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Details of Grant 

EPSRC Reference: EP/R041954/1
Title: Droplets With Dynamic Size On Smooth Surfaces
Principal Investigator: Pradas, Dr M
Other Investigators:
Researcher Co-Investigators:
Project Partners:
Department: Faculty of Sci, Tech, Eng & Maths (STEM)
Organisation: Open University
Scheme: New Investigator Award
Starts: 01 October 2018 Ends: 30 September 2020 Value (£): 203,009
EPSRC Research Topic Classifications:
Continuum Mechanics Numerical Analysis
EPSRC Industrial Sector Classifications:
No relevance to Underpinning Sectors
Related Grants:
Panel History:
Panel DatePanel NameOutcome
27 Feb 2018 EPSRC Mathematical Sciences Prioritisation Panel February 2018 Announced
Summary on Grant Application Form
Droplets interacting with solid surfaces are found in a wide variety of daily life experiences and natural phenomena. Their study serves as a canonical example of a wetting phenomenon which, despite its simplicity, has been shown to be a remarkably complicated problem. Many theoretical efforts over the last few years have focused their attention on understanding how the properties of the solid surface affect the dynamics of the droplet, with particular emphasis on droplet control and manipulation, which is important for a wide range of technological applications, including the rapidly growing fields of nano- and micro-fluidics.

Quite often the volume of the droplets is subject to external, time-dependent variations - a situation that we refer to as droplets with dynamic size. This occurs, for example, when there is mass exchange through the droplet interface (evaporation/condensation phenomena), or when droplets sit on porous materials so that liquid is absorbed through the pores.

When the volume of a droplet increases or decreases, it is widely accepted that microscopic defects on the surface (either chemical or topographical) induce pinning effects, which block the translational motion of the contact line, i.e. the line where the liquid/gas interface meets the solid surface. As a consequence, droplets exhibit what is known as stick-slip motion, which has crucial effects on, e.g., the way droplets evaporate, but has been proved to be notoriously difficult to predict, and more importantly control. Precisely because of this, the use of smooth, pinning-free surfaces with controllable macroscopic properties/topographies has become a major need in the design of many microfluidic/wetting systems. However, a quantitative understanding of the interplay between the volume changes in droplets and smooth variations on the surface, and how this affects both the dynamics and the shape of the droplet, still elude us.

This project will explore the fundamental interplay between a time-dependent variation of the droplet volume and simple smooth variations on solid surfaces. Using a balanced combination of analytical and computational techniques, we aim to investigate under which conditions a droplet may naturally exhibit lateral motion as its volume changes in time, and to exploit this in applications on droplet control, such as directed motion. We will also investigate whether simple configurations like periodic variations are able to induce complex dynamics, such as random walks and collective phenomena in a multi-droplet system.

The ultimate goal of the proposed research is the systematic and predictive theoretical and computational analysis of the dynamics of droplets with dynamic size on surfaces that have controllable and experimentally amenable properties. As a consequence, the outputs of this project can be used to recommend new design rules, geometries, and operational protocols for improved droplet control and manipulation in technological applications that rely on cooling/heating processes and/or porous-based micro-devices.

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