|Probst, C.; Meichner, C.; Audorff, H.; Walker, R.; Kreger, K.; Kador, L.; Schmidt, H.-W.: Improving Holographic Writing Performance of Photo-Orientable Azobenzene Polymers by Molecular Glasses, Journal of Polymer Science Part B: Polymer Physics, 54(20), 2110–2117 (2016) -- DOI: 10.1002/polb.24120|
Long-term stable holographic volume gratings in azobenzene-containing films have potential applications as forgery-proof security features or in holographic data storage. However, azobenzene-based polymer systems often lack sufficiently high writing speeds. Here, an approach to improve the holographic writing performance of photo-orientable azobenzene-containing polymers by blending with azobenzene molecular glasses is presented. The molecular glass enhances the photo-plastification effect and, consequently, the writing speed. This concept of improving the holographic performance of photo-orientable azobenzene polymers with azobenzene molecular glasses is demonstrated with a homopolymer and two block copolymers. In the azobenzene homopolymer, an addition of 10 wt % of the molecular glass leads to a doubling of the writing speed. Simultaneously, the long-term stability of inscribed gratings is maintained. In case of the block copolymers, the molecular glass is present in the polystyrene matrix and accumulates in the azobenzene minority phase. Adding 5–10 wt % of molecular glass improves the writing speed of the azobenzene block copolymer by a factor of 3–4. An addition of 15 wt % of molecular glass to the block copolymer containing azobenzene and nonphotoactive mesogenic side groups reduces the writing time by a factor of 15 and the long-term stability of the gratings is retained.