Masud Aurangzeb Rashid1 Tian-zi Shen1 Jang-Kun Song1

1, Sungkyunkwan University, Suwon, , Korea (the Republic of)

Liquid photonic crystal can be manipulated by applying external stimuli, which provides promising pathway for its applications in electro-optical devices, sensors, and displays. To date, most of photonic crystal colloid has been obtained by dispersing spherical nanoparticles in solvents. In the spherical colloids, the mean distance among spherical particles is the only parameter to achieve the controllable photonic crystallinity, and for the purpose, swelling/deswelling or concentration change is commonly used. Recently, another type of photonic crystal colloids using two-dimensional (2D) particles have been introduced. In these materials, not only the mean distance between particles but also the rotational ordering of particles can be controlled independently, that is, both the positional order and orientational order of particles are controlled to manipulate the photonic crystallinity in 2D colloids. In this presentation, we will introduce several new 2D colloids exhibiting abundant novel phenomena including controllable photonic crystallinity. In particular, we will demonstrate that the structural color reflection in 2D photonic crystal colloids can be electrically manipulated via three different physical mechanisms: the dielectrophoretic density modulation, the rotational manipulation of particles using the anisotropy in Maxwell-Wagner polarization, and electric field-induced anomalous orientation of 2D particles. The distinctive behaviors and features in each mechanism will be discussed. Differently from spherical colloids, not only the reflection peak wavelength but also the reflectance is electrically tuned, which is required to accomplish the full color and full gray scale display applications. We also demonstrate that the field-induced particle ordering structure is sustained even after turning off the signal, resulting in multi-stable photonic crystalline reflectance. Using the property, one can make a low-power reflective display with non-volatile images without power.