Thermo-sensitive colloidal crystals composed of monodisperse colloidal silica- and poly(N-isopropyl acrylamide) gel spheres

Abstract

Thermo-sensitive colloidal crystals were prepared simply and conveniently by mixing of colloidal silica spheres with a series of thermo-sensitive gel spheres, poly (N-isopropyl acrylamide) (pNIPAm, 225~1500 nm in hydrodynamic diameter, 0.5~5 mol% in degree of cross-linking and at 20~45 °C) in the deionized aqueous suspension. The thermo-reversible change in the lattice spacing of colloidal crystals of monodispersed silica spheres (CS83, 103 nm in diameter) depends on the size of the admixed pNIPAm. For gel spheres with similar or less than that of the silica spheres, the lattice spacing decreased with rising temperature. On the other hand, the spacing increased with temperature for the mixtures with pNIPAm spheres of larger than the size of the silica spheres. A mechanism, which is able to explain properly the several experiments including the present work, is proposed, i.e., balancing between the weak adsorption and segregation effects of silica with gel spheres.