Leading Article by Soft Matter 2014 Lectureship Winner

New article by the Soft Matter 2014 Lectureship winner, Eric Dufresne.

Surface tension and the mechanics of liquid inclusions in compliant solids

Robert W. Style, John S. Wettlaufer, and Eric R. Dufresne

Dufresne et al. graphical abstract

This article proposes a theory of fluid inclusions in soft solids and builds upon experimental findings of a previous paper recently published in Nature Physics – “Stiffening solids with liquid inclusions” doi:10.1038/nphys3181 – which revealed that Eshelby’s foundational theory fails to describe the mechanical response of soft composites. Eshelby’s theory of elastic inclusions is significantly cited and outlines the response of microscopic inclusions within an elastic solid when macroscopically stress is applied. Furthermore, Eshelby’s theory allows the prediction of bulk properties and is fundamental in calculating the stress field in fracture mechanics. It has been widely used in many other areas such as cell biology to predict cell interactions and seismology.

The theoretical study aims to rationalise the experimental results from the previous paper and explain that they were due to the surface tension of the solid-liquid interface, which is completely ignored in established theory.

The work expands previous theories based on strain-dependent surface stresses, relevant to nanoinclusions in stiffer materials, but not for softer materials such as gels. The group only considered isotropic loadings, used incorrect boundary conditions, or only considered incompressible solids and employed a dipole approximation to calculate composite properties.

The group adapted Eshelby’s inclusion theory so that it included surface tension for liquid inclusions in a linear elastic solid, giving both the microscopic behaviour and themacroscopic effects of inclusions in composites. The authors believe that these findings can be applied to a wide variety of soft material systems, especially composites comprising of soft materials such as gels and elastomers.

Full citation information:

Surface tension and the mechanics of liquid inclusions in compliant solids
Robert W. Style, John S. Wettlaufer and Eric R. Dufresne
Soft Matter, 2015, Advance Article
DOI: 10.1039/C4SM02413C

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Take 1…minute for chemistry in health

Can you explain the importance of chemistry to human health in just 1 minute? If you’re an early-career researcher who is up to the challenge, making a 1 minute video could win you £500.

The chemical sciences will be fundamental in helping us meet the healthcare challenges of the future, and we are committed to ensuring that they contribute to their full potential. As part of our work in this area, we are inviting undergraduate and PhD students, post-docs and those starting out their career in industry to produce an original video that demonstrates the importance of chemistry in health.Take 1... minute for chemistry in health

We are looking for imaginative ways of showcasing how chemistry helps us address healthcare challenges. Your video should be no longer than 1 minute, and you can use any approach you like.

The winner will receive a £500 cash prize, with a £250 prize for second place and £150 prize for third place up for grabs too.

Stuck for inspiration? Last year’s winning video is a good place to start. John Gleeson’s video was selected based on the effective use of language, dynamic style, creativity and its accurate content.

The closing date for entries to be submitted is 30 January 2015. Our judging panel will select the top five videos. We will then publish the shortlisted videos online and open the judging to the public to determine the winner and the runners up.

For more details on how to enter the competition and who is eligible, join us at the Take 1… page.

Good luck!

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A simple route to responsive, particle-stabilized foams using bare silica nanoparticles

Web writer Rob Woodward highlights a hot article from the journal


Defined as bubbles of gas in liquid-film matrix, foams are important precursors in the food and cosmetic industry and for the production of macroporous materials. In this report a simple, effective route to silica nanoparticle stabilised responsive aqueous foams has been demonstrated by the Binks group. Stimuli-responsive surface active particles have generated growing interest in recent years, utilising triggers including pH, temperature and light irradiation to create ‘switchable’ foams, i.e. the ability to “switch-off” the foaming capability of the particles. However, the production of responsive surface active particles usually involves surface coating of mineral particles or the complicated synthesis of functional polymer particles.

In order to address this problem Binks et al. utilise the interaction of N’-dodecyl-N,N-dimethylacetamidinium bicarbonate, a responsive surfactant, with anionic silica nanoparticles in water. By exposure to either CO2 or N2 the responsive surfactant can be switched between a cationic species and a surface-inactive neural form, respectively. On the formation of the cationic species, complexation of the surfactant to anionic silica nanoparticle surfaces gives an in situ increase in the hydrophobicity of the silica, yielding surface-active nanoparticles. Agitation of the resulting complexed system gives foams, however, on exposure to N2 the responsive surfactant returns to its neutral state and desorbs from the surface of the silica particles, resulting in desorption of the particles from the water-air interface.

