Pattern Formation of Binary Colloidal Particles

Abstract

Bottom-up self-organization approaches are promising for fabricating higher-order patterned surfaces composed of submicron particles. Thus far, several techniques have been reported to fabricate complex particulate films such as stripes, rings, and circular domain arrays. We have been studying an evaporation-induced self-assembly technique, and reported the stripe pattern formation on a completely hydrophilic substrate. By using this technique, a stripe pattern was produced simply by suspending a substrate in a fairly dilute suspension, without any complicated procedure; the stripes spontaneously aligned parallel to the contact line. In the present study, we examined the effects of salt concentration on the morphology of resultant particulate films. We found out that, under a specific condition, a Sierpinski gasket pattern formed in an ion concentration region around 10^－3 M. The requirement for the Sierpinski gasket formation was found out to be the use of a mica substrate and lithium or sodium ion. In this concentration region, alkali ions with a firm hydration layer would play a role as a lubricant between particles and a mica substrate which has an ion-exchange capacity to help the cations adsorbed on the substrate.