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Influence of Substrate Pattern and Colloidal pH on Self-Assembly of Polystyrene Microspheres
Colloidal crystals fabricated by self-assembly of monosized (mostly spherical) particles can be used as a template for making regularly arrayed porous membranes and for new optical devices possessing photonic band gap. In recent years, there has been much interest in the self-assembly of “bulk”colloidal crystals from spherical particles via the bottom-up approach. One might suspect that if the structure and defect of colloidal crystal can be properly controlled, their application would become more prominent. In this regard, our experiment was divided into two parts, and the self-assembly structure was examined.
First, we investigate the process variables influencing the self-assembly of spherical particles on patterned substrates. Colloidal solution consisting of polystyrene latex microspheres (PS microspheres) and water was used in the experiment. Evaporation and convection of liquid were the mechanisms involved in the self-assembly of PS microspheres on the patterned substrates with rectangular grooves prepared from photolithography. The evaporation temperature was adjusted to find the most favorable particle-packing condition. SEM images of the self-assembled PS microspheres were compared with theoretical estimate to analyze the variation of packing arrangement when the groove depth and groove width were varied.
Second, colloidal pH was changed and the variation of surface potential of the PS microsphere was measured by zeta potential analyzer. The self-assembly of PS microspheres at different pH conditions on bare (i.e. no pattern) substrate was examined. In the basic condition (pH=9 and pH=10), the self-assembly of monolayer PS microspheres was energetically favorable. This finding was then used to fabricate “binary” colloidal crystals consisting of colloidal particles of different sizes.
|Appears in Collections:||材料科學與工程學系|
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