This simple route to switchable particle-stabilized aqueous foams removes the need for the complicated synthesis of particles as ‘bare’ silica nanoparticles can be used. The synergistic effect of the responsive surfactant and the nanoparticles also allows for the production of foams using a much lower concentration of surfactant than in a responsive-surfactant system alone.

Micrographs of the bubbles in foams produced by shaking 10 cm3 of a dispersion of 0.5 wt% particles in a surfactant solution at different concentrations in bottles (25 cm3) taken immediately after shaking. Surfactant concentrations from A to F are: 0.1, 0.2, 0.3, 0.6, 1.0 and 2.0 mM.

To find out more read the full article:

Responsive aqueous foams stabilised by silica nanoparticles hydrophobised in situ with a switchable surfactant

Yue Zhu, Jianzhong Jiang, Zhenggang Cui and Bernie Binks

Soft Matter, 2014, Accepted Manuscript

DOI: 10.1039/C4SM01970A

This post was written by web writer Rob Woodward. Rob is currently based in Imperial College London working in the Polymer and Composite Engineering (PaCE) group. Rob has a background in both responsive polymeric surfactants and microporous organic polymers for carbon capture and storage.

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On polydispersity and the hard sphere glass transition – an overview of a hot article

On polydispersity and the hard sphere glass transition, Emanuela Zaccarelli, Siobhan M. Liddle and Wilson C. K. Poon, Soft Matter, 2014

DOI: 10.1039/C4SM02321H

The aim of this work was to investigate the dynamics of polydisperse hard spheres at high packing fractions φ. The effects of polydispersity and the detailed shape of the particle size distribution (PSD) were studied.


The glass transition is not fully understood despite many decades of research. The discovery that hard-spheres, sterically-stabilised polymethylmethacrylate (PMMA) colloids, underwent kinetic arrest at a packing fraction of φ = φg ≈ 0.58 led to hard sphere colloids becoming the preferred method to test mode coupling theory (MCT). This is a significant piece of work by Emanuela Zaccarelli, Siobhan M. Liddle and Wilson C. K. Poon who are the first to present simulations of a polydisperse system of hard spheres with a size distribution essentially identical to the experimental data. The findings of the authors are novel and very important, they also put forward a new interpretation of what is going on in glass transition of MCT experiments. Assumptions with regard to PSD are not made and a model as close to the experimental one as possible is designed.

Event-driven Molecular Dynamics (MD) simulations of hard spheres with different PSD were performed. Experimentally obtained PSD from ≈ 2200 PMMA particles were measured by transmission electron microscopy (TEM). N = 2309 particles were simulated with the experimental PSD, measurement noise was included to produce a realistic system representation. N = 2000 particles taken from Gaussian and top hat distributions were considered for comparison.

It was found that a mixed state of ergodic small particles and glassy large particles in a window of concentrations is present and results in a hybrid dynamical state that is fluid for a long time but shows an unusual type of ageing. The breakdown of the MCT-predictions is due to the existence of partial decoupling, which is not accounted for in the monodisperse-version of MCT. However, the results of MCT are recovered once the polydispersity is reduced. There is a non-monotonic dependence of the quality of the glass former on the polydispersity index, s. When s = 0, the system is prone to crystallization and strong glasses are formed when s = <8%. The glass transition is smeared out due to the emergence of the “ageing liquid” for higher values of s as well as for samples drawn from peaked distributions. The precise form of the size distribution is relevant, a peaked distribution that allows a distinction between small and large particles is essential but this is not the case in the top hat particle distribution.

In conclusion, at a fixed relative standard deviation of the PSD the exact shape of the PSD has little influence on the general behaviour of the dynamics, large differences between the dynamics of “small” and “large” particles are found for realistic PSD shapes.

The glass transition is smeared out in polydisperse hard spheres due to decoupling between small and large particles

Please follow the link for the full article.

