Zheng-Yu Wang

Sol—gel transition of alginate solution by additions of various divalent cations: critical behavior of relative viscosity

Abstract The critical behavior of viscosity near the gelation point was experimentally investigated for alginate solutions by additions of four different divalent cations. The critical exponent for viscosity was found to lie in the range 0.88–1.14 and is in good agreement with the predictions of percolation theory. The results are also comparable with those of several experiment systems reported in the literature.

Small angle X-ray scattering from phase separating n-paraffin binary mixtures

Small angle X-ray scattering from binary mixtures of deuterated and non-deuterated n-paraffins (carbon numbers n, between 18 and 36), quickly quenched from the melt, has been studied in order to understand the demixing process. For a large difference in n, such as C18/C36 the components separate into two distinct phases. These are both dilute solid solutions but, for example, despite the presence of the second component, the monoclinic forms characteristic of very pure C30H62, C32H66 and C36H74 appear. For mixtures with a weaker demixing tendency, a number of distinct phases, typically five, have been found, reflecting the complex polymorphic behaviour of the pure phases in this region of composition. For close n values, solid solutions form and ‘microphase separated’ states from these have been characterized by the appearance of a set of diffraction lines which grows into the pattern over a period of days to months at 25°C. We associate this with long density fluctuations in a lamellar ‘microphase’ struc...

Small‐angle light scattering of phase separation structures in polymer blends

The correlation function presented by Debye et al. for characterizing the random two‐phase structure in solids is further extended by considering an effect of partial ordering to describe the statistical features in phase separation structures of polymer blends. The new correlation function is in the form γ(r)=exp(−r/a0 )cos(q0 r) with two parameters. The scattering intensity distribution calculated from this function can predict a maximum whose sharpness and position are characterized by a0 and q0 . Good agreement was achieved between the calculated intensity and measured small‐angle light scattering curve from phase‐separated poly(methyl methacrylate)/poly(vinyl acetate) blends.The correlation function presented by Debye et al. for characterizing the random two‐phase structure in solids is further extended by considering an effect of partial ordering to describe the statistical features in phase separation structures of polymer blends. The new correlation function is in the form γ(r)=exp(−r/a0 )cos(q0 r) with two parameters. The scattering intensity distribution calculated from this function can predict a maximum whose sharpness and position are characterized by a0 and q0 . Good agreement was achieved between the calculated intensity and measured small‐angle light scattering curve from phase‐separated poly(methyl methacrylate)/poly(vinyl acetate) blends.

Dynamical study on the late stage of demixing in poly(methyl methacrylate) and poly(vinyl acetate) blends

Abstract A dynamical study was made on demixing of an immiscible polymer blend, whose specimens were prepared by solvent casting and had very finely phase separated structures in the initial stage of the demixing. Light scattering experiments showed the applicability of a scaling rule to the later stage of the growth of phase separation structures. The demixing can be described by a scaling theory proposed by Furukawa.

Interaction modes in sol–gel transition of alginate solutions by the addition of cupric ions

The interaction mode between cupric ions and alginate in aqueous solutions during sol–gel transition has been experimentally examined at different temperatures. Some clusters were found to pass through a conformational transformation as the temperature increased, i.e. clusters formed by intramolecular crosslinks turned into intermolecular crosslinking clusters. This transformation of the interaction mode is not reversible as the temperature decreases. The interaction mode between cupric ions and alginate was re-examined by optical absorption techniques, and results suggest that the coordination of cupric ions mainly occurs to carboxyl groups and that the stoichiometric ratio f is proportional to the fraction of crosslinks formed.