Abstract: A method for the preparation of polystyrene ( PS ) monolayer colloidal crystal ( MCC ) was presented in this paper. The sub-micrometer PS colloidal microspheres were self-assembled into MCC at the air-water interface of the emulsion using ethanol and water with certain mass ratio ( K, Mass ratio of ethanol and water) as mixed dispersed medium under definite temperature. The results indicate that the PS colloidal microspheres protrude easily from the water surface as a result of water convection. The strong attractive capillary force generated from the meniscus between two PS colloidal microspheres at the air-water interface causes the PS colloidal particles to assemble into the ordered regions ( nucleation ) . These ordered regions grow due to the convective transport of the particles to the ordered regions ( aggregation ) , and the MCC was obtained successfully. The attractive capillary force was changed correspondingly while the wettability between the dispersion medium and the PS colloidal microspheres at the air-water interface was adjusted by the K, therefore the K is a key factor in the formation of the MCC. The layer number of the colloidal crystal were influenced by the mass percentage concentration of the PS microspheres, however the MCC can't be obtained by reducing the concentration merely under the K<15∶1. The ordered arrangement and the number of defects of the MCC were related with temperature.

Key words: A method for the preparation of polystyrene ( PS ) monolayer colloidal crystal ( MCC ) was presented in this paper. The sub-micrometer PS colloidal microspheres were self-assembled into MCC at the air-water interface of the emulsion using ethanol and water with certain mass ratio ( K, Mass ratio of ethanol and water) as mixed dispersed medium under definite temperature. The results indicate that the PS colloidal microspheres protrude easily from the water surface as a result of water convection. The strong attractive capillary force generated from the meniscus between two PS colloidal microspheres at the air-water interface causes the PS colloidal particles to assemble into the ordered regions ( nucleation ) . These ordered regions grow due to the convective transport of the particles to the ordered regions ( aggregation ) , and the MCC was obtained successfully. The attractive capillary force was changed correspondingly while the wettability between the dispersion medium and the PS colloidal microspheres at the air-water interface was adjusted by the K, therefore the K is a key factor in the formation of the MCC. The layer number of the colloidal crystal were influenced by the mass percentage concentration of the PS microspheres, however the MCC can't be obtained by reducing the concentration merely under the K<15∶1. The ordered arrangement and the number of defects of the MCC were related with temperature.