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12th International Conference on Materials Chemistry (MC12) – call for abstracts

We are delighted to announce that 12th International Conference on Materials Chemistry (MC12) will be held at the University of York on 20 – 23 July 2015. Abstracts are now invited for this event so submit today and take advantage of this excellent opportunity to present your work alongside scientists from across the globe.

This cutting edge international research conference is organised around four exciting and diverse areas of the application of materials chemistry. One prominent theme at MC12 is Soft Matter Materials, which aims to cover the wide and varied aspects of soft matter materials showing the power of the interplay between a priori design and physical function. Visit http://rsc.li/mc12 to find out more and submit your abstract today.

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Making light of food allergies

Written by Katie Bayliss

Researchers in Spain are taking steps towards ‘allergy-free’ food, by treating allergy-inducing proteins with a pulsed light treatment that makes them easier to digest.

 The scientists at the University of Granada and the AZTI-Tecnalia Food Research Institute studied the protein β-lactoglobulin, which acts as an excellent emulsifier in milk and other food products but has a compact structure that defies easy digestion. This lack of digestibility is linked to allergenicity, explains team member Julia Maldonado-Valderrama: ‘If the protein is not completely digested, the body reacts as if it is an allergen, which can trigger an allergic reaction.’ Pre-treatment could break down the protein structure before eating; however, it’s a balancing act. ‘If you break the protein down too much in order to facilitate digestion, they lose their functionality and can’t be used to make foams and emulsions in food products,’ says Maldonado-Valderrama.

To read the full article please visit Chemistry World.

Improved digestibility of β-lactoglobulin by pulsed light processing: dilatational and shear study
Teresa del Castillo-Santaella, Esther Sanmartín-Sierra, Miguel Cabrerizo-Vílchez, J Arboleya and Julia Maldonado-Valderrama 
Soft Matter, 2014
DOI: 10.1039/C4SM01667J, Paper

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Block Copolymer Spheres or Block Copolymer Worms: Which Pickering Emulsifier Has More Backbone?

Web writer Rob Woodward highlights a hot article from the journal

This recent publication from the Armes group investigates the ability of a number of amphiphilic block copolymer nanoparticles to stabilize n-dodecane-in-water emulsions. The aim of the work was to compare spherical and worm-like nano-structures and their efficiency as Pickering emulsifiers, i.e. the ability of these solid particles to adsorb irreversibly at the liquid-liquid interface to form a Pickering emulsion.

Graphical abstract: Are block copolymer worms more effective Pickering emulsifiers than block copolymer spheres?

In previous work by the University of Sheffield group, a number of both linear and branched block copolymers were produced in the form of vesicular structures. It was found that branching was necessary in order to prevent the vesicles dissociating into individual copolymer chains when exposed to high-shear homogenization. In this work linear and branched analogues of the copolymer poly(glycerol monomethacrylate)–poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) are synthesized as both spherical and worm-like nanoparticles. Armes et al. report that the linear nano-structures are not sufficiently robust enough to survive the high-shear conditions necessary for emulsification, whereas the cross-linked copolymer structures are more likely to retain their morphologies and yield genuine Pickering emulsions. Spherical and worm-like structures are provided greater covalent stabilization via chemical cross-linking, allowing structures to survive homogenization as with the vesicles reported previously.

The use of the more hydrophobic poly(benzyl methacrylate) (PBzMA) in place of PHPMA was also investigated in order to examine if increased amphiphilicity could enhance the stability of linear nano-objects in the absence of chemical cross-linking. Both the spherical and worm-like structures comprised of these linear polymer chains formed stable Pickering emulsions, suggesting that branching is not mandatory for the formation of the particulate surfactants.

Due to strong adsorption at the liquid-liquid interface and their ability to produce smaller droplets at a given nanoparticle concentration, it is concluded that branched copolymers with worm-like morphologies are the more effective Pickering emulsifiers. This is also aided by the suggestion that they are at least as efficiently adsorbed at the interface as their spherical analogues.

K. L. Thompson, C. J. Mable, A. Cockram, N. J. Warren, V. J. Cunningham, E. R. Jones, R. Verber and S. P. Armes

This post was written by web writer Rob Woodward. Rob is currently based in Imperial College London working in the Polymer and Composite Engineering (PaCE) group. Rob has a background in both responsive polymeric surfactants and microporous organic polymers for carbon capture and storage.

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