Multifunctional graphene liquid crystal fibers and their fabric devices

Abstract

As the performance of portable electronic devices has been improved and multi-functions have been demanded, development of electric energy storage technology and flexible electronic materials has become very important recently. So smart textile for the manufacture of wearable electronics / devices has been come up for. Due to the smart textile, studies on multifunctional new materials are attracting attention and graphene is especially getting more attention for their physical and electrical properties. The graphene oxide exhibits liquid crystal properties due to the plate-like particles and has orientational order provoking isotropic-nematic phase transition above the critical concentration. Using these properties, it became possible to fabricate graphene oxide fibers with wet spinning. Graphene's fiberization technology has a textile characterization of 1D material, which was impossible with film-like flexible elements, which are conventional 2D materials. The fiberization of graphene has been specialized in wearable materials and devices as it becomes possible to knot, twist, weave, and sew. In this study, the graphene oxide liquid crystal properties were investigated and the characteristics of graphene oxide fiber were analyzed by the reduction mechanism. The isotropic-nematic phase transition of graphene oxide liquid crystals was confirmed by cross-polarized image and diameter dispersion analysis according to graphene oxide particle size. Particularly, particles in the range of 50-100μm were found to have a large influence on nematic properties. Graphene oxide fibers were fabricated by wet spinning using graphene oxide liquid crystal, and the characteristics of the fibers were compared and analyzed according to the change of HI / AcOH reducing agent concentration. The increase of the density was deduced from the reduction of the fiber diameter due to the reduction of the reducing agent concentration, which was confirmed to lead to an increase in the mechanical strength. In the electrical conductivity measurement, the electrical conductivity of the low density (10% HI / AcOH) reduced fiber was about 2 times higher than that of the high density (30% HI / AcOH) reduced fiber. It can be expected that the graphitic properties have been effectively restored. In particular, the electrochemical measurement results showed that the low-density-reduced fibers exhibited higher energy storage characteristics (211Fg-1 and 167Fg-1, respectively) than the high concentration, and the output density was about 77% higher. These facts suggest that the pathway of the reduction products depends on the HI concentration and that the reduction products may greatly affect the properties of the reduced graphene oxide fibers with or without double bond recovery. From these results, we propose optimization conditions of graphene oxide fiber by securing the characteristics of graphene oxide liquid crystal and establishing reducing agent reducing conditions.