scholarly journals Bulk fluid phase behaviour of colloidal platelet–sphere and platelet–polymer mixtures

2013 ◽  
Vol 371 (1988) ◽  
pp. 20120259 ◽  
Author(s):  
Daniel de las Heras ◽  
Matthias Schmidt
Keyword(s):  
Phase Diagrams ◽  
Nematic Phase ◽  
Density Functional ◽  
Hard Spheres ◽  
Hard Core ◽  
Fluid Phase ◽  
Phase Behaviour ◽  
Size Ratio ◽  
Polymer Mixtures ◽  
Bulk Fluid

Using a geometry-based fundamental measure density functional theory, we calculate bulk fluid phase diagrams of colloidal mixtures of vanishingly thin hard circular platelets and hard spheres. We find isotropic–nematic phase separation, with strong broadening of the biphasic region, upon increasing the pressure. In mixtures with large size ratio of platelet and sphere diameters, there is also demixing between two nematic phases with differing platelet concentrations. We formulate a fundamental measure density functional for mixtures of colloidal platelets and freely overlapping spheres, which represent ideal polymers, and use it to obtain phase diagrams. We find that, for low platelet–polymer size ratio, in addition to isotropic–nematic and nematic–nematic phase coexistence, platelet–polymer mixtures also display isotropic–isotropic demixing. By contrast, we do not find isotropic–isotropic demixing in hard-core platelet–sphere mixtures for the size ratios considered.

scholarly journals Evidence of Structural Inhomogeneities in Hard-Soft Dimeric Particles without Attractive Interactions

Materials ◽  
2019 ◽  
Vol 13 (1) ◽  
pp. 84 ◽  
Author(s):  
Gianmarco Munaò ◽  
Franz Saija
Keyword(s):  
Hard Spheres ◽  
Hard Core ◽  
Fluid Phase ◽  
Colloidal Dispersion ◽  
Systematic Investigation ◽  
Distribution Functions ◽  
Structure Factors ◽  
Soft Spheres ◽  
Wide Range ◽  
Structural Inhomogeneities

We perform Monte Carlo simulations of a simple hard-soft dimeric model constituted by two tangent spheres experiencing different interactions. Specifically, two hard spheres belonging to different dimers interact via a bare hard-core repulsion, whereas two soft spheres experience a softly repulsive Hertzian interaction. The cross correlations are soft as well. By exploring a wide range of temperatures and densities we investigate the capability of this model to document the existence of structural inhomogeneities indicating the possible onset of aggregates, even if no attraction is set. The fluid phase behavior is studied by analyzing structural and thermodynamical properties of the observed structures, in particular by computing radial distribution functions, structure factors and cluster size distributions. The numerical results are supported by integral equation theories of molecular liquids which allow for a finer and faster spanning of the temperature-density diagram. Our results may serve as a framework for a more systematic investigation of self-assembled structures of functionalized hard-soft dimers able to aggregate in a variety of structures widely oberved in colloidal dispersion.

Effect of elastic constants of liquid crystals in their electro-optical properties

2017 ◽  
Vol 14 (11) ◽  
pp. 1750163
Author(s):  
Z. Parang ◽  
T. Ghaffary ◽  
M. M. Gharahbeigi
Keyword(s):  
Optical Properties ◽  
Liquid Crystals ◽  
Elastic Constants ◽  
Density Functional ◽  
Hard Spheres ◽  
Hard Core ◽  
Molecular Fluids ◽  
Dipolar Fluid ◽  
The Density Functional Theory ◽  
Complex Liquids

