Azobenzene polymer stabilized ferroelectric liquid crystals: simultaneous photopolymerization and photoalignment

Abstract

A single linearly polarized irradiation was used to initiate cationic photopolymerization of an azobenzene-containing diepoxide monomer dissolved in a ferroelectric liquid crystal (FLC) and, at the same time, to induce fast trans-cis-trans photoisomerization cycles for the azobenzene chromophore which leads to a bulk alignment of the FLC in the absence of surface orientation layers. The spectral output of the light source is required to have separate UV and visible wavelengths, which allow for simultaneous photopolymerization of the monomer and photoalignment of the chromophore. Photopolymerization was allowed to take place in different phases of the FLC to reveal the effects on the FLC photoalignment; the interaction between the anisotropic azobenzene polymer network and the FLC host was also investigated using polarizing UV-Vis spectroscopy.

Photoinduced Bending Behavior of Cross‐linked Azobenzene Liquid‐Crystalline Polymer Films with a Poly(oxyethylene) Backbone

“…Because of the strong absorption of the azobenzene moieties to UV light irradiation around 360 nm (Figure S2, Supporting Information), the visible radical photoinitiator CQ that shows a strong absorption at 436 nm, and the cationic initiator DiPhIPF 6 were used as the photoinitiator mixture. In the free‐radical‐promoted cationic polymerization, photochemically formed radicals from the radical photoinitiator can be oxidized by onium salts, and the generated cations act as initiating species for the cationic polymerization of epoxide compounds …”

“…To date, the CLCPs with limited kinds of main chains have been investigated in the studies of photomechanical effects, in which polysiloxanes,[1d] polyacrylates,,[1g] and polymethacrylates[1e] are commonly used. However, to our knowledge, the CLCPs with poly(oxyethylene) backbone have rarely been reported up to now, and it is well known that epoxy‐based polymers are widely used as engineering materials due to their excellent mechanical and thermal properties.…”

“…However, the employment of photopolymerization to prepare the azobenzene‐containing CLCPs with poly(oxyethylene) backbone is infeasible due to the strong absorption of the azobenzene moieties to UV light and short‐wavelength visible light. Fortunately, free‐radical‐promoted cationic polymerization can be used to overcome the problem of limited absorption wavelength range of commonly used cationic photoinitiators . Furthermore, the employment of the cationic photopolymerization can potentially yield thicker samples due to frontal photopolymerization, and the samples also tend to be more homogenous across the thickness as well, while acrylate‐based systems can be heterogenous due to faster polymerization/consumption of monomer at the exposed surfaces …”

Synthesis and liquid crystalline behaviour of substituted (E)-phenyl-4-(phenyldiazenyl) benzoate derivatives and their photo switching ability

“…However, photolocking as an approach to produce long thermal back relaxation have yet to be studied. [29,30] If alkene monomer is substituted by a moiety conducive in the generation of liquid crystal phases, then the resulting polymer may exhibit liquid crystalline phases. It is possible to make azo dye molecules with terminal alkene which comprise an unsaturated carbon-carbon bond to polymerise the molecules.…”

Azo Monomers Exhibiting Low Layer Shrinkage at the SmA–SmC Transition and trans–cis Light‐Induced Isomerization

“…13 Some of these “azo monomers” are liquid crystals and their photoisomerization in a mesomorphic state has been used to enhance the molecular alignment 13. 14 This strategy avoids the use of prealigned substrates and/or the application of rubbing or some other surface treatment that promotes molecular orientation in a preferential direction,15, 16 and also allows the bulk alignment through the action of the photoactive azobenzene moieties 17…”