Optimized thermal treatment for preparation of double inverse opals incorporating movable cores

A combination of the co-assembling process to fabricate binary colloidal crystals (BCCs) and the successive heat treatment to selectively remove the polymer component from the BCCs was conducted to create double inverse opals (DIOs) in which a movable sphere was embedded within each inorganic compartment of nanoparticles. Micron-sized silica cores coated with polystyrene shell and silica nanoparticles were used as the BCC components in the co-assembling process. According to the residue profile measured in thermogravimetric analysis, the heat treatment at low temperatures of 250, 300 and 350°C was conducted to find a cost-effective process, resulting in finding that 300°C heating for 7 h was suitable for obtaining the high movability of micron-sized cores in the compartment. Application of 1 kHz electric field at strength higher than 100 V/mm could suppress the random motion of cores in a wet-state DIO.