Soft Matter Physics

"Soft matter" is a convenient term for materials that are easily deformed by thermal fluctuations and external forces. In short, it refers to ‘all things squishy’! Everyday examples include paint, blood, milk, spreads and ice cream. Soft materials share several characteristic features, e.g. that their building blocks are intermediate in size between atoms and grains, and this is crucial to understanding their behaviour. In the Edinburgh Soft Matter Physics group, we use experiments, computer simulations, and theoretical calculations to understand colloidal and granular model systems for phenomena ranging from jamming to bacterial colonies and to rationally design novel soft materials for use in applications ranging from foods to energy materials.

Overview

The experimental research in our group has two directions: ‘Soft Matter’, a sub-discipline of physics concerned with the study of colloidal suspensions, surfactants and polymers, and Active Matter (see also here) the active or life counterparts of soft matter, such as bacterial suspensions and biological polymers. A large number of the materials studied have industrial applications and the group has a dedicated team who undertake industrially linked research.

Soft matter displays many fascinating properties. One example is shown above, where suspensions of Perspex spheres that act as hard particles (~1 micron diameter), self assemble into ‘colloidal crystals’ at high densities. The right-hand-side movie, taken with confocal microscopy, shows the crystal growth process, while the iridescence in the main picture is due to individual colloidal crystallites Bragg-scattering incident white light. Soft matter also shows interesting mechanical behaviour. A well known ‘kitchen’ example is ‘shear thickening’ - a concentrated corn starch solution gets harder to stir the harder it is stirred. Significantly, biology is almost entirely made up of ‘living soft matter’ – globular proteins are colloids, DNA is a stiff polymer, and the lipids forming cell membranes are essentially surfactants.

Soft matter has been studied by chemists, chemical engineers and biologists for many years. It is increasingly clear, however, that these systems show generic properties independent of chemical details. For example, all polymers share certain properties simply because they are long strings of balls performing Brownian motion. This is the central reason why physicists are getting interested. Moreover, studying the generic properties of soft matter can give fresh insights into a broad range of fundamental questions that cut across the whole of condensed matter physics, e.g. concerning the nature of disordered solids.

Many experimental projects (mostly done in our interdisciplinary labs for physicists, physical chemists and biologists) are closely related to projects in theory and simulation in our group.

Research interests

Much of our research is funded by successive EPSRC programme grants, the current one running from December 2011 for 6 years. This flexible funding source gives significant scope for exploration of new topics and the exploitation of unexpected opportunities arising from on-going research, and for postdoctoral researchers to work on multiple projects. The main directions of our research are:

Rheophysics of soft matter

What physical mechanisms govern the yielding and flow of dense colloids, gels and emulsions and how are these related to the ‘dynamical arrest’ or jamming in these systems without flow? We study these problems via confocal microscopy of the flow (particle tracking and velocimetry) with simultaneous rheological measurement. These experiments give important new insights in this field, sometimes overthrowing accepted ideas and results in concentrated colloid rheology. For example, the flow of a concentrated hard sphere suspension in a rectangular channel (flow profile shown in figure) is not like that of a ‘yield stress fluid’, but behaves instead more like dry grains (click here for the paper). For more details on the various projects, see below.

Physics of barriers in soft matter and biology

The ‘aging’ of concentrated metastable states in colloids (‘glasses’), the switching between different phenotypes in bacteria, and the nucleation of growth of fibrillar aggregates in certain proteins (see picture, click here and here for related papers) share a common feature – all three processes involve crossing energy (or free energy) barriers. Experimental work in all three areas will be complemented by novel simulations and analytic theory. We believe generic features will emerge despite apparent dramatic differences between these experimental systems.

New soft materials

An emerging research focus is the study of colloidal particles dispersed in complex solvents, in particular various liquid crystals and phase-separating binary fluids. Often, new soft materials result. Because of the presence of an ‘intermediate length scale’ between colloids and the bulk, the properties of these materials can often be tuned by altering kinetic pathways during their preparation. For example, the picture shows what happens when a binary liquid mixture phase separates under the ‘spinodal’ mechanism in the presence of particles that wets the two phases equally – a bicontinuous jammed emulsion (bijel) is formed (see the paper announcing its discovery and a more recent one on the effect of the particle size). We are also interested in gels formed by fibrillar protein aggregates (see also under barrier crossing). While in vivo these are associated various neurodegenerative diseases, our interest is more in using these as structural elements in building new soft materials.

Physics of cellular motion

The current experimental focus here is on the motility of bacteria (see picture for E. coli cells with their flagella) in complex polymer media – concentrated polymer solutions as well as porous polymer gels (including agar, a standard microbiological culture medium). We are interested in how the polymer affects the motility of single cells, as well as how various kinds of collective motion may emerge, either ‘on its own’, or under the influence of external fields (such as gravity, or gradients in nutrients, etc.). Bacterial motility in confined geometries, such as inside microfluidics devices, is also of interest. This new area emerged partly because we started thinking about bacteria as colloids – they certainly fit into the colloidal domain in terms of size, with their locomotive ability adding extra features. (Click here for a chapter on bacteria as colloids published in the 39th IFF Spring School 2008 at Juelich.)

Physics of bacterial populations

Pseudomonas aeruginosa bacteria colonising an agar surface.
Pseudomonas aeruginosa bacteria colonising an agar surface.
Courtesy of Diarmuid Lloyd.

We are interested in the soft matter and statistical physics of bacterial populations. In particular, we are investigating how bacteria self-assemble to form biofilm communities on surfaces, how they aggregate together in suspension, how they respond to antibiotic treatment and how they interact with each other metabolically in complex and changing environments.

For further information, see Physics of Living Matter.

