News

Two (recent) group members have won class medals from the School of Physics and Astronomy at The University of Edinburgh. Michelle Turley, who has just finished a Senior Honours project in the group on measuring contact angles of particles at liquid interfaces, won the Junior Honours Class Medal. Iain Muntz, who is currently doing a PhD studentship in the group on flow and interactions of colloidal particles at liquid interfaces, won the Neil Arnott Certificate for Experimental Physics and the Physics Integrated Masters Class Medal. Congratulations to both!

News item at School of Physics & Astronomy website

Join Katy, Emily, Matthew and Job @PhysAstroEd @EdinburghUni for #DOD2016 #dodscot to discover soft matter physics through activities and tours! Discover what slime, silly putty, vinaigrette, spongy materials and colourful crystals have in common. And...punch some cornstarch!

Doors Open Day 2016 at King's Buildings

Quantitative Morphological Characterization of Bicontinuous Pickering Emulsions via Interfacial Curvatures

M. Reeves, K. Stratford, J. H. J. Thijssen

Soft Matter Advance Article, (2016)

Bicontinuous Pickering emulsions (bijels) are a physically interesting class of soft materials with many potential applications including catalysis, microfluidics and tissue engineering. They are created by arresting the spinodal decomposition of a partially-miscible liquid with a (jammed) layer of interfacial colloids. Porosity L (average interfacial separation) of the bijel is controlled by varying the radius (r) and volume fraction (f) of the colloids (L ~ r/f). However, to optimize the bijel structure with respect to other parameters, e.g. quench rate, characterizing by L alone is insufficient. Hence, we have used confocal microscopy and X-ray CT to characterize a range of bijels in terms of local and area-averaged interfacial curvatures; we further demonstrate that bijels are bicontinuous using an image-analysis technique known as `region growing'. In addition, the curvatures of bijels have been monitored as a function of time, which has revealed an intriguing evolution up to 60 minutes after bijel formation, contrary to previous understanding.

DOI: 10.1039/C5SM03102H

Compressing a spinodal surface at fixed area: the bijel in a centrifuge

K. A. Rumble, J. H. J. Thijssen, A. B. Schofield and P. S. Clegg

Soft Matter accepted, (2016)

Bicontinuous interfacially jammed emulsion gels (bijels) are solid-stabilised emulsions with two inter-penetrating continuous phases. Employing the method of centrifugal compression we find that macroscopically the bijel yields at relatively low angular acceleration. Both continuous phases escape from the top of the structure making any compression immediately irreversible. Microscopically, the bijel becomes anisotropic with the domains aligned perpendicular to the compression direction which inhibits further liquid expulsion; this contrasts strongly to the sedimentation behaviour of colloidal gels. The original structure can, however, be preserved close to the top of the sample and thus the change to an anisotropic structure suggests internal yielding. Any air bubbles trapped in the bijel are found to aid compression by forming channels aligned parallel to the compression direction which provide a route for liquid to escape.

DOI: 10.1039/C6SM00168H

Quantitative Morphological Characterization of Bicontinuous Pickering Emulsions via Interfacial Curvatures

M. Reeves, K. Stratford, J. H. J. Thijssen

Soft Matter accepted, (2016)

Bicontinuous Pickering emulsions (bijels) are a physically interesting class of soft materials with many potential applications including catalysis, microfluidics and tissue engineering. They are created by arresting the spinodal decomposition of a partially-miscible liquid with a (jammed) layer of interfacial colloids. Porosity L (average interfacial separation) of the bijel is controlled by varying the radius (r) and volume fraction (f) of the colloids (L ~ r/f). However, to optimize the bijel structure with respect to other parameters, e.g. quench rate, characterizing by L alone is insufficient. Hence, we have used confocal microscopy and X-ray CT to characterize a range of bijels in terms of local and area-averaged interfacial curvatures; we further demonstrate that bijels are bicontinuous using an image-analysis technique known as `region growing'. In addition, the curvatures of bijels have been monitored as a function of time, which has revealed an intriguing evolution up to 60 minutes after bijel formation, contrary to previous understanding.

DOI: 10.1039/C5SM03102H

Particle-size effects in the formation of bicontinuous Pickering emulsions

M. Reeves, A. T. Brown, A. B. Schofield, M. E. Cates and J. H. J. Thijssen

Physical Review E 92, E032308 (2015)

We demonstrate that the formation of bicontinuous emulsions stabilized by interfacial particles (bijels) is more robust when nanoparticles rather than microparticles are used. Emulsification via spinodal demixing in the presence of nearly neutrally wetting particles is induced by rapid heating. Using confocal microscopy, we show that nanospheres allow successful bijel formation at heating rates two orders of magnitude slower than is possible with microspheres. In order to explain our results, we introduce the concept of mechanical leeway, i.e., nanoparticles benefit from a smaller driving force towards disruptive curvature. Finally, we suggest that leeway mechanisms may benefit any formulation in which challenges arise due to tight restrictions on a pivotal parameter, but where the restrictions can be relaxed by rationally changing the value of a more accessible parameter.

DOI: 10.1103/PhysRevE.92.032308

Also featured in PRE's September 2015 Kaleidoscope.