A new mechanism of stable optical birefringence recording under polarized UV radiation in photocrosslinking polymeric materials

Abstract

The photoinduced birefringence in glassy layers of the new photocrosslinking polymers containing benzaldehyde groups in the side chain is experimentally investigated. The kinetics of the birefringence recording is revealed to have an untypical shape compared to the known photosensitive materials of the same type. Under polarized UV exposure, the negative and positive birefringence are formed consecutively, the positive one being stable to the influence of liquids and heating (up to 120 °C). A new qualitative mechanism explaining the features revealed is proposed and verified by numerical simulation. According to the assumptions made, the positive birefringence is formed by anisotropic photocrosslinks which ensure its stability, which is of great importance for the practical application of the polymers under study, including liquid crystal photoalignment.

Polymer composition with phenanthrenequinone for recording relief holographic gratings

“…На основе такого предположения для повышения эффективности рельефообразования в настоящей работе использована обратимая пластификация тонких (около 1 мкм) слоев после записи голографических решеток путем набухания материала в жидкой нерастворяющей среде и последующего высушивания. Первоначально такой способ был применен для усиления рельефных голографических решеток в слоях фотосшиваемых полимеров с боковой бензальдегидной группой [11,12]. Эффект усиления решеток получен также для композиции на основе антраценсодержащего сополимера [13].…”

Alignment materials with controllable anchoring energy

“…Photosensitive benzaldehyde polymers (BP) have found their application for optical phase polarization recording and as alignment materials for LC due to high photo and thermal stability, as well as the moisture resistance of the recorded image. Photochemical reaction of the BP causes photocrosslinking under the influence of ultraviolet (UV) radiation during which chemical bonds formed by products of photo‐reduction of benzaldehyde groups transform the polymer into an insoluble net state .…”

“…Photosensitive benzaldehyde polymers (BP) have found their application for optical phase polarization recording and as alignment materials for LC due to high photo and thermal stability, as well as the moisture resistance of the recorded image. Photochemical reaction of the BP causes photocrosslinking under the influence of ultraviolet (UV) radiation during which chemical bonds formed by products of photo‐reduction of benzaldehyde groups transform the polymer into an insoluble net state . Surface anisotropy of benzaldehyde‐containing polymer layers is achieved either by means of contactless – photoalignment technology with polarized UV exposure, or contact photostimulated rubbing alignment technology, with homogeneous rubbing of the polymer layer with a cloth followed by unpolarized UV exposure …”