An amorphous array of poly(N-isopropylacrylamide) brush-coated silica particles for thermally tunable angle-independent photonic band gap materials

We precisely prepared thermo-responsive fine core-shell particles consisting of submicron sized silica particles as cores and high-density polymer brushes of thermo-responsive poly(N-isopropylacrylamide) (PNIPA) as shells. The shells were grown by atom transfer radical polymerisation from the initiator that was modified on the surface of the cores. These core-shell particles tend to aggregate in water, even at lower temperatures than the lower critical solution temperature of linear PNIPA. Nevertheless, along with PNIPA in water, changes in the particle size are dependent on water temperature. In accordance with these properties, the amorphous array of the core-shell particles exhibits temperature-reversible changes in the position and the strength of the photonic band gap that does not depend on angle.