Thermo-cross-linked Elastomeric Opal Films

• Published in: ACS applied materials & interfaces Vol. 5; no. 21; pp. 10623 - 10632
• Main Authors: Schäfer, Christian G, Viel, Benjamin, Hellmann, Goetz P, Rehahn, Matthias, Gallei, Markus
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 13.11.2013
• Subjects: emulsion polymerization; self-assembly; photonic crystals; cross-linking; elastomers
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/am402588v

An efficient and convenient thermal cross-linking protocol in elastomeric opal films leading to fully reversible and stretch-tunable optical materials is reported. In this study, functional monodisperse core–shell particles were arranged in a face-centered cubic (fcc) lattice structure by a melt flow process. A problem up to now was that un-cross-linked films could not be drawn fully reversibly and hence lost their optical and mechanical performance. After thermal cross-linking reaction, the obtained films can be drawn like rubbers and the color of their Bragg reflection changes because of controlled lattice deformation, which makes the cross-linked films mechanochromic sensors. Different techniques were developed for the cross-linking of the films a posteriori, after their preparation in the melt flow process. A photo-cross-linking approach was reported earlier. This study now deals with a very efficient thermo-cross-linking approach based on the chemistry of hydroxyl- and isocyanate-functionalities that form urethane bridges. The focus of the present work is the mechanism and efficiency of this cross-linking process for elastomeric opal films with excellent mechanical and optical properties.