The fractal characteristics of atmospheric coated soot: Implication for morphological analysis
The fractal characteristics of atmospheric coated soot: Implication for morphological analysis
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DOI：
10.1016/j.jaerosci.2021.105804
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发表时间：
2021-04-26
影响因子：
4.5
通讯作者：
Chakrabarty, Rajan K.
中科院分区：
文献类型：
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作者：
Luo, Jie;Zhang, Qixing;Chakrabarty, Rajan K.
在这项工作中，我们数值研究了碳烟颗粒的分形特性的变化，作为碳烟涂层。我们发现，只有当包覆碳烟的回转半径（Rg）与碳烟核的回转半径相同时，理想的分形规律才能拟合包覆碳烟的形貌。在这种情况下，涂覆的烟炱的分形维数（Df）接近烟炱芯的分形维数，这可以解释为什么在烟炱被均匀涂覆时通过先前的研究观察到不变的分形维数。由于单体之间的空隙通常首先被填充，因此由二维（2D）方法获得的包覆烟炱的Rg将接近烟炱核的Rg，因此测量的分形维数将接近烟炱核的分形维数。研究结果还表明，不同尺度下的包覆碳烟的分形参数是不同的，因此理想的分形规律很难普适地适用于非均匀包覆碳烟的结构。此外，我们还发现，有效分形维数可以增加烟尘不均匀的涂层。Q空间分析结果表明，当碳烟颗粒被不均匀包覆时，结构因子S（q）与散射波矢量q的幂律指数趋于-4。这意味着，严重的，不均匀的涂层烟灰表现出近球形颗粒的特性。
In this work, we have numerically investigated the variation of fractal characteristics of soot particles as soot is coated. We found that the ideal fractal law can fit the morphologies of coated soot only when the radius of gyration (Rg) of coated soot is identical to that of the soot core. In that case, the fractal dimension (Df) of coated soot is close to that of the soot core, which can explain why the unchanged fractal dimension was observed by the previous study as soot was evenly coated. As the voids among monomers is commonly filled firstly, the Rg of coated soot obtained from the two-dimensional (2D) method would be close to that of the soot core, so the measured fractal dimension would be close to that of the soot core. Our results also show that the fractal parameters of coated soot at different size scales can be varied, so the ideal fractal law is difficult to fit the structures of unevenly coated soot universally. Besides, we also found that the effective fractal dimension can increase as soot is unevenly coated. The results of the Q-space analysis show that as soot particles are unevenly coated, the power-law exponent of the structure factor (S(q)) versus the scattering wave vector (q) tends to-4 for heavily coated soot. This means that heavily, unevenly coated soot exhibits the characteristics of nearly spherical particles.