Chen Guang, Perazzo Antonio, Stone Howard A
Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544, USA.
Phys Rev Lett. 2020 May 1;124(17):177801. doi: 10.1103/PhysRevLett.124.177801.
Polyelectrolytes (PEs) are charged polymers in polar solvents. Classical scaling theories suggest that the viscosity η for semidilute unentangled PE solutions in θ solvents obeys the empirical Fuoss law η∝n_{p}^{1/2} in the "salt-free" regime, and η∝n_{p}^{5/4} in the regime affected by added salt, where the polymer concentration n_{p} is defined as the number of monomers per volume. However, recent experiments have also reported η∝n_{p}^{0.68} and η∝n_{p}^{0.91}, which are at odds with the classical scaling theories. To rationalize the four distinct scaling laws, we probe the electrostatic energy per monomer under the influence of salt and their contributions to the viscosity of PE solutions. We identify four consecutive regimes dependent on the magnitude of the ratio of the polymer concentration n_{p} to the salt concentration n_{s}, which capture the unexplained observations, and provide physical insights for the influence of salt contamination and added salt on the properties of both weakly and strongly charged semidilute unentangled PE solutions.
聚电解质（PEs）是极性溶剂中的带电聚合物。经典标度理论表明，在θ溶剂中，半稀非缠结PE溶液的粘度η在“无盐”状态下服从经验性的福斯定律η∝np1/2，而在添加盐影响的状态下η∝np5/4，其中聚合物浓度np定义为每体积的单体数。然而，最近的实验也报道了η∝np0.68和η∝np0.91，这与经典标度理论不一致。为了使这四种不同的标度定律合理化，我们探究了单体在盐影响下的静电能及其对PE溶液粘度的贡献。我们确定了四个连续的状态，它们取决于聚合物浓度np与盐浓度ns之比的大小，这些状态解释了之前无法解释的观察结果，并为盐污染和添加盐对弱电荷和强电荷半稀非缠结PE溶液性质的影响提供了物理见解。
