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Sunday, 22 September 2019
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Raw materials & technologies, Technologies, Functional coatings

Funtional coatings: Breakthrough in dewetting surfaces

Friday, 30 September 2016

How would you like a kitchen surface that cleans itself? Technological advances such as this could be one step closer after a breakthrough by two British universities.

Researchers have made the first ever direct observation of the elusive dewetting process. Source: Northumbria University

Researchers have made the first ever direct observation of the elusive dewetting process. Source: Northumbria University

Wetting and dewetting are both fundamental modes of motion of liquids on solid surfaces. They are critically important for processes in biology, chemistry, and engineering, such as drying, coating, and lubrication. However, recent progress in wetting, which has led to new fields such as superhydrophobicity and liquid marbles, has not been matched by dewetting.

Novel method known as dielectrowetting

A significant problem has been the inability to study the model system of a uniform film dewetting from a nonwetting surface to a single macroscopic droplet - a barrier that does not exist for the reverse wetting process of a droplet spreading into a film. The researchers from Northumbria University and Nottingham Trent University report the dewetting of a dielectrophoresis-induced film into a single equilibrium droplet. The emergent picture of the full dewetting dynamics is of an initial regime, where a liquid rim recedes at constant speed and constant dynamic contact angle, followed by a relatively short exponential relaxation of a spherical cap shape. This sharply contrasts with the reverse wetting process, where a spreading droplet follows a smooth sequence of spherical cap shapes.

Results provide new approach to fluid manipulation

Complementary numerical simulations and a hydrodynamic model reveal a local dewetting mechanism driven by the equilibrium contact angle, where contact line slip dominates the dewetting dynamics. Our conclusions can be used to understand a wide variety of processes involving liquid dewetting, such as drop rebound, condensation, and evaporation. In overcoming the barrier to studying single film-to-droplet dewetting, the results provide new approaches to fluid manipulation and uses of dewetting, such as inducing films of prescribed initial shapes and slip-controlled liquid retraction.

The study is published in: Science Advances, Vol 2, No. 9, 02 September 2016

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