Liquid crystals alignment and switching between surface reinforced poly(ethylene-co-vinyl acetate) thin layers

Abstract

The alignment characteristics of liquid crystals (LCs) on poly(ethylene-co-vinyl acetate) (PEVA) films via ion-beam (IB) irradiation at incidence angles of 15°, 45°, or 75° were investigated. Uniform and homogeneous LC alignment were achieved with a PEVA film IB-irradiated at an incidence angle of 45°. Physicochemical modification progressed by IB irradiation were examined by using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The AFM results show that the plasma argon ions penetrated and thereby increased the surface roughness and decreased kurtosis of the PEVA. The XPS results suggest that chemical reconstruction of the PEVA film induced the van der Waals forces and dipole-dipole interactions with the LCs. These transformations resulted in uniform LC alignment at 45° IB incident angle, as confirmed by polarized optical microscopy and pre-tilt angle measurements. The 45° incidence-angle IB-irradiated PEVA film also showed high transmittance in the visible light region. A twisted nematic LC cell based-on the PEVA film showed successful electro-optical performance as stable switching behavior and fine operation characteristics. These results indicate that IB irradiation is an effective method for uniform LC alignment and the 45° incidence-angle IB-irradiated PEVA film can be adopted for LC alignment in future LC display applications.