Wetting of Auxetic Metamaterials

Lead Research Organisation: University of Edinburgh
Department Name: Sch of Engineering

Abstract

It is a common conception that when a material is stretched it becomes thinner. However, when an auxetic material is stretched it becomes wider (it possesses a negative Poisson's ratio). Since materials are never unbounded, they have surfaces. And surfaces inevitably come into contact with liquids. However, surprisingly, there is no published research that considers how the unusual properties of auxetic materials change the solid-liquid interaction and influence how liquids spread on the solid surface or the impact and rebound behaviour of droplets. It is even more surprising because expanded polytetrafluoroethylene (ePTFE), the microporous superhydrophobic waterproof and breathable layer in GoreTex, can be easily converted to an auxetic form.

When auxetic materials expand their surface area, it is by an increase in the space within the solid frame of a lattice. We can therefore expect changes to the wetting properties of the surface. This type of change will cause the solid surface (Cassie) fraction of the surface to decrease as the space between solid components increases. This balance between solid and liquid surface area is critical to how the surface chemistry properties are amplified by the surface topography/texture into super-liquid repellence, hemi-wicking and other wetting properties. It also controls whether the surface is one to which a liquid will stick or one which appears slippery to a liquid. An auxetic material has unusual impact resistance properties because material flows towards, rather than away, from the area of an impact. This offers a new approach to materials and surfaces for droplet impact and rebound.

In this project we therefore focus on the enabling materials-science to create a new class of wetting materials, which we refer to as "Auxetic Wetting Metamaterials". The project considers a range of techniques to fabricate auxetic materials with a focus on how the balance between solid surface area fraction and space area fraction change with strain. The project considers how this solid surface area fraction change with strain combines with hydrophilic and hydrophobic properties to manipulate the overall wetting properties of the surfaces and the wetting state transitions of these new materials. It will do so experimentally and be supported by a theoretical programme and by modelling and simulation. The work will also consider how strain can be used to control liquid friction and droplet rebound.

Planned Impact

Economic Relevance:
This project has relevance to a range of materials-based industries, including textiles, filters, coatings and packaging. For example, the 2018 Innovate UK KTN report "The UK Packaging Industry - A Strategic Opportunity: A Landscape Review and Technology Roadmap Report" notes that the UK Packaging Manufacturing Industry has annual sales of £11B and employs 85k people. The 2016 KTN report "A State-of-the-Art Review of Smart Materials: A Review of Auxetics in the UK" noted exponential growth in patent applications for auxetic technology most notably in the medical, aerospace and automotive sectors. The same report, however, noted a rapid rise in overseas competition recently, highlighting a strategic need to invest in the UK to ensure it benefits from the long-term impact in the materials/engineering sectors. The global auxetic materials market segments into structural and functional materials classified by whether they improve the mechanical or physical properties or detect events or stimuli. Their properties lead to use in fields such as biomedical (e.g. dilation, implants, prosthesis), filters and auxetic fibres. Auxetic materials impact resistance is important in manufacturing crash helmets, body armour, and sports clothing, as they provide resistance against cracks and dents (source: "Auxetic Materials Market - Global Industry Analysis, Size, Share, Growth, Trends and Forecast 2017-2025"). Understanding the interaction of auxetic materials with liquids at their surfaces and leveraging that understanding into new designs would broaden the application field. Doing so would provide the UK with unique innovation - a key objective of the UK Industrial Strategy.

Pathways to Economic Impact:
Invention records will be filed, IP workshops and IP reviews conducted, and these will be considered by the Universities' Innovation and Impact Teams. Patents will be filed if judged appropriate and the Research England Connected Capabilities Funded "The Northern Accelerator" project can provide Proof of Concept commercialisation projects, and seed funding for spin-out company proposals. We will leverage Knowledge Transfer Partnership and licensing opportunities working with a Business Development Manager and create links with companies through i) A North-East Coatings Consortium, ii) Industry Network Presentations on Smart Surfaces & Coatings, iii) the ERDF-funded Sheffield Innovation Programme, iv) Project Partners (CPI and Schlumberger) and v) existing auxetics industry links. We will contribute to the annual Knowledge Transfer Network Metamaterials Showcase Event. An end of project workshop with a target of 40 participants including 30% industrial industrialists will be held.

Training of Skilled People and People Pipeline:
The PDRFs will gain high level skills relevant to new materials and high value manufacturing via work on (i) surface coatings, (ii) measurement/instrumentation, (iii) experimental design and implementation, (iv) microfabrication techniques and (v) data analysis and interpretation. The PDRFs will also gain project, time and budget management experience and take part in the University Researcher and Career Development programme. They will attend a bespoke media and communications training residential programme. Two casual labour paid summer projects for undergraduate students will develop their interest in progression to PhD study.

