Kumar Ankush, Kulkarni G U
Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru 560064, India.
Langmuir. 2021 Nov 9;37(44):13141-13147. doi: 10.1021/acs.langmuir.1c02363. Epub 2021 Oct 27.
Cracks generated due to desiccation of wet colloidal systems are ubiquitous, examples being nanomaterial films, painted walls, cemented floors, mud fields, river beds, and even giant rocks. In all such cases, crack patterns are often appreciably similar but for the length and time scales, which can be widely differing. In this work, we have examined the crack formation more closely to see if there exists some generality with regard to the length scale of parameters and the formation time. Specifically, using a commonly used colloidal dispersion and optimized conditions to form polygonal network patterns rather than isolated cracks (films of subcritical thickness), we have studied the time evolution of the pattern parameters, the area occupied by the cracks, their lengths, and the widths. As is well known, initially, a network of cracks forms, which we term as the primary generation, followed by interconnecting cracks inside the polygonal regions (secondary) and, later, cracks spreading in local regions (tertiary). We find that the area and the width increase nearly linearly with time with the change in the slope corresponding to the change in the generation. When normalized with respect to the final values, the trends obtained for different film thicknesses overlap, the only exception being the pattern containing unconnected cracks. Thus, the time evolution of cracks is shown to be predictable based on width filtering. Including the angle between cracks as further input into the recursive model, the possibility of identifying the hierarchy of crack segments is also shown. The approach may be useful in determining the age, authenticity, and details of old paintings, understanding the stress profile of geological rocks, and analyzing various natural and manmade hierarchical structures.
由于湿胶体系统干燥而产生的裂缝无处不在，纳米材料薄膜、涂漆墙壁、水泥地面、泥地、河床甚至巨石都是例子。在所有这些情况下，除了长度和时间尺度可能有很大差异外，裂缝模式通常明显相似。在这项工作中，我们更仔细地研究了裂缝形成，以查看在参数的长度尺度和形成时间方面是否存在一些普遍性。具体而言，我们使用一种常用的胶态分散体并通过优化条件形成多边形网络模式而非孤立裂缝（亚临界厚度的薄膜），研究了模式参数、裂缝所占面积、裂缝长度和宽度的时间演变。众所周知，最初会形成一个裂缝网络，我们称之为初次生成，随后是多边形区域内的相互连接裂缝（二次生成），再后来是局部区域内扩展的裂缝（三次生成）。我们发现面积和宽度随时间几乎呈线性增加，斜率的变化对应于生成的变化。当相对于最终值进行归一化时，不同薄膜厚度获得的趋势会重叠，唯一的例外是包含未连接裂缝的模式。因此，基于宽度过滤表明裂缝的时间演变是可预测的。将裂缝之间的角度作为进一步输入递归模型，还展示了识别裂缝段层次结构的可能性。该方法可能有助于确定旧画的年代、真伪和细节，了解地质岩石的应力分布，以及分析各种自然和人造层次结构。
