ABSTRACT

In this article, we summarize a series of experimental works and qualitative modelling regarding the dynamics of a liquid contact line on gel substrates. Two different situations were investigated, i.e., water on hydrophilic poly (2-acrylamido-2-methyl-propane-sulfonic acid-co-acrylamide) (PAMPS−PAAM) gels and water on hydrophobic poly (styrene-butadienestyrene)(SBS)−paraffin gels. In both situations, different gel characteristics largely affect the contact line dynamics: liquid diffusion and surface deformation by capillary force. On hydrophilic gels, the contact line of a sessile droplet exhibits successively two different behaviors: pinned and receding, and the transition between the behaviors is closely related to the local deformation of the gel surface due to swelling. On hydrophobic gels, the contact line exhibits several different regimes of motions, i.e., stick-slip, and two continuous motions. These transitions are characterized by a frequency f built upon the apparent contact line velocity v and the droplet radius R as f = v/R, indicating that the gel rheology largely affects the dynamics of liquid contact line. Our results provide a synthetic view of the characteristic features of how the wetting is different on gel surfaces. Finally, we designate unsolved problems and future directions.