The Interphase And Thermal Conductivity Of Graphene Oxide/Butadiene-styrene-vinyl Pyridine Rubber Composites:a Combined Molecular Simulation And Experimental Study

Rubber,an indispensable material for defense,industry and daily supplies,possess unique viscoelasticity.However,the property of pure rubber matrix is difficult to meet the demand for high-performance rubber in practical applications.Therefore,it is necessary to add fillers to the rubber matrix for reinforcement or functionalization.The dispersion of the filler and the interfacial interaction between the inorganic fillers and the organic matrix are generally acknowledged to be two key factors determining the final properties of the composites,both of which are highly dependent on the surface chemistry of the fillers.Thus,optimizing the surface chemical structure of the fillers to facilitate the dispersion of the fillers and strengthen the interaction with the matrix is beneficial to improve the overall performance of rubber composites.In this study,how the oxidation degree of graphene oxide(GO)affects the dispersion of GO and the interfacial adhesion in butadiene-styrene-vinyl pyridine rubber(VPR)/GO composites,as well as the interfacial thermal transport of the composites were investigated by molecular dynamics(MD)simulation.Subsequently,the composites containing different oxidation degrees of GO were prepared by the chemical reduction GO in situ to verify the theoretical results,and analyzed the influence of oxidation degree of GO on the mechanical and thermal conductivity of the composites.Finally,combining molecular simulation and experimental results to explore the relationship between the microstructures and macroscopic performance.The main research contents include the following two parts:(1)The two-component solubility parameters of GO with different oxidation degrees and pure VPR were calculated by MD simulations to study compatibility between them.The results suggested that with the oxygen content increases,the compatibility between GO and VPR first decrease and then increase,the best compatibility obtains when the oxidation degree is 15%.In addition,binding energy,the number of intermolecular hydrogen bonding and fractional free volume of the GO/VPR system were also figured out to investigate the influence of oxidation degree of GO on interface adhesion from molecular level.The results showed that with the increase of the oxidation degree of GO,the number of intermolecular hydrogen bonds gradually increased,and the binding energy also increased,resulting in the rubber molecular chains being packed closer together and the fractional free volume gradually decreased.The interface double-layer structure of rubber composites can be identified by calculating the mean square displacement curves of VPR molecular chains at different distances from the filler surface.As the oxidation degree of GO increases,the interface interaction increase,and more VPR molecular chains are adsorbed on the GO surface to form a thick interface layer.Non-equilibrium molecular dynamics simulation was used to calculate the phonon vibration power spectrum and interface thermal resistance to analyze the effect of GO oxidation degree on micro-interface thermal transfer.The results showed that increasing the oxidation degree of GO was beneficial to reduce phonon scattering at the interface and interface thermal resistance of the composites.(2)The different oxidation degrees of GO and GO/VPR composites containing GO with tailored reduction extent were prepared by the chemical reduction method.The surface energy of GO with different oxidation degrees and pure VPR matrix were obtained according to the Fowkes'model to investigate the effects of the oxidation degree of GO on the interfacial adhesion and the re-aggregation of the filler during processing.The results showed that the higher the oxidation degree of GO,the stronger the interface adhesion,while the re-aggregation driving force first decreases and then slightly increases with the increase of oxidation degree,which is consistent with the conclusions of binding energy and compatibility analysis in molecular simulations.Although increasing of the oxidation degree of GO was beneficial to the interface adhesion,the GO/VPR composites with high oxidation degree do not have the maximum weight fraction of the interface layer according to the results of the heat capacity at the glass transition temperature(?Cpn)and loss factor(tan?),which is caused by its poor dispersion that reduces the effective specific surface area of the filler.With the preparation of GO samples,the optimal dispersion did achieve as the GO oxidation degree reaches 1.5%in VPR/GO85e composites,in which case the composites have the best mechanical properties,and the tensile strength and tensile moduli(stress at 100%strain)increased by 339.8%and 237.8%versus that of neat VPR matrix,respectively.Although increasing the oxidation degree of GO was beneficial to improve the phonon transport and interface thermal conductivity of the composite,the moderate oxidation degree sample,here is the VPR/GO85e composites,exhibits the maximum thermal conductivity.This is because the low intrinsic thermal conductivity and poor dispersion of GO with high oxidant degree limit the increase in thermal conductivity of the composites.