The spreading and imbibition behaviour of structured fluids on porous substrates is necessary to understand, as they were involved in numerous industrial applications and real-life engineering problems. Drop spreading on a solid substrate are quite common. Drop spreading of complex fluids on solid substrates and Newtonian fluids on porous substrates are available in the literature. But the kinetics of structured fluid drop spreading on the porous substrate was not explored at all. This work investigates the dynamics of the yield stress and shear thinning fluid drop spreading on different porous media of similar pore sizes with different wettability.
Two polysaccharide fluids with different concentrations, one with yield stress (Xanthan gum) and the other without yield stress but equivalently shear thinning (Guar gum), were used to study the spreading and imbibition behaviour. Hydrophilic PTFE, hydrophobic PTFE and PVDF porous membranes of the same size were used as porous substrates on which drop spreading is studied to understand the effect of wettability. Drop diameter and drop height as a function of time have been recorded for different porous substrates and fluid combinations to understand the spreading and imbibition dynamics.
The drop spreading on a porous substrate is divided into three different stages namely, the spreading stage, pinning stage and imbibition stage. Based on these, the spreading of fluids on porous substrates had been classified into two different universal behaviour such as partial wetting and complete wetting.
From experimental results, the spreading and imbibition behaviour of every fluid-substrate combination has been categorized, analysed and understood.