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Polymers and rod-like colloids (PaRC) adopt a favorable orientation under sufficiently strong flows. However, how the flow kinematics affect the alignment of such nanostructures according to their extensibility remains unclear. By analysing the shear- and extension-induced alignment of chemically and structurally different PaRC, we show that extensibility is a key determinant of the structural response to the imposed kinematics. We propose a unified description of the effectiveness of extensional flow, compared to shearing flow, at aligning PaRC of different extensibility.

We report chain self-diffusion and viscosity data for sodium polystyrene sulfonate (NaPSS) in semidilute salt-free aqueous solutions measured by pulsed field gradient NMR and rotational rheometry respectively. The observed concentration dependence of $\eta$ and $D$ are consistent with the Rouse-Zimm scaling model with a concentration dependent monomeric friction coefficient. The concentration dependence of the monomeric friction coefficient exceeds that expected from free-volume models of diffusion, and its origin remains unclear. Correlation blobs and dilute chains with equivalent end-to-end distances exhibit nearly equal friction coefficients, in agreement with scaling. The viscosity and diffusion data are combined using the Rouse model to calculate the chain dimensions of NaPSS in salt-free solution, these agree quantitatively with SANS measurements., Comment: 12 pages, 8 figures

We report results of small angle neutron scattering measurements made on sodium polystyrene sulfonate in aqueous salt solutions. The correlation length and osmotic compressibility are measured as a function of polymer (c) and added salt ($c_S$) concentrations, and the results are compared with scaling predictions and the random-phase approximation (RPA). In Dobrynin et al's scaling model the osmotic pressure consists of a counter-ion contribution and a polymer contribution. The polymer contribution is found to be two orders of magnitude smaller than expected from the scaling model, in agreement with earlier observations made on neutral polymers in good solvent condition. RPA allows the determination of single-chain dimensions in semidilute solutions at high polymer and added salt concentrations, but fails for $c_S < 2$ M. The \chi parameter can be modelled as the sum of an intrinsic contribution and an electrostatic term: $\chi \simeq \chi0+K/c_S^{1/2}$, where $\chi_0 > 0.5$ is consistent with the hydrophobic nature of the backbone of NaPSS. The dependence of $\chi_{elec} \simeq 1/c_S^{1/2}$ disagrees with the random-phase approximation ($\chi_{elec} \simeq 1/c_S$), but agrees with the light scattering results in dilute solution and Dobrynin et al's scaling treatment of electrostatic excluded volume., Comment: 16 pages, 7 figures