Controlling the Pretilt Angles of Guest–Host Liquid Crystals via a Hydrophilic Polyimide Layer through Oxygen Plasma Treatment

The control of the liquid crystal (LC) alignment is an important factor for practical applications. The conventional method typically used is the rubbing of the polyimide (PI) layer. However, it is difficult to obtain intermediate pretilt angles by employing such a method. In this paper, control of the pretilt angle of the LC is achieved by modifying the surface wettability of the PI films via oxygen plasma treatment. A new mode for guest–host liquid crystal (GHLC) smart windows is achieved with intermediate initial transmittance by controlling the pretilt angle, which can turn from the initial state to either the transparent or dark states. Different modes for the GHLC-based smart windows can be fabricated that are dependent on the environmental conditions.