Enhancement of Thermosensitivity of Gel-Immobilized Tunable Colloidal Photonic Crystals with Anisotropic Contraction

A thermosensitive poly(N-isopropylacrylamide) (PNIPAM) circular gel film containing single-crystalline colloidal crystals was prepared, and the circular edge was pinched with washers to restrain the in-plane shrinkage of the gel film. Upon heating, the film shrunk in the thickness direction selectively, resulting in a change in the crystal structure of colloids embedded in the anisotropic shrunken gel. This led to the manipulation of the optical stop-band wavelength of the colloidal photonic crystals with a higher thermosensitivity and over a wider range of wavelengths covering a wide margin on either side of the visible-light region. The present method for enhancement of the sensitivity is very simple, and the principle should also be applicable to the gel-immobilized colloidal crystals that respond to stimuli other than temperature changes. The present findings contribute to the progress of practical applications of gel-immobilized colloidal photonic crystals as tunable photonic crystals and biological and chemical sensors.