Network structure of curdlan in DMSO and mixture of DMSO and water

The viscoelastic property of curdlan solution in dimethyl sulfoxide (DMSO) was investigated. We discuss the difference in the viscoelastic properties of curdlan solution in DMSO and that in 0.1 N NaOH aqueous solution. The viscoelastic function for curdlan solution in 0.1 N NaOH aqueous solution showed the Newtonian flow at the concentration of curdlan as high as 10 wt %. On the other hand, the Newtonian flow was observed in the concentrations below 7 wt % for curdlan solution in DMSO, and the plateau region appeared beyond this concentration. It was revealed by small angle x-ray diffraction measurements that the difference in the mechanical property would be originated from the difference in the network structure. The overlapping concentration c* was calculated on the basis of the mean field theory, and disagreement between theoretical prediction and experimental result was shown. We clarified that the above disagreement can be explained by the polydispersity of the curdlan sample, assuming adequate distribution functions. The static structure of the gel prepared by adding water to curdlan solution in DMSO was investigated. It was clarified by the dynamic viscoelasticity measurement that the cross-linking density increases with increasing the water content.