Particulate pattern formation and its morphology control by convective self-assembly

• We review our recent results on the formation of patterned structures of particles.
• We use a bottom-up self-assembly process for the pattern formation.
• The self-assembly process produces various patterns on a completely flat substrate.
• The microstructure of particles varies depending on the macroscopic parameters.
• The self-assembly process forms a template-free technique for pattern formation.

Bottom-up self-organization approaches are promising for fabricating higher-order patterned surfaces composed of colloidal 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. Driven by this finding, we further investigate this self-assembly process, and find out that the convective self-assembly is quite promising as a template-free pattern formation technique. In the present paper, we first overview the convective self-assembly technique which is originally developed for uniform film formation, and then present our recent results on the pattern formation of colloidal particles through the convective self-assembly. This technique can produce various patterns including stripes, cluster arrays, and grids in response to macroscopic experimental parameters such as particle concentration and temperature.

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