Khobaib K, Mikkelsen A, Vincent-Dospital T, Rozynek Z
Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego 2, 61-614 Poznań, Poland.
PoreLab, The Njord Centre, Department of Physics, University of Oslo, Blindern, N-0316 Oslo, Norway.
Soft Matter. 2021 May 19;17(19):5006-5017. doi: 10.1039/d1sm00125f.
Droplets covered with densely packed solid particles, often called Pickering droplets, are used in a variety of fundamental studies and practical applications. For many applications, it is essential to understand the mechanics of such particle-laden droplets subjected to external stresses. Several research groups have studied theoretically and experimentally the deformation, relaxation, rotation, and stability of Pickering droplets. Most of the research concerns spherical Pickering droplets. However, little is known about non-spherical Pickering droplets with arrested particle shells subjected to compressive stress. The experimental results presented here contribute to filling this gap in research. We deform arrested non-spherical Pickering droplets by subjecting them to electric fields, and study the effect of droplet geometry and size, as well as particle size and electric field strength, on the deformation and yielding of arrested non-spherical Pickering droplets. We explain why a more aspherical droplet and/or a droplet covered with a shell made of larger particles required higher electric stress to deform and yield. We also show that an armored droplet can absorb the electric stress differently (i.e., through either in-plane or out-of-plane particle rearrangements) depending on the strength of the applied electric field. Furthermore, we demonstrate that particle shells may fail through various crumpling instabilities, including ridge formation, folding, and wrinkling, as well as inward indentation.
覆盖着紧密堆积的固体颗粒的液滴，通常称为皮克林液滴，被用于各种基础研究和实际应用中。对于许多应用来说，了解这种承载颗粒的液滴在外部应力作用下的力学原理至关重要。几个研究小组已经从理论和实验上研究了皮克林液滴的变形、松弛、旋转和稳定性。大多数研究都涉及球形皮克林液滴。然而，对于承受压缩应力的具有停滞颗粒壳的非球形皮克林液滴却知之甚少。这里给出的实验结果有助于填补这一研究空白。我们通过对停滞的非球形皮克林液滴施加电场使其变形，并研究液滴的几何形状和尺寸、颗粒尺寸以及电场强度对停滞的非球形皮克林液滴变形和屈服的影响。我们解释了为什么更非球形的液滴和/或覆盖有由较大颗粒制成的壳的液滴需要更高的电应力才能变形和屈服。我们还表明，根据所施加电场的强度，装甲液滴可以通过不同方式（即通过面内或面外颗粒重排）吸收电应力。此外，我们证明颗粒壳可能会通过各种褶皱不稳定性失效，包括脊形成、折叠和起皱，以及向内凹陷。
