| dc.description.abstract | Nowadays, liquid crystal (LC) technology is getting more and more mature due to its novel developments and applications in electro-optical fields. Recently, we would like to invent some new devices which can be applied to billboards, electronic tags, etc. By using bi-stable textures of cholesteric LCs, the structures can be chosen to be stabilized in the desired state. According to the experimental results, it shows that it can be kept in the desired state for more than two weeks.
This study presents the multi-stable and reusable LC display devices using 12-hydroxysteric acid (HSA)-doped LCs in a poly(N-vinylcarbazole) (PVK) film-coated LC cell. Through the branches of hydrogen-bond of HSA, the structures of the cholesteric LC can be stabilized. By increasing the temperature over the melting point of HSA, the hydrogen bonds break down and HSA molecules dissolve in the LC host. If we keep increasing the temperature to the clearing point of the LC host, the cholesteric LC will turn into its isotropic state. With the application of suitable external voltages onto the LC cell at the temperature between the melting points of HSA and the clearing point of LC, we can get the focal conic state of cholesteric LC. Keep applying voltage onto the LC cell and then decrease the temperature of the LC cell to room temperature. After that, keeping at the room temperature and applying a suitable voltage onto the LC cell to make sure the structures are stable enough. Through the method described above, the LC cell will be kept in the state of the focal conic. If we decrease the temperature of the LC cell slowly without applying any voltage, the LC cell will present planar textures with the conditions of long pitch length and small cell gap. Because of the homogeneous alignment films, long pitch length, and small cell gap, the LC cell will tend to stay in the planar textures without applying any voltage. As the two methods mentioned above, the LC cell can have two different stable structures.
According to the method described above, PVK films are coated onto the LC cell and expose the PVK to UV light through a photo-mask having the desired patterns simultaneously. In the meantime, an external voltage is applied to the LC cell. The regions with UV exposure present focal conic textures, and the regions without UV exposure present planar textures. We cool down the temperature slowly and apply a suitable voltage simultaneously. Thereafter, the LC cell will have the pattern we want. | en_US |