Dynamic wetting of multicomponent particle systems

The wetting kinetics of powder-liquid systems represent an important factor with regards to many practical applications, such as coating, granulation, agglomeration or powder reconstitution. Wetting as the first step during food powder reconstitution strongly depends on the interactions of the wetting liquid and the particle surface, expressed by the contact angle. Due to the heterogeneous composition of food materials including hydrophilic and hydrophobic surfaces, also the wetting process heterogeneous in nature. Furthermore, the solubility of food ingredients, such as sugars, increases the complexity of understanding and describing the wettability. We investigated the liquid penetration into heterogeneous, soluble model food powders using a Washburn setup. Soluble sucrose was used as hydrophilic food component and silanized glass beads were prepared as hydrophobic, inert material. Both materials were characterized in terms of contact angle and powder properties. Different mixtures of hydrophilic, soluble sucrose and hydrophobic glass beads were produced and their wetting performance was determined. For predicting the liquid penetration into food powders, the model developed in our previous study (Kammerhofer et al., 2018a [1]) about the penetration of aqueous solutions into food powders was extended. It now considers solute concentration-dependent liquid properties and the heterogeneity of solid surfaces. The model is based on the solution of a coupled system of two differential equations representing capillary rise into a pore network and the mass transfer equation. Two main factors were identified as having a major influence on the wetting kinetics: the viscosity and the contact angle. Increasing either of these factors reduces the penetration performance, but each of them is dominant in a different concentration range. Our adapted model predicts penetration rates which are close to the experimental data. Thus, we can conclude that it is suitable for predicting the capillary penetration into heterogeneous, soluble food powders.