8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

Fri 911:10-14:00P4.9Ultrasoft primitive model of polyelectrolytes in solutionDaniele Coslovich, 1 Jean-Pierre Hansen, 2 and Gerhard Kahl 31 Université Montpellier 2, Place Eugene Bataillon, 34095, Montpellier, France2 University of Cambridge, Cambridge, United Kingdom3 Technische Universitaet Wien, Vienna, AustriaWe present a new, ultrasoft core model of interpenetrating polycations and polyanions with continuousGaussian charge distributions, to investigate polyelectrolyte aggregation in dilute and semidilute,salt-free solutions [1, 2]. The effective interaction between the polyions is given by abounded potential at short distances and a long-range Coulomb interaction. The model is studiedby a combination of approximate integral equation theories and numerical simulations. Thecalculated pair structure, thermodynamics, phase diagram and polyion dynamics of the symmetricversion of the model (the “ultrasoft restricted primitive model”) differ significantly from thecorresponding properties of the widely studied “restricted primitive model” (RPM), where ionshave hard cores. At sufficiently low temperatures and densities, oppositely charged polyionsform weakly interacting, polarizable neutral pairs. The clustering probabilities, dielectric behaviorand electrical conductivity point to a line of sharp conductor-insulator transitions in thedensity-temperature plane. At very low temperatures, the conductor-insulator transition line terminatesnear the top of a first order coexistence curve separating a high-density, liquid phase froma low-density, vapor phase. The simulation data hint at a tricritical point, reminiscent of thatobserved in the two-dimensional Coulomb Gas, which contrasts with the Ising criticality of itsthree-dimensional counterpart, the RPM. [1] D. Coslovich, J. -P. Hansen, and G. Kahl, Soft Matter7, 1690 (2011) [2] D. Coslovich, J. -P. Hansen, and G. Kahl, submitted to J. Chem. Phys. (2011)9