Project Details
Projekt
Dynamics of Liquid-Liquid-Elastic Three Phase Lines
Applicant
Professor Dr. Stefan Karpitschka
Subject Area
Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics
Term
since 2019
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 422877263
The dynamical wetting of rigid surfaces is governed by a balance of capillary forces and viscous dissipation inside the liquid. On soft surfaces however, spreading dynamics are typically slowed down tremendously by viscoelastic braking. Capillary forces at the three phase line deform the soft solid into a sharp wetting ridge, which is dragged along with the liquid interface. This contributes the dominant part of the overall dissipation, and thus governs the spreading motion. A quantitative understanding of the wetting dynamics on soft surfaces remains elusive because available theories are limited to the regime of linear viscoelasticity, but experiments with liquid-vapor-soft solid contact lines show strong nonlinear behavior. The origin of the experimentally observed nonlinearities lies in the strong tractions that liquid-vapor interfaces exert on soft solids, deforming them to strains of order unity and larger. This may excite a number of non-linear effects, ranging from geometry over variable solid surface tensions, to the extraction of un-crosslinked materials. These factors are discussed controversially in recent literature, and in the proposed research we want to advance, if not settle, this discussion. We will focus on soft polymer gels, the most widely used material in soft wetting studies, and specifically address the consequences of the liquid phase that is present in these gels. Liquid surfaces exert one of the sharpest known line tractions on their substrate, thus generating a sharp fold at the tip of a wetting ridge. As a consequence, the solid pressure diverges at the tip of the wetting ridge, which may well alter the solid-liquid equilibrium in the phase. Pressure-induced extraction of the liquid phase, as is known to occur at the edge of adhesive solid-solid contacts, would be the consequence. We will experimentally study the impact of such an oil skirt, artificially added or provided by the gel substrate, to unravel the self-lubricating properties observed for soft gels.
DFG Programme
Priority Programmes
