An experimental and numerical study of droplet spreading and imbibition on microporous membranes

Abstract

Microporous membranes are permeable substrates primarily used for wastewater treatment and desalination. The lab-fabricated and commercial polyethersulfone (PES) microporous membranes are characterized for permeability by filtration test, cross-section thickness by SEM images, surface roughness by AFM data, and hydrophilicity by dynamic contact angle measurements. The choice of membranes of different nominal pore sizes ensures a diverse range of imbibition time scale. The hydrodynamic permeability of these membranes is calculated based on the cross-section thickness and its resistance, which is obtained from filtration test. A lubrication-based mathematical model using precursor film approximation is used to study the behavior of droplet spreading and imbibition on the membrane surface. The theoretical disjoining pressure is also shown to be related to its numerical value obtained from the mathematical model, in the case of apolar and polar interactions. The effective permeability obtained by validating the numerical predictions with contact angle experiments, is then matched to hydrodynamic permeability by introduction of lubrication ratio at the equilibrium stage.