Spontaneous Pattern Formation of Colloidal Particles by Evaporation-Induced Self Assembly

自下而上的自组织方法有望用于制备由亚微米颗粒组成的高阶图案化表面。第一个被广泛研究的图案是条纹;然而，条纹图案的形成迄今为止仅限于部分或完全疏水的表面。相比之下，我们已经成功地制备了明确的条纹图案，即使在强亲水性基板上通过对流自组装技术。通过使用这种技术，简单地通过将衬底悬浮在稀悬浮液中来产生条纹图案，而没有任何复杂的过程;条纹自发地平行于接触线排列。我们发现，无论是粘滑运动，也不去湿，疏水表面上的控制过程，是相关的这项技术，相反，颗粒浓度的负反馈，引起的凹弯曲形状的弯月面，支配条纹的形成。然后我们研究了悬浮液中离子浓度的影响。在低浓度区，由于弯月面尖端的指进不稳定性，形成了垂直于接触线的条纹。另一方面，在高浓度区域中形成衬垫图案，这将是因为离子起到颗粒和基板之间的润滑剂的作用。

Bottom-up self-organization approaches are promising for fabricating higher-order patterned surfaces composed of submicron particles. The first example among the patterns that have been extensively studied would be stripes; however, the formation of stripe patterns has so far been confined to partially or fully hydrophobic surfaces. By contrast, we have succeeded in preparing well-defined stripe patterns even on strongly hydrophilic substrates via a convective self-assembly technique. By using this technique, a stripe pattern was produced simply by suspending a substrate in a dilute suspension, without any complicated procedure; the stripes spontaneously aligned parallel to the contact line. We reveal that neither stick-slip motion nor dewetting, which control processes on hydrophobic surfaces, is relevant to this technique; instead, negative feedback of particle concentration, induced by a concavely curved shape of the meniscus, governs the stripe formation. Then we examined the effect of ion concentration in a suspension. In a low concentration region, stripes formed vertical to the contact line, which would be due to the fingering instability of the tip of the meniscus. On the other hand, a gasket pattern formed in a high concentration region, which would be because ions play a role as a lubricant between particles and a substrate.