Rodrigo Ledesma‐Aguilar

University of Edinburgh

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Trends

Author Order

Document Type

Co-Authors

Glen McHale

University of Edinburgh

Gary G. Wells

University of Edinburgh

A. Hernández–Machado

Universitat de Barcelona

ÉR

Élfego Ruiz-Gutiérrez

Newcastle University

Ignacio Pagonabarraga

Universitat de Barcelona

Julia M. Yeomans

University of Oxford

Steven Armstrong

University of Edinburgh

Khellil Sefiane

University of Edinburgh

Prashant Agrawal

Indian Institute of Technology Delhi

Halim Kusumaatmaja

Durham University

Cooperative Institutions

Northumbria University

University of Edinburgh

Nottingham Trent University

University of Oxford

Durham University

Universitat de Barcelona

University of Twente

Centre National de la Recherche Scientifique

The University of Texas at Austin

Newcastle upon Tyne Hospital

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Field

Self-propelled droplet transport on shaped-liquid surfaces

Scientific Reports (2020)

Gaby Launay Muhammad Subkhi Sadullah Glen McHale Rodrigo Ledesma‐Aguilar Halim Kusumaatmaja

Abstract The transport of small amounts of liquids on solid surfaces is fundamental for microfluidics applications. Technologies allowing control of droplets of liquid on flat surfaces generally involve the generation of a wettability contrast. This approach is however limited by the resistance to motion caused by the direct contact between the droplet and the solid. We show here that this resistance can be drastically reduced by preventing direct contact with the help of dual-length scale micro-structures and the concept of “liquid-surfaces”. These new surfaces allow the gentle transport of droplets along defined paths and with fine control of their speed. Moreover, their high adhesion permits the capture of impacting droplets, opening new possibilities in applications such as fog harvesting and heat transfer.

Solid surface

Digital Microfluidics

10.1038/s41598-020-70988-x

Cite

Citations (50)

Easier sieving through narrower pores: fluctuations and barrier crossing in flow-driven polymer translocation

Soft Matter (2012)

Rodrigo Ledesma‐Aguilar Takahiro Sakaue Julia M. Yeomans

We show that the injection of polymer chains into nanochannels becomes easier as the channel becomes narrower. This counter intuitive result arises because of a decrease in the diffusive time scale of the chains with increasing confinement. The results are obtained by extending the de Gennes blob model of confined polymers, and confirmed by hybrid molecular dynamics - lattice-Boltzmann simulations.

Lattice Boltzmann methods

Lattice (music)

10.1039/c2sm25201e

Cite

Citations (18)

Self-Propelled Droplet Transport on Shaped-Liquid Surfaces

arXiv (Cornell University) (2019)

Gaby Launay Muhammad Subkhi Sadullah Glen McHale Rodrigo Ledesma‐Aguilar Halim Kusumaatmaja

The transport of small quantities of liquid on a solid surface is inhibited by the resistance to motion caused by the contact between the liquid and the solid. To overcome such resistance, motion can be externally driven through gradients in electric fields, but these all inconveniently involve the input of external energy. Alternatively, gradients in physical shape and wettability - the conical shape of cactus spines to create self-propelled motion. However, such self-propelled motion to date has limited success in overcoming the inherent resistance to motion of the liquid contact with the solid. Here we propose a simple solution in the form of shaped-liquid surface, where solid topographic structures at one length scale provides the base for a smaller length-scale liquid conformal layer. This dual-length scale render possible slippery surfaces with superhydrophobic properties. Combined to an heterogeneous topography, it provides a gradient in liquid-on-liquid wettability with minimal resistance to motion and long range directional self-propelled droplet transport. Moreover, the liquid-liquid contact enables impacting droplets to be captured and transported, even when the substrate is inverted. These design principles are highly beneficial for droplet transport in microfluidics, self-cleaning surfaces, fog harvesting and in heat transfer.

10.48550/arxiv.1908.01305

Cite

Citations (0)

Bidirectional Motion of Droplets on Gradient Liquid Infused Surfaces

arXiv (Cornell University) (2020)

Muhammad Subkhi Sadullah Gaby Launay Jayne Parle Rodrigo Ledesma‐Aguilar Yonas Gizaw

We demonstrate spontaneous bidirectional motion of droplets on liquid infused surfaces in the presence of a topographical gradient, in which the droplets can move either toward the denser or the sparser solid fraction area. Our analytical theory explains the origin of this bidirectional motion. Furthermore, using both lattice Boltzmann simulations and experiments, we show that the key factor determining the direction of motion is the wettability difference of the droplet on the solid surface and on the lubricant film. The bidirectional motion is shown for various combinations of droplets and lubricants, as well as for different forms of topographical gradients.

Lattice Boltzmann methods

Solid surface

Fluid motion

Source

Cite

Citations (0)

Self Propelled Droplet on Shaped-Liquid Surfaces

Bulletin of the American Physical Society (2019)

Gary G. Wells Gaby Launay Rodrigo Ledesma‐Aguilar Glen McHale Muhammad Subkhi Sadullah

Source

Cite

Citations (0)

Shape bifurcations of evaporating droplets on smooth patterned surfaces

Bulletin of the American Physical Society (2019)

M. P. Haynes Gary G. Wells Rodrigo Ledesma‐Aguilar Marc Pradas

Source

Cite

Citations (0)

Contact-Angle Hysteresis and Contact-Line Friction on Slippery Liquid-like Surfaces

Langmuir (2020)

Hernán Barrio-Zhang Élfego Ruiz-Gutiérrez Steven Armstrong Glen McHale Gary G. Wells

