由多分散初级颗粒组成的团聚体的凝聚,Langmuir

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由多分散初级颗粒组成的团聚体的凝聚
Langmuir ( IF 3.7 ) Pub Date : 2016-08-31 00:00:00 , DOI: 10.1021/acs.langmuir.6b02455
E Goudeli ₁ , M L Eggersdorfer ₁ , S E Pratsinis ₁

Affiliation

通过事件驱动 (ED) 方法研究了多分散颗粒的弹道团聚，并与球形颗粒和由单分散初级颗粒 (PP) 组成的团聚体的凝聚进行了比较。据我们所知，这是第一次表明，增加 PP 尺寸分布的宽度或多分散性最初会加速其团聚体的凝结速率，但会延迟其渐近分形结构和自保尺寸分布 (SPSD) 的实现，而无需改变它们，前提是使用了足够多的 PP。例如，标准渐近质量分形维数D _f当形成平均包含约 15 个单分散 PP 的簇时，达到 1.91，与分形理论和文献一致。相比之下，当使用几何标准偏差为 3 的多分散 PP 时，需要大约 500 个 PP 才能达到D _f。尽管无论 PP 多分散性如何，都可以获得相同的渐近D _f和质量迁移率指数D _fm，但D _f和D _fm的渐近先导因子或缺陷随 PP 多分散性而增加。对于单分散 PP，团聚体的平均回转半径r _g变得大于流动半径r_m，当团聚体由超过 15 个 PP 组成时。增加 PP 多分散性会增加 PP 的数量，与上述类似，以获得渐近D _f或D _fm. 团聚动力学通过整体碰撞频率函数进行量化。当达到 SPSD 时，碰撞频率与 PP 多分散性无关。一旦达到 SPSD，在整体附聚物碰撞频率中考虑 SPSD 多分散性与来自详细 ED 模拟的频率非常一致。最重要的是，附聚物的凝结可以通过附聚物和 PP 尺寸的单分散模型很好地描述，而详细的附聚物尺寸分布可以通过将平均附聚物尺寸缩放到 SPSD 来获得。

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Coagulation of Agglomerates Consisting of Polydisperse Primary Particles

The ballistic agglomeration of polydisperse particles is investigated by an event-driven (ED) method and compared to the coagulation of spherical particles and agglomerates consisting of monodisperse primary particles (PPs). It is shown for the first time to our knowledge that increasing the width or polydispersity of the PP size distribution initially accelerates the coagulation rate of their agglomerates but delays the attainment of their asymptotic fractal-like structure and self-preserving size distribution (SPSD) without altering them, provided that sufficiently large numbers of PPs are employed. For example, the standard asymptotic mass fractal dimension, D_f, of 1.91 is attained when clusters are formed containing, on average, about 15 monodisperse PPs, consistent with fractal theory and the literature. In contrast, when polydisperse PPs with a geometric standard deviation of 3 are employed, about 500 PPs are needed to attain that D_f. Even though the same asymptotic D_f and mass-mobility exponent, D_fm, are attained regardless of PP polydispersity, the asymptotic prefactors or lacunarities of D_f and D_fm increase with PP polydispersity. For monodisperse PPs, the average agglomerate radius of gyration, r_g, becomes larger than the mobility radius, r_m, when agglomerates consist of more than 15 PPs. Increasing PP polydispersity increases that number of PPs similarly to the above for the attainment of the asymptotic D_f or D_fm. The agglomeration kinetics are quantified by the overall collision frequency function. When the SPSD is attained, the collision frequency is independent of PP polydispersity. Accounting for the SPSD polydispersity in the overall agglomerate collision frequency is in good agreement with that frequency from detailed ED simulations once the SPSD is reached. Most importantly, the coagulation of agglomerates is described well by a monodisperse model for agglomerate and PP sizes, whereas the detailed agglomerate size distribution can be obtained by scaling the average agglomerate size to the SPSD.

更新日期：2016-08-31

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