Thermo-cross-linked
Elastomeric Opal Films
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Abstract
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