Study On The Interfacial Properties Of Rubber Nanocomposites Based On Quantitative Nanomechanics Technology Of Atomic Force Microscope

Rubber materials with high elasticity at room temperature have important strategic significance in the fields of aerospace,weapons and tires.It is a necessary way to prepare high-performance rubber materials by reinforcing rubber with nano fillers.The influence of fillers on the properties of rubber materials is determined by multi-scale microstructure of nanocomposites,including rubber network,filler-filler network and filler-rubber network.The latter two factors depend on the interaction between filler and rubber.The interfacial interaction affects the dispersion of fillers,the orientation of rubber molecular chain and the properties of interphase,and ultimately affects the reinforcing effect of fillers on rubber.Therefore,it is very important to find out the microstructure and nano mechanical properties of interphase of rubber nanocomposites for the design and preparation of rubber materials with high mechanical properties.The interphase between filler and rubber matrix,also known as "bound rubber",is defined as a rubber film fixed at the filler/rubber interphase and cannot be dissolved in solvent.Although there are many indirect evidences and conjectures about the existence of interphase,it is very challenging to quantitatively characterize the thickness and nanomechanical properties of the interphase because the size of the interphase is usually only about tens of nanometers.Before this,our team have preliminary established a quantitative characterization method of the interfacial thickness of rubber nanocomposites by using the quantitative nanomechanics technology of atomic force microscope(AFM-QNM).However,the mechanical properties of interphase with nanometer scale are not accurately measured.In addition,carbon black/rubber composites,which are widely used in rubber reinforcement,and fibrillar-silicate/rubber composites,which have important applications in triangle rubber of tire,need to be studied.Therefore,the research contents are as follows:(1)Based on AFM-QNM and the previous work of the research group,the quantitative characterization method of interphase was optimized,and a more accurate and reliable scientific method for characterizing the thickness and nanomechanical properties of interface was obtained.Accurate identification of interphase region and accurate analysis of nanomechanical properties of interphase are based on accurate measurement of nanomechanical properties.The Johnson-Kendall-Robert(JKR)mechanical model,which is more suitable for the analysis of rubber materials,is used to calculate the nano mechanical properties such as modulus.After the force-deformation curve measured by AFM-QNM is successfully fitted with JKR model,it is found that the forcedeformation curve is basically consistent with JKR model,which verifies the accuracy of modulus calculation model selection and mechanical properties measurement.Based on this,the force-deformation curves of different regions of the interphase are compared and found that the tightly bound rubber(TBR)near the filler surface has higher slope than the loosely bound rubber(LBR)near the rubber matrix,which means TBR layer has better nano mechanical properties.In conclusion,we have successfully obtained a more accurate and reliable scientific method to characterize the interfacial thickness and nanomechanical properties by optimizing the quantitative characterization method of the interphase.(2)In view of the excellent reinforcing properties of carbon black,the micro mechanism of carbon black reinforced rubber was explored based on the quantitative characterization method.It is found that carbon black with high specific surface area and high structure degree has better reinforcement effect because of the formation of interphase with thicker thickness and higher modulus,and this interphase is more favorable for stress transfer.At the same time,AFM-QNM shows that the interfacial interaction increases with the increase of the specific surface area and the structure degree of carbon black,which is verified by the analysis of the chain segment content and the movement ability in the interfacial region.When discussing the effect of specific surface area of carbon black on the interfacial properties,it is found that the surface of carbon black with high specific surface area has more complex.surface roughness structure,which may be the essential reason for its thicker interface,higher interfacial modulus and stronger interface interaction.Besides,the interfacial interaction mechanism between carbon black with different specific surface area and rubber matrix was analyzed.When discussing the influence of carbon black structure degree,it is found that the difference of reinforcing effect of carbon black with different structure degree is not caused by the surface structure of single carbon black,but by the whole complex chain branch structure of aggregate.Carbon black aggregates with higher structure degree can bind more rubber molecular chains because of their more developed chain branch structure,so the interphase is thicker and the interfacial modulus is higher.(3)Based on the quantitative characterization method of the interphase,the micro mechanism of the influence of molecular polarity of hydrogenated nitrile rubber(HNBR)on the interfacial properties of rubber nanocomposites was explored,and the differences of interfacial properties and interaction between silica and carbon black reinforced HNBR were investigated.It is found that the molecular polarity of HNBR rubber molecules has a similar effect on the silica/rubber composites and carbon black/rubber composites,that is,with the increase of the molecular polarity of HNBR,the total interfacial thickness and modulus increase,indicating that the interfacial interaction increases gradually.However,the thickness of TBR layer is almost unchanged,which is mainly due to the similar molecular chain length and mobility of the four kinds of HNBR rubbers.At the same time,it was found that the interfacial thickness and interfacial modulus of carbon black/rubber composites were significantly larger than that of silica/rubber composites,which confirmed the research results in a large number of literatures,that is,compared with the smooth surface structure of silica,the complex topological structure of carbon black surface led to stronger interfacial interaction between carbon black with rubber molecular chain.(4)The effects of different surface modification treatments on the interfacial properties of fibrillar-silicate/rubber composites(FS/NR)were investigated by using the established quantitative characterization method.The results show that the modified FS/NR composites have thicker interfacial thickness and higher interfacial modulus than the unmodified FS/NR composites,which is due to the strong interfacial interaction between the modified-FS and NR rubber matrix.Besides,it was found that the interfacial thickness and modulus of FS-Si69/NR composites were larger than FSKH570/NR,which indicated that there was the strongest interfacial interaction between FS modified by Si69 and rubber molecular chain.The reason is that the number of reaction groups on Si69 and FS surface is twice that of KH570.