Polyelectrolyte chain dimensions and concentration fluctuations near phase boundaries

We have measured the temperature ~T! dependence of the correlation length ~j! for concentration fluctuations in aqueous solutions of sodium–poly~styrene sulfonate! with a fixed level of added barium chloride salt. Apparent critical behavior is observed upon lowering the temperature to precipitation phase boundaries that complements our earlier work on salt-dependent behavior. We interpret experimental deviations from j versus T as crossover from the mean field to the Ising universality class. We also measured the radius of gyration (Rg) of labeled chains and j for semidilute polyelectrolyte solutions at low ionic strengths. We recovered the familiar result of j scaling with polymer concentration (Cp) and degree of polymerization ~N!, such that j5(7369) NCp 20.4860.03 @Å# , and using SANS high concentration labeling Rg5(400628)Cp 20.2460.01 @Å# ~for N5577) and Rg5(2.862.1)N 0.660.1 @Å# ~for Cp5206 gL ), respectively. The indices recovered are in agreement with theoretical predictions for low ionic strength semidilute solutions. Such experiments offer insight into relatively unexplored phase behavior in charged macromolecular solutions. © 2003 American Institute of Physics. @DOI: 10.1063/1.1592496#