Dynamic Of Self-assembly And Optical Properties Of Colloidal Crystals

Colloidal system is considered as a good counterpart of atomic system (or molecular system) to study cooperative phenomena which are not likely to be investigated directly in atomic system, such as nucleation, phase transition and defect dynamics. In general, the colloidal system in a certain volume fraction can gather together under the applied electric field, magnetic field, capillary force, gravity, etc. Therefore, the external field can be used as the driving force to change the aggregate state (phase change). Among the above external field, the external electric field has been widely used because it is easy to control and can be used in a wide range. Although many theories on colloidal behavior and crystallization process are well known until now, among them many controversies still exist. And thus more experimental results are needed to confirm them.And besides, preparation of the uniform scale, size controlled colloidal particles and the large area assembly of colloids are still not resolved. In this thesis, research was carried out from the two above aspects. The main content and results achieved in this paper are summarized as follows:1. we have studied the behavior of colloids under the alternating electric field: firstly, we built up a experimental sealed cell with one ITO conducting glass on which there are negative photoresist patterns and another ITO glass as electrodes and a piece of silica plate as a spacer. And then, the alternating electric signal was switched on after adding colloidal suspension in the sealed experimental cell. While changing the frequency of alternating electric field, the real time behavior of colloids was observed and recorded using the optical microscope. Finally, the colloids'behavior was analyzed from the point of mechanical analyze and the further complete explanation was put forward to explain why the colloids moved in that way with tuning the frequency.2. Polystyrene colloidal particles with high roundness, narrow size distribution, monodisperse and controllable sizes were prepared using emulsion polymerization method. By changing the amount of initiator, polystyrene colloidal particles with sizes of 200 nm, 250 nm and 285 nm were prepared. The SEM images of the particles were characterized by statistical analysis and three different particle size distributions were 1.2 %, 1.6 % and 0.7 % respectively, less than 5 %. It turns out the colloidal particles meet the distribution conditions to prepare colloidal crystals.3. 3D colloidal crystal films with monodisperse PS colloids were prepared by inclined deposition method. And then the effects of temperature, dispersion medium, colloids'sizes, colloids'concentration and the additives SDS on quality and optical property of colloidal crystals were surveyed. The photonic band gap, structure and morphology of colloidal crystals were analyzed by UV-Vis spectra and SEM images respectively. We determined the optimum conditions for preparation of colloidal crystals and made further discussion and find out how the various factors effected on the morphology, structure and the photonic band gap of colloidal crystals.