Triplet forces between star polymers

We analyze the effective triplet interactions between the centers of star polymers in a good solvent. Using an analytical short distance expansion inspired by scaling theory, we deduce that the triplet part of the three-star force is attractive but only 11% of the pairwise part even for a close approach of three star polymers. We have also performed extensive computer simulations for different arm numbers to extract the effective triplet force. The simulation data show good correspondence with the theoretical predictions. Our results justify the effective pair potential picture even beyond the star polymer overlap concentration.Comment: 14 pages, 5 figure

Enhanced structural correlations accelerate diffusion in charge-stabilized colloidal suspensions

Theoretical calculations for colloidal charge-stabilized and hard sphere suspensions show that hydrodynamic interactions yield a qualitatively different particle concentration dependence of the short-time self-diffusion coefficient. The effect, however, is numerically small and hardly accessible by conventional light scattering experiments. Applying multiple-scattering decorrelation equipment and a careful data analysis we show that the theoretical prediction for charged particles is in agreement with our experimental results from aqueous polystyrene latex suspensions.Comment: 1 ps-file (MS-Word), 14 page

Polyelectrolyte stars in planar confinement

We employ monomer-resolved Molecular Dynamics simulations and theoretical considerations to analyze the conformations of multiarm polyelectrolyte stars close to planar, uncharged walls. We identify three mechanisms that contribute to the emergence of a repulsive star-wall force, namely: the confinement of the counterions that are trapped in the star interior, the increase in electrostatic energy due to confinement as well as a novel mechanism arising from the compression of the stiff polyelectrolyte rods approaching the wall. The latter is not present in the case of interaction between two polyelectrolyte stars and is a direct consequence of the impenetrable character of the planar wall.Comment: 34 pages, 8 figures. Revised version of the manuscript. To appear in J. Chem. Phys. May, 200

Nanotechnology and Quasicrystals: From self assembly to photonic applications.

After providing a concise overview on quasicrystals and their discovery more than a quarter of a century ago, I consider the unexpected interplay between nanotechnology and quasiperiodic crystals. Of particular relevance are efforts to fabricate artificial functional micro- or nanostructures, as well as efforts to control the self-assembly of nanostructures, where current knowledge about the possibility of having long-range order without periodicity can provide significant advantages. I discuss examples of systems ranging from artificial metamaterials for photonic applications, through self-assembled soft matter, to surface waves and optically-induced nonlinear photonic quasicrystals. 1 Nanotechnology and quasicrystals? When organizers of the NATO Advanced Research Workshop on nanotechnology, held in St. Petersburg in June 2008, asked me to deliver a keynote lecture on quasicrystals I was certain that they had made a mistake. I have been studying quasicrystals for over 15 years and investigating nanomechanical systems for just about a decade, and although one always finds connections between different scientific fields, I had never expected such an invitation