Suppression of the coffee-ring effect by shape-dependent capillary interactions

被引:1339
作者
Yunker, Peter J. [1 ]
Still, Tim
Lohr, Matthew A.
Yodh, A.G.
机构
[1] Univ Penn, Dept Phys & Astron, Philadelphia, PA 19104 USA
[2] CNRS Rhodia Univ Pennsylvania, Complex Assemblies Soft Matter, UMI 3254, Bristol, PA 19007 USA
基金
美国国家科学基金会;
关键词
AIR-WATER-INTERFACE; ELLIPSOIDAL PARTICLES; PATTERN-FORMATION; EVAPORATION; DROPLETS; DROPS;
D O I
10.1038/nature10344
中图分类号
O [数理科学和化学]; P [天文学、地球科学]; Q [生物科学]; N [自然科学总论];
学科分类号
07 ; 0710 ; 09 ;
摘要
When a drop of liquid dries on a solid surface, its suspended particulate matter is deposited in ring-like fashion. This phenomenon, known as the coffee-ring effect(1-3), is familiar to anyone who has observed a drop of coffee dry. During the drying process, drop edges become pinned to the substrate, and capillary flow outward from the centre of the drop brings suspended particles to the edge as evaporation proceeds. After evaporation, suspended particles are left highly concentrated along the original drop edge. The coffee-ring effect is manifested in systems with diverse constituents, ranging from large colloids(1,4,5) to nanoparticles(6) and individual molecules(7). In fact-despite the many practical applications for uniform coatings in printing(8), biology(9,10) and complex assembly(11)-the ubiquitous nature of the effect has made it difficult to avoid(6,12-16). Here we show experimentally that the shape of the suspended particles is important and can be used to eliminate the coffee-ring effect: ellipsoidal particles are deposited uniformly during evaporation. The anisotropic shape of the particles significantly deforms interfaces, producing strong interparticle apillary interactions(17-23). Thus, after the ellipsoids are carried to the air-water interface by the same outward flow that causes the coffee-ring effect for spheres, strong long-ranged interparticle attractions between ellipsoids lead to the formation of loosely packed or arrested structures on the air-water interface(17,18,21,24). These structures prevent the suspended particles from reaching the drop edge and ensure uniform deposition. Interestingly, under appropriate conditions, suspensions of spheres mixed with a small number of ellipsoids also produce uniform deposition. Thus, particle shape provides a convenient parameter to control the deposition of particles, without modification of particle or solvent chemistry.
引用
收藏
页码:308 / 311
页数:4
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