Search results for "Atomic packing factor"
showing 10 items of 35 documents
The Influence of Crystal Size Distributions on the Rheology of Magmas: New Insights From Analog Experiments
2017
This study examines the influence of particle size distributions on the rheology of particle suspensions by using analogue experiments with spherical glass beads in silicone oil as magma equivalent. The analyses of 274 individual particle-bearing suspensions of varying modality (uni-, bi- tri- and tetramodality), as well as of polymodal suspensions with specific defined skewness and variance, are the first data set of its kind and provide important insights in the relationship between the solid particles of a suspension and its rheological behaviour. Since the relationship between the rheology of particle bearing suspensions and its maximum packing fraction ϕm is well established by several…
An expanded model and application of the combined effect of crystal-size distribution and crystal shape on the relative viscosity of magmas
2018
International audience; This study examines the combined effect of crystal-size distributions (CSD) and crystal shape on the rheology of vesicle free magmatic suspensions and provides the first practical application of an empirical model to estimate the relative effect of crystal content and CSD's on the viscosity of magma directly from textural image analysis of natural rock samples in the form of a user-friendly texture-rheology spreadsheet calculator. We extend and apply established relationships between the maximum packing fraction ϕm of a crystal bearing suspension and both its rheological properties and the polydispersity γ of a CSD. By using analogue rotational rheometric experiments…
Monte Carlo simulations of the solid-liquid transition in hard spheres and colloid-polymer mixtures
2010
Monte Carlo simulations at constant pressure are performed to study coexistence and interfacial properties of the liquid-solid transition in hard spheres and in colloid-polymer mixtures. The latter system is described as a one-component Asakura-Oosawa (AO) model where the polymer's degrees of freedom are incorporated via an attractive part in the effective potential for the colloid-colloid interactions. For the considered AO model, the polymer reservoir packing fraction is eta_p^r=0.1 and the colloid-polymer size ratio is q=sigma_p/\sigma=0.15 (with sigma_p and sigma the diameter of polymers and colloids, respectively). Inhomogeneous solid-liquid systems are prepared by placing the solid fc…
Critical behavior of a colloid-polymer mixture confined between walls
2006
We investigate the influence of confinement on phase separation in colloid-polymer mixtures. To describe the particle interactions, the colloid-polymer model of Asakura and Oosawa [J. Chem. Phys. 22, 1255 (1954)] is used. Grand canonical Monte Carlo simulations are then applied to this model confined between two parallel hard walls, separated by a distance D=5 colloid diameters. We focus on the critical regime of the phase separation and look for signs of crossover from three-dimensional (3D) Ising to two-dimensional (2D) Ising universality. To extract the critical behavior, finite size scaling techniques are used, including the recently proposed algorithm of Kim et al. [Phys. Rev. Lett. 91…
Detailed Analysis of Packing Efficiency Allows Rationalization of Solvate Formation Propensity for Selected Structurally Similar Organic Molecules
2018
In structural study of seven bile acids it was identified that their propensity for solvate formation is directly related to the packing efficiency of the unsolvated phases: low packing index, voids, and unsatisfied hydrogen bonding lead to extensive solvate formation, whereas efficient packing leads to the opposite. This was determined to be caused by the presence of OH group attached to carbon C12. Solvate formation was determined to provide a noticeable improvement in the packing efficiency for compounds having ansolvates with inefficient packing.
Mode coupling approach to the ideal glass transition of molecular liquids: Linear molecules
1997
The mode coupling theory (MCT) for the ideal liquid glass transition, which was worked out for simple liquids mainly by Gotze, Sjogren, and their co-workers, is extended to a molecular liquid of linear and rigid molecules. By use of the projection formalism of Zwanzig and Mori an equation of motion is derived for the correlators S[sub lm,l[sup (prime)]m[sup (prime)]]([bold q],t) of the tensorial one-particle density rho [sub lm]([bold q],t), which contains the orientational degrees of freedom for l(greater-than)0. Application of the mode coupling approximation to the memory kernel results into a closed set of equations for S[sub lm,l[sup (prime)]m[sup (prime)]]([bold q],t), which requires t…
Direct observation of a buckling transition during the formation of thin colloidal crystals
2007
We have investigated a colloidal suspension in a thin wedge formed by two glass plates in the presence of a lateral pressure. Starting with a single hexagonal layer, with increasing separation between the glass plates additional layers are added. This process is accompanied by a number of structural transitions necessary to maintain a high packing fraction under the given boundary conditions. Besides the well-known sequence of hexagonal and quadratic phases, we observe two new phases which are identified with the buckling and the rhombic phase recently predicted by other authors.
Brownian dynamics of polydisperse colloidal hard spheres: Equilibrium structures and random close packings
1994
Recently we presented a new technique for numerical simulations of colloidal hard-sphere systems and showed its high efficiency. Here, we extend our calculations to the treatment of both 2- and 3-dimensional monodisperse and 3-dimensional polydisperse systems (with sampled finite Gaussian size distribution of particle radii), focusing on equilibrium pair distribution functions and structure factors as well as volume fractions of random close packing (RCP). The latter were determined using in principle the same technique as Woodcock or Stillinger had used. Results for the monodisperse 3-dimensional system show very good agreement compared to both pair distribution and structure factor predic…
Phase transitions and phase equilibria in spherical confinement
2013
Phase transitions in finite systems are rounded and shifted and affected by boundary effects due to the surface of the system. This interplay of finite size and surface effects for fluids confined inside of a sphere of radius $R$ is studied by a phenomenological theory and Monte Carlo simulations of a model for colloid-polymer mixtures. For this system the phase separation in a colloid-rich phase and a polymer-rich phase has been previously studied extensively in the bulk. It is shown that spherical confinement can strongly enhance the miscibility of the mixture. Depending on the wall potentials at the confining surface, the wetting properties of the wall can be controlled, and this interpl…
Frustration of structural fluctuations upon equilibration of shear melts
2002
Abstract We report on the formation of amorphous solids from aquaeous suspensions of charged colloidal spheres. Comprehensive light scattering and microscopic studies show that in these systems the nucleation rate density continuously increases to very high values. At the highest particle densities of 47.5 μm −3 (packing fraction Φ =0.146) an amorphous state is observed of only short range order, finite static shear modulus and frozen long time dynamics. This state is composed of a piling of––as we propose pre-critical––nuclei. Differences from the Hard Sphere case are discussed in some detail. There the arrest of density fluctuations is observed and described by Mode Coupling scenarios. In…