Recently following the success of the density functional theory (DFT) in obtaining the structure and thermodynamics of homogeneous and inhomogeneous classical systems such as simple fluids, dipolar fluid and binary hard spheres, this theory was also applied to obtain the density profile of a molecular fluid in between hard planar walls by Kalpaxis and Rickayzen. In the theory of molecular fluids, the direct correlation function (DCF) can be used to calculate the equation of state, free energy, phase transition, elastic constants, etc. It is well known that the hard core molecular models play an important role in understanding complex liquids such as liquid crystals. In this paper, a classical fluid of nonspherical molecules is studied. The required homogeneous (DCF) is obtained by solving Orenstein–Zernike (OZ) integral equation numerically. Some of the molecules in the liquid crystals have a sphere shape and this kind of molecular fluid is considered here. The DCF sphere of the molecular fluid is calculated and it will be shown that the results are in good agreement with the pervious works and the results of computer simulation. Finally the electro-optical properties of ellipsoid liquid crystal using DCF of these molecules are calculated.

scholarly journals Liquid–liquid phase transition in hydrogen by coupled electron–ion Monte Carlo simulations

2016 ◽  
Vol 113 (18) ◽  
pp. 4953-4957 ◽  
Author(s):  
Carlo Pierleoni ◽  
Miguel A. Morales ◽  
Giovanni Rillo ◽  
Markus Holzmann ◽  
David M. Ceperley
Keyword(s):  
Phase Transition ◽  
Monte Carlo ◽  
Density Functional ◽  
Fluid Phase ◽  
Transition Line ◽  
Energy Applications ◽  
First Order Phase Transition ◽  
Fundamental Research ◽  
Diamond Anvil ◽  
First Order Phase

The phase diagram of high-pressure hydrogen is of great interest for fundamental research, planetary physics, and energy applications. A first-order phase transition in the fluid phase between a molecular insulating fluid and a monoatomic metallic fluid has been predicted. The existence and precise location of the transition line is relevant for planetary models. Recent experiments reported contrasting results about the location of the transition. Theoretical results based on density functional theory are also very scattered. We report highly accurate coupled electron–ion Monte Carlo calculations of this transition, finding results that lie between the two experimental predictions, close to that measured in diamond anvil cell experiments but at 25–30 GPa higher pressure. The transition along an isotherm is signaled by a discontinuity in the specific volume, a sudden dissociation of the molecules, a jump in electrical conductivity, and loss of electron localization.

Density Functional Theory for Small Systems: Hard Spheres in a Closed Spherical Cavity

1997 ◽  
Vol 79 (13) ◽  
pp. 2466-2469 ◽  
Author(s):  
A. González ◽  
J. A. White ◽  
F. L. Román ◽  
S. Velasco ◽  
R. Evans
Keyword(s):  
Density Functional Theory ◽  
Spherical Cavity ◽  
Density Functional ◽  
Hard Spheres ◽  
Functional Theory ◽  
Small Systems

scholarly journals METHODS TO COMPUTE PRESSURE AND WALL TENSION IN FLUIDS CONTAINING HARD PARTICLES

2012 ◽  
Vol 23 (08) ◽  
pp. 1240011 ◽  
Author(s):  
DEBABRATA DEB ◽  
DOROTHEA WILMS ◽  
ALEXANDER WINKLER ◽  
PETER VIRNAU ◽  
KURT BINDER
Keyword(s):  
Comparative Evaluation ◽  
Hard Spheres ◽  
Excess Energy ◽  
Attractive Potential ◽  
Wall Tension ◽  
Pressure Tensor ◽  
Colloidal Systems ◽  
Polymer Mixtures ◽  
Hard Particles ◽  
Mutual Agreement

Colloidal systems are often modeled as fluids of hard particles (possibly with an additional soft attraction, e.g. caused by polymers also contained in the suspension). In simulations of such systems, the virial theorem cannot be straightforwardly applied to obtain the components of the pressure tensor. In systems confined by walls, it is hence also not straightforward to extract the excess energy due to the wall (the “wall tension”) from the pressure tensor anisotropy. A comparative evaluation of several methods to circumvent this problem is presented, using as examples fluids of hard spheres and the Asakura–Oosawa model of colloid-polymer mixtures with a size ratio q = 0.15 (for which the effect of the polymers can be integrated out to yield an effective attractive potential between the colloids). Factors limiting the accuracy of the various methods are carefully discussed, and controlling these factors very good mutual agreement between the various methods is found.

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