Cholesteric Polymer Scaffolds Filled with Azobenzene-Containing Nematic Mixture with Phototunable Optical Properties

Abstract

The past two decades witnessed tremendous progress in the field of creation of different types of responsive materials. Cholesteric polymer networks present a very promising class of smart materials due to the combination of the unique optical properties of cholesteric mesophase and high mechanical properties of polymer networks. In the present work we demonstrate the possibility of fast and reversible photocontrol of the optical properties of cholesteric polymer networks. Several cholesteric photopolymerizable mixtures are prepared, and porous cholesteric network films with different helix pitches are produced by polymerization of these mixtures. An effective and simple method of the introduction of photochromic azobenzene-containing nematic mixture capable of isothermal photoinducing the nematic-isotropic phase transition into the porous polymer matrix is developed. It is found that cross-linking density and degree of polymer network filling with a photochromic nematic mixture strongly influence the photo-optical behavior of the obtained composite films. In particular, the densely cross-linked films are characterized by a decrease in selective light reflection bandwidth, whereas weakly cross-linked systems display two processes: the shift of selective light reflection peak and decrease of its width. It is noteworthy that the obtained cholesteric materials are shown to be very promising for the variety applications in optoelectronics and photonics.

Photocontrollable Photonic Crystals Based on Porous Silicon Filled with Photochromic Liquid Crystalline Mixture

“…The main feature of 6DABU is reversible E-Z isomerization leading to extreme decrease in molecular anisometry (see Figure 2a). As it was shown before, [24] irradiation of the 5CB+6DABU mixture by UV light induces isothermal phase transition from the nematic phase to the isotropic phase (see Figure 2b). Due to the presence of lateral methyl substituents in azobenzene chromophores, photoinduced Z isomer possesses high thermal stability, thus back transition from isotropic to nematic phase occurs very slowly with characteristic time of about 20 days.…”

From Smart Denpols to Remote‐Controllable Actuators: Hierarchical Superstructures of Azobenzene‐Based Polynorbornenes

“…Light is a well‐known external stimulus that can be controlled sequentially, remotely, and rapidly . Photochromic molecules have been intensively studied for their significances in scientific studies and real applications . Owing to the resolved photoisomerization between trans ‐ and cis ‐form, azobenzene is perhaps the most common moiety to produce dramatic changes at molecular order and macroscopic dimensions .…”

Mechanical Adaptability of Artificial Muscles from Nanoscale Molecular Action

“…Recent literature also unequivocally demonstrates that nonreactive liquid crystals can swell liquid crystal networks only up to a certain threshold, and this partial miscibility decreases markedly once the azobenzene has switched to the cis form 47,48 . Ryabchun et al 47 have shown how a liquid crystal gel with a low polymer content expels a free liquid crystal doped with azobenzenes upon irradiation with light. Broer et al have reported that azobenzeneactivated smectic gels behave as photo-sponges, because of a photo-induced miscibility with the liquid crystal solvent.…”