Ferroelectric nematic phase at a photosensitive polymer substrate: comparing thermo-mechanical effect with photo-reorientation

The average direction of the molecules (director) of nematic liquid crystals (LCs) can be easily oriented by light using photosensitive surfaces (photoalignment). Recently, it was shown that in polar nematic (N ) liquid crystals the director field can be manipulated by laser light induced temperature gradient. Here we investigate how the photoalignment compares to the thermo-mechanical effect in the N phase. For that we study photo-reorientation phenomena on a photosensitive polymer substrate in the prototype ferroelectric nematic liquid crystal compound DIO. It is found that, while in the nonpolar nematic and antiferroelectric mesophases the photoalignment is observed, in the ferroelectric nematic phase the thermo-mechanical (TM) coupling determines the director alignment. • Photo-reorientation phenomena were studied in all mesophases of DIO liquid crystal. • In the non-polar nematic (N) phase an almost complete photoalignment occurred. • In the antiferroelectric M mesophase a very weak photoalignment was detected. • In the ferroelectric nematic phase (N ) the robust thermo-mechanical effect acts.