SECONDMENTS

The functionalized substrate consists of thermally poled ionic glass surfaces, a treatment that brings an electrical function to the material. This electrical function can be further used to tailor liquid crystals alignments. Recently, it has been shown that it is possible to produce µ-meter sized multi-domain liquid-crystals alignments using such functionalized substrates. This proof of concept was an important milestone and demonstrates the potential of poled glass liquid crystal systems.

The next step consists in the rationalization of the alignment phenomenon occurring when putting ionic poled glass surfaces in contact with liquid crystals. Two studies are conducted here: First study on the origin of the electrical function via an investigation of the glass structure (objective 1), second study on the interaction between the poled glass substrate and the liquid crystal (objective 2). During this secondment, the work will be focused on the second study.

To quantify the interaction between the poled substrate and the molecules, an important parameter to know is the anchoring energy of the substrate. This parameter can be seen as the energy necessary to deform the liquid crystal molecules alignment from their initial equilibrium position. To determine the value of the poled glass substrate anchoring energy, several samples were fabricated at ISM prior to this secondment. The samples consist of two substrates, a poled glass on one side and a conventional polymer layer on the other side, glued together with only a thin space between them (usually a few micrometres). This space is then filled with liquid crystals molecules and the final product is called a liquid crystal cell (LC cell). Two types of LC cells were conceived: In-Plane Switching (IPS) cells, Vertical Alignment (VA) cells.  Polarization microscopy setup will be used at COPL to collect data on the interactions between the molecules and the electrically functionalized glass substrate. Most importantly, Pr. Tigran Galstian will contribute to the theoretical understanding of the phenomena, which is essential to quantify the anchoring energy.

Along this main objective, EDS analysis will be performed on poled glass substrates to complete the structural study of the objective 1. Also, reference IPS and VA LC cells with no poled substrate will be fabricated, and experiments on the aging of poled glass and its effects on the liquid crystal alignment at its contact will be done if time allows to.

• Polarization microscopy measurements of IPS liquid crystal cells:
  • IPS poled glass liquid crystal cell measurements
  • IPS reference liquid crystal cell measurements
• Polarization microscopy measurements of VA liquid crystal cells:
  • VA poled glass liquid crystal cell measurements
  • VA reference liquid crystal cell measurements
• Estimation of the anchoring energy of a poled glass:
  • Theoretical background
  • Results analysis
• EDS analysis of poled glass