Quantitative Characterization Of The Three-Dimensional Dispersion Structure Of Filler In Carbon Black/Rubber Nanocomposites Based On 3D-STEM And X-ray Nano-CT

As an important strategic resource,rubber materials have a wide range of industrial applications,such as automobile tires,sealing materials,shock-absorbing materials,conveyor belt materials,etc.However,due to the low mechanical strength of pure rubber materials,it is generally necessary to add carbon black(CB)and white carbon black to improve its mechanical properties,the resulting rubber nanocomposites have a multi-level and multi-scale structure.Among them,the three-dimensional spatial dispersion of nanoparticles is the key to efficient reinforcement of rubber composites.However,the traditional two-dimensional characterization methods are mostly qualitative and semi-quantitative,and there is a lack of a comprehensive understanding of the spatial dispersion of fillers.Nevertheless,the traditional two-dimensional characterization methods are mostly qualitative and semi-quantitative,there is still a lack of comprehensive understanding of the spatial dispersion of fillers.In this paper,we adopt scanning transmission electron microscopy tomography(3D-STEM)imaging technique and in-situ synchrotron radiation X-ray nano-computed tomography(X-ray Nano-CT)imaging technique to characterize the three-dimensional dispersion structure of fillers in nanocomposites from the nanometer to micrometer scale,respectively.It not only realizes the visualization of spatial dispersion morphology of the filler,but also quantifies the three-dimensional dispersion structure parameter of the filler.This method systematically explores and reveals relationship between the three-dimensional dispersion structure parameter of fillers and the macroscopic properties of nanocomposites,providing guidance for the design and preparation of high-performance rubber nanocomposites.The main three contents are as follows:1.The 3D-STEM and X-ray Nano-CT imaging technique are adopted to obtain the three-dimensional visualization images of CB/rubber nanocomposites.Binarization and skeletonization processing are carried out on the visualization images to obtain the parameters of aggregate structure and skeletonization structure on the nanometer scale and the micron scale,so as to realize the multi-scale quantitative characterization of the three-dimensional dispersion structure of the filler.2.Based on the multi-scale quantitative characterization method of three-dimensional dispersion structure for filler established above,the effect of CB with different particle size on the three-dimensional dispersion structure of filler in CB/SSBR nanocomposites was studied.CB with three different particle sizes were selected.When the CB loading amounts is 40 phr,as the CB particle size increases,within the nanometer scale,the degree of structure of the CB filler aggregate is getting lower and lower,the connectivity of the small-scale filler network is reduced,and the morphology of CB aggregates changes from stretched to compact.The connectivity and branching degree of local and overall structure of CB filler network gradually decrease.In addition,RPA analyzes the connectivity of the filler network from a macro perspective,which is consistent with the three-dimensional dispersion results of CB filler characterized by 3D-STEM imaging technique and X-ray Nano-CT imaging technique,thus verifying the accuracy of this multi-scale quantitative characterization method of filler three-dimensional dispersion structure.3.Based on the multi-scale quantitative characterization method of three-dimensional dispersion structure for filler established above,the effect of CB with different loading amounts on the three-dimensional dispersion structure of filler in CB/NR nanocomposites was studied.N220 with three different loading amounts were selected as 10phr,20phr,40phr,60phr,respectively.As the N220 loading amount increases,in the nanometer and micrometer scale,the filler aggregate gradually develops from a uniform dispersion to form a complex filler network.There is a threshold for the critical loading amount between 20-40 phr.When the loading amount is lower than this threshold,the fractal branch tends to increase in number,and when the loading amount is higher than this threshold,the fractal branches will tend to connect with each other to form a filler network.In addition,according to the results of RPA,it is found that the strength of the filler network is directly proportional to the loading amounts of the filler,which is consistent with the connectivity results of N220 filler characterized by 3D-STEM imaging technique and X-ray Nano-CT imaging technique.