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 <i>Aphanothece sacrum</i> 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 sacran networks in the hydrogel state