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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - LubISS (Lubricant impregnated slippery surfaces)

Teaser

Summary

The LubISS project aims to explore the expansive potential of lubricant impregnated surfaces, focusing on three applications of high societal, environmental, industrial and medical impact: Anti-icing, easy-to-clean and anti-fouling. Textured substrates which are infiltrated with a lubricant form a new class of functional surfaces, referred to as Lubricant Impregnated Slippery Surfaces (LubISS). The mobility of the lubricating film greatly reduces the (lateral) adhesion. Therefore, deposited liquids, bacteria or other microorganisms can slide off easily as soon as the surface is tilted by a few degrees. Although capillary forces help to keep the lubricant in place, LubISS face the problem of limited durability. The lubricant needs to be replenished after some time. To develop durable and environmentally friendly LubISS, we are establishing a fundamental understanding of the interplay between the solid surface topography, the lubricating film and the liquid (liquids, bacteria, etc.) under static and flow conditions. This guides the i) development of strategies to optimize the lubricant stability under static and dynamic flow conditions and ii) design of improved and novel methods for replenishing the lubricant for long-term applications. These most promising strategies and methods are benchmarked against current strategies. Furthermore, the network aims to educate and train young interdisciplinary researchers in this vital area of technology.

Work performed

Our network is working on the main research objectives:

â€¢ Fabrication of lubricant impregnated surfaces
The beneficiaries developed a large scale roll-to-roll process to fabricate lubricant impregnated surfaces with easily feasible raw materials, such as membranes and supporting layers. Furthermore, the beneficiaries of the network developed thermally sprayed slippery surfaces. Both approaches are well-suited for large scale production. In another project, micropillar arrays and silicone structures - such as Silicone Nanofilaments (SNFs) and Silicone Nanorods - are fabricated and tested. The surfaces are coated using different strategies to optimize the chemical compatibility between the coating and the lubricant.

â€¢ 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 static and dynamic properties of drops on super-liquid repellent surfaces in 3D.
The long-term stability of lubricant impregnated surfaces was tested under flow conditions. A flow induced and shear-resistant slippery surface can form if an oil-in-water emulsion flows over a micropillar array, forming 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. Moreover, the friction force a drop experiences while sliding off a lubricant infiltrated surface has been measured and modelled. We tested the adhesion of E. coli bacteria to 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 a nanofilament coated surface that was infiltrated by water. Icephobic characteristics of SLIPS and slippery coatings have been studied under ice accretionâ€“detachment cycles and compared with hydrophobic surfaces. After the ice is formed, the ice adhesion is measured using the centrifugal ice adhesion test. The baseline data now covers a range of 28 different surfaces in 4 different icing conditions. Some coatings show favorable ice adhesion performance.

â€¢ Theoretical modelling of the static and dynamic properties of the lubricating film, ice adhesion and interaction with particular matter
Using molecular dynamic modeling and the lubrication approximation, 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 is studied theoretically and numerically. Moreover, the beneficiaries simulated droplet dynamics on lubricated slippery interfaces using a Lattice Boltzmann model that can simulate multiple components but is capable of handling 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 modeled 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.

Final results

In order to design durable and environmentally friendly LubISS, our network strives to understand the interplay between the physical- and chemical interactions between the surface topography, the lubricating film and the droplet under both static and flow conditions. LubISS is the first world-wide, cooperative research and training initiative to comprehensively address this expanding research field. The knowledge acquired through exchange and expertise holds promise for major breakthroughs and innovations.