Weon Byung Mook, Je Jung Ho
Department of Physics, School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2010 Jul;82(1 Pt 2):015305. doi: 10.1103/PhysRevE.82.015305. Epub 2010 Jul 26.
When a coffee drop dries on a solid surface, it leaves a ringlike deposit along the edge and this is known as the "coffee-ring effect." We find a different motion of particles repelling the coffee-ring effect in drying droplets; the motion of particles that is initially toward the edge by the coffee-ring effect is reversed toward the center by a capillary force. The reversal takes place when the capillary force prevails over the outward coffee-ring flow. We discuss the geometric constraints for the capillary force and the reverse motion. Our findings of reversal phenomena would be important in many scenarios of drying colloidal fluids.
当一滴咖啡在固体表面干燥时，它会在边缘留下环状沉积物，这就是所谓的“咖啡环效应”。我们发现在干燥液滴中存在一种不同的粒子运动，它能抵消咖啡环效应；最初因咖啡环效应而向边缘移动的粒子运动，会被毛细作用力反转，使其向中心移动。当毛细作用力超过向外的咖啡环流时，就会发生这种反转。我们讨论了毛细作用力和反向运动的几何约束条件。我们关于反转现象的发现，在许多干燥胶体流体的场景中都将具有重要意义。
