Holographic Recording in a Photoactive Elastomer

Abstract

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.

Light‐Responsive Block Copolymers

“…Reproduced with permission from ref. [87] obtained, they were however not as clear and stable as those obtained by the first method.…”

Dual‐Mode Switching of Diffraction Gratings Based on Azobenzene‐ Polymer‐Stabilized Liquid Crystals

“…The gratings were observed on a polarizing optical microscope (Leitz DMR-P). To record holographic gratings, an optical setup similar to that described elsewhere was employed [19]. An Arion laser (k = 514 nm) was used to produce the interference pattern for photopolymerization under similar conditions; the two beams were polarized parallel to the fringes of the grating (s±s geometry).…”

New photoactive polymer and liquid-crystal materials

“…On one hand, the easy deformation can be used to enhance the diffraction efficiency, as can be seen in the experiment of recording holographic gratings on films stretched to various strains ( Fig. 1) [21]. Note that these grating formation dynamics measurements also revealed two volume gratings of different natures: the one formed quickly upon excitation is from the photoisomerization of oriented trans-azobenzene mesogens, and the one developed at longer exposure times may originate from structural changes of the SBS matrix as being activated by the photochemical phase transition in the polymer.…”

“…Note that these grating formation dynamics measurements also revealed two volume gratings of different natures: the one formed quickly upon excitation is from the photoisomerization of oriented trans-azobenzene mesogens, and the one developed at longer exposure times may originate from structural changes of the SBS matrix as being activated by the photochemical phase transition in the polymer. On the other hand, the large and reversible elastic deformation gives the tunability to the grating in such a way that the period of grating, diffraction angle, and efficiency can be changed reversibly by simple mechanical deformation [21]. Figure 2 shows optical micrographs of a grating in a relaxed film (1 µm period) and in the film under a strain of 150 % (2.5 µm period).…”

“…These are covalently crosslinked elastomers, and the interest of study is the development of optical actuators. We have prepared the first azobenzene thermoplastic elastomer by grafting a side-chain LCP with an azobenzene moiety onto a styrene-butadiene-styrene (SBS) triblock copolymer [18][19][20][21], whose basic structure is shown in Fig. 1.…”