Surface memory effect enhanced by atmospheric pressure plasma jet treatment for liquid crystal alignment

In the present work we tried to study Polyimide (PI) film surface memory effect (SME) enhanced by atmospheric pressure plasma jet (APPJ) treatment for liquid crystal (LC) alignment. To evaluate and describe structural changes on the PI film surface, contact angle measurements and Fourier Transformed Infrared (FTIR) Spectroscopy methods were used. After each treatment cycle, the water drop contact angle to the treated surface decreases and FTIR spectra show an increase of CO bonds. When LCs in mesophase are injected into a cell flow alignment occurs, and SME imprints the LC flow alignment pattern onto the surface. Some materials like glass and PI films naturally have SME to some degree; however, in our work we show that treatment by APPJ leads to the enhancement of this effect. Kinetics of the alignment pattern imprinting process was investigated by varying the incubation duration, and at room temperature the minimum required time for the imprinting alignment pattern was found to be 20 min. It was shown that the imprinted alignment of LCs on APPJ treated PI films has excellent heat resistance up to 150 °C.