Public Understanding/Outreach:
The PDRFs will take part in our Nature's Raincoats Outreach Exhibition (e.g. Big Bang Fairs, etc) and the Sheffield Festival of Science and Engineering, work with the NUSTEM team in developing research-based Schools experiments and assist the Think Week Summer Schools (focused on children from Schools - primary and secondary - in areas of deprivation) thereby contributing to the pipeline of the future STEM workforce. NUSTEM targets under-represented groups, with a focus on gender, and progression into STEM careers.
 
Description Mechanical metamaterials, also known as auxetics, are a type of material with unconventional properties inherited from their structure. They have tended to be viewed in terms of their properties for resisting impact and for being able to fold around double curved surfaces without the need for the material to be elastic. However, how their unconventional properties change their interactions with liquids has never previously been considered. Here we hypothesized and constructed new materials which demonstrated experimentally that auxetic metamaterial have a unique behaviour with strain and are able to transfrom into a new type superhydrophobic surface (doi: 10.1002/sstr.202300458). We also demonstrated that it was possible for the wetting state to change into one whereby the material lattice is penetrated by a liqud when its surface tension is changed (doi: 10.1063/5.0173464). In both cases, we produced supporting theoretical models which were confirmed by the experimental results. These are the first results to ever demonstrate a special relationship between auxetic metamaterial surfaces and their wetting properties.
Exploitation Route The reasearch establishes the fundamental principles relating to wettability of auxetic metamaterial surfaces. Others may use additive manufacturing (e.g. 3D printing) or Kirigami (e.g. laser cutting) approaches to create auxetic surfaces with specifically designed wettability. In doing so, these could be used to conformally cover double-curved surfaces with strong and resilient facings without using, e.g. spray coating, or elastic materials. It will also be possible to use material chemistry approaches (e.g. shape memory foams) to create materials without a specifically designed lattice, but with auxetic properties with wettability. At present, auxetics are used for their mechanical properties in, e.g., sports equipment to mitigate impact, and medical textiles, e.g. bandages, adhesive patches, etc, so the work opens up a new dimension for their consideration when in contact with liquids.
Sectors Construction

Energy

Healthcare

Leisure Activities

including Sports

Recreation and Tourism

Manufacturing

including Industrial Biotechology

Pharmaceuticals and Medical Biotechnology

 
Description Northumbria Auxetic Wetting Grant 
Organisation Northumbria University
Department Department of Mathematics, Physics and Electrical Engineering
Country United Kingdom 
Sector Academic/University 
PI Contribution Leadership of joint grant, and design, manufacture and testing of substrates, and conceptual and theoretical frameworks around wetting.
Collaborator Contribution Knowledge and modelling of mechanical metamaterials. Please note collaboration began prior to grant starting as part of developing the proposal.
Impact See other sections of Research Fish.
Start Year 2019
 
Description Schlumberger Cambridge Research Limited for Auxetic Wetting Grant 
Organisation Schlumberger Limited
Department Schlumberger Cambridge Research
Country United Kingdom 
Sector Academic/University 
PI Contribution xxx
Collaborator Contribution Project Meetings and Applications Advice. Please note this commenced prior to the award of the grant but was an integral part of discussions and preparations for the grant application.
Impact See other sections of Research Fish
Start Year 2019
 
Description Sheffield Hallam Auxetic Wetting Grant 
Organisation Sheffield Hallam University
Department Materials and Engineering Research Institute (MERI)
Country United Kingdom 
Sector Academic/University 
PI Contribution Leadership of joint grant, and design, manufacture and testing of substrates, and conceptual and theoretical frameworks around wetting.
Collaborator Contribution Knowledge and modelling of mechanical metamaterials. Please note collaboration began prior to grant starting as part of developing the proposal.
Impact See other sections of Research Fish.
Start Year 2019
 
Description 2021 - SOFI2, Durham, UK. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Postgraduate students
Results and Impact 2021 - SOFI2, Durham, UK. 15 December 2021. Invited Research Seminar - "Strategies for Slippery Surfaces" (15/12/2021). Talk given by Glen McHale.
Year(s) Of Engagement Activity 2021
URL https://soficdt.webspace.durham.ac.uk/
 
