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We present a novel simulation technique derived from Brownian cluster dynamics used so far to study the isotropic colloidal aggregation. It now implements the classical Kern-Frenkel potential to describe patchy interactions between particles. This technique gives access to static properties, dynamics and kinetics of the system, even far from the equilibrium. Particle thermal motions are modeled using billions of independent small random translations and rotations, constrained by the excluded volume and the connectivity. This algorithm, applied to a single polymer chain leads to correct static and dynamic properties, in the framework where hydrodynamic interactions are ignored. By varying patch angles, various local chain flexibilities can be obtained. We have used this new algorithm to model step-growth polymerization under various solvent qualities. The polymerization reaction is modeled by an irreversible aggregation between patches while an isotropic finite squarewell potential is superimposed to mimic the solvent quality. In bad solvent conditions, a competition between a phase separation (due to the isotropic interaction) and polymerization (due to patches) occurs. Surprisingly, an arrested network with a very peculiar structure appears. It is made of strands and nodes. Strands gather few stretched chains that dip into entangled globular nodes. These nodes act as reticulation points between the strands. The system is kinetically driven and we observe a trapped arrested structure. That demonstrates one of the strengths of this new simulation technique. It can give valuable insights about mechanisms that could be involved in the formation of stranded gels. [ABSTRACT FROM AUTHOR]

Dynamic and static light scattering measurements have been made on lysozyme solutions at 25 °C in 0.1 M phosphate buffer, pH 6.88, in the presence of sodium dodecyl sulfate (SDS). The concentration of SDS has been varied over a wide range (0–0.2 g/ml). It is found that under these conditions both SDS micelles and lysozyme(Lys)–SDS complexes coexist. Addition of lysozyme at constant SDS concentration leads to formation of more lysozyme–SDS complex. The translational diffusion coefficient of the complex increases with SDS concentration. It is also found that two lysozyme molecules are associated in the protein–surfactant complex. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

: We present off-lattice Monte Carlo simulations of site-bond percolation of semi-penetrable spheres or, equivalently, of hard spheres with a finite bond range. We will show that the crucial parameter is the effective volume fraction ( φe), i.e. the volume that is occupied or within the bond range of at least one particle. For the equivalent system of semi-penetrable spheres 1 - φe is the porosity. The bond percolation threshold (pb) can be described in terms of φe by a simple analytical expression: log(φe)/log(φec) + log(pb)/log(pbc) = 1, with pbc = 0.12 independent of the bond range and φec a constant that decreases with increasing bond range. [ABSTRACT FROM AUTHOR]