News Release 

Researchers capture footage of fluid behaving like a solid

Swansea University

Swansea University researchers from the College of Engineering have captured the moments a fluid reacts like a solid through a new method of fluid observation under pressurised conditions.

The research comes from the Complex Flow Lab, based within the Institute for Innovative Materials, Processing and Numerical Technologies (IMPACT). The lab studies the intricate flow patterns that often develop in granular materials, porous media, and complex fluids such as foams, gels and pastes.

This latest study looks at fluids that have a solid-like response to stress, a phenomenon called Discontinuous Shear Thickening (DST). This is when liquid (in this case, a corn starch mixture) abruptly thickens and becomes solid when disturbed.

The tests involved a new method of observation involving a high-speed camera with results offering an innovative approach to future engineering practices.

Research author Dr Deren Ozturk, who recently completed his PhD in this area, comments:

"Our findings are of particular interest to the burgeoning DST field of research as it is a novel visual indication of DST behaviour that could be used to calibrate future theoretical models. The DST phenomenon is being researched for unique engineering applications such as soft body armour, "smart" speed bumps, and food production.

The research team used regular kitchen corn starch mixed with water. This is then placed in a narrow cell; pressurised air is released into the corn starch-water fluid and forces its way through.

How the air escapes is filmed using a high-speed camera to visualise invasion patterns - which either present as fluid-like fingers or solid-like fractures depending on the concentration of corn starch and the pressure in the air."

Dr Ozturk continues:

"We used corn starch (as a model system for the wider class of shear thickening materials) as it is convenient, widely available and shows a dramatic shear thickening response. As this kind of invasion experiment (which we have a lot of experience with) had not been previously performed on a DST fluid, our main objective was to just try them in the hopes of seeing something interesting.

Our main hypothesis was that the fluid would "fracture" like a solid if given enough stress. This would be a great thing to see since a fluid ought to exhibit wide finger patterns. We were, therefore, delighted to see a narrow fracturing response as this meant we had developed a new kind of experiment to probe the conditions for which DST is observed."

Co-author Dr Bjornar Sandnes, head of the Complex Flow Lab, comments:

"What is particularly interesting about the corn starch studied here is that friction can be turned on or off like a switch.

When only gently disturbed, the grains repel each other and since they are not in contact there is no friction and the material flows like a liquid.

Disturb it more forcefully however, and the grains are pushed into contact such that friction stops the grains freely sliding. The material then behaves more like a solid, and that is when we observe fracturing in our experiments."

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The paper is published in Communications Physics. It is part of the project: Frictional flow patterns shaped by viscous and capillary forces (FriicFlow), funded by EPSRC - a study examining how friction between grains carried by a fluid changes the flow behaviour of the fluid.

It is a collaboration between Swansea University (IMPACT), University of Oxford and PoreLab Centre of Excellence in Norway.

The IMPACT operation is part-funded by the European Regional Development Fund through the Welsh Government and Swansea University.

Visuals:

Footage: Fluids that have a solid-like response to stress: a phenomenon called Discontinuous Shear Thickening (DST). This footage shows viscous fingering. When the concentration of cornflour and the pressure of air were both high enough to force a DST response, we observed the air invading through narrow branching fractures, indicating the fluid was behaving like a solid.

This footage is filmed at 1000 frames per second but shown at 24 frames per second. So each second of displayed video is equivalent to 0.024 seconds of real time.

Air makes fluid fracture: three consecutive frames from the high-speed camera as air is forced into the corn starch suspension. Abrupt shear thickening makes it fracture like a solid. The suspension "melts" back to a liquid once the fracture front has passed.

Three flow patterns: Left: Rounded liquid-like "Viscous fingers" at low concentration and low injection rate, middle: tree-like fractures when the suspension shear-thickens reversibly into a solid, and right: Big fractures when the suspension is so dense that it jams up completely when the air is injected.

Notes to Editor:

The research paper is entitled: "Flow-to-fracture transition and pattern formation in a discontinuous shear thickening fluid" and is published in Communications Physics

The Complex Flow lab is led by Bjornar Sandnes, Associate Professor at College of Engineering, Swansea University. The lab is part of the IMPACT operation housed in the new Engineering North building on the Bay Campus.

The team are members of the Centre for Complex Fluids Processing and the Systems and Process Engineering Centre at the College of Engineering, Swansea University.

Bjornar Sandnes is an Associate Member of the new Centre of Excellence "Porelab - Porous Media Laboratory" at NTNU/University of Oslo.

https://complexflowlab.com/

The Institute for Innovative Materials, Processing and Numerical Technologies (IMPACT) is a state-of-the-art engineering research institute specialising in fundamental and applied research and innovation in advanced engineering, modelling and materials. The operation has been part-funded by the European Regional Development Fund through the Welsh Government and Swansea University.

As a Centre of Excellence, IMPACT supports the regional, the UK and global engineering economy with collaborative, fundamental and applied research. The Engineering North building, home to IMPACT, is based at Swansea University Bay Campus and forms part of the College of Engineering - offering a unique colocation facility for academia-industry partnerships within a transformative research environment.

Completed in May 2019, the building comprises of two distinct areas - linked by the central, light filled atrium: a research office building and a laboratory block: with 1,600m2 open plan laboratory space. Together they house 80 single occupancy offices, provide hub space for over 150 researchers and colocation space for 50 industrial and academic collaborators. Externally, the north entrance features a large living wall of plants and flowers, approximately 114m2 square, promoting biodiversity, and providing year-round texture and colour.

The ethos of IMPACT is to foster academia-industry partnerships, promoting cross-disciplinary fertilisation of ideas in the pursuit of new pioneering science and technology. This will be achieved by bringing together first-class expertise from the College, attracting leading talent and partnering with the World's innovative companies and regional partners.

Designed to BREEAM* excellent standards, it will provide future proof highly specialised laboratories with a dynamic environment for collaboration of industry and academia. This unique operation aims to attract world leading expertise and significant research funding.

*BREEAM is the world's leading sustainability assessment method for master planning projects, infrastructure and buildings. It recognises and reflects the value in higher performing assets across the built environment lifecycle, from new construction to in-use and refurbishment.

@SU_engIMPACT

Swansea University is a world-class, research-led, dual campus university offering a first-class student experience and has one of the best employability rates of graduates in the UK. The University has the highest possible rating for teaching - the Gold rating in the Teaching Excellence Framework (TEF) in 2018 and was commended for its high proportions of students achieving consistently outstanding outcomes.

Swansea climbed 14 places to 31st in the Guardian University Guide 2019, making us Wales' top ranked university, with one of the best success rates of graduates gaining employment in the UK and the same overall satisfaction level as the Number 1 ranked university.

The 2014 Research Excellence Framework (REF) 2014 results saw Swansea make the 'biggest leap among research-intensive institutions' in the UK (Times Higher Education, December 2014) and achieved its ambition to be a top 30 research University, soaring up the league table to 26th in the UK.

The University is in the top 300 best universities in the world, ranked in the 251-300 group in The Times Higher Education World University rankings 2018. Swansea University now has 23 main partners, awarding joint degrees and post-graduate qualifications.

The University was established in 1920 and was the first campus university in the UK. It currently offers around 350 undergraduate courses and 350 postgraduate courses to circa 20,000 undergraduate and postgraduate students. The University has ambitious expansion plans as it moves towards its centenary in 2020 and aims to continue to extend its global reach and realise its domestic and international potential.

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Kevin Sullivan, Swansea University Public Relations Office k.g.sullivan@swansea.ac.uk

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