Structure of ternary additive hard-sphere fluid mixtures

Monte Carlo simulations on the structural properties of ternary fluid mixtures of additive hard spheres are reported. The results are compared with those obtained from a recent analytical approximation [S. B. Yuste, A. Santos, and M. Lopez de Haro, J. Chem. Phys. 108, 3683 (1998)] to the radial distribution functions of hard-sphere mixtures and with the results derived from the solution of the Ornstein-Zernike integral equation with both the Martynov-Sarkisov and the Percus-Yevick closures. Very good agreement between the results of the first two approaches and simulation is observed, with a noticeable improvement over the Percus-Yevick predictions especially near contact.Comment: 11 pages, including 8 figures; A minor change; accepted for publication in PR

Macromolecular theory of solvation and structure in mixtures of colloids and polymers

The structural and thermodynamic properties of mixtures of colloidal spheres and non-adsorbing polymer chains are studied within a novel general two-component macromolecular liquid state approach applicable for all size asymmetry ratios. The dilute limits, when one of the components is at infinite dilution but the other concentrated, are presented and compared to field theory and models which replace polymer coils with spheres. Whereas the derived analytical results compare well, qualitatively and quantitatively, with mean-field scaling laws where available, important differences from ``effective sphere'' approaches are found for large polymer sizes or semi-dilute concentrations.Comment: 23 pages, 10 figure

Determination of the osmotic second virial coefficient and the dimerization of β-lactoglobulin in aqueous solutions with added salt at the isoelectric point

Aqueous solutions of β-lactoglobulin (at the isoelectric point pH=5.18) have been studied by membrane osmometry. The osmotic second virial coefficient as well as the monomer–dimer equilibrium of β-lactoglobulin have been found to depend significantly on the salt concentration. At low salt concentration the virial coefficient becomes negative, which could be attributed to dipole–dipole interactions which become important at the isoelectric point of the protein when the salt concentration decreases

Protein-polysaccharide interactions: The determination of the osmotic second virial coefficients in aqueous solutions of ß-lactoglobulin and dextran

Solutions containing dextran and solutions containing mixtures of dextran +ß-lactoglobulin are studied by membrane osmometry. The low concentration range of these solutions is considered. From the measured osmotic pressures the virial coefficients are obtained. These are analyzed using the osmotic virial coefficient of ß-lactoglobulin solutions published earlier by us [Schaink, H.M., & Smit, J. A.M. (2000). Determination of the osmotic second virial coefficient and the dimerization of beta-lactoglobulin in aqueous solutions with added salt at the isoelectric point. PCCP, 2, 1537¿1541]. The second cross-virial coefficient A12 is found to be positive indicating a repulsive and probably mainly steric interaction between neutral in nature dextran and and practically uncharged ß-lactoglobulin (pH=5.18). The measurements show that the ß-lactoglobulin has only a small tendency to form multimers in the presence of dextran. The phase diagram of solutions of dextran+Whey Protein Isolate (appr. 60% ß-lactoglobulin) is also presented. The McMillan¿Mayer equation of state that considers only the second virial coefficients is found to be unreliable for the extrapolation up to the concentrations at which phase separation is expected Keywords: Proteins; Polysaccharides; Osmotic pressure; Virial coefficients; Phase separatio

The van der Waals Equation of State and the Law of Corresponding States: A Spreadsheet Experiment

In normal physical chemistry courses the student is told how the van der Waals equation works. The mathematics needed for making a Maxwell construction is difficult for the average chemistry student. This makes it difficult to show how the liquid-gas digram is obtained from the equation of state. Here a spreadsheeet-experiment is presented that can be used to illustrate various aspects of the van der Waals equation of state. With this spreadsheet the students are able to play around with the van der Waals equation so that they can see how this equation works

Shear Modulus of Sintered 'House of Cards'-Like Assemblies of Crystals

A cell model of a 'house of cards'-like assembly of crystals is used for the study of the evolution of the shear modulus during sintering. The crystals are assumed to have a lozenge shape. The cell model takes different crystal-crystal contacts into account. The force needed to separate two sintered crystals is calculated using the minimum surface area (MSA) approximation. By varying the thickness, long axis, and short axis of the crystals, it is possible to make space-filing configurations which have a nonzero shear modulus at crystal volume fraction that can be as low as Ø= 0.03. This is significantly lower than the volume fractions Ø > 0.52 that are found in studies where the MSA approximation is applied to assemblies of spherical particles. It is found that sintering may cause a nonlinear volume fraction dependence of the shear modulus, which depends on the shape of the crystals, the type of crystal-crystal contacts, and the character of the crystal assembly. The calculated shear modulus is analyzed using the phenomenological expression (Ø -Ø 0)beta, where 0 represents the volume fraction at the start of sintering. The exponent beta is found to vary between 1 and 2. The interpretation of the shear modulus using a fractal model is also discussed