Description 2022 - APS DFD 75th Annual Meeting - Indianapolis, USA 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact APS DFD 75th Annual Meeting
Indianapolis, USA 19/11/2022-22/11/2022
Contributed Research Talk - Wetting of Auxetic Metamaterials 20/11/2022
Professor Glen McHale
Year(s) Of Engagement Activity 2022
URL https://www.apsdfd2022.org/
 
Description 2022 - Metamaterials Network Conference 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Other audiences
Results and Impact 2022 - Metamaterials Network Conference
Wotton House, Surrey, UK 23/5/2022-27/5/2022
Participation by invitation
Industry/Academia Knowledge Transfer Event
Year(s) Of Engagement Activity 2022
URL https://metamaterials.network/home/conference/
 
Description 2022 - NPE International Series Forum XIII (On-line). 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact International Forum on Nanotechnology & Precision Engineering (NPE)
NPE International Series Forum XIII (On-line) 8/11/2022

Invited Research Talk - A Tale of Two Surfaces: How do we Make Surfaces Slippery to Liquids? 8/11/2022
Year(s) Of Engagement Activity 2022
URL https://aip.scitation.org/npe/info/webinar
 
Description 2022 - Nature Inspired Surface Engineering (NISE 2022) - Auxetics Wetting Concepts Topic 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact 2022 - Nature Inspired Surface Engineering (NISE 2022) - Auxetic Wetting Concept Topic
Seoul, Korea 17/08/2022-19/08/2022
Contributed Research Talk - Wetting of Auxetic Metamaterials 17/08/2022
Glen McHale
Year(s) Of Engagement Activity 2022
URL https://ameriscience.org/nise-2021/
 
Description 2022 - Nature Inspired Surface Engineering (NISE 2022) - Auxetics Wetting Theory Topic 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact 2022 - Nature Inspired Surface Engineering (NISE 2022) - Auxetic Theory Topic
Seoul, Korea 17/08/2021-19/08/2022
Contributed Research Poster - Analytical Models For The Wettability Of Auxetic Metamaterials 17-19/08/2022
Shruti Mandhani
Year(s) Of Engagement Activity 2022
URL https://ameriscience.org/nise-2021/
 
Description 2022 - UK Fluids Conference Sheffield, UK - Auxetics Wetting Concepts Topic 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Other audiences
Results and Impact 2022 - UK Fluids Conference - Auxetics Concepts Topic
Sheffield, UK 6/09/2022-8/09/2022
Contributed Research Talk - Wetting of Auxetic Metamaterials 6/09/2022

Steven Armstrong
Year(s) Of Engagement Activity 2022
URL https://ukfluids2022.sheffield.ac.uk/
 
Description 2022 - UK Fluids Conference Sheffield, UK - - Auxetics Wetting Theory Topic 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Other audiences
Results and Impact 2022 - UK Fluids Conference - Auxetics Theory Topic
Sheffield, UK 6/09/2022-8/09/2022
Contributed Research Talk - Analytical Models For The Wettability Of Auxetic Metamaterials 6/09/2022

Shruti Mandhani
Year(s) Of Engagement Activity 2022
URL https://ukfluids2022.sheffield.ac.uk/
 
Description 2023 - APS DFD 76th Annual Meeting - Auxetics Topic 1 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact 17. 2023 - APS DFD 76th Annual Meeting
Washington DC, USA 19/11/2023-21/11/2023

Contributed Research Talk (Gary) - Superhydrophobicity of Auxetic Metamaterials 20/11/2023
Gary Wells
Year(s) Of Engagement Activity 2023
URL https://www.2023apsdfd.org/?_gl=1%2A1qsu8zd%2A_ga%2AMTE2NDkxMzY3LjE2OTY3ODIwNDI.%2A_ga_1CCM6YP0WF%2A...
 
Description 2023 - APS DFD 76th Annual Meeting - Auxetics Topic 2 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact 2023 - APS DFD 76th Annual Meeting - Auxetics Topic 2
Washington DC, USA 19/11/2023-21/11/2023

Contributed Research Poster (Rodrigo) - Wetting Transitions on an Auxetic Metamaterial 20/11/2023
Rodrigo Ledesma Aguilar
Year(s) Of Engagement Activity 2023
URL https://www.2023apsdfd.org/?_gl=1%2A1qsu8zd%2A_ga%2AMTE2NDkxMzY3LjE2OTY3ODIwNDI.%2A_ga_1CCM6YP0WF%2A...
 
