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

NamePositionContact detailsLocationPhoto
Academic staff
Rosalind AllenLecturer
JCMB
2507
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Aidan BrownChancellor's Fellow
JCMB
2610
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Paul CleggReader
JCMB
2614
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Oliver HenrichAdvanced Fellow EPCC
JCMB
2405
Cait MacPheeProfessor
JCMB
2613
Photo of Cait MacPhee
Davide MarenduzzoPersonal Chair in Computational Biophysics
JCMB
2506
Photo of Davide Marenduzzo
Alexander MorozovReader
JCMB
2616
Photo of Alexander Morozov
Wilson PoonProfessor
JCMB
2620
Photo of Wilson Poon
John RoyerChancellor's Fellow
JCMB
2610
Job ThijssenChancellor's Fellow
JCMB
2421
Photo of Job Thijssen
Simon TitmussLecturer
JCMB
2504
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Research staff
Jochen ArltResearch Fellow
JCMB
2601
Photo of Jochen Arlt
Elena BlancoPDRA
JCMB
1508
Photo of Elena Blanco
Matthew BlowPDRA
JCMB
1506
Keith BromleyPostdoctoral Research Fellow
JCMB
1601
Dongyu CaiResearch Fellow
JCMB
2610
Niccolo De FrancescoResearch Assistant
JCMB
2612
Joost de GraafMarie Curie Fellow
JCMB
2601
Clemence DevaillyPDRA
JCMB
1508
David FrenchPDRA
JCMB
1509
Photo of David French
Steven GardnerPostdoctoral Research Associate
JCMB
1603
Martin GormanPDRA
CSEC
2.2805
Daniel HodgsonPDRA
JCMB
2603
Michal KepaPDRA
JCMB
3.3812
Nick KoumakisPDRA
JCMB
2621
Thomas Le GoffPostdoctoral Research Associate
JCMB
1509
Benno LiebchenMarie Curie Fellow
JCMB
1506
Elin LiljaPDRA
JCMB
1510
Alex LipsHonorary Professor
JCMB
Diarmuid LloydPDRA
JCMB
1505
Vincent MartinezPDRA
JCMB
2609
Photo of Vincent Martinez
Andrew MathesonPostdoctoral Research Associate
JCMB
2603
Gavin MelaughPDRA
JCMB
1508
Davide MichielettoPDRA
JCMB
1505
Rory O'NeillPDRA
JCMB
1510
Nikola OjkicPDRA
JCMB
1505
Javier Otero MarquezEarly Stage Researcher
JCMB
1509
Anne PawseyImpact Acceleration Associate
JCMB
1601
Matthew ReevesImpact Acceleration Associate
JCMB
2605
Andrew SchofieldPDRA
JCMB
2203
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Marieke SchorPDRA
JCMB
2617
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Jana Schwarz-LinekPDRA
JCMB
2609
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Sharareh TavaddodPDRA
JCMB
1510
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Teun VissersMarie Curie Fellow
JCMB
2621
Tiffany WoodDirector of the Edinburgh Complex Fluids Partnership
JCMB
2611
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Other staff
Hugh VassTechnical Staff
JCMB
2310
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Research postgraduates
Veronika AfoninaPostgraduate Student
JCMB
2805
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Giovanni BrandaniPostgraduate Student
JCMB
2510
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Giulio De MagistrisPostgraduate Student
JCMB
2501
Katy DickinsonPostgraduate Student
JCMB
1511
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Ana FialhoPostgraduate Student
JCMB
1511
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Milana FilatenkovaPostgraduate Student
JCMB
2510
Martina FoglinoEarly Stage Researcher
JCMB
2509
Photo of Martina Foglino
Mark Fox-PowellPostgraduate Student
JCMB
1607
Joe FrenchPostgraduate Student
JCMB
1616
Jay GillamPostgraduate Student
JCMB
2603
Photo of Jay Gillam
Emily GouldPostgraduate Student
JCMB
1616
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Samuel GriffithsPostgraduate Student
JCMB
2510
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Ben GuyPostgraduate Student
JCMB
2510
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Tom IvesPostgraduate Student
JCMB
2501
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James JohnsonPostgraduate Student
JCMB
2501
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Navneeta KatyanPostgraduate Student
JCMB
2510
Nico KronbergPostgraduate Student
JCMB
4401
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Hanna LandenmarkPostgraduate Student
JCMB
1511
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Tao LiPostgraduate Student
JCMB
2510
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Benjamin LittlePostgraduate Student
JCMB
2603
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Christian LoachPostgraduate Student
JCMB
3311
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Fergus MackayPostgraduate Student
JCMB
2510
Iva ManasiPostgraduate Student
JCMB
2510
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Elliot MarsdenPostgraduate Student
JCMB
1509
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Laura McKinleyPostgraduate Student
JCMB
2510
Alexander McVeyPostgraduate Student
G.25
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Rudi MearsPostgraduate Student
JCMB
2618
Ryan MorrisPostgraduate Student
JCMB
1601
Francois MouvetVisitor
JCMB
1510
Ed MuirPostgraduate Student
JCMB
2510
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Iain MuntzPostgraduate Student
JCMB
1616
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Jakub PastuszakPostgraduate Student
JCMB
1510
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Chay PatersonPostgraduate Student
JCMB
2501
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Samuel PaylerPostgraduate Student
JCMB
1607
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Carolina PereiraPostgraduate Student
JCMB
1511
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Ciprian PruteanuPostgraduate Student
JCMB
3311
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James RichardsPostgraduate Student
JCMB
1616
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Marion RoulletPostgraduate Student
JCMB
1506
Katherine RumblePostgraduate Student
JCMB
2510
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Toby SamuelsPostgraduate Student
JCMB
1607
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Laura SawiakPostgraduate Student
JCMB
2601
Alexander SlowmanPostgraduate Student
JCMB
2501
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Daniel TaylorPostgraduate Student
JCMB
2510
Pat TeeratchananPostgraduate Student
JCMB
3311
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Stuart ThomsonPostgraduate Student
JCMB
2510
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Robin TurnbullPostgraduate Student
CSEC
2.2804
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Simon WeirPostgraduate Student
JCMB
2611
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Joshua WilliamsPostgraduate Student
JCMB
2510
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Anthony WoodPostgraduate Student
JCMB
2618
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Xuemao ZhouPostgraduate Student
JCMB
2510
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