Dynamic pattern selection in polymorphic elastocapillarity
Dynamic pattern selection in polymorphic elastocapillarity
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DOI：
10.1039/d1sm01376a
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发表时间：
2021-11-24
期刊：
影响因子：
3.4
通讯作者：
Tawfick, Sameh
中科院分区：
文献类型：
--
作者：
Ha, Jonghyun;Kim, Yun Seong;Tawfick, Sameh
干燥的细头发和纤维引起显着的毛细驱动变形，与自然现象和工业过程中的重要影响。我们最近观察到特殊的自组装成各种不同的模式取决于束的长度和液体排水率之间的相互作用的头发束。在这里，我们提出了一种机制，这种模式的选择，并推导和验证理论的多边形头发束的多态性自组装的比例律。实验是通过将束浸入液体浴中，然后排出液体来进行的。根据纤维的流失率和长度之间的相互作用，我们观察到纤维束变形为星形（具有凹面），多边形（具有直边和圆角）或圆形。在高漏区的自组装机制是由两个连续的阶段。在高排出速率状态的第一阶段中，液体覆盖束的外部，并且由于高粘性应力，从束内部的排出在自组装中不起作用。湿束角部的局部压力向内压缩纤维，使角部变钝，并且内部润滑促进纤维重排。在第二阶段中，液体从纤维间隔内缓慢排出，并且在周边处的负毛细管压力导致纤维紧密堆积。在缓慢排水制度，第一阶段是缺席的，和纤维慢慢聚集没有初始的动态重排。了解动态弹性毛细现象的机理，为研究湿颗粒干燥的复杂物理过程提供了新的思路。
Drying of fine hair and fibers induces dramatic capillary-driven deformation, with important implications on natural phenomena and industrial processes. We recently observed peculiar self-assembly of hair bundles into various distinct patterns depending on the interplay between the bundle length and the liquid drain rate. Here, we propose a mechanism for this pattern selection, and derive and validate theoretical scaling laws for the polymorphic self-assembly of polygonal hair bundles. Experiments are performed by submerging the bundles into a liquid bath, then draining down the liquid. Depending on the interplay between the drain rates and the length of the fibers, we observe the bundles morphing into stars (having concave sides), polygons (having straight edges and rounded corners), or circles. The mechanism of self-assembly at the high drain regime is governed by two sequential stages. In the first stage of the high drain rate regime, the liquid covers the outside of the bundles, and drainage from inside the bundle does not play a role in the self-assembly due to the high viscous stress. The local pressure at the corners of the wet bundles compresses the fibers inward blunting the corners, and the internal lubrication facilitates fiber rearrangement. In the second stage, the liquid is slowly draining from within the fiber spacing, and the negative capillary pressure at the perimeter causes the fibers to tightly pack. In the slow drainage regime, the first stage is absent, and the fibers slowly aggregate without initial dynamic rearrangement. Understanding the mechanism of dynamic elastocapillarity offers insights for studying the complicated physics of wet granular drying.