Laboratoire Matière et Systèmes Complexes, CNRS UMR 7057, Universitée Denis Diderot, 10 Rue A. Domon et L. Duquet, Paris, France.
Soft Matter. 2017 Dec 20;14(1):61-72. doi: 10.1039/c7sm01757j.
Elastocapillarity describes the deformations of soft materials by surface tensions and is involved in a broad range of applications, from microelectromechanical devices to cell patterning on soft surfaces. Although the vast majority of elastocapillarity experiments are performed on soft gels, because of their tunable mechanical properties, the theoretical interpretation of these data has been so far undertaken solely within the framework of linear elasticity, neglecting the porous nature of gels. We investigate in this work the deformation of a thick poroelastic layer with surface tension subjected to an arbitrary distribution of time-dependent axisymmetric surface forces. Following the derivation of a general analytical solution, we then focus on the specific problem of a liquid drop sitting on a soft poroelastic substrate. We investigate how the deformation and the solvent concentration field evolve in time for various droplet sizes. In particular, we show that the ridge height beneath the triple line grows logarithmically in time as the liquid migrates toward the ridge. We then study the relaxation of the ridge following the removal of the drop and show that the drop leaves long-lived footprints after removal which may affect surface and wetting properties of gel layers and also the motion of living cells on soft materials. Preliminary experiments performed with water droplets on soft PDMS gel layers are in excellent agreement with the theoretical predictions.
弹性毛细现象描述了软物质在表面张力作用下的变形，广泛应用于从微机电系统到软表面细胞图案化等领域。尽管绝大多数弹性毛细现象实验都是在软凝胶上进行的，因为它们具有可调节的机械性能，但迄今为止，这些数据的理论解释仅在线性弹性框架内进行，忽略了凝胶的多孔性质。在这项工作中，我们研究了具有表面张力的厚多孔弹性层在任意分布的时间相关轴对称表面力作用下的变形。在推导出一般解析解之后，我们然后专注于液滴坐在软多孔弹性衬底上的具体问题。我们研究了在各种液滴尺寸下，变形和溶剂浓度场随时间的演化。特别是，我们表明，随着液体向脊线迁移，三线下方的脊高随时间呈对数增长。然后，我们研究了液滴去除后脊线的松弛，并表明液滴去除后会留下持久的足迹，这可能会影响凝胶层的表面和润湿性以及活细胞在软材料上的运动。在软 PDMS 凝胶层上进行的初步水滴实验与理论预测非常吻合。
