Two-photon absorption initiating crosslinking of diacrylate mesogen RM257 has been studied. Two-photon absorption process in the diacrylate mesogen is trigged by a low-power continuous laser irradiation at 632.8 nm wavelength. In order to manipulate the diacrylate mesogen to contain local structures, a thin layer of RM257 was exposed to a holographic irradiation produced by means of two-beam interferometry, in which the two coherent beams were provided by a HeNe laser. The holography irradiation acts double as the optical source that provides energy to produce freeradicals for initiating the crosslinking of the acrylate units and the driving force for the alignment of mesogenic groups in the diacrylate mesogen. The regions in the resultant diacrylate polymer exposed to the constructive fringes are found to contain ordered polymer network whose mesogenic groups orient perpendicular to the polarization of the holographic field, whereas those regions exposed to the destructive fringes present isotropic polymer networks.
The effect of self-assembled monolayers on the molecular stack of discotic liquid crystals has been studied. The self-assembled
monolayers, which consist of functional groups on the terminal of the silane molecules, were formed by
attaching themselves on a solid surface, and the surface energies of substrates were found to be varied greatly. On the
substrates modified by the 3-aminopropyltriethoxysilane, which possess higher surface free energy, discotic molecules
tend to assemble with disk-face-on anchoring; whereas discotic molecules tend to assemble with disk-edge-on anchoring
when stacking on the substrate surface modified by the octadecyltrichlorosilane, which possess lower surface free
energy. The initial observation also revealed the capability to imprint specific patterns of discotic molecular orientation
on the substrate surfaces via silane modifications.
The effects of plasma surface treatment on molecular stacking of a discotic liquid crystal are studied. Glass substrates are
bombarded by an obliquely incident O<sub>2</sub> plasma beam. Plasma treatment causes an increase in surface free energy of the
substrates, and in addition, the oblique plasma beam generates a preferential direction on the surface processed. The
configuration of the cell is found to be crucial to achieve alignment of the discotic columns, and in general, cells with
anti-parallel configuration of substrates should be used to achieve uniform alignment of the columnar phase.
Homeotropic alignment of dichotic columns can be produced on plasma treated glass substrates with high surface free
energy. When the surface free energy of the substrate decreases, the axes of the discotic columns will tilt from the
normal of the substrate and towards the preferential direction.
Molecular stacking of discotic liquid crystals through self-assembly on solid substrates is observed. During the
molecular stacking, thermal conditions can strongly affect the arrangement of discotic molecules. For ordered molecular
stacking of discotic molecules slow and smooth variation in temperature is necessary. By carefully controlling cooling
rate below 0.3°C min<sup>-1</sup>, orientational molecular stacking of discotic molecules and uniaxial aggregation of discotic
columns can be produced on planar glass and indium-tin-oxide surfaces. If the temperature of discotic compound drops
too fast, ordered molecular stacking may be destroyed by thermal turbulence due to fast change of temperature in