粘度作为溶液中复杂形成程度的证据：以Fe$^{2+}$和Mg$^{2+}$氯化物为例
Viscosity as a Smoking Gun for Complex Formation in Solution: Fe$^{2+}$ and Mg$^{2+}$ Chlorides as Examples
AI总结：
通过粘度测定揭示Fe$^{2+}$和Mg$^{2+}$氯化物溶液中复杂形成程度差异，利用分子动力学模拟和实验数据支持结论。
摘要：
高浓度电解质溶液是不可或缺的，但目前仍缺乏深入理解。特别是，在高浓度离子溶液中，物种间复杂形成程度的测定在理论和实验上都极具挑战性，但对溶液性质有显著影响。文献中充斥着实验得出的复杂形成程度的矛盾估计。我们发现复杂形成影响传输性质，因此是准确建模高浓度溶液的必要前提。我们利用这一发现，展示粘度可用于确定高浓度水溶液中复杂形成程度。给出了模拟结果以及实验测量结果。原子级马德里-2019力场被扩展以建模FeCl$_2$。比较了FeCl$_2$和MgCl$_2$溶液，并通过更复杂的复杂形成解释了观察到的粘度差异，这一结论得到了最近报道的X射线吸收和中子散射实验的支持。
英文摘要：
Electrolyte solutions at high concentration are indispensable and yet poorly understood. In particular, the extent of speciation -- the formation of complexes composed of multiple species -- in concentrated ionic solutions is very challenging to obtain theoretically and experimentally, but can have a strong effect on solution properties. The literature is rife with contradictory estimates of speciation from experiments. We find that speciation affects transport properties, and is therefore, a prerequisite to accurately model concentrated solutions. We turn this to our advantage by showing that the viscosity can be used to determine the extent of complexation in concentrated aqueous solutions. Results of simulations as well as experimental measurements are presented. The atomistic Madrid-2019 force-field is extended to model FeCl$_2$. Solutions of FeCl$_2$ and MgCl$_2$ are compared and the observed difference in viscosity explained by more complexation in the former, a conclusion supported by recently reported X-ray absorption and neutron scattering experiments.
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