Max-Planck-Institut für Metallforschung, Heisenbergstr. 3, D-70569 Stuttgart, Germany.
J Chem Phys. 2010 Aug 21;133(7):074702. doi: 10.1063/1.3464770.
Colloids immersed in a critical or near-critical binary liquid mixture and close to a chemically patterned substrate are subject to normal and lateral critical Casimir forces of dominating strength. For a single colloid, we calculate these attractive or repulsive forces and the corresponding critical Casimir potentials within mean-field theory. Within this approach we also discuss the quality of the Derjaguin approximation and apply it to Monte Carlo simulation data available for the system under study. We find that the range of validity of the Derjaguin approximation is rather large and that it fails only for surface structures which are very small compared to the geometric mean of the size of the colloid and its distance from the substrate. For certain chemical structures of the substrate, the critical Casimir force acting on the colloid can change sign as a function of the distance between the particle and the substrate; this provides a mechanism for stable levitation at a certain distance which can be strongly tuned by temperature, i.e., with a sensitivity of more than 200 nm/K.
胶体沉浸在临界或近临界二元液体混合物中，并靠近化学图案化的基底，会受到正常和横向临界 Casimir 力的强烈影响。对于单个胶体，我们在平均场理论中计算这些吸引力或排斥力以及相应的临界 Casimir 势能。在这种方法中，我们还讨论了 Derjaguin 近似的质量，并将其应用于可用于研究系统的蒙特卡罗模拟数据。我们发现，Derjaguin 近似的有效范围相当大，并且仅在表面结构与胶体的几何平均值及其与基底的距离相比非常小的情况下才失效。对于基底的某些化学结构，作用在胶体上的临界 Casimir 力可以随粒子与基底之间的距离而改变符号；这为在一定距离处稳定悬浮提供了一种机制，这种悬浮可以通过温度进行强烈调节，即，灵敏度超过 200nm/K。
