Existing theories of diffusioosmosis have neglected ion–ion electrostatic correlations, which are important in concentrated electrolytes. Here, we develop a mathematical model to numerically compute the diffusioosmotic mobilities of binary symmetric electrolytes across low to high concentrations in a charged parallel-plate channel. We use the modified Poisson equation to model the ion–ion electrostatic correlations and the Bikerman model to account for the finite size of ions. We report two key findings. First, ion–ion electrostatic correlations can cause a unique reversal in the direction of diffusioosmosis. Such a reversal is not captured by existing theories, occurs at ≈ 0.4 M for a monovalent electrolyte, and at a much lower concentration of ≈ 0.003 M for a divalent electrolyte in a channel with the same surface charge. This highlights that diffusioosmosis of a concentrated electrolyte can be qualitatively different from that of a dilute electrolyte, not just in its magnitude but also its direction. Second, we predict a separate diffusioosmotic flow reversal, which is not due to electrostatic correlations but the competition between the underlying chemiosmosis and electroosmosis. This reversal can be achieved by varying the magnitude of the channel surface charge without changing its sign. However, electrostatic correlations can radically change how this flow reversal depends on the channel surface charge and ion diffusivity between a concentrated and a dilute electrolyte. The mathematical model developed here can be used to design diffusioosmosis of dilute and concentrated electrolytes, which is central to applications such as species mixing and separation, enhanced oil recovery, and reverse electrodialysis.

中文翻译：

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由于离子-离子静电相关性导致的扩散渗透流逆转

现有的扩散渗透理论忽略了离子-离子静电相关性，这在浓电解质中很重要。在这里，我们开发了一个数学模型来数值计算带电平行板通道中二元对称电解质从低浓度到高浓度的扩散渗透迁移率。我们使用修正的泊松方程来模拟离子-离子静电相关性，并使用 Bikerman 模型来解释离子的有限尺寸。我们报告了两个重要发现。首先，离子-离子静电关联可以引起扩散渗透方向的独特逆转。现有理论无法捕捉到这种反转，对于具有相同表面电荷的通道中的单价电解质，发生在 ≈ 0.4 M 的浓度，而对于二价电解质，发生在 ≈ 0.003 M 的低得多的浓度下。这突出表明，浓电解质的扩散渗透与稀电解质的扩散渗透有本质上的不同，不仅在其大小上，而且在其方向上。其次，我们预测单独的扩散渗透流逆转，这不是由于静电相关性而是由于潜在的化学渗透和电渗透之间的竞争。这种反转可以通过改变沟道表面电荷的大小而不改变其符号来实现。然而，静电相关性可以从根本上改变这种流动逆转对通道表面电荷以及浓电解质和稀电解质之间的离子扩散率的依赖程度。这里开发的数学模型可用于设计稀释和浓缩电解质的扩散渗透，这对于物质混合和分离、提高采油率和反向电渗析等应用至关重要。