It's delightful, it's dynamic, it's dewetting!

How would you like a kitchen surface that cleans itself? Technological advances such as this could be one step closer after a breakthrough by Nottingham Trent University and Northumbria University.

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NTU scientists have shed light on the elusive "dewetting" process

How would you like a kitchen surface that cleans itself? Technological advances such as this could be one step closer after a breakthrough by Nottingham Trent University and Northumbria University.

Using experimental techniques, researchers have made the first ever direct observation of the elusive "dewetting" process, which takes place when a liquid film retracts to form a bead-shaped drop. The achievement could now spark a new line of research and lead to breakthroughs involving the use of liquids, such as better coatings and more effective self-cleaning surfaces.

Dewetting is the opposite of "spreading", a familiar process which can be observed day-to-day, such as when a drop of oil is placed on the surface of a pan. The liquid initially has a bead-like shape, and it slowly spreads to form a thin film. The opposite process, called "dewetting", occurs when a liquid film retracts from a solid surface to form a bead-shaped drop. This can be observed when a wet window is left to dry up.

Unveiling the dynamics of a dewetting film in all its detail has been a mind-blowing experience

Andrew Edwards, Nottingham Trent University

The details of dewetting are extremely important to any situation involving the removal or drying of a liquid. Despite its apparent simplicity, the direct observation of the full dewetting of a droplet into a single drop had remained elusive and difficult to achieve until Nottingham Trent University and Northumbria University completed this recent experiment.

In a recent paper in the journal Science Advances, the research team came up with an ingenious solution to this problem. Using a novel method known as "dielectrowetting", they exploited the electric properties of liquids to force a liquid to coat a solid surface using an applied voltage.

Professor Glen McHale, Pro-Vice Chancellor (Engineering and Environment) at Northumbria University and Professor of Applied and Material Physics, said: "Our experimental setup opens up the possibility of preparing liquid shapes in a very controlled manner, which then dewet. This can lead to new methods for liquid manipulation in technologies such as coating and self-cleaning surfaces."

By embedding very thin patterned electrodes in the solid and carefully arranging them into a circular pattern, the team achieved the formation of a thin circular liquid film. By switching off the voltage, they revealed, for the first time, the full dewetting process of the liquid film back to a bead-like drop shape.

Professor Carl Brown, Coordinator of the Nottingham Trent University Engineering Research Unit, and Professor of Physics in the School of Science and Technology, said: "At first sight, one might have expected that dewetting is just the time reversal of spreading. Surprisingly, we found that dewetting is not spreading in reverse. Instead of a smooth sequence of drop-like shapes, the dewetting film forms a rim at its own edge which retracts at constant speed for most of the dewetting process".

To understand this behaviour, the team used a combination of theory and numerical simulations to rationalise the experiments. Dr Rodrigo Ledesma-Aguilar, from Northumbria, said: "Both the simulations and the theory support that the liquid tends to adopt the closest local equilibrium shape it can during dewetting. This explains the smooth rim shape which survives for most of the process."

Nottingham Trent University's Andrew Edwards, first author of the paper, said: "Unveiling the dynamics of a dewetting film in all its detail has been a mind-blowing experience. This is my first original contribution as a PhD student and has allowed me to apply a range of knowledge gained in my first degree as a physicist. It is extremely pleasing to see how our experiments are so well described by the theory and the simulations."

Dr Michael Newton, Reader in Experimental Physics in the School of Science and Technology at Nottingham Trent University, added: "Our method can be used to learn more about the underlying physics behind other dewetting phenomena such as condensation, evaporation and droplet rebound. These processes are critical for applications such as fog-collection, coating and lubrication. The technique developed can also be used for characterising liquid properties when only small volumes are available."

Read the Science Advances paper.

  • Notes for editors

    Press enquiries please contact Dave Rogers, Media Relations Manager, on telephone +44 (0)115 848 8782, or via email.

    Nottingham Trent University's five-year strategic plan Creating the University of the Future has five main ambitions: Creating Opportunity, Valuing Ideas, Enriching Society, Connecting Globally, and Empowering People.

    The Queen's Anniversary Prize for Higher and Further Education was awarded to Nottingham Trent University in November 2015. It is the highest national honour for a UK university and recognises the institution's world-class research. Pioneering projects to improve weapons and explosives detection in luggage, enable safer production of powdered infant formula, and combat food fraud, led to the prestigious award.

    Northumbria University, Newcastle is a research-rich, business-focused, professional university with a global reputation for academic excellence. Northumbria is one of the largest universities in the UK with almost 34,000 students from 131 countries and over 186,000 alumni worldwide.

    The University has invested more than £250 million in its estate to improve the student experience, including a new Student Central zone, new buildings for students on Computing and Information Sciences and Architecture and Built Environment courses, and £6.7m investment in STEM (Science, Technology, Engineering and Mathematics) facilities and laboratories.

    Northumbria is ranked top 50 in the UK for research power and had the fourth largest increase in quality research funding (REF 2014). According to Times Higher Education, Northumbria had the biggest rise in research power of any university in the UK.

It's delightful, it's dynamic, it's dewetting!

Published on 3 October 2016
  • Category: Research; School of Science and Technology

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