An Exfoliaction Approach For Production Of Graphene Sheets In Aqueous Phase And Anticorrosion Properties In Graphene Composite Coatings

Graphene is a new two-dimensional(2D)carbon nanomaterial that is considered a revolutionary material of the future.Due to its unique mechanical,electronic,physical and thermal properties,graphene has a wide range of applications in transparent/flexible electrodes,sensors,energy storage and composites.In important applications such as printed electronics,conductive coatings and composite fillers,a key bottleneck is the lack of industrial-scale methods to produce high-quality graphene in liquid suspensions,inks or dispersions.Aiming at the above problems,this paper proposed a method to prepare high concentration and high quality graphene in aqueous phase,and studied its dispersion and redispersion effect,as well as its application effect in coatings..Details are as follows:(1)The physical method of gas diffusion between graphite layers is used to increase the graphite layer spacing,so that the graphite gradually changes from crystal structure to amorphous state,forming a gas expanded graphite with specific surface area(SSA)of 202.6m²/g.The larger spacing between graphite layers weakens the van der Waals force between the graphite layers,which facilitates the subsequent graphene exfoliation.The yield of the prepared graphene slurry(4wt%)was 94%.It can be seen from the STM that the structure of the peeled graphene is complete.In addition,the specific surface area SSA of graphene is 1051.7 m²/g,and the number of layers as a whole is 2.5.TEM characterization and AFM statistics showed that about the graphene with thickness less than 2 nm accounts for about 96%,which further proved that it is single-layer or two-layer graphene.About 73%of the graphene sheet diameter has smaller sheet diameter(less than 2?m).The dispersion of graphene depends on the p H value.The exfoliated graphene dispersed in water or NMP has excellent performance in a variety of practical applications,such as flexible electronic products,intelligent film heaters,EMI shielding and energy storage devices.(2)Polyvinylpyrrolidone(PVP)was added in the preparation process to prepare redispersible graphene.Materials with different graphene/PVP content ratio(PVP@G(graphene:PVP=1:4),PVP@G2(graphene:PVP=1:2))were prepared.The structure characterization and dispersion test were carried out respectively.TEM result shows that there is a layer of organic coating on the surface of graphene,and the number of graphene layers is few(2-4 layers).The structure characterization of freeze-dried graphene shows that PVP is successfully adsorbed on the surface of graphene,and there is no agglomeration of graphene after drying.In addition,the graphene did not agglomerate after drying.The morphology of PVP@G and PVP@G2 after freeze-drying was characterized,and it was found that graphene in PVP@G2 was stacked seriously,while graphene in PVP@G was completely wrapped by PVP.Solid PVP@G was redispersed in ethanol,water,chloroform and other solvents.It was found that PVP@G had the best dispersion stability in ethanol and remained stable after 10days.(3)PVP@G dispersant was used as an additive for waterborne polyurethane coatings(WPU)to improve the mechanical properties and corrosion resistance of the coatings.The physical properties of the composite coating with different PVP@G content were studied.It was found that the mechanical properties of the composite coating were improved with the addition of PVP@G,and the adhesion increased from 4.7 MPa to 8.9 MPa.The electrochemical properties of the composite coating were studied.It was found that with the increase of PVP@G content,the corrosion resistance of the composite coating was gradually improved,and the corrosion resistance was the best when a content was 0.075wt%,which had the lowest corrosion current density(2.0×10^-7 A/cm²),minimum corrosion rate(2.40×10^-3 mm/year).