A dip-coating method was developed to fabricate two-dimensional colloidal crystal films. The thickness of the films fabricated by this method can be obviously controlled from one layer to several tens of layers by adjusting the concentration of suspension and the rate of substrate withdrawing speed. We have performed the dip-coating at air/water and oil/water interface. To compare with the thickness of layers and optical property of colloidal crystals in each case, we have achieved the experiments which showed that the spheres form a face-centered cubic structure, that single crystals in the film can extend to centimeter dimensions and that the thickness of layers is related to the concentration and withdrawing speed. The optimal thickness of colloidal layers is indicated by measurement of optical property of colloidal crystals.
The alkoxide sol-gel synthesis of nano sized titania has been achieved to control crystallite size and phase. It is possible that the rates of hydrolysis and condensation reaction have been modulated. Through these methods, nonaggregated, ultrafine anatase titania and rutile titania particles have been generated respectively. However, amorphous, intermediated structured polyoxotitanate are made use of the mediums that can be translated to rutile titania and anatase titania each other by peroxo treating. The degree of crystallinity and purity of the synthesized materials could affect their structural evolution during heat treatment from 100℃ to 500℃. It was found that the several nanometer titania derived by acidic condition and heating time. According to XRD data of samples heated for several times at 100℃, anatase titania may either transform to rutile titania, or to brookite titania and then to rutile titania or vice versa.
Polymeric colloidal crystals have a pseudo photonic band gap due to small refractive index contrast. Thus, we have synthesized nano sized titania which have a high refractive index of 2.6~2.9, to be applied to the ...