刚性胶体的弱电解质扩散电泳
Weak-electrolyte diffusiophoresis for rigid colloids
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中文总结 AI 辅助
本研究建立弱电解质中刚性胶体扩散电泳模型，通过求解耦合方程揭示双电层及离子反应对迁移率的影响，发现反应-极化耦合无法由完全解离模型仅调整离子强度重现。
中文摘要 AI 辅助
我们建立了单价弱电解质中化学惰性、固定表面电荷的刚性球形胶体的扩散电泳模型，其中中性溶质可逆解离为离子，且中性物种浓度存在弱远场梯度。在快反应极限下，局部质量作用和体相电中性确定远场离子梯度，体相零电流条件确定扩散电势梯度。我们求解了任意双电层厚度下耦合的Nernst-Planck、Poisson和Stokes方程，在保留非线性Poisson-Boltzmann平衡的同时对梯度强度进行线性化。在Debye-Hückel极限下，迁移率包含匹配的完全解离响应的一半，以及由中性-离子耦合导致的有限双电层修正；该修正会在Hückel和Smoluchowski极限下消失。超出该极限时，对代表性系统的数值解显示，随着表面电势幅值增大，会出现分支选择性响应：当反离子比共离子慢时，解离-缔合会减弱阻滞性的浓度极化层，使迁移率超过完全解离值；当反离子更快时，响应保持接近质量作用设定的一半标度。这种反应-极化耦合无法通过在完全解离模型中仅调整体相离子强度（即Debye长度）来重现。
英文摘要
We develop a model for the diffusiophoresis of a chemically inert, rigid spherical colloid with fixed surface charge in a monovalent weak electrolyte, in which a neutral solute reversibly dissociates into ions. A weak far-field gradient is imposed in the neutral-species concentration. In the fast-reaction limit, local mass action and bulk electroneutrality determine the far-field ionic gradients, while the bulk zero-current condition determines the diffusion-potential gradient. We solve the coupled Nernst-Planck, Poisson and Stokes equations for arbitrary double-layer thickness, linearising in the gradient strength while retaining the nonlinear Poisson-Boltzmann equilibrium. In the Debye-Hückel limit, the mobility consists of one half of the matched fully dissociated response and a finite-double-layer correction due to neutral-ion coupling; the correction vanishes in both the Hückel and Smoluchowski limits. Beyond this limit, numerical solutions for the representative systems reveal a branch-selective response as the surface potential magnitude increases. When the counterion is slower than the co-ion, dissociation-association weakens a retarding concentration-polarisation layer, allowing the mobility to exceed the fully dissociated value. When the counterion is faster, the response remains close to the one-half scaling set by mass action. This reaction-polarisation coupling cannot be reproduced by adjusting only the bulk ionic strength, and hence the Debye length, in a fully dissociated model.
