Project Details
Projekt
Droplet behaviour on switchable and adaptive soft and hard spiropyran-based materials
Applicant
Dr. Dorothea Helmer
Subject Area
Synthesis and Properties of Functional Materials
Term
since 2019
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 422798085
The behaviour of droplets on hard surfaces and the wetting of liquids on liquids have experimentally and theroretically been described in detail. Wetting on hard surfaces (Young Equation), neglects the forces acting on the surface, which are a direct result of the droplet surface energy. On soft surfaces, these forces cause a deformation of the surface by the droplet – and the formation of the “wetting ridge” at the three-phase contact line. The behaviour of the ridge under dynamic conditions is not yet fully understood. The experimental evaluation of the dynamics of the three phase contact line and thus the deformation is of great interest, as in nature most wetting phenomena are characterized by the dynamic of the surface. This project will therefore study the influence of substrate dynamics on the behaviour of droplets on surfaces. For this purpose, different surfaces are generated with soft and hard properties. To achieve switchable surfaces, spiropyran (SP) photoswitches are used, which are integrated into the materials. SP switches under UV light from hydrophobic SP to more hydrophilic merocyanine (MC) form. This way, SP can change the surface energy of substrates, so that a switch between two states of contact angles is possible. The wetting properties of SP-containing hard polymeric materials can be further enhanced by introducing a surface structure. In this project, materials with a bulk micro-/nanoporosity will be produced by polymerization induced phase separation. For the evaluation of soft surfaces, this project uses physical and chemical gels. Physical gels consist of wormlike micelles which show viscoelastic behaviour analogous to polymer gels. Polydimethylsiloxan (PDMS) serves as a classical chemical gel, because it can be conveniently tuned in terms of surface stiffness. The PDMS gels will be coated with artificial “skin” layers of parylene to study the effect of dangling chains and monomer leakage into the wetting fluid and to further understand the influence of these factors on PDMS soft wetting. All hard and soft materials of this projects will be analyzed in terms of their switching and dynamics. Here, the focus will be on high-resolution switching of surfaces to allow for the study of the dynamics of individual small droplets on surface patterns. This Schwerpunktprogramm aims at experimental and theoretical analysis of wetting phenomena on switchable, flexible and adaptive surfaces. This project offers substrates of each of these categories and will make a significant contribution to understanding the dynamics of the three-phase contact line under changing substrate dynamics. Collaborations with experimental groups to improve the properties and dynamics of the surfaces as well as with theoretically oriented groups to utilize experimental data for the improvement and adaption of theoretical models are planned.
DFG Programme
Priority Programmes
