Di Leonardo R, Ianni F, Ruocco G
CNR-INFM, CRS-SOFT c/o Dipartimento di Fisica, Universitá di Roma La Sapienza, Roma, Italy.
Langmuir. 2009 Apr 21;25(8):4247-50. doi: 10.1021/la8038335.
Colloidal crystals are of extreme importance for applied research and for fundamental studies in statistical mechanics. Long-range attractive interactions, such as capillary forces, can drive the spontaneous assembly of such mesoscopic ordered structures. However, long-range attractive forces are very rare in the colloidal realm. Here we report a novel strong, long-ranged attraction induced by a thermal gradient in the presence of a wall. By switching the thermal gradient on and off, we can rapidly and reversibly form stable hexagonal 2D crystals. We show that the observed attraction is hydrodynamic in nature and arises from thermally induced slip flow on particle surfaces. We used optical tweezers to measure the force law directly and compare it to an analytical prediction based on Stokes flow driven by Marangoni-like forces.
胶体晶体对于应用研究以及统计力学的基础研究极为重要。长程吸引相互作用，如毛细作用力，能够驱动此类介观有序结构的自发组装。然而，长程吸引力在胶体领域非常罕见。在此，我们报道了一种在有壁存在的情况下由热梯度诱导产生的新型强长程吸引力。通过开启和关闭热梯度，我们能够快速且可逆地形成稳定的二维六角形晶体。我们表明，观察到的吸引力本质上是流体动力学的，并且源于颗粒表面的热致滑移流。我们使用光镊直接测量力定律，并将其与基于类马兰戈尼力驱动的斯托克斯流的解析预测进行比较。
