Research On Controlled Preparation And Applications Of Graphene Fibers

Graphene as a two-dimensional carbon-based nanomaterial,with only one atomic thickness,has excellent mechanical,electrical,thermal and optical properties.Graphene-based materials including one-dimensional,two-dimensional and threedimensional materials,have very broad application prospects in transparent conductive films,energy storage materials,catalyst carriers,gas sensitive materials,single molecule detectors and so on.Especially graphene and graphene-based composite fibers,with high strength,high conductivity,knittability,are suitable for applications such as lightweight wire,flexible wearable devices,intelligent fabrics.However,most of the reports on graphene fibers mainly focued on improving the fracture strength.But the tensile strain is very low because of the brittle fracture of the fibers and the flexibility of the graphene fibers also should to be improved.The graphene fibers with unique helical structure can obtain high strength and high flexible simultaneously,which is helpful for the development of stretchable and wearable devices with high performance.In this paper,purity graphene oxide was prepared by the modified hummers method with sulfuric acid-phosphoric acid-potassium permanganate system.The flexible and transparent graphene films were prepared by casting method.The morphologies and properties of the graphene oxide films were investigated by different reduction methods.The results showed that the surface morphology of the graphene oxide film was maintained well after the reduction of 45% hydroiodic acid compared with other reducing agents,and the graphene film obtained by this method also had good electrical conductivity and flexibility properties.The large area graphene oxide films were prepared on a polytetrafluoroethylene substrate and cut into strips with different widths after natural drying.The stretchable pure graphene helical fibers with different diameters,smooth surface and long continuous and uniform helical structure were prepared by dry spinning method with water vapor adjusting the moisture of the graphene oxide strips.The conductive helical graphene fibers obtained by reducing the helical graphene oxide fibers with hydroiodic acid maintained the helical structure and smooth surface.The helical graphene fibers have good mechanical properties with maximum strain of 60% and tensile strength of 12 MPa.The helical fiber exhibits good recoverability in a tensile cycle of 20% strain.And during this process,the resistance of the fibers show a regular change,and this good electromechanical property remains in a variety of strains.The applications of helical graphene fiber as extensible temperature sensor and electrical suction were explored.The resistance of the fiber was decreased with the increase of the temperature due to the semiconducting behavior of the graphene.The helical fiber also exhibited stable thermal properties at high temperatures of 300 oC with a strain of 50%,which showing the potential value of being used as a flexible thermal device.Based on through-channel structure due to the empty space in fiber,a fiber-shaped graphene sucker with channel size of 100 nm was constructed through controlling threshold electrical potential(~0.8 V),the electrolyte imbibition in our helical reduced graphene oxide fibers could be switched “on” and “off” by the applied bias.The fibers could absorb water about 6 times of its own weight when the liquid was aspirated to saturation.In order to further improve the performance of helical graphene fibers,this paper presents a new method for the preparation of composite films consisting of graphene oxide and the single-walled carbon nanotubes(SWNTs)film.It is different from the mechanical stirring method,and the composite film can be prepared in one step with graphene oxide and SWNTs film alternately superimposed layer by layer.The composite film has excellent flexibility and deformation stability.The composite helical fiber could produce good actuation effects in the adsorption and desorption processes of liquids such as water,ethanol and acetone,and could pull up the object which weight was 300 times of the fiber's weight.The tensile strength and tensile strain of the composite helical fiber after reduction of HI acid were 135 MPa and 130%,which were 10 times and 2 times of that of pure graphene helical fibers respectively.As a temperature sensor,the response was six times higher than that of pure graphene spiral fiber.Furthermore,a flexible and stretchable supercapacitor based on the composite helical fiber net by a weaving method was prepared,showing a good electrochemical performance,with a specific capacitance of 44 m F/cm2(100 m V/s).