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Fractal approaches to characterize the structure of capillary suspensions using rheology and confocal microscopy
Journal of Rheology ( IF 3.3 ) Pub Date : 2018-01-01 , DOI: 10.1122/1.4997889
Frank Bossler 1, 2 , Johannes Maurath 1 , Katrin Dyhr 1 , Norbert Willenbacher 1 , Erin Koos 1, 2
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The rheological properties of a particle suspension can be substantially altered by adding a small amount of a secondary fluid that is immiscible with the bulk phase. The drastic change in the strength of these capillary suspensions arises due to the capillary forces, induced by the added liquid, leading to a percolating particle network. Using rheological scaling models, fractal dimensions are deduced from the yield stress and from oscillatory strain amplitude sweep data as function of the solid volume fraction. Exponents obtained using aluminum-oxide-based capillary suspensions, with a preferentially wetting secondary fluid, indicate an increase in the particle gel's fractal dimension with increasing particle size. This may be explained by a corresponding relative reduction in the capillary force compared to other forces. Confocal images using a glass model system show the microstructure to consist of compact particle flocs interconnected by a sparse backbone. Thus, using the rheological models two different fractal dimensionalities are distinguished - a lower network backbone dimension (D = 1.86-2.05) and an intrafloc dimension (D = 2.57-2.74). The latter is higher due to the higher local solid volume fraction inside of the flocs compared to the sparse backbone. Both of these dimensions are compared with values obtained by analysis of spatial particle positions from 3D confocal microscopy images, where dimensions between 2.43 and 2.63 are computed, lying between the two dimension ranges obtained from rheology. The fractal dimensions determined via this method corroborate the increase in structural compactness with increasing particle size.

中文翻译:

使用流变学和共聚焦显微镜表征毛细管悬浮液结构的分形方法

通过添加少量与本体相不混溶的二次流体,可以显着改变颗粒悬浮液的流变特性。这些毛细悬浮液强度的剧烈变化是由于毛细力引起的,由添加的液体引起,导致渗滤颗粒网络。使用流变标度模型,从屈服应力和振荡应变幅度扫描数据推导出分形维数作为固体体积分数的函数。使用基于氧化铝的毛细管悬浮液获得的指数,具有优先润湿的二次流体,表明颗粒凝胶的分形维数随着颗粒尺寸的增加而增加。这可以通过与其他力相比毛细力的相应相对减小来解释。使用玻璃模型系统的共焦图像显示微观结构由通过稀疏骨架互连的致密颗粒絮凝物组成。因此,使用流变模型可以区分两种不同的分形维数——较低的网络主干维数 (D = 1.86-2.05) 和絮内维数 (D = 2.57-2.74)。后者更高,因为与稀疏骨架相比,絮凝物内部的局部固体体积分数更高。这两个维度都与通过分析 3D 共聚焦显微镜图像的空间粒子位置获得的值进行比较,其中计算了 2.43 和 2.63 之间的维度,位于从流变学获得的两个维度范围之间。通过这种方法确定的分形维数证实了结构致密性随着粒度的增加而增加。
更新日期:2018-01-01
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