Tuning the Properties of Photonic Films from Polymer Beads by Chemistry

This paper describes the preparation of monodisperse colloids from various methacrylates. These colloids sediment well on glass slides and form in the dried state large three-dimensional face-centered cubic photonic crystal films with Bragg reflection in the visible region. Depending on crystallization conditions, the domain sizes vary between 50 and 300 μm. By cross-linking the polymer within the colloids, it is possible to increase the thermal stability of the polymeric photonic structure tremendously (up to 1 h at 200 °C). These photonic structures soften above T g (rubbery photonic structure), but they cannot fuse. Cross-linked colloids from poly( tert -butyl methacrylate) can either thermally or chemically be modified. During thermal treatment (above 200 °C) the colloids shrink, as isobutene is split off. This allows a change of the lattice constant and the reflection color of an already crystallized dry photonic film. The acid-catalyzed cleavage of the ester bond allows the conversion of existing photonic structures into photonic crystals from core−shell colloids with hydrophilic polyelectrolytes in the shell.