Wetting on soft absorbing substrates: experiment, simulation and theory

• Applicants: Dr. Sissi de Beer; Professor Jacobus Snoeijer, Ph.D.; Professor Dr. Uwe Thiele
• Subject Area: Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics ; Experimental Condensed Matter Physics ; Mathematics ; Physical Chemistry of Solids and Surfaces, Material Characterisation ; Theoretical Chemistry: Molecules, Materials, Surfaces ; Theoretical Condensed Matter Physics
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 422913191

The wetting on soft polymeric substrates offers a richness of phenomena, which, owing to the versatility of polymer networks, constitute a great potential for designing adaptive surfaces. Much progress has been made on elastocapillary phenomena for the situation where liquid drops are not absorbed into the substrate. However, polymer networks can greatly enhance their functionality by liquid and vapor absorption, which can be tuned by the physical chemistry of the substrate and the ambient conditions. To leverage the full potential of soft substrates one thus needs to go beyond non-absorbing systems, involving new mechanisms that come on top of the elastocapillary phenomena studied in Phase 1 for non-absorbing substrates.The follow-up project in Phase~2 aims at obtaining and experimentally validating a coherent multiscale description that predicts the wetting (dynamics) on soft absorbing substrates. Several experimental setups, Molecular Dynamics simulations, nonlinear macroscopic poroelasticity theory, and effective mesoscale gradient dynamics models are developed to investigate the behaviour of drops of simple nonvolatile and volatile liquids on polymer brushes and hydrogel layers. This combination shall allow us to study the multiscale interplay of absorption and large-deformation mechanics near resting and moving contact lines. Dedicated experiments and simulations will provide calibration and validation of all modelling ingredients necessary for the systematic incorporation of new interactions and new modes of mass transfer into our flexible gradient dynamics modelling framework. Subsequently, we will explore how the swelling and spreading behaviour changes when a mixture of simple liquids is used instead of a single one. Since the composition of the absorbed solvent likely differs from the drop composition, nonlinear effects of the droplet composition on brush wetting and miscibility effects can be expected to influence droplet spreading and contact line motion. Finally, we investigate how the intriguing nonequilibrium phenomenon of the stick-slip motion of driven contact lines depends on the properties of absorbing substrates.At all stages, the project will be pursued in close cooperation between theory (Westfälische Wilhelms-Universität Münster), experiment and simulation (University of Twente). The flexible gradient dynamics modelling framework will be readily available to other SPP projects, and, more generally, will provide a toolbox for the study and design of soft absorbing substrates.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2171: Dynamic wetting of flexible, adaptive and switchable surfaces
• International Connection: Netherlands, United Kingdom
• Cooperation Partners: Professor Andrew J. Archer, Ph.D.; Professor Dr. Harald Van Brummelen