Water migration through fat-based semi solid heterogeneous materials

Abstract

• Water migration through fat-based composites is mediated by percolation process. • Permeating water network is provided by hydrophilic inclusions. • Size of percolating water cluster diverges with percolation exponent. • Water bridges between hydrophilic inclusions lead to mechanical stiffening. • Percolating moisture network enhances water loss in the heterogeneous material. Water migration through heterogeneous soft materials is central to many applications including oil recovery and consumer product stability of foods and cosmetics. This slow water transport affects all material properties such as mechanical, optical and electrical, but its understanding and modelling remains challenging due to complex wetting and diffusion processes across the heterogeneous material. Here, we study experimentally the penetration of water through a soft composite with hydrophobic (fat) and hydrophilic (salt) components. Conductivity measurements indicate the emergence of a percolating water network above critical water and salt volume fractions. This is corroborated by mechanical measurements revealing a concomitant stiffening of the material due to proliferating water bridges. Simulations of water absorption at spherical inclusions confirm this scenario and show the underlying cluster growth and percolation process.