Abstract: The effect of the relative molecular mass of poly(ethylene oxide) on the phase behavior of its mixture with charge stabilized poly(methyl methacrylate) colloidal dispersion was investigated by means of synchrotron small-angle X-ray scattering technique. The phase structure of the mixture is generally determined by the volume fraction of the colloidal dispersion and the concentration of the polymer. At a certain volume fraction of colloidal dispersion, the mixtures present a homogeneous state when the polymer concentration is below a critical value. When the polymer concentration is larger than the critical concentration, sedimentation can be observed. The mixtures are in a cluster phase or a crystalline state with a face-centered cubic structure. The relative molecular mass of poly(ethylene oxide) also plays an important role in the phase behavior of the mixture. Our results show that the critical concentration of the polymer is low for the mixtures with the polymer of high relative molecular mass. The relative molecular mass of the polymer also affects the formation of crystals.

Key words: colloid, synchrotron small-angle X-ray scattering, phase separation, crystallization