002
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Melting and Premelting : Background and Evidence
2006
When the free surfaces of most solids approach their bulk melting temperatures from below, the molecular structure of the material gives way to a disordered structure with some attributes of both the solid and liquid phases. When the temperature is sufficiently close to that of bulk transition, the surface melts and literally flows as a viscous fluid. This phenomenon, called interfacial premelting, lies at the heart of the microscopic theory of melting of solid matter, and captures the interest of condensed matter physicists and physical chemists alike. The process is ubiquitous and responsible for a wide range of consequences in materials with biological, geophysical, and technological significance. Because such systems are often exposed to spatial or temporal variations in thermodynamic forcing, there are a host of fluid mechanical phenomena that result from this underlying melting behavior. The fluid dynamics of unfrozen surfaces holds clues for understanding the bulk behavior of...
The dynamics of melt and shear localization in partially molten aggregates
Nature, 2006
The volcanoes that lie along the Earth's tectonic boundaries are fed by melt generated in the mantle. How this melt is extracted and focused to the volcanoes, however, remains an unresolved question. Here we present new theoretical results with implications for melt focusing beneath mid-ocean ridges. By modelling laboratory experiments 1,2 , we test a formulation for magma dynamics and provide an explanation for localized bands of high-porosity and concentrated shear deformation observed in experiments. These bands emerge and persist at 158-258 to the plane of shear. Past theoretical work on this system predicted the emergence of melt bands 3,4 but at an angle inconsistent with experiments. Our results suggest that the observed band angle results from a balance of porosity-weakening and strain-rate-weakening deformation mechanisms. Lower band angles are predicted for greater strainrate weakening. From these lower band angles, we estimate the orientation of melt bands beneath mid-ocean ridges and show that they may enhance magma focusing toward the ridge axis.
Melting Driven by Particle Size Dispersity: A Study in Two Dimensions
We study the e ect of particle size-dispersity on solids and melting of solids by molecular dynamics simulation on a two-dimensional size-dispersed Lennard-Jones system. We ÿnd that size-dispersity disfavours solidiÿcation and on increasing the dispersity, the solid 'melts', at a critical dispersity, to a liquid. The solid-liquid transition depends on the density -the transition is continuous through the 'hexatic' phase at low densities and abrupt ÿrst order transition at higher densities. We ÿnd that size-dispersity creates topological defects in the close-pack solid structure which destroy the crystalline order in solids. .in (P. Ray) 0378-4371/99/$ -see front matter c 1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 -4 3 7 1 ( 9 9 ) 0 0 1 5 1 -X