Melting temperature of colloidal crystals of monodisperse silica spheres in ethanol-water and ethylene glycol-water mixtures

The melting temperature (T_m) of colloidal crystals of monodisperse silica spheres in ethanol-water and ethylene glycol-water suspensions has been measured by reflection spectroscopy. A sphere of 110 nm in diameter and 0.041 in monodispersity index is used after purification and deionization processes. Transformation from the body-centered cubic lattice to the face-centered cubic lattice subphases is observed as the suspension temperature rises, which is similar to the purely aqueous suspension of the same sphere. A phase diagram including liquid-like and crystal-like structures is obtained in the presence of ion-exchange resins coexisted. The data ofT_m are analyzed successfully with the theory of Williams, Crandall, and Wojtowicz. The heat of melting decreases by the addition of ethanol or ethylene glycol in the mixtures.