Drying and cracking mechanisms in a starch slurry

TL;DR

This paper investigates the drying and cracking mechanisms in starch-water slurries, revealing how distinct transport regimes influence fracture patterns and developing a multiphase transport model to explain these phenomena.

Contribution

It introduces a detailed physical analysis and a multiphase transport model for drying starch-cakes, highlighting the separation of water transport mechanisms as key to columnar fracture formation.

Findings

Starch-cakes exhibit nonlinear elastic behavior.

Two drying regimes are identified, controlled by liquid and vapor transport.

Separation of transport mechanisms leads to columnar fracture patterns.

Abstract

Starch-water slurries are commonly used to study fracture dynamics. Drying starch-cakes benefit from being simple, economical, and reproducible systems, and have been used to model desiccation fracture in soils, thin film fracture in paint, and columnar joints in lava. In this paper, the physical properties of starch-water mixtures are studied, and used to interpret and develop a multiphase transport model of drying. Starch-cakes are observed to have a nonlinear elastic modulus, and a desiccation strain that is comparable to that generated by their maximum achievable capillary pressure. It is shown that a large material porosity is divided between pore spaces between starch grains, and pores within starch grains. This division of pore space leads to two distinct drying regimes, controlled by liquid and vapor transport of water, respectively. The relatively unique ability for drying starch to generate columnar fracture patterns is shown to be linked to the unusually strong separation of these two transport mechanisms.