Contact-line pinning and dynamic friction are fundamental forces that oppose the motion of droplets on solid surfaces. Everyday experience suggests that if a solid surface offers low contact-line pinning, it will also impart a relatively low dynamic friction to a moving droplet. Examples of such surfaces are superhydrophobic, slippery porous liquid-infused, and lubricant-impregnated surfaces. Here, however, we show that slippery omniphobic covalently attached liquid-like (SOCAL) surfaces have a remarkable combination of contact-angle hysteresis and contact-line friction properties, which lead to very low droplet pinning but high dynamic friction against the motion of droplets. We present experiments of the response of water droplets to changes in volume at controlled temperature and humidity conditions, which we separately compare to the predictions of a hydrodynamic model and a contact-line model based on molecular kinetic theory. Our results show that SOCAL surfaces offer very low contact-angle hysteresis, between 1 and 3°, but an unexpectedly high dynamic friction controlled by the contact line, where the typical relaxation time scale is on the order of seconds, 4 orders of magnitude larger than the prediction of the classical hydrodynamic model. Our results highlight the remarkable wettability of SOCAL surfaces and their potential application as low-pinning, slow droplet shedding surfaces.

Hysteresis

10.1021/acs.langmuir.0c02668

Cite

Citations (60)

Friction Coefficients for Droplets on Solids: The Liquid–Solid Amontons’ Laws

Langmuir (2022)

Glen McHale Nan Gao Gary G. Wells Hernán Barrio-Zhang Rodrigo Ledesma‐Aguilar

The empirical laws of dry friction between two solid bodies date back to the work of Amontons in 1699 and are pre-dated by the work of Leonardo da Vinci. Fundamental to those laws are the concepts of static and kinetic coefficients of friction relating the pinning and sliding friction forces along a surface to the normal load force. For liquids on solid surfaces, contact lines also experience pinning and the language of friction is used when droplets are in motion. However, it is only recently that the concept of coefficients of friction has been defined in this context and that droplet friction has been discussed as having a static and a kinetic regime. Here, we use surface free energy considerations to show that the frictional force per unit length of a contact line is directly proportional to the normal component of the surface tension force. We define coefficients of friction for both contact lines and droplets and provide a droplet analogy of Amontons' first and second laws but with the normal load force of a solid replaced by the normal surface tension force of a liquid. In the static regime, the coefficient of static friction, defined by the maximum pinning force of a droplet, is proportional to the contact angle hysteresis, whereas in the kinetic regime, the coefficient of kinetic friction is proportional to the difference in dynamic advancing and receding contact angles. We show the consistency between the droplet form of Amontons' first and second laws and an equation derived by Furmidge. We use these liquid-solid Amontons' laws to describe literature data and report friction coefficients for various liquid-solid systems. The conceptual framework reported here should provide insight into the design of superhydrophobic, slippery liquid-infused porous surfaces (SLIPS) and other surfaces designed to control droplet motion.

Hysteresis

Normal force

Static friction

Surface force

Contact area

10.1021/acs.langmuir.2c00178

Cite

Citations (37)

Snap evaporation of droplets on smooth topographies

Nature Communications (2018)

Gary G. Wells Élfego Ruiz-Gutiérrez Youen Le Lirzin Anthony Nourry Bethany V. Orme

Abstract Droplet evaporation on solid surfaces is important in many applications including printing, micro-patterning and cooling. While seemingly simple, the configuration of evaporating droplets on solids is difficult to predict and control. This is because evaporation typically proceeds as a “stick-slip” sequence—a combination of pinning and de-pinning events dominated by static friction or “pinning”, caused by microscopic surface roughness. Here we show how smooth, pinning-free, solid surfaces of non-planar topography promote a different process called snap evaporation. During snap evaporation a droplet follows a reproducible sequence of configurations, consisting of a quasi-static phase-change controlled by mass diffusion interrupted by out-of-equilibrium snaps. Snaps are triggered by bifurcations of the equilibrium droplet shape mediated by the underlying non-planar solid. Because the evolution of droplets during snap evaporation is controlled by a smooth topography, and not by surface roughness, our ideas can inspire programmable surfaces that manage liquids in heat- and mass-transfer applications.

10.1038/s41467-018-03840-6

Cite

Citations (34)

Beyond Leidenfrost levitation: A thin-film boiling engine for controlled power generation

Applied Energy (2021)

Prashant Agrawal Gary G. Wells Rodrigo Ledesma‐Aguilar Glen McHale Khellil Sefiane

Overcoming friction between moving components is important for reducing energy losses and component wear. Hydrodynamic lubrication via thin-film boiling provides an opportunity for reduced friction energy and mass transport. A common example of such lubrication is the Leidenfrost effect, where a liquid droplet levitates on a cushion of its own vapor on a surface heated to temperatures above the liquid's boiling point. An asymmetry in this vapor flow, self-propels the droplet on the surface due to viscous drag, converting thermal energy to mechanical motion, like a heat engine. Although levitation significantly reduces friction, the induced self-propulsion depends on substrate geometry and material properties, which limits dynamic propulsion control. Therefore, the ability to control the power output is a significant challenge in realizing operational mm and sub-mm scale virtually frictionless engines. Here, we present a thin-film boiling engine where we control the power output mechanically. The rotor, which comprises of a working liquid coupled to a non-volatile solid, is manually positioned over a heated turbine-inspired stator in a thin-film boiling state. We show that by controlling the position of the rotor over the substrate the power output from the rotation can be controlled above and below the Leidenfrost temperature (~250 °C). We explain these experimental observations using a hydrodynamic analytical model. Additionally, we achieve propulsion outputs almost 4 times higher than levitation-based propulsion systems. The ability to control the rotation characteristics of such virtually frictionless engines allows potential applications in extreme environments such as at microscales or for space and planetary exploration.

Leidenfrost effect

Heat Engine

10.1016/j.apenergy.2021.116556

Cite

Citations (14)