PhD project opportunities in Soft Matter Physics

People in Soft Matter Physics

Academic staff
Name Position Contact details Location Photo
Rosalind Allen Lecturer
JCMB
2507
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Paul Clegg Reader
JCMB
2614
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Oliver Henrich Advanced Fellow EPCC
JCMB
2405
Cait MacPhee Professor
JCMB
2613
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Davide Marenduzzo Personal Chair in Computational Biophysics
JCMB
2506
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Alexander Morozov Reader
JCMB
2616
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Wilson Poon Professor
JCMB
2620
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Job Thijssen Chancellor's Fellow
JCMB
2421
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Simon Titmuss Lecturer
JCMB
2504
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Research staff
Name Position Contact details Location Photo
Jochen Arlt Research Fellow
JCMB
2601
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Elena Blanco PDRA
JCMB
1508
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Matthew Blow PDRA
JCMB
1506
Keith Bromley Postdoctoral Research Fellow
JCMB
1601
Aidan Brown PDRA
JCMB
2610
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Timothy Bush PDRA
JCMB
2509
Dongyu Cai Research Fellow
JCMB
2610
Niccolo De Francesco Research Assistant
JCMB
2612
Joost de Graaf Marie Curie Fellow
JCMB
2601
Clemence Devailly PDRA
JCMB
1508
David French PDRA
JCMB
1509
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Steven Gardner Postdoctoral Research Associate
JCMB
1603
Daniel Hodgson PDRA
JCMB
2510
Michal Kepa PDRA
JCMB
3.3812
Nick Koumakis PDRA
JCMB
2621
Thomas Le Goff Postdoctoral Research Associate
JCMB
1509
Benno Liebchen Marie Curie Fellow
JCMB
1506
Alex Lips Honorary Professor
JCMB
Diarmuid Lloyd PDRA
JCMB
1505
Vincent Martinez PDRA
JCMB
2609
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Andrew Matheson Postdoctoral Research Associate
JCMB
2603
Gavin Melaugh PDRA
JCMB
1508
Davide Michieletto PDRA
JCMB
1505
Javier Otero Marquez Early Stage Researcher
JCMB
1509
Anne Pawsey Impact Acceleration Associate
JCMB
1601
Andrew Schofield PDRA
JCMB
2203
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Marieke Schor PDRA
JCMB
2617
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Jana Schwarz-Linek PDRA
JCMB
2609
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Teun Vissers Marie Curie Fellow
JCMB
2621
Tiffany Wood Director of the Edinburgh Complex Fluids Partnership
JCMB
2611
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Other staff
Name Position Contact details Location Photo
Siobhan Liddle Tutor
JCMB
2510
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Hugh Vass Technical Staff
JCMB
2310
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Research postgraduates
Name Position Contact details Location Photo
Veronika Afonina Postgraduate Student
JCMB
2805
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Giovanni Brandani Postgraduate Student
JCMB
2510
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Flaviu Cipcigan Postgraduate Student
JCMB
1605
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Giulio De Magistris Postgraduate Student
JCMB
2501
Katy Dickinson Postgraduate Student
JCMB
1511
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Ana Fialho Postgraduate Student
JCMB
1511
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Milana Filatenkova Postgraduate Student
JCMB
2510
Martina Foglino Early Stage Researcher
JCMB
1510
Mark Fox-Powell Postgraduate Student
JCMB
1607
Joe French Postgraduate Student
JCMB
2603
Jay Gillam Postgraduate Student
JCMB
2603
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Ben Guy Postgraduate Student
JCMB
2510
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Tom Ives Postgraduate Student
JCMB
2501
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James Johnson Postgraduate Student
JCMB
2501
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Nico Kronberg Postgraduate Student
JCMB
4401
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Hanna Landenmark Postgraduate Student
JCMB
1511
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Tao Li Postgraduate Student
JCMB
2510
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Benjamin Little Postgraduate Student
JCMB
2603
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Christian Loach Postgraduate Student
JCMB
3311
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Iva Manasi Postgraduate Student
JCMB
2510
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Elliot Marsden Postgraduate Student
JCMB
1509
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Laura McKinley Postgraduate Student
JCMB
2510
Alexander McVey Postgraduate Student
G.25
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Rudi Mears Postgraduate Student
JCMB
2618
Ryan Morris Postgraduate Student
JCMB
1601
Francois Mouvet Visitor
JCMB
1510
Jakub Pastuszak Postgraduate Student
JCMB
1510
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Chay Paterson Postgraduate Student
JCMB
2501
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Samuel Payler Postgraduate Student
JCMB
1607
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Carolina Pereira Postgraduate Student
JCMB
1511
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Ciprian Pruteanu Postgraduate Student
JCMB
3311
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Matthew Reeves Postgraduate Student
JCMB
2510
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James Richards Postgraduate Student
JCMB
2603
Marion Roullet Postgraduate Student
JCMB
1506
Katherine Rumble Postgraduate Student
JCMB
2510
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Toby Samuels Postgraduate Student
JCMB
1607
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Laura Sawiak Postgraduate Student
JCMB
2601
Alexander Slowman Postgraduate Student
JCMB
2501
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Daniel Taylor Postgraduate Student
JCMB
2510
Pat Teeratchanan Postgraduate Student
JCMB
3311
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Stuart Thomson Postgraduate Student
JCMB
2510
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Robin Turnbull Postgraduate Student
CSEC
2.2804
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Simon Weir Postgraduate Student
JCMB
2611
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Joshua Williams Postgraduate Student
JCMB
2510
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Anthony Wood Postgraduate Student
JCMB
2618
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Xuemao Zhou Postgraduate Student
JCMB
2510
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