Bijels formed by mixing: Escaping from phase separating liquids

The liquid-liquid phase separation of binary fluids, induced by a temperature quench, can be arrested by colloidal particles trapped at the interface. The arrested structure, a novel soft solid known as a bicontinuous interfacially-jammed emulsion gel (bijel), is a variant of a Pickering emulsion [1]. The mechanical properties are controlled by the interfacial tension between the two fluid domains (e.g. a deeper quench yields a stronger bijel) and the volume fraction of particles. Similar structures have also been created using the biopolymer phase separation (e.g. of gelatin and starch) and also using phase separation driven by the transfer of a solvent out of a pre-mix [2]. Please click Additional Files below to see the full abstract

Particle-stabilized oscillating diver: a self-assembled responsive capsule

We report the experimental discovery of a self-assembled capsule, with density set by interfacial glass beads and an internal bubble, that automatically performs regular oscillations up and down a vial in response to a temperature gradient. Similar composites featuring interfacial particles and multiple internal compartments could be the solution to a variety of application challenges.Comment: 7 pages, 3 figure

Field-Induced Breakup of Emulsion Droplets Stabilized by Colloidal Particles

We simulate the response of a particle-stabilized emulsion droplet in an external force field, such as gravity, acting equally on all $N$ particles. We show that the field strength required for breakup (at fixed initial area fraction) decreases markedly with droplet size, because the forces act cumulatively, not individually, to detach the interfacial particles. The breakup mode involves the collective destabilization of a solidified particle raft occupying the lower part of the droplet, leading to a critical force per particle that scales approximately as $N^{-1/2}$.Comment: 4 pages, plus 3 pages of supplementary materia

Joining emulsion droplets using colloidal rods

Many of the differences between conventional emulsions and particle-stabilized emulsions stem from the fact that the particles are mesoscopic objects. One curious difference is the phenomenon of bridging.[1] This is where colloidal particles are shared by more than one droplet. It results in emulsions with clusters of droplets that are all attached and it has the effect of making the emulsions very fragile.[2] Previous work in this area has focused on colloidal spheres. Here we explore the bridging behavior of droplets stabilized by colloidal rods. Our rods are spherocylinders which have an iron oxide core coated with a silica shell; in this work we use rods with aspect ratios 3 and 15. We find that bridging is ubiquitous for rod shaped particles, especially at high aspect ratio. Previously, computer simulations have shown that the adsorption of colloidal rods to liquid interfaces is likely to involve two steps which happen sequentially.[3] In the first step the rods are adsorbed to the interface; in the second step the rods reorient to lie with their long axis in the plane of the interface. Please click Additional Files below to see the full abstract

Rheology of protein-stabilised emulsion gels envisioned as composite networks. 1 - Comparison of pure droplet gels and protein gels

Protein-stabilised emulsion gels can be studied in the theoretical framework of colloidal gels, because both protein assemblies and droplets may be considered as soft colloids. These particles differ in their nature, size and softness, and these differences may have an influence on the rheological properties of the gels they form. Pure gels made of milk proteins (sodium caseinate), or of sub-micron protein-stabilised droplets, were prepared by slow acidification of suspensions at various concentrations. Their microstructure was characterised, their viscoelasticity, both in the linear and non-linear regime, and their frequency dependence were measured, and the behaviour of the two types of gels was compared. Protein gels and droplet gels were found to have broadly similar microstructure and rheological properties when compared at fixed volume fraction, a parameter derived from the study of the viscosity of the suspensions formed by proteins and by droplets. The viscoelasticity displayed a power law behaviour in concentration, as did the storage modulus in frequency. Additionally, strain hardening was found to occur at low concentration. These behaviours differed slightly between protein gels and droplet gels, showing that some specific properties of the primary colloidal particles play a role in the development of the rheological properties of the gels.Comment: 27 pages, 6 figure

Autonomous analysis to identify bijels from two-dimensional images

Bicontinuous interfacially jammed emulsion gels (bijels) are novel composite materials that can be challenging to manufacture. As a step towards automating production, we have developed a machine learning tool to classify fabrication attempts. We use training and testing data in the form of confocal images from both successful and unsuccessful attempts at bijel fabrication. We then apply machine learning techniques to this data in order to classify whether an image is a bijel or a non-bijel. Our principal approach is to process the images to find their autocorrelation function and structure factor, and from these functions we identify variables that can be used for training a supervised machine learning model to identify a bijel image. We are able to categorise images with reasonable accuracies of 85.4% and 87.5% for two different approaches. We find that using both the liquid and particle channels helps to achieve optimal performance and that successful classification relies on the bijel samples sharing a characteristic length scale. Our second approach is to classify the shapes of the liquid domains directly; the shape descriptors are then used to classify fabrication attempts via a decision tree. We have used an adaptive design approach to find an image pre-processing step that yields the optimal classification results. Again, we find that the characteristic length scale of the images is crucial in performing the classification

Foaming, emulsifying and rheological properties of extracts from a co-product of the Quorn fermentation process

Julien Lonchamp - ORCID: 0000-0001-7954-4745 https://orcid.org/0000-0001-7954-4745Item also deposited in University of Edinburgh repository, available at: https://www.research.ed.ac.uk/portal/en/publications/foaming-emulsifying-and-rheological-properties-of-extracts-from-a-coproduct-of-the-quorn-fermentation-process(c1316b1e-0940-4329-8b28-f010f4156548).htmlThis study assessed the functional profile (foaming, emulsifying and rheological properties), proteomic and metabolomic composition of a naturally foaming and currently unexploited co-product (centrate) from the Quorn fermentation process. Due to the low environmental footprint of this process the centrate is a potential source of sustainable functional ingredients for the food industry. A range of fractions were isolated from the centrate via successive ultrafiltration steps. The retentate 100 (R100) fraction, which was obtained following a 100 kDa ultrafiltration, displayed good foaming, emulsifying and rheological properties. R100 solutions and oil-in-water emulsions displayed high viscosity, while R100 solutions and hydrogels showed high viscoelasticity. R100 foams displayed high stability while oil-in-water R100 emulsions showed small and stable oil droplet size distributions. Large mycelial aggregates were reported in R100 solutions and gels, correlating with their high viscosity and viscoelasticity. A dense mycelial network was observed in R100 foams and contributing to their stability. In parallel tensiometry measurements highlighted the presence of interfacially active molecules in R100 which formed a rigid film stabilising the oil/water interface. A number of functional metabolites and proteins were identified in the centrate, including a cerato-platanin protein, cell membrane constituents (phospholipids, sterols, glycosphingolipids, sphingomyelins), cell wall constituents (chitin, chitosan, proteins), guanine and guanine-based nucleosides and nucleotides. This study highlighted the potential of functional extracts from the Quorn fermentation process as novel ingredients for the preparation of sustainable food products and the complex and specific nature of the centrate’s functional profile, with contributions reported for both mycelial structures and interfacially active molecules.This work was supported by the Engineering and Physical Sciences Research Council (Grant number EP/J501682/1 Foaming and Fat Replacer Ingredients).https://doi.org/10.1007/s00217-019-03287-z245pubpu

Compositional ripening of particle-stabilized drops in a three-liquid system

A composition gradient between drops drives diffusion between them and the spontaneous formation of droplets which gel in the surrounding bath.</p