Study On Microscopic Heat Transport Properties Of Functionalized Graphene-Water Interface

Graphene,as a two-dimensional material with special layered structure,has many excellent properties,especially its super-high thermal conductivity,which has attracted the attention of many researchers in the field of thermodynamics.Graphene is considered as a kind of revolutionary material which is expected to affect the development of science and technology in the future.Therefore,with the in-depth work of researchers,we began to explore more fields of graphene applications and super performance.Efficient heat transfer between graphene and water has important applications in micro-scale radiators,solar thermal steam generations,nanoscale microchannels,biomedical and other fields.Although graphene itself has super high in-plane thermal conductivity,the interfacial thermal conductance between graphene and water is not very high.At present,there are only two ways to improve the thermal conductance of graphene-water interface:oxygen atom modification and charge decoration.However,the effect of oxygen atom modification on improving the thermal conductance of graphene-water interface is not very effective,and the practical operation of charge decoration is difficult.So,the researches on this aspect are still very scarce so far.In recent years,functionalized graphene has begun to enter our vision.Functionalized graphene has been partially applied in graphene composites.Functionalized graphene can effectively improve the properties of graphene-polymer and graphene-metal interface,and functionalized graphene can also effectively control the in-plane thermal conductivity of materials to a certain extent.In this paper,the effect of functionalized modification to graphene on the thermal transport properties of graphene-water interface was studied.In this paper,theoretical simulations are used to carry out the calculations,combining with molecular dynamics simulations,phonon transport analyses and surface structure effects,to study the enhancement of thermal transport properties of functionalized graphene-water interface at room temperature under different lengths,concentrations and hydrophobicity of graphene functionalized groups,and obtain the rules and optimal designs of thermal performance enhancement of functionalized graphene-water interface,and the mechanism of this enhancement was analyzed at the same time.Molecular dynamics simulations are used to simulate the interfacial thermal conductance of the alkane functionalized graphene and water.It is found that the interfacial thermal conductance of the graphene and water has been greatly improved,and the increase of thermal conductivity can be up to?4 times compared with the pristine graphene-water interface.Combined with phonon transport analysis,it is found that the addition of sp3 hybrid C-C bond and C-H bond in the functional groups of alkane chain changed the phonon vibration mode of graphene,and make the phonon vibration mode of graphene fit with water to a large extent.Moreover,the alkane functionalized graphene provides many high frequency and high energy carriers for the graphene-water interface,which enhances the heat transport at the interface.Normal analysis may show that the elevation will continue to increase with the increase of the length and coverage of alkane chains.However,the results show that when the alkane chain is too long and the coverage of alkane chains is too high,the increasing trend will not continue,and the interfacial heat transport will be hindered by the disorder of functional groups.In addition,when the alkane chain is too short and the coverage of alkane chains is too low,the thermal conductance of graphene-water interface is also very low.Therefore,only under the conditions of appropriate the length and coverage of alkane chains,can the optimal thermal conductance of functionalized graphene-water interface be improved.Based on the enhancement of the thermal conductance of functionalized graphene-water interface,hydrophilic groups were further modified to improve the hydrophilicity of functionalized graphene to further enhance the thermal conductance of functionalized graphene-water interface.Similarly,combined with molecular dynamics simulations and phonon transport analyses,it is found that complex hydrophilic modification of alkane functional groups could compensate for the lack of H-O bonds in functionalized graphene,and further enhance phonon transport at the interface between graphene and water,and further improve the thermal transport performance at the interface between functionalized graphene and water.