Cracking to curling transition in drying colloidal films
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THE EUROPEAN PHYSICAL JOURNAL E
Regular Article
Cracking to curling transition in drying colloidal films Weipeng Meng1 , Mingchao Liu1,2 , Yixiang Gan3 , Ludovic Pauchard4 , and C.Q. Chen1,a 1 2 3 4
Department of Engineering Mechanics, CNMM & AML, Tsinghua University, Beijing 100084, China Mathematical Institute, University of Oxford, Oxford, OX2 6GG, UK School of Civil Engineering, The University of Sydney, Sydney, NSW 2006, Australia Universit´e Paris-Saclay, CNRS, FAST, 91405, Orsay, France Received 29 April 2020 / Received in final form 28 August 2020 / Accepted 31 August 2020 Published online: 1 October 2020 c EDP Sciences / Societ` a Italiana di Fisica / Springer-Verlag GmbH Germany, part of Springer Nature, 2020 Abstract. Drying-induced cracking is widely encountered in nature and is of fundamental interest in industrial applications. During desiccation, the evolution of water content is nonlinear. Considering the inhomogeneous procedure of desiccation, it is worth considering whether water content will affect the crack pattern formation. To address this concern, in this paper, we report an experimental investigation on the effect of water content on the failure mode in drying colloidal films. A distinct failure transition from random cracking to curling is found when the initial water content increases gradually. When the water content is below a critical value for given film thickness, random desiccation cracking driven by shrinkage is observed. Beyond this critical water content, the film curls with the advent of several main cracks. It is also found that the critical water content corresponding to the transition point depends on the film thickness. In order to qualitatively interpret the experimental observation, a theoretical model is established by adopting the fracture mechanics based on the energy method. The model is found to agree well with the experimental results, elucidating the effects of initial water content on the crack patterns and the transition of failure modes.
1 Introduction From cracks in dried mud to craquelure pattern in old paintings, the formation of cracks due to desiccation of colloidal films is commonly observed. This interesting phenomenon has a long history of both scientific and industrial applications, including the production of industrial and functional coatings [1–3], templates for photonics [4, 5], geophysical phenomena [6,7], and so on. Successful applications rely heavily on the knowledge of the physical processes that determine crack formations. So far, extensive relevant works have been done to improve the understanding of this complex phenomenon [8]. Regarding the desiccation crack of colloidal films, the fundamental mechanisms have been explored and clarified in the past couple of decades. During the drying process, the stress in the films increases, and the films usually fail with cracks on the surface due to the inner stress gradient [9,10]. Three basic failure mechanisms are found for releasing the stress inside the films, including shrinkage cracks perpendicular to the fi
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