Photochemical phase transition behaviour of polymer azobenzene liquid crystals with flexible siloxane units as a side-chain spacer

Abstract

The in¯uence of the spacer structure on the photochemical phase transition behaviour was explored for azobenzene polymer liquid crystals (azo-PLCs) possessing siloxane spacers in the polymer side chain, and for analogue without the siloxane spacer. The photochemical phase transition of the azo-PLC with the siloxane spacer was found to proceed less e ectively than that of the azo-PLC without the siloxane spacer. It was also con® rmed that the spacer structure does not a ect the trans± cis photoisomerizatio n behaviour of the azobenzene moieties. These results were interpreted in terms of stabilization of the alignment of the mesogens in the liquid crystalline phase by the siloxane spacer, since the siloxane chain is one of the most¯exible spacers and decouples the motion of the polymer backbone from that of the aligned mesogens. Furthermore, the response of the azo-PLCs in the photochemical phase transition was evaluated by means of a laser pulse. The phase transition occurred iñ 300 ms for both samples.

Photocontrollable Liquid‐Crystalline Actuators

“…[ 97 ] It was found that PA6AB2 underwent the nematic LC-isotropic phase transition in 200 ns upon irradiation with a laser pulse (20 ps). [ 98 ] This fast response of LCPs is an encouraging result from the viewpoint of applications in photonic devices.…”

“…To overcome this diffi culty, a new system has been developed, in which each mesogen in LCPs is provided with a photoresponsive moiety. [97][98][99] For instance, in AZ-containing LCPs, the AZ moiety could play both roles as a mesogen and as a photoresponsive group when it is connected with polymer main with a soft spacer. As shown in Figure 9 A, LCPs with AZ moieties in the side chain shows a very stable nematic LC phase between the glass transition temperature ( T g ) of the LCP, and the clearing point (about 150 ° C).…”

“…This is obviously attributed to the stiffness of the main chain of the polymethacrylate, which signifi cantly affects the reorientation process of the trans -AZ mesogens after cis-trans back-isomerization. [ 98 ] In the measurement of photoresponse of LCPs, transmission mode is generally used. Similarly, a novel refl ection mode was developed, which also shows a fast photochemical phase transition in AZcontaining LC materials.…”

Optical switching behavior of polymer‐dispersed liquid crystal composite films with various novel azobenzene derivatives

“…Therefore, the ordered nematic phase is isothermally transformable into a disordered isotropic phase by the trans – cis photoisomerization of the guest azobenzene. The photochemical phase transition of liquid crystals has been examined by transmission and reflection mode analyses 10–14…”

Reversible optical control of transmittance in polymer/liquid crystal composite films by photoinduced phase transition

“…18, 19 We have already reported several attempts to provide LCs with photoresponsive property, and have demonstrated the photonic control of light by means of the photochemical phase transition of azobenzene LCs. [20][21][22][23][24][25] Such photochemical phase transition behavior was investigated by monitoring the intensity of polarized light through a pair of crossed polarizers with the sample between them. In the previous work, we reported all-optical control of the composite films containing a conventional azobenzene ͑i.e., non donor-acceptor type azobenzene͒ as a guest molecule by the photochemical phase transition trigged by photoisomerization of the azobenzene molecule.…”