Regulations of hydrophilicity of cellulosic nanosheets by polarity of coagulation bath

Abstract

Regeneration from cellulose solution is an effective way for processing and regulating the cellulose-based materials, during which the coagulation bath plays an important role that has been paid insufficient attention. Herein, we investigate the effect of polarity of the coagulation baths on the hydrophilicity of the regenerated cellulose, and the results show that polarity of the coagulation bath affects the crystalline assembly along different crystal plane by regulating the molecular interactions, leading to discriminating surfaces of hydrophilicity. Strong-polar coagulation bath, such as H2O, induces the regeneration of cellulosic molecules along 11¯0 crystal plane, leading to form hydrophilic nanosheets. Lowering the polarity of the coagulation baths results in fragmenting the morphology and reducing the hydrophilicity of the nanosheets that regenerate along the 110 or 020 crystal planes. Molecular dynamics simulations reveal the mechanisms for the interactions between the polar groups in cellulosic molecules and the hydrophilic facet of the regenerated cellulose. During the regeneration process, the cellulosic molecules are assembled under the influence of van der Waals interactions, resulting in crystallizing along the direction of 110 face to form the two-dimensional nanosheets. As the polarity of the coagulation bath changes from strong to weak, the assembly regeneration evolves from along 11¯0 to 110 or 020 crystal planes, which is recognized by the interaction changing from Van der Waals to hydrogen bond in cellulosic chains. As a result, the cellulose regenerates two-dimensional nanosheets with different hydrophilicity on the surface. The experimental and calculating results provide the feasibility for structural regulation of regenerated cellulosic materials with demand performance of different hydrophilicity.