Thermoplastic elastomers of a styrene-butadiene-styrene (SBS) triblock copolymer containing grafts of an azobenzene side-chain liquid crystalline polymer were prepared by polymerization of an azobenzene acrylate monomer in solutions with dissolved SBS. Stretching thin films at room temperature induces long-range orientation of the azobenzene mesogenic groups along the strain direction. Upon irradiation with polarized or unpolarized UV light at 360 nm, the orientation of azobenzene moieties in stretched films is erased as a result of the trans-to-cis photoisomerization, while on subsequent irradiation with polarized or unpolarized visible light at 440 nm, the initial stretching-induced orientation is recovered due to the cis-to-trans back-isomerization. Gratings can be inscribed on stretched films at different alignments with respect to the strain direction, whose fringe spacing can be modified through elastic extension or retraction of the films.
This work explores the use of photoactive elastomers as elastic holographic materials. Holographic gratings were recorded on stretched films of an azobenzene elastomer, which is composed of a side‐chain liquid‐crystalline polymer with azobenzene mesogens, grafted to the rubbery polybutadiene block of a styrene–butadiene–styrene (SBS) triblock copolymer. The grating‐formation dynamics measurements revealed the formation of two gratings of different natures resulting from the coupled mechanical and optical effects. A first grating, formed quickly upon exposure, is due to the photoisomerization of oriented azobenzene groups. A second grating, developed at longer exposure times, may originate from changes in the anisotropic structure of the SBS matrix, which is induced by the photochemical phase transition of azobenzene mesogens. The first grating is unstable, but the second grating remains in relaxed films. Both mechanisms can be enhanced by deformation of the film.
Three azobenzene-containing side-chain liquid crystalline polymers (SCLCPs) were grafted onto a styrene−butadiene−styrene (SBS) triblock copolymer to yield photoactive thermoplastic elastomers. The SCLCPs used were a polymethacrylate and two polyacrylates having different glass and phase transition temperatures. We have investigated the stretching-induced orientation of azobenzene mesogens, the orientation erasure by UV irradiation, and the consequences on the formation of diffraction gratings on stretched films. The results show that a combination of high degree of orientation of trans-azobenzene in nonirradiated areas with an efficient photoisomerization leading to disordered cis-azobenzene in irradiated areas is necessary for an efficient diffraction grating. However, this is not the only mechanism responsible for the formation of grating. Changes in the anisotropic morphology of stretched SBS may occur in these elastomers as a result of the photoisomerization process, which contributes to the formation of grating in films under strain and accounts for the stable diffraction grating remained in the relaxed state. These azobenzene elastomers can be used to record gratings that display reversible changes in diffraction angle and efficiency and the diffraction efficiency of which also depends strongly on the polarization of the probe light as well as the alignment of the fringes with respect to the strain of the film.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.