Axial and polar orientational changes by rubbing/photoalignment processes in a liquid crystal alignment layer studied by optical second-harmonic generation

Molecular reorientation by rubbing and photoalignment processes in polymer alignment layer for liquid crystals has been studied by linear optical abso rption and surface optical second-harmonic generation. It was found that ru bbing produces polar and axial orders in the photoisomerizable polyamic aci d (PAA) containing azobenzene groups in the main chain, while photoalignmen t after rubbing destroys the polar order but is capable of reorienting the PAA main chain without creating further polar order.