Phase diagram of colloidal crystals of poly(methyl methacrylate) spheres in the exhaustively deionized dispersion
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Phase diagram of colloidal crystals of poly(methyl methacrylate) (PMMA) spheres (100 to 300 nm in diameter) was measured precisely for the exhaustively deionized aqueous dispersion. Strong iridescent colors changed from bluish to reddish and metallic as sphere size increased at high sphere concentrations around 0.1 in volume fraction. Large single crystals, on the other hand, were recognized with the naked eyes at low sphere concentrations around 0.0005 to 0.001 especially for PMMA spheres smaller than 200 nm. The critical concentrations of melting (or crystallization), ϕc of all the PMMA spheres examined were quite low between 0.00025 and 0.00060 in volume fraction. The ϕc values were insensitive to kind (polystyrene, silica, and fluorine-containing spheres) and also to size (90~300 nm) of colloidal spheres. The ϕc value of the deionized dispersion with the coexistence of the ion-exchange resins was lowest, and that without resins was tenfold large. Addition of sodium chloride increased the ϕc values sharply. Extension of the electrical double layers forming around the colloidal spheres is most important to determine the ϕc values.
KeywordsPhase diagram Critical concentration of melting Poly(methyl methacrylate) spheres Colloidal crystal Deionized dispersion
Dr. Susumu Kawase of Soken Chemical & Engineering Co. (Tokyo) are acknowledged greatly for kind supplying monodispersed colloidal sphere samples of poly(methyl methacrylate).
This study was not funded by any other organization.
Compliance with ethical standards
Conflict of interest
The authors declare that we have no conflict of interest.
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