牛眼图案上方胶体的临界卡西米尔悬浮
Critical Casimir levitation of colloids above a bull's-eye pattern
AI总结：
本研究利用近临界流体中的临界卡西米尔力，实现胶体在牛眼图案化基底上方的悬浮，揭示了多种悬浮行为及参数依赖关系，为胶体分选和临界距离测定提供了新途径。
摘要：
临界卡西米尔力产生于浸没在近临界流体中的颗粒或表面之间，力的符号由表面性质决定，其强度可通过微小的温度变化进行调节。本文中，我们展示了如何利用这类力捕获胶体颗粒，并使其悬浮在带有牛眼图案的基底上方；该牛眼图案由一个表面性质与基底其余部分相反的环构成。借助德贾金（Derjaguin）近似和平均场计算，我们发现球形胶体在这种图案化表面上呈现出丰富的行为，包括向环沉降、在环上方悬浮（环悬浮）以及在牛眼中心上方悬浮（点悬浮）。在德贾金近似框架内，我们计算了点悬浮的悬浮相图，给出了捕获势深度与胶体悬浮高度，二者均取决于图案性质、胶体尺寸以及溶液温度。我们的计算表明，当系统被驱离临界点时，与点悬浮相关的参数空间会缩小，但出人意料的是，捕获力会变得更强。我们讨论了临界卡西米尔悬浮在按尺寸分选胶体、测定到临界态的热力学距离方面的应用。研究结果表明，临界卡西米尔力为调控图案化表面上胶体颗粒的行为提供了丰富的可能性。
英文摘要：
Critical Casimir forces emerge among particles or surfaces immersed in a near-critical fluid, with the sign of the force determined by surface properties and with its strength tunable by minute temperature changes. Here, we show how such forces can be used to trap a colloidal particle and levitate it above a substrate with a bull's-eye pattern consisting of a ring with surface properties opposite to the rest of the substrate. Using the Derjaguin approximation and mean-field calculations, we find a rich behavior of spherical colloids at such a patterned surface, including sedimentation towards the ring and levitation above the ring (ring levitation) or above the bull's-eye's center (point levitation). Within the Derjaguin approximation, we calculate a levitation diagram for point levitation showing the depth of the trapping potential and the height at which the colloid levitates, both depending on the pattern properties, the colloid size, and the solution temperature. Our calculations reveal that the parameter space associated with point levitation shrinks if the system is driven away from a critical point, while, surprisingly, the trapping force becomes stronger. We discuss the application of critical Casimir levitation for sorting colloids by size and for determining the thermodynamic distance to criticality. Our results show that critical Casimir forces provide rich opportunities for controlling the behavior of colloidal particles at patterned surfaces.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
