# Self-Assembly of Gradient Concentric Rings via Solvent Evaporation from a Capillary Bridge

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Jun Xu, Jianfeng Xia, Suck Won Hong, Zhiqun Lin, Feng Qiu and Yuliang Yang, Self-Assembly of Gradient Concentric Rings via Solvent Evaporation from a Capillary Bridge, PRL 96 066104 (2006) [1]

### Brief Summary

The dewetting of a liquid forming a capillary bridge between a plane and a sphere is studied. The evaporating liquid carries MEH-PVV (a non-volatile polymer with optical applications) which in a sense acts to record the drying dynamics of the carrier liquid (toluene). In fact, the polymers also perturb the dewetting process via a slip-stick" mechanism similar to the effect observed when a drop dries off of an unclean surface. The evaporation process produces a pattern concentric rings of polymer on the Si substrate, with a non-trivial radial scaling of ring spacing: an artifact of the drying geometry.

### Capillarity Phenomena

Figure 1: a) Drying geometry: The solute containing MEH-PVV is bound to the volume formed by a capillary bridge between a Si wafer and a microsphere. b) As the toluene evaporates, a pattern of concentric rings forms at certain critical radii of the triple line, producing a non-constant inter-ring spacing $\lambda_{cc}$