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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.
Stokesian dynamics simulations are presented of suspensions of sterically stabilized spheres in a viscous medium, subjected to simple shear. The steric repulsion between the grafted polymer layers of different particles is modeled using an interaction potential that is calculated using a self-consistent field lattice theory. The shear rate dependence and the volume fraction dependence of the suspension viscosity are calculated and compared to experimental data [Nommensen et al. Phys. Rev. E 59, 3147 (1999)]. It is found that shear thinning is mainly caused by the interaction contribution to the viscosity. The present paper, combined with a recent paper of Nommensen et al. [Langmuir 16, 1902 (2000)], shows that computer simulations, theoretical analysis, and experimental work give a consistent physical picture of the rheology of these s...
An extensive Stokesian dynamics study of the rheological behavior of suspensions of rigid spheres subjected to an oscillating shear strain is presented. Two types of suspensions are considered: (1) rigid spheres in a viscous medium, and (2) rigid spheres in a viscoelastic medium. For this latter system we need to extend the Stokesian dynamics method, which was originally developed by Brady and Bossis for particles suspended in a viscous medium. The derivation of the necessary equations for these extended Stokesian dynamics simulations is given. In this derivation we use the well known correspondence principle and apply it to the set of equations for the hydrodynamic forces and stresslets that are valid for spheres suspended in a viscous medium. Then, using Fourier transformation we obtain differential equations for these forces and str...
We present the Rayleigh-Brillouin light scattering data for He + Xe mixtures of various compositions and pressures between 2 and 10 MPa. We compare our experimental data to calculations for a mixture that behaves according to the van der Waals equation of state. Our analysis shows that the contribution of concentration fluctuations to the Landau-Placzek ratio is very important. Furthermore, we demonstrate experimentally the relation between the Landau-Placzek ratio, the adiabatic velocity of sound, and the reduced second moment of the dynamic light scattering spectrum. We show that the van der Waals equation of state can be used to predict the Landau-Placzek ratio in these mixtures quantitatively for mixtures with compositions xu < 0.9. For mixtures with higher xenon concentrations, experimental results agreed quantitatively up to 5 M...
We present new data on Hz + Xe mixtures that support the existence of a fast sound mode in binary gas mixtures. In addition we show that using an approriate scaling, the behaviour of the slow sound mode in systems with different mass ratios, i.e. Hz + Xe, H, + Ar and He + Xe, is identical.
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