Colloidal dispersions confined in voids of polymer gel matrix

Dispersions of ionic polymer latex (diameter = 600 nm) consisted of 10 to 1 000 particles were confined in spherical voids having diameters of several tens um formed in a hydrogel (agarose) matrix. The system was constructed f irst by confining the latex dispersions in giant liposomes, immobilizing th e liposomes by using the hydrogel matrix, and then removing the liposome me mbranes from the matrix. The latex particles inside the voids showed an ext ensive Brownian motion. This system, as a whole, could be regarded as a mod el system of one superfine particle. The solid-liquid phase transition uas examined both for bulk and the confined colloids, by applying confocal lase r scanning microscopy and phase contrast microscopy. The salt concentration was 2 muM. In bulk, the solid-liquid phase boundary laid at particle conce ntration, Cp = 1.0 similar to 1.5 vol%. On the other hand, the confined dis persion took a Liquid state even at Cp = 2.5 vol%. The present observation might correspond to a size effect for the melting point of a superfine part icle system.