Development and comparison of azimuthal anchoring energy using novel photo-initiators

Abstract

We synthesized two novel photo-initiators to increase the surface energy of liquid crystal (LC) and reduce the UV irradiation time what is the worst problems of photo-alignment method at the same time. Photo-initiators were respectively synthesized by using hexanoic anhydride and crotonic anhydride and then analyzed to confirm the synthesis by FT-IR, H-NMR and UV-Vis and were measured for contact angle, pretilt angle and azimuthal anchoring energy. In the UVVis spectra, Photo-initiator what synthesized by crotonic anhydride (CAP) showed the faster reactivity than photo-initiator what synthesized by hexanoic anhydride (HAP). Photo-initiators had gradually decreased in absorbance and characteristic bimodal shape at 270~280nm and completed the photo-degradation reaction within 1 minute as soon as possible within 5 minutes at the latest and a photo-initiator using hexanoic anhydride(HAP) generally had the largest decrease width. Also, CAP had nearly twice maximum anchoring energy, 6.93*10-5 J/m2 at 10 minutes of UV irradiation time, as likely to HAP, 3.68*10-5 J/m2 at 8 minutes. Each photoinitiators have the specific time what indicates the maximum anchoring energy and this results from its difference of molecular structures.