Colloidal Cluster as, Model System for Ultrafine Particle

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Dispersions of ionic polymer latex (diameter = 600nm) consisted of 10 to 1000 particles were confined in spherical voids having a diameter of several tens \am 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, and did not show aggregation even after one month. This system, as a whole, could be regarded as a model system of one superfine particle. The solid-liquid phase transition was examined both in bulk and the confined colloids, by applying confocal laser scanning microscopy and phase contrast microscopy. The salt concentration was 2μM, In bulk, the solid-liquid phase boundary laid at particle concentration = 1.0〜1.5 vol %. On the other hand, the confined dispersion took a liquid state even at 2.5 vol %. The present observation might correspond to a size effect for the melting point of a superfine particle system.