135 research outputs found
Rheology of protein-stabilised emulsion gels envisioned as composite networks. 2 - Framework for the study of emulsion gels
The aggregation of protein-stabilised emulsions leads to the formation of
emulsion gels. These soft solids are classically envisioned as droplet-filled
matrices. Here however, it is assumed that protein-coated sub-micron droplets
contribute to the network formation in a similar way to proteins. Emulsion gels
are thus envisioned as composite networks made of proteins and droplets.
Emulsion gels with a wide range of composition are prepared and their
viscoelasticity and frequency dependence are measured. Their rheological
behaviours are then analysed and compared with the properties of pure gels
presented in the first part of this study. The rheological behaviour of
emulsion gels is shown to depend mostly on the total volume fraction, while the
composition of the gel indicates its level of similarity with either pure
droplet gels or pure protein gels. These results converge to form an emerging
picture of protein-stabilised emulsion gel as intermediate between droplet and
protein gels. This justifies a posteriori the hypothesis of composite networks,
and opens the road for the formulation of emulsion gels with fine-tuned
rheology.Comment: 22 pages, 5 figure
DNA-coated Functional Oil Droplets
Many industrial soft materials often include oil-in-water (O/W) emulsions at
the core of their formulations. By using tuneable interface stabilizing agents,
such emulsions can self-assemble into complex structures. DNA has been used for
decades as a thermoresponsive highly specific binding agent between hard and,
recently, soft colloids. Up until now, emulsion droplets functionalized with
DNA had relatively low coating densities and were expensive to scale up. Here a
general O/W DNA-coating method using functional non-ionic amphiphilic block
copolymers, both diblock and triblock, is presented. The hydrophilic
polyethylene glycol ends of the surfactants are functionalized with azides,
allowing for efficient, dense and controlled coupling of dibenzocyclooctane
functionalized DNA to the polymers through a strain-promoted alkyne-azide click
reaction. The protocol is readily scalable due to the triblock's commercial
availability. Different production methods (ultrasonication, microfluidics and
membrane emulsification) are used with different oils (hexadecane and silicone
oil) to produce functional droplets in various size ranges (sub-micron, and ), showcasing the generality of
the protocol. Thermoreversible sub-micron emulsion gels, hierarchical
"raspberry" droplets and controlled droplet release from a flat DNA-coated
surface are demonstrated. The emulsion stability and polydispersity is
evaluated using dynamic light scattering and optical microscopy. The generality
and simplicity of the method opens up new applications in soft matter and
biotechnological research and industrial advances.Comment: 7 pages, 2 figures, 1 tabl
Self-assembly of twisted, multi-sheet aggregates
Hierarchical self-assembly underpins much of the diversity of form and function seen in soft systems, yet the pathways by which they achieve their final form are not always straightforward – intermediate steps, kinetic effects and finite sizes of aggregates all influence the self-assembly pathways of these systems. In this paper, we use molecular dynamics simulations of binary mixtures of spheres and ellipsoidal discs to investigate the self-assembly of anisotropic aggregates with internal structures. Through this, the full aggregation pathways of spontaneously chiral, multi-bilayer and multi-layer assemblies have been tracked and characterised via a semi-qualitative analysis. This includes the unambiguous identification of first-, second- and third-generation hierarchical assemblies within a single simulation. Given the significant challenge of tracking full aggregation pathways in experimental systems, our findings strongly support the notion that molecular simulation has much to contribute to improving our understanding of hierarchical self-assembling systems
Viscosity of protein-stabilised emulsions:contributions of components and development of a semi-predictive model
Protein-stabilised emulsions can be seen as mixtures of unadsorbed proteins
and of protein-stabilised droplets. To identify the contributions of these two
components to the overall viscosity of sodium caseinate o/w emulsions, the
rheological behaviour of pure suspensions of proteins and droplets were
characterised, and their properties used to model the behaviour of their
mixtures. These materials are conveniently studied in the framework developed
for soft colloids. Here, the use of viscosity models for the two types of pure
suspensions facilitates the development of a semi-empirical model that relates
the viscosity of protein-stabilised emulsions to their composition.Comment: 28 pages, 11 figure
Thermal hysteresis and seeding of twisted fibers formed by achiral discotic particles
In this paper, molecular dynamics simulations of simple disc-shaped particles are used to investigate the free self-assembly of defect-free fibers. Depending on the choice of particle shape and interaction strength, the formed fibers are reproducibly either straight or, for reasons of packing efficiency, spontaneously chiral. As they grow radially, increasing stresses cause chiral fibers to untwist either continuously or via morphological rearrangement. It is also found that, due to the kinetics of fiber initiation, the isotropic solution has to be significantly supercooled before aggregation takes place. As a result, the thermal hysteresis of one formed fiber extends to 13.9% of the formation temperature. In the presence of a three-thread seed cluster of 15 particles, however, monotonic fiber growth is observed 9.3% above the normal formation temperature. Thus, as in many experimental systems, it is the kinetic pathway, rather than the thermodynamic stability of the final assembly, that dominates the observed behavior
Direct measurement of the effective charge in nonpolar suspensions by optical tracking of single particles
We demonstrate a novel technique for the measurement of the charge carried by
a colloidal particle. The technique uses the phenomenon of the resonance of a
particle held in an optical tweezers trap and driven by a sinusoidal electric
field. The trapped particle forms a strongly damped harmonic oscillator whose
fluctuations are a function of , the ratio of the root-mean square
average of the electric and thermal forces on the particle. At low applied
fields, where , the particle is confined to the optical axis
while at high fields () the probability distribution of the
particle is double-peaked. The periodically-modulated thermal fluctuations are
measured with nanometer sensitivity using an interferometric position detector.
Charges, as low as a few elementary charges, can be measured with an
uncertainty of about 0.25 . This is significantly better than previous
techniques and opens up new possibilities for the study of nonpolar
suspensions
4th Biennial Employment Law Institute
Materials from the 4th Biennial Employment Law Institute held by UK/CLE in June 1994
The state of the Martian climate
60°N was +2.0°C, relative to the 1981–2010 average value (Fig. 5.1). This marks a new high for the record. The average annual surface air temperature (SAT) anomaly for 2016 for land stations north of starting in 1900, and is a significant increase over the previous highest value of +1.2°C, which was observed in 2007, 2011, and 2015. Average global annual temperatures also showed record values in 2015 and 2016. Currently, the Arctic is warming at more than twice the rate of lower latitudes
Brain Activation Patterns Characterizing Different Phases of Motor Action: Execution, Choice and Ideation.
Motor behaviour is controlled by a large set of interacting neural structures, subserving the different components involved in hierarchical motor processes. Few studies have investigated the neural substrate of higher-order motor ideation, i.e. the mental operation of conceiving a movement. The aim of this functional magnetic resonance imaging study was to segregate the neural structures involved in motor ideation from those involved in movement choice and execution. An index finger movement paradigm was adopted, including three different conditions: performing a pre-specified movement, choosing and executing a movement and ideating a movement of choice. The tasks involved either the right or left hand, in separate runs. Neuroimaging results were obtained by comparing the different experimental conditions and computing conjunction maps of the right and left hands for each contrast. Pre-specified movement execution was supported by bilateral fronto-parietal motor regions, the cerebellum and putamen. Choosing and executing finger movement involved mainly left fronto-temporal areas and the anterior cingulate. Motor ideation activated almost exclusively left hemisphere regions, including the inferior, middle and superior frontal regions, middle temporal and middle occipital gyri. These findings show that motor ideation is controlled by a cortical network mainly involved in abstract thinking, cognitive and motor control, semantic and visual imagery processes
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