Parthasarathy Dinesh, Chandragiri Santhan, Thampi Sumesh P, Ravindran Parag, Basavaraj Madivala G
Polymer Engineering and Colloid Science Laboratory (PECS), Department of Chemical Engineering, Indian Institute of Technology Madras, Chennai - 600036, India.
Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai - 600036, India.
Soft Matter. 2022 Mar 23;18(12):2414-2421. doi: 10.1039/d2sm00142j.
The coffee ring effect, which refers to the formation of a ring-like deposit along the periphery of a dried particle laden sessile drop, is a commonly observed phenomenon. The migration of particles from the interior to the edge of a drying drop as a result of evaporation driven flow directed outwards, is well studied. In this article, we document the inward drift of a coffee stain, which is governed by the descent of the water-air interface of the drying drop due to solvent evaporation. A combination of experimental study and model predictions is undertaken to elucidate the effect of the diameter of particles in the drying drop, the wettability of the substrate on which the drop resides, and the concentration of particles on the inward drift of the coffee stain. This work also suggests a novel method to estimate the coefficient of friction between the particles and the substrate.
咖啡环效应是一种常见现象，它指的是沿着载有颗粒的静止液滴干燥边缘形成环状沉积物。由于向外的蒸发驱动流，颗粒从干燥液滴内部迁移到边缘的现象已得到充分研究。在本文中，我们记录了咖啡渍的向内漂移，这是由干燥液滴的水 - 空气界面因溶剂蒸发而下降所控制的。我们进行了实验研究和模型预测相结合的工作，以阐明干燥液滴中颗粒直径、液滴所在基底的润湿性以及颗粒浓度对咖啡渍向内漂移的影响。这项工作还提出了一种估计颗粒与基底之间摩擦系数的新方法。
