Structure-regulated tough elastomers of liquid crystalline inorganic nanosheet/polyurethane nanocomposites

Abstract

Liquid crystalline nanosheet/polyurethane composite elastomers with superior mechanical properties were successfully synthesized using the newly developed in situ polymerization technique. A layered clay mineral fluorohectorite was fully exfoliated into single-layer nanosheets and formed a nematic liquid crystalline (LC) state in the N,N′-dimethylformamide/water mixture added with the prepolymer, isocyanate-terminated low-molecular-weight poly(ethylene oxide). The composite elastomer fibers were obtained by injecting this LC mixture into a solution of a four-functional crosslinker molecule, triethylenetetramine, followed by solvent removal. In the composite fibers, the single-layer LC nanosheets were macroscopically aligned along the long axis of the fibers as revealed by polarizing microscope and small angle X-ray scattering. Tensile tests showed that the composite fibers have superior mechanical strength while maintaining a large breaking strain compared to the pristine polyurethane fibers without the nanosheets. The outstanding improvements were due to the physical crosslinks at multiple points between polymer chains and the single-layer nanosheets that are macroscopically ordered.