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 O2 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-1, 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
adjacent regions.
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