Capillary bridges can form between colloids immersed in a two-phase fluid, e.g., in a binary liquid mixture, if the surface of the colloids prefers the species other than the one favored in the bulk liquid. Here, we study the formation of liquid bridges induced by confining colloids to a slit, with the slit walls having a preference opposite to the one of the colloid surface. Using mean field theory, we show that there is a line of first-order phase transitions between the bridge and the no-bridge states, which ends at a critical point. By decreasing the slit width, this critical point is shifted toward smaller separations between the colloids. However, at very small separations and far from criticality, we observe only a minor influence of the slit width on the location of the transition. Monte Carlo simulations of the Ising model, which mimics incompressible binary liquid mixtures, confirm the occurrence of the bridging transitions, as manifested by the appearance of “spinodal” regions where both bridge and no-bridge configurations are stable or metastable. Interestingly, we find that there is no such spinodal region in the case of small colloids, but we observe a sharpening of the transition when the colloid size increases. In addition, we demonstrate that the capillary force acting between the colloids can depend sensitively on the slit width and varies drastically with temperature, thus achieving strengths orders of magnitude higher than at criticality of the fluid.

中文翻译：

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缝隙中胶体的桥接过渡和毛细作用力。

如果胶体的表面较之于散装液体中所偏爱的物种更喜欢，那么在浸入两相流体（例如二元液体混合物）的胶体之间可能会形成毛细管桥。在这里，我们研究了将胶体限制在缝隙中而引起的液桥的形成，缝隙壁的优先级与胶体表面之一相反。使用平均场理论，我们表明，在电桥状态和非电桥状态之间有一线一阶相变，其终止于临界点。通过减小缝隙宽度，该临界点向胶体之间的较小间距移动。但是，在很小的间距和远非临界的情况下，我们仅观察到缝隙宽度对过渡位置的微小影响。伊辛模型的蒙特卡洛模拟，模拟不可压缩的二元液体混合物的过程，确认了桥接过渡的发生，如桥和非桥构型均稳定或亚稳的“尖峰”区域的出现所证明的。有趣的是，我们发现在小胶体的情况下没有这样的旋节线区域，但是当胶体尺寸增加时，我们观察到过渡的锐化。此外，我们证明了作用在胶体之​​间的毛细作用力可以敏感地取决于缝隙的宽度，并且随着温度的变化而急剧变化，因此所获得的强度要比流体的临界强度高几个数量级。如“尖峰”区域的出现所表明的，其中桥和非桥构型都是稳定或亚稳的。有趣的是，我们发现在小胶体的情况下没有这样的旋节线区域，但是当胶体尺寸增加时，我们观察到过渡的锐化。此外，我们证明了作用在胶体之​​间的毛细作用力可以敏感地取决于缝隙的宽度，并且随着温度的变化而急剧变化，因此所获得的强度要比流体的临界强度高几个数量级。如“尖峰”区域的出现所表明的，其中桥和非桥构型都是稳定或亚稳的。有趣的是，我们发现在小胶体的情况下没有这样的旋节线区域，但是当胶体尺寸增加时，我们观察到过渡的锐化。此外，我们证明了作用在胶体之​​间的毛细作用力可以敏感地取决于缝隙的宽度，并且随着温度的变化而急剧变化，因此所获得的强度要比流体的临界强度高几个数量级。