Optical anisotropy and molecular orientation of neutralized Curdlan gels

Curdlan gels were prepared by dialyzing its alkaline solutions in HCl solutions, and its optical anisotropy and molecular orientation in the gel were investigated by birefringence and small-angle X-ray scattering (SAXS). The observed asymmetrical two-dimensional SAXS pattern indicated that the orientation of polymer chains was perpendicular to the inflow of H⁺ in the gelation process. The birefringence results suggested that phase-separated domains were elongated along the molecular orientation. When the gel was dried, inversion of the birefringence sign was observed. This was attributed to the competing effects of the form birefringence due to the deformation of the domains and the intrinsic birefringence due to the molecular orientation.