Pretilt angle control of main-chain liquid crystal polymer in photoalignment process
The modulation of azimuth and pretilt angle of liquid crystals(LCs)is widely used in the study of various liquid crystal photonic devices.Comparing to unstability and unreliability of small molecule LC devices fabricated by pretilt angle modulation,LC polymers have some prominent advantages like high phase transition temperature,heating and glaring resistance,stability of mechanical vibration,and so on.Since the LC monomer is affected by the anchoring energy at the interface between LC and air,the pretilt angle of LC polymers is related to the thickness of the LC layer,which makes it difficult to achieve a stable and controllable pretilt angle.In this study,a two-step exposure of azo-dye bright yellow(BY)film was used to guide the tilt of LC monomer RM257,and the effect of the anchoring force at the LC-air interface was reduced by using multilayer spin-coating process and the photopolymerization of LC monomer RM257.Through the controllable preparation of pretilt angle of the LC polymers,it shows that the range of pretilt angle can be continuously adjusted between 0° and 16° with the photo-thermal stability and the potential patterning capability for LC photonic devices.This study is expected to provide a new way for the preparation of LC photonic and display devices.
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