Uniaxial Swelling in LC Hydrogels Formed by Two-Step Cross-Linking

Abstract

Molecularly oriented hydrogels of sacran, which is a supergiant liquid crystalline polysaccharide extracted from Aphanothece sacrum biomaterials, showing ultrahigh anisotropy of swelling is successfully prepared by two-step chemical cross-linking. Divinyl sulfone (DVS) works as a chemical cross-linker of sacran chains in a dilute aqueous solution to form hydrogels, but some of the added DVS remains in the hydrogel without cross-linking. The remaining DVS cross-links further with the preformed networks of sacran chains in liquid crystalline state during slow drying to produce in-plane oriented xerogels. The xerogels show heterogeneous anisotropy in the successive swellings steps; the linear swelling ratio in the thickness direction is 10000–40000-fold higher than that in the width direction due to the molecular orientation of the sacran hydrogels. X-ray diffraction imaging of the hydrogels reveal not only the orientation of the xerogel films but also the unusual orientation of water molecules binding to sa...