Micro-and nano-scale flow phenomena PACS 47.57.Ng -Polymers and polymer solutions PACS 83.50.-v -Deformation and flow PACS 82.20.Wt -Computational modelling; simulationsAbstract. -The non-equilibrium structural and dynamical properties of flexible polymers confined in a square microchannel and exposed to a Poiseuille flow are investigated by mesoscale simulations. The chain length and the flow strength are systematically varied. Two transport regimes are identified, corresponding to weak and strong confinement. For strong confinement, the transport properties are independent of polymer length. The analysis of the long-time tumbling dynamics of short polymers yields non-periodic motion with a sublinear dependence on the flow strength. We find distinct differences for conformational as well as dynamical properties from results obtained for simple shear flow.

We present an extensive Monte Carlo study on systems of many semiflexible chains with excluded volume and electrostatic interactions within the Debye−Hückel approximation. The model is tuned to mimic charged wormlike micelles in solution under different conditions. Simulations have been performed at different ionic strengths of added salt, charge densities, chain lengths, and volume fractions (η), covering the dilute to concentrated regime. The simple model used is able to reproduce the structural peak of the scattering function S(q), observed in many experiments, and other important features of polyelectrolytes in solution. Universal behavior of S(0) is established after a rescaling of η. Single-chain scattering functions, radii of gyration, and end-to-end distances have been sampled and compared with data from previous simulation studies and theories. The persistence length has also been analyzed and compared with the Odijk−Skolnick−Fixman predictions. The behavior of the quantities studied is in general found to be more complex than scaling theory predictions.

We demonstrate that aqueous solutions of giant polymer-like nonionic micelles “doped” with small amounts of ionic surfactants serve as ideal model systems for “equilibrium polyelectrolytes”. We report systematic light and neutron scattering investigations of the effect of ionic strength, doping level, and total concentration on the static properties of dilute and semidilute micellar solutions. In dilute solutions, we observe a dramatic influence of (intramicellar) electrostatic interactions on the micellar flexibility, and the results are in close agreement with Monte Carlo simulations. We also analyze the effect of electrostatic contributions to intermicellar interactions and micellar growth. In the semidilute regime, strong long-range interactions between micelles occur at low ionic strength and induce liquidlike ordering, and the resulting structure factor peak exhibits the same concentration dependence as previously observed for polyelectrolytes.