Effect of evaporation temperature on the quality of colloidal crystals at the water-air interface

Three-dimensional assemblies of 230 nm polystyrene (PS) colloidal particles were prepared on the suspension surface by evaporating the water in which the particles were suspended. The assembled colloidal particles were then transferred from the water surface onto a glass substrate by simple evaporation and sedimentation. In this study, we analyzed the structures of the colloidal assemblies formed at evaporation temperatures of 30, 40, 60, and 90 degreesC. At 30 degreesC, the rate of particle sedimentation is faster than the rate of crystallization on the water surface. Consequently, the PS particles randomly stack on the glass substrate before forming nuclei on the water surface. At higher evaporation temperatures, on the other hand, the rate of crystallization on the water surface exceeds the sedimentation rate, leading to an improvement in the quality of the resulting colloidal crystal. However, crystalline quality diminishes at evaporation temperatures greater than 60 degreesC because the high crystal growth rate leads to the formation of defects. As a result, there exists an optimum evaporation temperature that yields the highest quality crystals. Importantly, this novel process enables the rapid (within I h) fabrication of large-scale three-dimensional colloidal crystals.