1. The research team reported in Nature Materials  (2014) that a 2D nano colloid can be used in liquid crystal display; and since then, has kept pursuing the research to advance and accomplish application technologies. The relevant research results have been published in more than 10 journal papers including Optics Express, Journal of Physical Chemistry C, Carbon, and Langmuir.

    In conventional LCD devices, the application of electric fields higher than 1 V/μm is required to induce dynamic switching of liquid crystal molecules. In comparison, the team discovered that the electric field required for the switching of graphene-oxide (GO) 2D colloid was about 0.01 V/μm, which is 1/100 of conventional LCDs. Unlike the conventional liquid crystals based on organic molecules, the 2D particles with high aspect ratio have thick electrical double layers (EDL) near the surface, and the EDL is sensitively modulated by electric fields. As a result, the corresponding Kerr coefficient, which represents the optical sensitivity of material by electric field, is the highest in GO colloid among all known materials.

 
Recently, the team continued this research using another 2D material, functionalized ZrP, which has higher optical transmittance and better chemical stability. In particular, the interparticle interactions between ZrP particles such as friction and electrostatic repulsion can be controlled by decorating them with appropriate polymers. Using this technology, the team demonstrated that the electrical switching of 2D colloid can be obtained even in nematic phase, in which the interparticle interactions is rather strong. The advantage of the switching of 2D colloind in nematic phase is that even after tuning off the external power, the written information can be retained, differently from usual LCDs.

- Selected paper: Electro-optical switching of graphene-oxide liquid crystals with an extremely large Kerr coefficient (Nature Materials, 2014).
- Relevant articles in media: ‘Development of graphene oxide liquid crystal materials with 1000 times higher performance.’

2. The research team is also studying photonic crystal materials using 2D colloid. Photonic crystals can emit structural color without any dye or phosphor materials by using the interference between the periodic matter assembly and the external light, and so, it attracts increasing attention because of its high applicability in future display devices, solar cells, and photo-sensors. In particular, controllable photonic crystal is essential to achieve the display applications, and the only known technology for the controllable photonic crystals was to use a colloid of spherical particles, in which swelling and deswelling of spherical particle colloid exhibits the shift of reflection color. However, the technology is difficult to accomplish and brightness control is not possible.

To overcome the problem, the research team introduced the 2D particle colloid for the controllable photonic crystal devices. The reflection color can be controlled by modifying the concentration of 2D particles, and the brightness can be electrically controlled by rotating the alignment direction of 2D particles. In addition, the research team reveals the mechanism that the photonic crystal alignment can be obtained in flexible 2D particle colloid, by revealing the alignment of 2D particles in colloidal state. The relevant research results were published in NPG Asia Materials, Optics Express, etc.

- Selected paper: Bottom-up and top-down manipulations for multi-order photonic crystallinity in a graphene-oxide colloid, (NPG Asia Materials, 2016)
- Relevant articles in media: ‘Development of controllable photonic crystal device using graphene-oxide colloid’