713 research outputs found
Particles at oil–air surfaces : powdered oil, liquid oil marbles, and oil foam
The type of material stabilized by four kinds of fluorinated particles (sericite and bentonite platelet clays and spherical zinc oxide) in air–oil mixtures has been investigated. It depends on the particle wettability and the degree of shear. Upon vigorous agitation, oil dispersions are formed in all the oils containing relatively large bentonite particles and in oils of relatively low surface tension (γla < 26 mN m⁻¹) like dodecane, 20 cS silicone, and cyclomethicone containing the other fluorinated particles. Particle-stabilized oil foams were obtained in oils having γla > 26 mN m⁻¹ where the advancing air–oil–solid contact angle θ lies between ca. 90° and 120°. Gentle shaking, however, gives oil-in-air liquid marbles with all the oil–particle systems except for cases where θ is <60°. For oils of tension >24 mN m⁻¹ with omniphobic zinc oxide and sericite particles for which advancing θ ≥ 90°, dry oil powders consisting of oil drops in air which do not leak oil could be made upon gentle agitation up to a critical oil:particle ratio (COPR). Above the COPR, catastrophic phase inversion of the dry oil powders to air-in-oil foams was observed. When sheared on a substrate, the dry oil powders containing at least 60 wt % of oil release the encapsulated oil, making these materials attractive formulations in the cosmetic and food industries
Effect of the depth on the pattern formation of Faraday waves
The symmetry of standing wave patterns on the surface of a vertically oscillated fluid layer depends on the depth of the layer. In a large experiment we trace out the stability diagram. The dependency can be understood on the basis of the oscillatory character of the waves and the dispersion relation. A simple amplitude equation can be constructed with the variation with depth of the dispersion relation and a general quadratic nonlinearity as its only ingredients. The predictions of this model agree well with the experiment
Saddle-splay modulus of a particle-laden fluid interface
The scaled-particle theory equation of state for the two-dimensional
hard-disk fluid on a curved surface is proposed and used to determine the
saddle-splay modulus of a particle-laden fluid interface. The resulting
contribution to saddle-splay modulus, which is caused by thermal motion of the
adsorbed particles, is comparable in magnitude with the saddle-splay modulus of
a simple fluid interface.Comment: 10 pages, 2 figure
Parametrically excited surface waves in magnetic fluids: observation of domain structures
Observations of parametrically excited surface waves in a magnetic fluid are
presented. Under the influence of a magnetic field these waves have a
non--monotonic dispersion relation, which leads to a richer behavior than in
ordinary liquids. We report observation of three novel effects, namely:
i) domain structures,
ii) oscillating defects and
iii) relaxational phase oscillations.Comment: to be published in Physical Review Letter
Arresting bubble coarsening: A two-bubble experiment to investigate grain growth in presence of surface elasticity
Many two-phase materials suffer from grain-growth due to the energy cost
which is associated with the interface that separates both phases. While our
understanding of the driving forces and the dynamics of grain growth in
different materials is well advanced by now, current research efforts address
the question of how this process may be slowed down, or, ideally, arrested. We
use a model system of two bubbles to explore how the presence of a finite
surface elasticity may interfere with the coarsening process and the final
grain size distribution. Combining experiments and modelling in the analysis of
the evolution of two bubbles, we show that clear relationships can be predicted
between the surface tension, the surface elasticity and the initial/final size
ratio of the bubbles. We rationalise these relationships by the introduction of
a modified Gibbs criterion. Besides their general interest, the present results
have direct implications for our understanding of foam stability
Colloid-stabilized emulsions: behaviour as the interfacial tension is reduced
We present confocal microscopy studies of novel particle-stabilized
emulsions. The novelty arises because the immiscible fluids have an accessible
upper critical solution temperature. The emulsions have been created by
beginning with particles dispersed in the single-fluid phase. On cooling,
regions of the minority phase nucleate. While coarsening these nuclei become
coated with particles due to the associated reduction in interfacial energy.
