Synthesis And Properties Of Graphene Oxide/Laponite Dual Nanocomposite Hydrogels

Nanocomposites are identified to be a simple way of enhancing the mechanical properties of hydrogels through the addition of reinforcing organic/inorganic fillers such as clay,graphene oxide,carbon nanotubes,etc into hydrogel matrix.To further enhance the gel strength,in our work,we developed a dual nanocomposite hydrogel with GO and Laponite nanosheets as nanofillers.The dual nanocomposite hydrogels can effectively dissipate mechanical energy under large deformation and maintain high elasticity.However,it keeps unknown about the intrinsic toughing mechanisms of the dual nanocomposite hydrogels.And to extend their practical applications,many types of functional hydrogels,such as conductive hydrogels,have been developed.In this paper,the dual nanocomposite hydrogels were synthesized by in situ polymerization of monomer AM in the GO and Laponite aqueous dispersion.The intrinsic toughing mechanisms of GO and Laponite were explored.And the conductive hydrogels were prepared successfully by introducing the conductive polyaniline.The main contents of this paper are as follows.(1)Both GO and Laponite were used as crosslinkers and reinforcing-fillers.And the dual nanocomposite hydrogels were prepared by in situ free radical polymerization of AM in the GO and Laponite homogeneous dispersion initiated by KPS and TEMED with excellent mechanical properties.Through the rheological test,the interactions between GO and Laponite nanosheets in the mixed dispersion have been proved,which can promote adsorption of Laponite on the surface and edge of GO to prevent the aggregation of GO.FTIR and XRD tests confirmed the synthesis of the dual nanocomposite hydrogels and the uniform dispersion of inorganic nanosheets in the hydrogels.And the mechanical properties of the hydrogels were heavily dependent of the dispersing of GO and Laponite.These hydrogels exhibited a high mechanical strength of 391 kPa with extensibility of up to 1420%.The hydrogel at low concentration of GO possessed more effective network chain density and superior mechanical properties.Laponite is a more effective crosslinking agent than GO.The presence of both Laponite and GO improved Tg of the hydrogels.The dual enhancement mechanism of GO and Laponite nanosheets improves mechanical strength of the hydrogels and provides a new idea to synthesize tough hydrogels.(2)To meet the needs of more practical applications,the conductive hydrogels with semi-interpenetrating structure were prepared by interfacial polymerization of aniline monomers within the dual nanocomposite hydrogels.The tensile strength of the hydrogels reached 20 kPa while the elongation at break was about 300%.The hydrogels could return to the initial position after 5 cycles of compression and show a good compression recovery performance.GO and Laponite nanosheets in the hydrogels can effectively improve electrochemical performance due to their shortened paths for fast electrolyte ion diffusion and large exposed surface offering more active sites for charge storages.The electrochemical performance of the hydrogels were estimated by means of cyclic voltammetry(CV),galvanostatic charge-discharge(G-CD)and electrochemical impedance spectroscopy(EIS).Its specific capacitance(Cs)can reach 136 F/g at a current density of 1 A/g.(3)Introduction of water in the interface polymerization method to synthesize the conductive hydrogels resulted in the reduced overall mechanical properties due to the polymer chain being stretched.Hydrophilic modification of polyaniline followed by crosslinking polymerization is a good solution to prepare conductive hydrogel.So the composite polyaniline/polyacrylic acid/GO aqueous dispersion was prepared,and then Laponite and AM were added into the dispersion followed by free-radical polymerization to form the conductive hydrogel.The mechanical strength increased by 8 times and reached up to 180 kPa.Through the electrochemical performance characterization,the specific capacitance of the conductive hydrogel was obviously lower than that of the composite.When the current density was 1 A/g,the specific capacitance was only 75 F/g.It was possibly due to low content of 0.4 wt% of active material in the conductive hydrogel,which resulted in discontinuous distribution and thus weakened the capacitance properties.But the charge resistance of the conductive hydrogel was lower,indicating that the hydrogel network contributed to charge transfer.