Characterization Of Interfacial Properties Of Carbon Nanotubes/Rubber Composites Based On Atomic Force Microscopy

The rubber material with high elasticity at room temperature,widely used in industrial products,such as tires,pipes and sealants,etc.In addition,the inorganic nanoparticles were added into the rubber matrix to obtain the rubber nanocomposites with better performance,such as good mechanical properties,electrical conductivity,thermal conductivity,flame retardant and magnetic properties,etc.For rubber nanocomposites,the interfacial interaction between inorganic nanoparticles and rubber is dominated by on the physical and chemical properties of rubber macromolecules and inorganic nanoparticles.It affects the interfacial properties(thickness and nanomechanical properties,etc.),which in turn affects the dispersion of the nanofiller and the transfer of stress,and finally affects the macroscopic properties of the rubber elastomer nanocomposites.Therefore,the interfacial properties of rubber elastomer nanocomposites are closely related to the physical and chemical properties of rubber macromolecules and inorganic nanoparticles.Many studies have pointed out that in the interface region,the chain accumulation density and molecular chain conformation are different with the surface distance of inorganic nanoparticles,so the quantitative characterization of the interface region is a key problem.In this study,the peak force quantitative nanomechanical mode of atomic force microscopy(AFM-QNM)combined with the Johnson-Kendall-Robert(JKR)model fitting and verification was attempted to quantify the interfacial properties of carbon nanotubes/rubber composites,including interfacial nanomechanical properties and interfacial thickness.On this basis,the effects of the specific surface area of carbon nanotubes and the polarity of rubber macromolecules on the interfacial properties of carbon nanotubes/rubber composites were also studied.This study provides a new insight on the effects of physical and chemical properties of elastomer matrix and nanofiller on the interfacial interaction and the reinforcement mechanism in composites,which will provide a theoretical guidance for the design and preparation of high-performance elastomer nanocomposites.The main research contents are as follows:(1)AFM-QNM was developed to quantify the interfacial nanomechanical properties and the interfacial thickness of carbon nanotubes/rubber composites.Firstly,the " line-method " combined with the JKR model was used to calculate the corresponding Young's modulus of the interface region,and the curves between the Young's modulus and the displacement of the interface region were obtained.In this way,the interfacial nanomechanical properties of carbon nanotubes/rubber composites were quantified.In addition,the JKR model was also used to certify the original AFM-QNM nanomechanical mapping results of carbon nanotubes/rubber composites.On this basis,the "line-method" was used to obtain the modulus-displacement curves of the interface region in the modulus images and the interfacial thickness of the carbon nanotubes/rubber composites was also calculated based on the gradient change of the modulus.(2)Based on the method of AFM-QNM established above for quantifying the interfacial properties of carbon nanotubes/rubber composites,the effects of specific surface area of carbon nanotubes on the interfacial nanomechanical properties and the interfacial thickness of carbon nanotubes/solution polymerized butadiene styrene rubber(CNT/SSBR)nanocomposites were further investigated.As the specific surface areas of carbon nanotubes increased from 40m2/g to 350m2/g,the Young's modulus ranges of interface region for the CNT/SSBR nanocomposites changed from 11.4?34.9 MPa to 11.7?59.7 MPa,and the average Young's modulus of interface region increased from 20.1±0.8 MPa to 31.8±0.9 MPa,and the interfacial thickness of CNT/SSBR nanocomposites increased from 7.4±3.1 nm to 13.8±3.3 nm,respectively.The results show that with the increase of the specific surface area of carbon nanotubes,both the interfacial nanomechanical properties and the interfacial thickness of CNT/SSBR nanocomposites increase gradually.Furthermore,the rubber molecular chain dynamics at the interface region of CNT/SSBR nanocomposites were characterized by differential scanning calorimetry(DSC),indicating that the content of molecular chains bound in the interface layer of the composites increased with the increase of the specific surface area of CNT,that is,the interfacial interaction was enhanced,which was consistent with AFM results.(3)Based on the method of AFM-QNM established above,the impacts of the polarity of rubber macromolecules on the interfacial nanomechanical properties and the interfacial thickness of carbon nanotubes/hydrogenated butadiene-acrylonitrile rubber(CNT/HNBR)nanocomposites were further investigated.With the increase of acrylonitrile content in HNBR from 19wt%to 44wt%,that is,with the increase of the polarity of HNBR,the Young's modulus ranges of the interface region for the CNT/HNBR nanocomposites changed from 6.1-25.8 MPa to 12.2-78.5 MPa,and the average Young,s modulus of the interface region increased from 14.8±0.2 MPa to 40.0±0.4 MPa,and the interfacial thickness of CNT/HNBR nanocomposites increased from 9.3±1.6 nm to 16.4±2.3 nm,respectively.The results show that both the interfacial nanomechanical properties and the interfacial thickness of CNT/HNBR nanocomposites increase gradually with the increase of rubber macromolecular polarity.Furthermore,the dispersion of the nanofiller was observed by scanning electron microscope(SEM),and the dynamic parameters and thermodynamic parameters of the CNT/HNBR nanocomposite were characterized by DSC and contact angle test respectively.The results showed that the interfacial interaction of the composites was enhanced with the increase of HNBR polarity,and the results were consistent with AFM.