The resulting emulsion is arrested, and the particle-coated interfaces have
intriguing properties. Having made use of the binary-fluid phase diagram to
create the emulsion we then make use of it to study the properties of the
interfaces. As the emulsion is re-heated toward the single-fluid phase the
interfacial tension falls and the volume of the dispersed phase drops.
Crumpling, fracture or coalescence can follow. The results show that the
elasticity of the interfaces has a controlling influence over the emulsion
behaviour.Comment: Submitted for the proceedings of the 6th Liquid Matter Conference,
held in Utrecht (NL) in July 200
Portraying the hosts: Stellar science from planet searches
Information on the full session can be found on this website: https://sites.google.com/site/portrayingthehostscs18/We present a compendium of the splinter session on stellar science from planet searches that was organized as part of the Cool Stars 18 conference. Seven speakers discussed techniques to infer stellar information from radial velocity, transit and microlensing data, as well as new instrumentation and missions designed for planet searches that will provide useful for the study of the cool stars
Preparation of double emulsions using hybrid polymer/silica particles: New pickering emulsifiers with adjustable surface wettability
A facile route for the preparation of water-in-oil-in-water (w/o/w) double emulsions is described for three model oils, namely, n-dodecane, isopropyl myristate, and isononyl isononanoate, using fumed silica particles coated with poly(ethylene imine) (PEI). The surface wettability of such hybrid PEI/silica particles can be systematically adjusted by (i) increasing the adsorbed amount of PEI and (ii) addition of 1-undecanal to the oil phase prior to homogenization. In the absence of this long-chain aldehyde, PEI/silica hybrid particles (PEI/silica mass ratio = 0.50) produce o/w Pickering emulsions in all cases. In the presence of 1-undecanal, this reagent reacts with the primary and secondary amine groups on the PEI chains via Schiff base chemistry, which can render the PEI/silica hybrid particles sufficiently hydrophobic to stabilize w/o Pickering emulsions at 20 °C. Gas chromatography, 1H NMR and X-ray photoelectron spectroscopy provide compelling experimental evidence for this in situ surface reaction, while a significant increase in the water contact angle indicates markedly greater hydrophobic character for the PEI/silica hybrid particles. However, when PEI/silica hybrid particles are prepared using a relatively low adsorbed amount of PEI (PEI/silica mass ratio = 0.075) only o/w Pickering emulsions are obtained, since the extent of surface modification achieved using this Schiff base chemistry is insufficient. Fluorescence microscopy and laser diffraction studies confirm that highly stable w/o/w double emulsions can be achieved for all three model oils. This is achieved by first homogenizing the relatively hydrophobic PEI/silica hybrid particles (PEI/silica mass ratio = 0.50) with an oil containing 3% 1-undecanal to form an initial w/o emulsion, followed by further homogenization using an aqueous dispersion of relatively hydrophilic PEI/silica particles (PEI/silica mass ratio = 0.075). Dye release from the internal aqueous cores into the aqueous continuous phase was monitored by visible absorption spectroscopy. These studies indicate immediate loss of 12-18% dye during the high speed homogenization that is required for double emulsion formation, but no further dye release is observed at 20 °C for at least 15 days thereafter
Amplitude equations and pattern selection in Faraday waves
We present a systematic nonlinear theory of pattern selection for parametric
surface waves (Faraday waves), not restricted to fluids of low viscosity. A
standing wave amplitude equation is derived from the Navier-Stokes equations
that is of gradient form. The associated Lyapunov function is calculated for
different regular patterns to determine the selected pattern near threshold.
For fluids of large viscosity, the selected wave pattern consists of parallel
stripes. At lower viscosity, patterns of square symmetry are obtained in the
capillary regime (large frequencies). At lower frequencies (the mixed
gravity-capillary regime), a sequence of six-fold (hexagonal), eight-fold, ...
patterns are predicted. The regions of stability of the various patterns are in
quantitative agreement with recent experiments conducted in large aspect ratio
systems.Comment: 12 pages, 1 figure, Revte
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