Insights into the assembling parameters of colloidal crystal fabricated by floatage self-assembly method

For the fabrication of colloidal crystal by floatage self-assembly, the influence of parameters was investigated. The three-dimensional structure of the colloidal crystal was characterized by synchrotron radiation x-ray phase-contrast computed tomography, and the quantitative analysis was conducted. We found that the transferring speed of the spheres in the assembling process is significant and can be influenced by the sphere size, ratio of mixed solvents, and assembling temperature, which actually introduce the effect of density and viscosity of the solvent. The decreasing sphere size and solvent viscosity both help reduce the porosity of the array. The concentration of the suspension should be enough to supply sufficient spheres up to the growing front under the action of floatage for ordered arrangement. The floatage self-assembly method with capillary force and floatage could promote an arrangement with strong attraction among the spheres, especially for the first template layer; thus, it enables a broad concentration range for preparation with steady porosity, and the final drying process has little impact on the structure. For the elevated assembling temperature, it has many positive impacts on the orderliness, including decreasing the transferring speed for a steady assembly process, strengthening the lateral capillary force for nucleation, raising the kinetic energy of spheres for assembling, and restraining the disturbance of hcp structure in thermodynamics. However, the temperature should also be restricted in a certain range to repress the excessive solvent evaporation.