Abstract
In this communication, we summarise our results related to light-induced orientational phenomena at liquid crystal–polymer interfaces. We investigated photoalignment for various nematics at the interface with the photosensitive polymer layer polymethyl methacrilate functionalised with azo dye Disperse Red 1. It was found that the efficiency of photoalignment exhibits marked differences depending on the structure of the rigid core of the liquid crystal molecules. It was demonstrated that the photo-orientation process is also significantly affected by the type of mesophase in which irradiation is carried out. The observations highlight the importance of the mutual influence of the polymer and the liquid crystal in light-induced processes.
Highlights
We suggest that the interaction between the liquid crystal and the azo dye molecules at the polymer–liquid crystal interface leads to a sort of guest–host effect, in the sense that the liquid crystal has an orienting effect on the dye molecules
The above results clearly indicate that the photoalignment efficiency does not solely depend on the composition of the photo-orienting layer, and on the liquid crystal interfacing the layer
Azimuthal and zenithal photoalignments were found to be sensitive to the molecular structure of the liquid crystals (LCs), as shown in the example of nematics having biphenyl, phenylcyclohexane and bicyclohexane in the rigid core
Summary
In an important part of the investigations, photo-orientation was realised with the help of azo compounds, exploiting light-induced trans-cis isomerisation. With this method, one can switch the liquid crystal configuration between planar and homeotropic alignment [13,14], or it is possible to control the azimuthal orientation of a nematic liquid crystal on a photosensitive polymer substrate [15,16,17]. The purpose of the present communication was to show that the efficiency of photoorientation depends, in addition to the composition of the photosensitive polymer film, on the structure of the liquid crystal as well.
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