The main research objectives of our network were:
• Fabrication of lubricant impregnated surfaces
The beneficiaries developed thermally sprayed slippery surfaces. Coatings composed of densely packed nanoparticles were also prepared by spray coating. Both methods are well suited for large-scale production. In another project, micropillar arrays, nanoparticles and silicone structures - such as Silicone Nanofilaments (SNFs) and Silicone Nanorods - were fabricated and tested. The influence of chemical modification of the surfaces was investigated. Good chemical compatibility between the lubricant and the surface reduces dewetting. Typically, a hydrophobic surface is sufficient. Although, coating the rough or porous surface with PDMS brushes is most favourable.
• Experimental characterization of the shape & stability of the lubricating film and of the adhesion of ice, dispersions and microorganisms
The beneficiaries have shown that laser scanning confocal microscopy is well suited to investigate the moving drops on super-liquid repellent surfaces in 3D. Quantitative information on the temporal evolution of the shape of the wetting ridge of moving drops is obtained.
The long-term stability of lubricant impregnated surfaces was tested under flow conditions. A shear-resistant slippery surface can form if an oil-in-water emulsion flows over a micropillar array. It reprensents a novel and promising method to form a lubricant impregnated surface. The filling mechanism seems to be generic and it can be extended to different solid-lubricant combinations. The friction force a drop experiences while sliding off a lubricant infiltrated surface has been measured and modelled. We tested biofouling of surfaces of different topography and wettability (hydrophilic and hydrophobic). We observed that an irregular three-dimensional layer of silicone nanofilaments suppresses bacterial adhesion. Indeed, bacteria hardly adhered to nanofilament coated surfaces that were infiltrated by water. Icephobic characteristics of SLIPS and slippery coatings have been studied under ice accretion–detachment cycles. The findings are compared with hydrophobic surfaces. The baseline data now covers a range of 28 different surfaces in 4 different icing conditions. Notably, lubricant impregnated densely packed nanoparticles show superior long-term anti-icing performance.
• Theoretical modelling of the static and dynamic properties of the lubricating film, ice adhesion and interaction with particular matter
Using mean field models the dynamics of droplets on solid substrates covered by a thin lubrication layer is investigated. The dynamics of a thin, viscous lubrication layer during and after impact of solid spheres and liquid droplets were studied experimentally, analytically and numerically. Quantitative agreement has been achieved, demonstrating the predictive power of the analytical model and numerical method. Moreover, the beneficiaries simulated droplet dynamics on lubricated slippery interfaces using a Lattice Boltzmann model - both able to simulate multiple components and to handle high-density ratios. The motion of bacteria and particular matter was studied using a hybrid lattice Boltzmann programming method. The hydrodynamic theory of bacteria, cells and self-driven particles was modelled using the concepts of active nematics. The beneficiaries investigated both, the single and collective flow behaviour of swimming organisms, e.g. bacteria, in response to surrounding liquid and surfaces. Furthermore, the network derived a model to describe the growth of frost on lubricated surfaces. The results obtained were consistent with the experimental features, hinting that the important processes were considered.
