Wetting phenomena observed in evaporating droplets on structured surfaces

Abstract

A study was undertaken of ethanol droplet evaporation on structured surfaces of pillars (square pillars of variable dimensions and spacing of order microns, and cylindrical of various spacings). On seasoned perflourodecyltrichlorosilane surfaces, significant films were observed extending far beyond the initial contact line for pure ethanol droplets, most prominently for 4 microlitre droplets. On parylene coated surfaces, similar imbibed films were seen for 1.5 microlitre droplets of 50% by volume ethanol-water mixture. This film acts as an additional surface for evaporation and it appears that the droplet then serves as a reservoir for feeding the film until the evaporation process is completed, rather than evaporation being governed by evaporation at the contact line. The droplets with films show higher evaporation rates.

Acknowledgements

The authors would like to thank MEMStar for the coatings used in this work.

Additional information

Notes on contributors

Revekka Tekidou

Revekka Tekidou is an MSc research student at the University of Edinburgh in the Institute of Multiscale Thermofluids. She is a graduate of the Aristotle University of Thessaloniki.

Gail Duursma

Gail Duursma is a Senior Lecturer in Chemical Engineering at the University of Edinburgh. She obtained her D.Phil. from the University of Oxford and after post-doctoral study at the University of Oxford, she joined the University of Edinburgh. She is a Member of the IChemE.

Coinneach Mackenzie-Dover

Coinneach Mackenzie-Dover is a Research Associate at the University of Edinburgh (Institute for Integrated Micro and Nano Systems). He has a PhD in Condensed Matter Physics subsequent to undergraduate studies at the University of Edinburgh. He is currently undertaking work examining the relationship between surface structure and wettability.

Veronika Kubyshkina

Veronika Kubyshkina is a PhD student at the University of Edinburgh in the Institute of Multiscale Thermofluids. She graduated with an MEng in Chemical Engineering in 2017 from the University of Edinburgh.

Jonathan Terry

Jonathan Terry is a Chancellor’s Fellow and Lecturer in the School of Engineering at University of Edinburgh for over fifteen years primarily researching the development of more-than-Moore technologies, the integration of novel fabrication processes and materials with foundry CMOS to create smart sensors and microsystems.

Khellil Sefiane

Khellil Sefiane has MSc and PhD degrees in Chemical Engineering. He presently holds the Chair of Thermophysical Engineering at the University of Edinburgh. He is also ExxonMobil Fellow at the University of Edinburgh.