Experimental characterization of breakage rate of colloidal aggregates in axisymmetric extensional flow.
Experimental characterization of breakage rate of colloidal aggregates in axisymmetric extensional flow.
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DOI：
10.1021/la502686b
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发表时间：
2014-11
期刊：
影响因子：
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通讯作者：
D. Saha;M. Šoóš;B. Lüthi;M. Holzner;Alexander Liberzon;M. Babler;W. Kinzelbach
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文献类型：
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作者：
D. Saha;M. Šoóš;B. Lüthi;M. Holzner;Alexander Liberzon;M. Babler;W. Kinzelbach
在完全不稳定的条件下通过布朗运动的作用制备的聚集体暴露于在突然收缩的入口处产生的拉伸流。两种非侵入性技术被用来监测其破碎过程[即光散射和三维（3D）粒子跟踪测速（3D-PTV）]。虽然第一种方法可用于测量破碎事件后形成的碎片的大小和形态，但后者能够解析直至破碎点的单个聚集体的轨迹以及形成的碎片的轨迹。此外，测量的速度梯度被用来确定在破碎点的当地水动力条件。将所有这些信息结合起来，以实验方式首次确定单个聚集体的破碎率，以尺寸减小率K（R）的形式给出，作为施加的应变率的函数，以及形成的碎片的性质（即，形成的碎片的数量和最大碎片与原始聚集体之间的尺寸比）。结果发现，K（R）与施加的应变速率根据幂律的斜率是依赖于初始分形维数，而所获得的数据表明的K（R）与初始骨料尺寸的线性依赖关系。此外，所形成的碎片的数量的概率分布函数（PDF）和最大碎片与原始聚集体之间的尺寸比的概率分布函数（PDF）表明，断裂将以高概率（75%）导致形成具有约0.8的相当不对称的尺寸比的两个至三个碎片。所得结果与文献中发表的数值模拟结果吻合较好。
Aggregates prepared under fully destabilized conditions by the action of Brownian motion were exposed to an extensional flow generated at the entrance of a sudden contraction. Two noninvasive techniques were used to monitor their breakup process [i.e. light scattering and three-dimensional (3D) particle tracking velocimetry (3D-PTV)]. While the first one can be used to measure the size and the morphology of formed fragments after the breakage event, the latter is capable of resolving trajectories of individual aggregates up to the breakage point as well as the trajectories of formed fragments. Furthermore, measured velocity gradients were used to determine the local hydrodynamic conditions at the breakage point. All this information was combined to experimentally determine for the first time the breakage rate of individual aggregates, given in the form of a size reduction rate K(R), as a function of the applied strain rate, as well as the properties of the formed fragments (i.e., the number of formed fragments and the size ratio between the largest fragment and the original aggregate). It was found that K(R) scales with the applied strain rate according to a power law with the slope being dependent on the initial fractal dimension only, while the obtained data indicates a linear dependency of K(R) with the initial aggregate size. Furthermore, the probability distribution function (PDF) of the number of formed fragments and the PDF of the size ratio between the largest fragment and the original aggregate indicate that breakage will result with high probability (75%) in the formation of two to three fragments with a rather asymmetric ratio of sizes of about 0.8. The obtained results are well in agreement with the results from the numerical simulations published in the literature.