Colloidal dispersions confined in voids of polymer gel matrix

Dispersions of ionic polymer latex (diameter = 600 nm) consisted of 10 to 1000 particles were confined in spherical voids having diameters of several tens pm formed in a hydrogel (agarose) matrix. The system was constructed first by confining the latex dispersions in giant liposomes, immobilizing the liposomes by using the hydrogel matrix, and then removing the liposome membranes from the matrix. The latex particles inside the voids showed an extensive Brownian motion. This system, as a whole, could be regarded as a model system of one superfine particle. The solid-liquid phase transition was examined both for bulk and the confined colloids, by applying confocal laser scanning microscopy and phase contrast microscopy. The salt concentration was 2 pM. In bulk, the solid-liquid phase boundary laid at particle concentration, Cp =1.0 1.5 vol%. On the other hand, the confined dispersion 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 particle system.