Liu Tingting, Luo Hao, Ma Jun, Xie Weiguang, Wang Yan, Jing Guangyin
School of Physics, Northwest University, 710069, Xi'an, China.
Department of Physics, The Hong Kong University of Science and Technology, Hong Kong, China.
Eur Phys J E Soft Matter. 2016 Feb;39(2):24. doi: 10.1140/epje/i2016-16024-7. Epub 2016 Feb 26.
We investigate crack formation in deposition films from drying colloidal suspension drops, by varying the roughness and texture of the substrate. The experimental results indicate that the crack number or crack spacing presents a general dependence on the substrate roughness, despite the orientation of the substrate textures. Interestingly, the crack spacing decreases with the increase of the roughness. Two possible mechanisms are proposed to understand the dependence of the cracks on roughness. Firstly, the concentration reduction of the drying suspension due to collecting colloidal particles from the substrate textures decreases the crack spacing. Secondly, stress concentration resulting from the defects (the notches in textures) in the dried deposition enhances crack formation. However, a quantitative estimation by the calculation of the stress concentrating factors reveals that the notch of the substrate textures dominates crack variation. The results here bring forth a practical method for controlling the crack orientation and suppression, and a potential application to crack-free coatings, films and paintings during the drying of complex fluids.
我们通过改变基底的粗糙度和纹理来研究干燥胶体悬浮液滴沉积薄膜中的裂纹形成。实验结果表明，尽管基底纹理的取向不同，但裂纹数量或裂纹间距总体上依赖于基底粗糙度。有趣的是，裂纹间距随着粗糙度的增加而减小。提出了两种可能的机制来解释裂纹对粗糙度的依赖性。首先，由于从基底纹理收集胶体颗粒导致干燥悬浮液浓度降低，从而减小了裂纹间距。其次，干燥沉积物中缺陷（纹理中的缺口）引起的应力集中增强了裂纹形成。然而，通过计算应力集中系数进行的定量估计表明，基底纹理的缺口主导了裂纹变化。这里的结果提出了一种控制裂纹取向和抑制裂纹的实用方法，以及在复杂流体干燥过程中对无裂纹涂层、薄膜和绘画的潜在应用。
