Model aggregated 2D suspensions in shear and compression: From a fluid layer to an auxetic interface?

J Colloid Interface Sci

Department of Materials, ETH Zurich, Vladimir-Prelog-Weg 5, Zurich 8093, Switzerland. Electronic address:

Published: December 2023

AI Article Synopsis

  • - The study focuses on how particle-laden interfaces influence the stability of multiphase systems, specifically looking at their mechanical properties under shear and compression, with attention to changes in microstructural dynamics.
  • - Experiments were conducted to measure interfacial rheological properties under different conditions using shear flow and isotropic compression, while also observing microstructural evolution.
  • - Results show that compressive moduli increase non-monotonically with decreasing voids, while shear moduli rise steadily, with interfaces displaying unexpected auxetic behavior at certain coverages, indicating potential resilience benefits for particle-coated bubbles or droplets under varying pressure.

Article Abstract

Hypothesis: 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.

Experiments: 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.

Findings: 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.

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Source
http://dx.doi.org/10.1016/j.jcis.2023.07.159DOI Listing

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