Alicke Alexandra, Stricker Laura, Vermant Jan
Department of Materials, ETH Zurich, Vladimir-Prelog-Weg 5, Zurich 8093, Switzerland.
Department of Materials, ETH Zurich, Vladimir-Prelog-Weg 5, Zurich 8093, Switzerland.
J Colloid Interface Sci. 2023 Dec 15;652(Pt A):317-328. doi: 10.1016/j.jcis.2023.07.159. Epub 2023 Aug 4.
Particle-laden interfaces play a crucial role in engineering stability of multiphase systems. However, a full understanding of the mechanical properties in shear and compression, especially in relation to the underlying microstructural changes, is as yet lacking. In this study, we investigate the interfacial rheological moduli in heterogeneous networks of aggregated 2D suspensions using different deformation modes and relate these moduli to changes in the microstructure.
Interfacial rheological experiments were conducted at different surface coverages and clean kinematic conditions, namely in (i) simple shear flow in a modified double wall-ring geometry and (ii) isotropic compression in a custom-built radial trough, while monitoring the evolution of the microstructure.
The compressive moduli increase non-monotonically with decreasing void fraction, reflecting the combined effect of aggregate densification and reduction of void structures, with rotation of rigid clusters playing a significant role in closing voids. However, the shear moduli increase monotonically, which correlates with the increase in fractal dimension of the aggregates making up the backbone network. We also observe that these interfaces act as 2D auxetic materials at intermediate coverages, which is surprising given their amorphous structure. This finding has potential implications for the resilience of particle-coated bubbles or droplets subjected to time-varying compression-expansion deformations.
负载颗粒的界面在多相系统的工程稳定性中起着关键作用。然而，目前尚缺乏对剪切和压缩过程中力学性能的全面理解，特别是与潜在微观结构变化相关的理解。在本研究中，我们使用不同的变形模式研究了聚集二维悬浮液异质网络中的界面流变模量，并将这些模量与微观结构的变化联系起来。
在不同的表面覆盖率和清洁运动学条件下进行界面流变实验，即在（i）改进的双壁环几何结构中的简单剪切流和（ii）定制的径向槽中的各向同性压缩中，同时监测微观结构的演变。
压缩模量随着孔隙率的降低而非单调增加，这反映了聚集体致密化和孔隙结构减少的综合作用，刚性团簇的旋转在封闭孔隙中起重要作用。然而，剪切模量单调增加，这与构成骨架网络的聚集体分形维数的增加相关。我们还观察到，这些界面在中间覆盖率下表现为二维负泊松比材料，考虑到它们的无定形结构，这一发现令人惊讶。这一发现对于经受时变压缩 - 膨胀变形的颗粒包覆气泡或液滴的弹性具有潜在意义。
