Liquid crystal-substrate interaction

Alignment of liquid crystal’s orientational order, through its interaction with the substrate, is a critical element in liquid crystal (LC) displays. As an extension of the pioneering study on such interactions [1,2], the recent research focus on this topic is on the use of micro / nanotextured substrates for producing uniform alignment of nematic LC’s orientational ordering [3,4]. The basic principle underlying this approach is “frustration,” i.e., when the elastic energy required for the boundary LC layer to following the micro / nanotextured pattern exceeds a certain threshold, it becomes energetically favorable to sacrifice the interfacial interaction energy so as to minimize the elastic energy, by making a transition to a uniform alignment. What we have found is that by using such micro / nanotextured substrates, one can achieve large pretilt angles, e.g., on the order of 40 degrees (between the symmetry axis of the nematic LC and the substrate). This has been experimentally verified [3]. Large pretilt angles are useful for making bistable LC displays, with the advantage of energy savings.



Optical reflection micrographs taken with crossed polarizers of LC cells made from a series of microtextured substrates. The upper plates of the cells are ITO/glass coated with PI uniaxially rubbed along y


Representative publications:

  1. “Phase Transition in Surface-Aligned Nematic Films,” P. Sheng, Phys. Rev. Lett. 37, 1059 (1976).
  2. “Boundary-layer phase transition in nematic liquid crystals,” P. Sheng, Phys. Rev. A26, 1610 (1982).
  3. “Liquid crystal orientation transition on microtextured substrates,” B. S. Zhang, F. K. Lee, O. K. C. Tsui and P. Sheng, Phys. Rev. Lett. 91, 215501 (2003).
  4. “Liquid-crystal phase transitions induced by microtextured substrates,” T. Z. Qian and P. Sheng, Phys. Rev. Lett. 77, 4564 (1996).