Lopez Carlos G, Horkay Ferenc, Mussel Matan, Jones Ronald L, Richtering Walter
Institute of Physical Chemistry, RWTH Aachen University, Landoltweg 2, 52056 Aachen, Germany.
Soft Matter. 2020 Aug 21;16(31):7289-7298. doi: 10.1039/d0sm00464b. Epub 2020 Jul 15.
We report results of small angle neutron scattering measurements made on sodium polystyrene sulfonate in aqueous salt solutions. The correlation length (ξ) and osmotic compressibility are measured as a function of polymer (c) and added salt (c) 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≤ 2 M. The χ parameter can be modelled as the sum of an intrinsic contribution (χ) and an electrostatic term: χ∼χ + K'/√c, where χ > 0.5 is consistent with the hydrophobic nature of the backbone of NaPSS. The dependence of χ∼ 1/√c disagrees with the random-phase approximation (χ∼ 1/c), but agrees with the light scattering results in dilute solution and Dobrynin et al.'s scaling treatment of electrostatic excluded volume.
我们报告了在盐水溶液中对聚苯乙烯磺酸钠进行小角中子散射测量的结果。测量了相关长度（ξ）和渗透压缩性作为聚合物浓度（c）和添加盐浓度（c）的函数，并将结果与标度预测和随机相位近似（RPA）进行了比较。在多布林宁等人的标度模型中，渗透压由抗衡离子贡献和聚合物贡献组成。发现聚合物贡献比标度模型预期的小两个数量级，这与早期在良溶剂条件下对中性聚合物的观察结果一致。RPA允许在高聚合物和添加盐浓度下测定半稀溶液中的单链尺寸，但对于c≤2 M时不适用。χ参数可以建模为固有贡献（χ）和静电项的总和：χ∼χ + K'/√c，其中χ>0.5与NaPSS主链的疏水性质一致。χ∼1/√c的依赖性与随机相位近似（χ∼1/c）不一致，但与稀溶液中的光散射结果以及多布林宁等人对静电排除体积的标度处理一致。
