Study on the molecular orientation of liquid crystals induced by crosslinked and patterned poly(vinyl cinnamate) photoalignment layer

Abstract

This work dealt with the improvement of the pretilt angle of the photo-induced liquid crystal alignment. Basically, the incorporation of PDMS into the PVCi network, which was widely used as a photoalignment layer, is the strategy for the full control of the pretilt angle. Another problem of using photoalignment layer to fabricate the full control of the pretilt angle is reduction of azimuthal anchoring energy. Previous researchers reported that the defect of LC orientation is observed during the intermediate pretilt angle range. The content of the alignment layer favoring vertical alignment of LC has no contribution to the azimuthal anchoring energy of the LCs, and thus the ability of in-plane LC orientation becomes weaker at the intermediate pretilt angle where PDMS has a significant role. To solve these problems, we prepared new photoalignment layer which can completely control LC pretilt angle by using organic/inorganic hybrid IPN. This IPN structure with TMSPM could provide high transmittance, which is an important requisite for the alignment layer. The homogeneous dispersion of inorganic clusters within organic networks were verified by FTIR and TEM measurement. Pretilt angle measurement shows a change of the pretilt angle of the hybrid IPN alignment layers as a function of PDMS content. As expected, the pretilt angle shows an increasing tendency with increasing content of PDMS because of high hydrophobicity of PDMS. The plot of azimuthal anchoring energy represents the azimuthal anchoring energy is gradually decreased with increase of PDMS content. In addition, it is noticeable that rather a high azimuthal anchoring energy (~6 × $10^{-6}$ J $m^{-2}$) could be achieved at intermediate pretilt angle.