Morphometric analysis of polygonal cracking patterns in desiccated starch slurries

Abstract

We investigate the geometry of two-dimensional polygonal cracking that forms on the air-exposed surface of dried starch slurries. Two different kinds of starches, made from potato and corn, exhibited distinguished crack evolution, and there were contrasting effects of slurry thickness on the probability distribution of the polygonal cell area. The experimental findings are believed to result from the difference in the shape and size of starch grains, which strongly influence the capillary transport of water and tensile stress field that drives the polygonal cracking.

Universal scaling of polygonal desiccation crack patterns

“…As reported by previous authors [69,72,82], the primary cracks are a result of film shrinkage induced by the Laplace pressure on the scale of the particle size. As the water evaporates, menisci form between individual particles of radius R ≈ 5 µm.…”

“…The pattern morphology of polygonal cracks is also of interest since it reveals information about the formation and history of the cracking process [3]. For example, the distribution of angles at crack junctions [67,68,72] and statistical analysis of the correlation length in crack patterns [73] are commonly quantified from images of the surface. Repeated wetting and drying of the material can lead to more "Y"-shaped junctions rather than "T"shaped junctions [10,11].…”

Drying colloidal systems: Laboratory models for a wide range of applications

“…The work of Müller [84,111,112], however, began the modern interest in analogue experiments with starch. Over the past few years, there has been a rigorous series of experiments involving potato starch [85,113] and, more commonly, corn starch [86,87,[113][114][115][116][117][118][119]. A typical experiment consists of mixing a few hundred grams of commercial starch powder with an equal mass of water, and some antiseptic such as a tablespoon of household bleach.…”

“…25(d). Potato starch is coarser than corn starch, and this variation in grain size can be linked to subtle differences in how these materials dry and crack [113,116], but the basic experiment is similar in both cases.…”

“…The crosssectional pattern of polygonal columns can be described by metrics such as the relative distributions of the polygon areas, the numbers of their neighbours, their edge lengths, the angles between their edges, and so on [86]. Many of these metrics come from the study of 2D foams [133] and there are, indeed, similarities in the dynamics allowed in the two systems [86,113,115]. As they grow, columns can merge by a crack, defining the edge between them, failing to propagate.…”