Drops on soft solids: Free energy and double transition of contact angles

Abstract

The equilibrium shape of liquid drops on elastic substrates is determined by minimising elastic and capillary free energies, focusing on thick incompressible substrates. The problem is governed by three length scales: the size of the drop $R$, the molecular size $a$, and the ratio of surface tension to elastic modulus $\gamma /E$. We show that the contact angles undergo two transitions upon changing the substrates from rigid to soft. The microscopic wetting angles deviate from Young's law when $\gamma /Ea\gg 1$, while the apparent macroscopic angle only changes in the very soft limit $\gamma /ER\gg 1$. The elastic deformations are worked out in the simplifying case where the solid surface energy is assumed constant. The total free energy turns out lower on softer substrates, consistent with recent experiments.

References in corpus (2)

• Why is surface tension a force parallel to the interface?
• Straight contact lines on a soft, incompressible solid

Cited by in corpus (28)

• Elastocapillarity: Surface Tension and the Mechanics of Soft Solids
• Droplets move over viscoelastic substrates by surfing a ridge
• Wetting and phase separation in soft adhesion
• Withdrawing a solid from a bath: how much liquid is coated?
• Solid Capillarity: When and How does Surface Tension Deform Soft Solids?
• Soft wetting and the Shuttleworth effect, at the crossroads between thermodynamics and mechanics
• Out-of-contact elastohydrodynamic deformation due to lubrication forces
• Mechanisms for bacterial gliding motility on soft substrates
• The paradox of contact angle selection on stretched soft solids
• Soft particles at a fluid interface
• Gradient-dynamics model for liquid drops on elastic substrates
• Droplets sit and slide anisotropically on soft, stretched substrates
• Gradient dynamics model for drops spreading on polymer brushes
• Electrically modulated dynamic spreading of drops on soft surfaces
• Soft wetting with (a)symmetric Shuttleworth effect
• Elastocapillary Levelling of Thin Viscous Films on Soft Substrates
• Drops on polymer brushes -- advances in thin-film modelling of adaptive substrates
• Wetting States of Two-Dimensional Drops under Gravity
• Electrowetting of a nano-suspension on a soft solid
• On the singular nature of the elastocapillary ridge
• Soft electrowetting
• Nanoscale fluid structure of liquid-solid-vapour contact lines for a wide range of contact angles
• Emergence and Growth Dynamics of Wetting-induced Phase Separation on Soft Solids
• The role of substrate mechanics in osmotic biofilm spreading
• Modelling ternary fluids in contact with elastic membranes
• Effect of external tension on the wetting of an elastic sheet
• Drops of volatile binary mixtures on brush-covered substrates
• Releasing trapped Taylor bubbles via centrifugation and inclination