Description 2023 - EcoMat (Wiley) Webinar 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact 15. 2023 - EcoMat (Wiley) Webinar
EcoMat (Wiley) Webinar Series (On-line) 25/10/2032

Invited Research Talk - Wetting of Auxetic Metamaterials 25/10/2023

https://onlinelibrary.wiley.com/journal/25673173/homepage/ecomat-activities
https://players.brightcove.net/3806881048001/default_default/index.html?videoId=6339897145112
Glen McHale
Year(s) Of Engagement Activity 2023
URL https://players.brightcove.net/3806881048001/default_default/index.html?videoId=6339897145112
 
Description 2023 - International Meeting on Wetting and Carbon Neutralisation (IMWCN 2023) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact 2023 - International Meeting on Wetting and Carbon Neutralisation (IMWCN 2023)
Queen Mary University, London 23/07/2023-28/07/2023

Invited Keynote Talk - Wetting of Auxetic Metamaterials 25/07/23
Glen McHale
Year(s) Of Engagement Activity 2023
URL https://meetwetting.org/
 
Description 2023 - UK Fluids Conference - Auxetic Concepts Topic 2 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Other audiences
Results and Impact 2023 - UK Fluids Conference - Auxetic Concepts Topic 2
Glasgow, UK 17/09/2023-19/09/2023
Contributed Research Poster (Wells PST-014) - Wetting Transitions on an Auxetic Metamaterial 19/09/23
Gary Wells
Year(s) Of Engagement Activity 2023
URL https://www.gla.ac.uk/events/conferences/ukfc2023/
 
Description 2023 - UK Fluids Conference - Auxetics Concepts Topic 1 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Other audiences
Results and Impact 2023 - UK Fluids Conference - Auxetics Concepts Topic 1
Glasgow, UK 17/09/2023-19/09/2023
Contributed Research Talk (Wells - SSD-017) - Superhydrophobicity of Auxetic Metamaterials 19/09/2023
Gary Wells
Year(s) Of Engagement Activity 2023
URL https://www.gla.ac.uk/events/conferences/ukfc2023/
 
Description 2023 - UK Metamaterials Network Workshop 2023 (Andy) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Other audiences
Results and Impact 2023 - UK Metamaterials Network Workshop 2023
Manchester Metropolitan University, Manchester, UK 04/09/2023-06/09/2023

Contributed Talk - Strain-responsive Wetting Properties of Bioinspired Auxetic Metasurfaces 6/09/23
Andrew Alderson
Year(s) Of Engagement Activity 2023
URL https://metamaterials.network/uk-metamaterials-network-international-conference-on-mechanical-metama...
 
Description 2023 - UK Metamaterials Network Workshop 2023 (Steven) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Other audiences
Results and Impact 2023 - UK Metamaterials Network Workshop 2023
Manchester Metropolitan University, Manchester, UK 04/09/2023-06/09/2023

Contributed Talk - Superhydrophobicity and Wetting Transitions on an Auxetic Metamaterial1. 6/09/23
Steven Armstrong
Year(s) Of Engagement Activity 2023
URL https://metamaterials.network/uk-metamaterials-network-international-conference-on-mechanical-metama...
 
Description Preston Street Primary School Science Fair (19/05/2023) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact On Friday 19th of May, 2023, Dr. Steven Armstrong and Dr. Hernán Barrio-Zhang took part in an outreach event representing the University of Edinburgh as judges of a science fair at the Preston Street Primary School. They judged over 50 P7 students' science projects, where the students had to choose a topic, formulate a hypothesis, perform the experiments, and draw scientific conclusions from the results. They interacted with the students directly and provided feedback on the science projects of the students.
Year(s) Of Engagement Activity 2023
 
Description The University of Edinburgh PGR Conference public outreach (21/04/2023) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact On Friday, 21st of April, 2023, Dr. Steven Armstrong, Dr. Hernán Barrio-Zhang and members of the WISE lab organised an outreach event during School of Engineering Post-Graduate Conference hosted by the University of Edinburgh. Along with the participation from P7 students from the Preston Street Primary School, the outreach event consisted of a show-and-tell table where the group designed special experiments to highlight the research topics of the Institute of Multiscale Thermofluids and the importance of the research we perform. The experiments covered fundamental concepts of wetting and capillarity which were demonstrated though hydrophobic and ultra-smooth coatings such as Slippery Omniphobic Covalently Attached Liquid (SOCAL) surfaces, Slippery Liquid Infused Porous Surfaces (SLIPS), PEGylated surfaces and Glaco. This also included demonstrations on macro scale auxetic metamaterials with discussions on their wetting properties. The P7 students were tasked with going around the show-and-tell tables from the different institutes in the School of Engineering and voting for the ones that they learned from the most. Our group, the WISE lab, was voted as the best outreach table by the students.
Year(s) Of Engagement Activity 2023