Studies On Preparation Of PS Colloid Crystal Templates And Assembly Of SnO₂ Porous Films

Polystyrene (PS) spheres colloid crystal array was assembled by dip-drawing method and ordered SnO2 macroporous thin films were fabricated by using the PS colloid crystal as template. The forming mechanism of colloid crystal was discussed; the advantage of dip-drawing method to assemble PS template and fill SnO2 sol was exhibited; the influence of fabricating parameters on the array quality, the number of spheres and morphology of porous films was studied; and the structure and optical properties of PS array and SnO2 porous films were analyzed.In the course of PS sphere assembly in meniscus at the solid/liquid interface, the absorption force, flotage and capillary force are responsible to the nucleation and growth of colloid crystal. Dip-drawing method enlarges the evaporation area of the wet array due to the quicker movement of leading edge, so that the solvent evaporation and solution flux are accelerated.The increasing PS volume fraction in emulsion enhances the effective sphere transfer into the meniscus by the solution flux. The emulsion temperature during dip-drawing directly impacts the solvent evaporation and then PS sphere transfer. High temperature leads to faster colloid crystal growth. A proper temperature makes the PS spheres transfer to lattice site with lower free energy, so as to improve the array quality. Increasing drawing rate also promotes the evaporation in the wet array region and thus the sphere transfer to the meniscus, which accelerates the crystal growth. To obtain a perfect colloid crystal, the parameter mentioned above should cooperate with the sphere size. After drawing the substrate, the wet film should be dried horizontally in the air at 20℃to keep drying uniformity.The PS crystal array films obtained by dip-drawing method appeared prismatic colors like rainbow due to Bragg diffraction on the parallel planes of fcc (111). The visible attenuation dips in the UV-VIS transmission spectra appeared near 390 nm, 678nm and 800nm corresponding to the 305nm, 510nm and 650nm sphere array, respectively.With dip-drawing method used to fill sol into the PS array, filling content of SnO2 sol can be balanced by capillary force and gravity, leading to a stable filling content, avoiding the difficulty of control on the required content of precursor in vertical pouring method.The suitable sol concentrations which have a satisfactory permeation and...