Study On Three-dimensional Multi-scale Dispersion Structure Of Nano-silica In Solution-polymerized Styrene Butadiene Rubber

As one of the three major polymer materials,rubber is considered to be an indispensable strategic material which has a wide range of applications in the industrial field due to its unique high elasticity.However,the pure rubber matrix often has the weakness of low strength and low modulus,which greatly limits its further applications.Therefore,in actual industrial production,inorganic nanofillers are often added as reinforcing agent to improve its performance.Thus,the dispersibility of the nanofillers is one of the key factors that affecting the macro-properties of the rubber nanocomposites.Good dispersibility will significantly improve the performance of the nanocomposites.The traditional methods used to characterize the dispersion structure are mainly about microscopes.The microscopes can visualize the two-dimensional(2D)dispersion morphology of the nanofillers.Combining with the scattering methods,which is suitable for statistical analysis,the dispersion structure can be understood qualitatively or semi-quantitatively.However,as the nanocomposites are more complicated,the dispersion morphology of nanofillers tends to be multi-scale,and simple 2D-images can no longer meet the needs of quantitative research.This article aims to establish a three-dimensional(3D)quantitative characterization method to deeply understand the 3D multi-scale dispersion structure of nanofillers in the rubber matrix,and to explore the influence of the nanofiller-rubber interaction on the dispersion of nanofillers in the rubber matrix.It may provide a theoretical basis for designation and preparation high-performance rubber nanocomposites in the future.The main research contents of this article are as follows:(1)Based on three dimensional-Scanning Transmission Electron Microscopy(3D-STEM)with high resolution(about 2 nm)and synchrotron radiation X-ray computerized tomography(X-ray CT)with big viewfield(about 60×60 ?m²),a quantitative characterization of nanofillers in rubber nanocomposites is established at the nano-to micro-meter scale.This method displays the 3D dispersion structure of nanofillers visually,and can quantify the following parameters:concentration fluctuation of filler agglomerates(STDEV),equivalent diameter(Eq D),compactness,the branching degree(Nbn/Ntn,Nseg)and connectivity(Nb,Lseg)of filler branches,the branching degree(NBN/NTN,NSEG)and connectivity(NN,LSEG)of filler networks.(2)Based on the 3D quantitative characterization method established above,we choose the silica(SiO₂)/solution polymerized styrene butadiene rubber(SSBR)nanocomposites as the research objects,and explore the effect of functionalized modified SSBR on SiO₂/SSBR nanocomposite materials in the three-dimensional multi-scale dispersion structure of the influence.From the results we can found that when modified SSBR is used as the rubber matrix,the intrfaical interaction between SiO₂ and SSBR was inhanced,the dispersion uniformity of filler particles was improved and the compactness of filler agglomerates decreased,which means the adjacent agglomerats were more likely to overlap with each other.The branching degree and the connectivity of nanofiller agglomerates are increase,so the branching degree and the connectivity of nanofiller networks which are composed of these small branches also increase.These parameters all indicate the improved dispersity of SiO₂.Using the above quantitative characterization results of dispersion structure,changes of the nonlinear viscoelasticity of nanocomposites can be well understand.Using the above quantitative characterization results of the subtle changes of the dispersion structure,the changes of the nonlinear viscoelasticity exhibited by the composite material in the rheological test can be well explained.(3)Based on the three-dimensional quantitative characterization method established above,we select SiO₂/SSBR nanocomposites as the research objects,and explore the influence of SiO₂ surface hydroxyl content changes on the 3D multi-scale dispersion structure in the SiO₂/SSBR nanocomposites.From the results we can found that with the decrease of the surface hydroxyl contents of SiO₂,the intrfaical interaction between SiO₂ and SSBR was increased gradually,the dispersion uniformity of filler particles was improved,the compactness of filler agglomerates decreased,which means the adjacent agglomerats were easier to build up with each other.The connectivity and the branching degree of branches increase,so the connectivity and the branching degree of networks which are composed of these small branches also increase.These parameters all indicate the improved dispersity of SiO₂.Using the above quantitative characterization results of dispersion structure,changes of the nonlinear viscoelasticity of nanocomposites can be well understand.Using the above quantitative characterization results of the subtle changes of the dispersion structure,the changes of the nonlinear viscoelasticity exhibited by the composite material in the rheological test can be well explained.