Universality and specificity in molecular orientation in anisotropic gels prepared by diffusion method

• We obtained anisotropic gels by dialysis of solutions of polysaccharides and DNA.
• The molecular orientation in the gels was studied by birefringence measurements.
• The orientation of chitosan and DNA is perpendicular to the diffusion direction.
• The anisotropic gel of Curdlan shows a specific multi-layered structure.
• The structure of the Curdlan gel was studied by birefringence, rheology and SAXS.

Molecular orientation in anisotropic gels of chitosan, Curdlan and DNA obtained by dialysis of those aqueous solutions in gelation-inducing solutions was investigated. In this diffusion method (or dialysis method), the gel formation was induced by letting small molecules diffuse in or out of the polymer solutions through the surface. For the gels of DNA and chitosan, the polymer chains aligned perpendicular to the diffusion direction. The same direction of molecular orientation was observed for the Curdlan gel prepared in the dialysis cell. On the other hand, a peculiar nature was observed for the Curdlan gel prepared in the dialysis tube: the molecular orientation was perpendicular to the diffusion direction in the outermost layer of the gel, while the orientation was parallel to the diffusion direction in the inner translucent layer. The orientation parallel to the diffusion direction is attributed to a small deformation of the inner translucent layer caused by a slight shrinkage of the central region after the gel formation. At least near the surface of the gel, the molecular orientation perpendicular to the diffusion direction is a universal characteristic for the gels prepared by the diffusion method.