Shear banding in drying films of colloidal nanoparticles.
Shear banding in drying films of colloidal nanoparticles.
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DOI：
10.1021/acsnano.5b00127
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发表时间：
2015-04
期刊：
影响因子：
17.1
通讯作者：
Bin Yang;J. S. Sharp;M. Smith
中科院分区：
文献类型：
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作者：
Bin Yang;J. S. Sharp;M. Smith
胶体纳米颗粒的干燥悬浮液在成膜过程中表现出多种有趣的应变释放机制。这些导致在故障过程中，如开裂和随后的分层的特征长度尺度的选择。广泛的材料（例如，块状金属玻璃）通过塑性变形释放应变，所述塑性变形发生在被称为剪切带的窄材料带中。在这里，我们表明，干燥的胶体膜也表现出剪切带。观察到条带在干燥前沿后面的一小段距离处形成，然后以与干燥方向成45°的角度迅速传播。结果表明，谱带的间距取决于盐浓度和胶体悬浮液的蒸发速率。这些综合观察表明，存在一个临界剪切速率（与薄膜屈服应力有关），它控制着带宽与带间距的比值。在干燥的早期阶段，使用荧光示踪颗粒测量局部变形。测量结果表明，剪切带的存在与垂直于干燥前沿的颗粒压实有关。剪切带的间距也被发现是密切相关的特征长度尺度的压实过程。这些结合的研究阐明了在图案形成过程中的胶体纳米粒子的干燥膜的塑性变形的作用。
Drying suspensions of colloidal nanoparticles exhibit a variety of interesting strain release mechanisms during film formation. These result in the selection of characteristic length scales during failure processes such as cracking and subsequent delamination. A wide range of materials (e.g., bulk metallic glasses) release strain through plastic deformations which occur in a narrow band of material known as a shear band. Here we show that drying colloidal films also exhibit shear banding. Bands are observed to form a small distance behind the drying front and then to propagate rapidly at ∼45° to the direction of drying. It is shown that the spacing of the bands depends on salt concentration and the evaporation rate of the colloidal suspension. These combined observations suggest that there is a critical shear rate (related to the film yield stress) which controls the ratio of bandwidth to band spacing. Local deformations were measured in the early stages of drying using fluorescent tracer particles. The measurements were used to show that the existence of shear bands is linked to the compaction of particles perpendicular to the drying front. The spacing of shear bands was also found to be strongly correlated with the characteristic length scale of the compaction process. These combined studies elucidate the role of plastic deformation during pattern formation in drying films of colloidal nanoparticles.