Preparation and Properties of Graphene/Polymer Conductive Nano-Composites

Author:Hu Cheng Yuan

Supervisor:zhou xiao dong


Degree Year:2018





Graphene is a new two-dimensional material,with lots of unique properties.It has very good conductivity,high electron mobility,and good light transmittance by single layer graphene,strong mechanical properties and good thermal conductivity.It has a lot of potential applications in a wide range area;it can be combined with polymer to prepare high performance composites.In this paper,graphite oxide was prepared from natural flake graphite by chemical-oxidation,and then was stripped to graphene oxide;reducing agent was added to reduce graphene oxide to graphene.Graphene was composited with polyaniline(PANI),polyvinyl alcohol(PVA)to prepare conductive nano-composites.The conductive mechanism of multiphase-multicomponent conductive composites was studied.Graphite was oxidized to graphite oxide by modified Hummers method from natural flake graphite.Graphite oxide has a high oxidation degree and a large interlayer spacing,which is beneficial to stripping and reduction.Graphite oxide was exfoliated to graphene oxide with high-speed shearing and ultrasonic wave.Graphite oxide which treated with high-speed shearing 1 hour can be exfoliated to graphene oxide easily.The results show that the optimal operating conditions of ultrasonic wave are 20 KHz of ultrasonic frequency,300W of ultrasonic power,2 hours of ultrasonic time and the type of ultrasonic probe direct mode.The pH value has a great influence on the exfoliation of graphene oxide.The exfoliation effect is better while the pH value is higher.Graphene oxide was reduced to graphene by chemical-reduction method.The reducing agents are hydrazine hydrate and hydroiodic acid,respectively.The conductivity of graphene reduced by hydrazine hydrate is 28.09 S/cm;the conductivity of graphene reduced by hydroiodic acid is 44.91 S/cm.The reduction effect is better while the reducing time is longer;the conductivity is the highest when the reducing time is 5 hours by hydroiodic acid.Combination of hydrazine hydrate and hydroiodic acid has stronger reduction ability.The conductivity of graphene which reduced by hydrazine hydrate with 24 hours and hydroiodic acid with 5 hours is 79.89 S/cm.Graphene reduced by chemical reduction was then reduced by high-temperature thermal reduction can effectively repair the defect that unreduced by chemical reduction,and make the graphene graphitized highly,the electrical conductivity of graphene increased greatly,but the cost of high-temperature thermal reduction is much larger.The affecting factors of polyaniline preparation were studied.The optimum conditions for preparation are hydrochloric acid as a dopant,the molar ratio of aniline to ammoniurm persulfate is 1:1,the reaction temperature is o℃(ice water bath),and the reaction time is 4 hours.Conductive composite was prepared from graphene oxide,graphene with PANI by in-situ polymerization.The results show that graphite oxide was exfoliated to graphene oxide well,and has a well dispersion in PANI.The conductivity of composite decrease while the addition of graphene oxide.The reducing agent can improve the electrical conductivity of composite.Graphene oxide was reduced to graphene,and then was dispersed with aniline monomer,was prepared to PANI/graphene composite by chemical-oxidation method.The results show that graphene was dispersed well in PANI,the thermal stability of composite is significantly improved as well as the electrical conductivity,and the electrical conductivity is about 9.916 S/cm.Graphene oxide and graphene were composited with polyvinyl alcohol to prepare conductive composite.Graphene oxide and graphene has good dispersion in polyvinyl alcohol,and improve the water resistance of composite membrane.The water resistance of composite membrane is best when the content of graphene oxide and graphene is 1%.Graphite oxide and graphene can significantly increase the tensile strength of polyvinyl alcohol,which are 127.57 MPa and 124.45 MPa respectively.The conductivity of the composite was also significantly improved.When the amount of was 5%,the conductivity of PVA/graphite oxide composite was 1.217×10-10 S/cm,and the conductivity of PVA/graphene composite increased to 1.059×10-5 S/cm.Graphene can be dispersed in polyvinyl alcohol very well,thereby constructing an effective and conductive network and improving the electrical conductivity of composite.PANI was added to PVA/graphene composite as a conductive reinforcement to enhance the electrical conductivity of composite.PVA/PANI,PVA/PANI/GO,and PVA/PANI/RGO were prepared by in-situ polymerization.The polyaniline dispersion in polyvinyl alcohol has a great influence on the properties of composite.The polyaniline in the composite prepared by direct dispersion method show obvious agglomeration,and the electrical conductivity is only 1.113×10-3 S/cm.The polyaniline has good dispersion in the composite prepared by "dispersion after polymerization" method,and the composite electrical conductivity is 0.114 S/cm.The composite conductivity increased with the addition of PANI.The conductivity of the composite raise from 0.0122 S/cm to 0.114 S/cm while the PANI addition amount increase from 11.1%to 33.3%.The polyaniline molecular chain can be dispersed in polyvinyl alcohol well,which can connect graphene and polyaniline molecular chains together to form a good conductive network,which effectively improves the composite conductivity,thereby obtaining better graphene/polymer nano composites.