42 research outputs found
Self-propulsion of pure water droplets by spontaneous Marangoni stress driven motion
We report spontaneous motion in a fully bio-compatible system consisting of
pure water droplets in an oil-surfactant medium of squalane and monoolein.
Water from the droplet is solubilized by the reverse micellar solution,
creating a concentration gradient of swollen reverse micelles around each
droplet. The strong advection and weak diffusion conditions allow for the first
experimental realization of spontaneous motion in a system of isotropic
particles at sufficiently large P\'eclet number according to a straightforward
generalization of a recently proposed mechanism. Experiments with a highly
concentrated solution of salt instead of water, and tetradecane instead of
squalane, confirm the above mechanism. The present swimming droplets are able
to carry external bodies such as large colloids, salt crystals, and even cells.Comment: 5 pages, 5 figure
Realisation of the Brazil-nut effect in charged colloids without external driving
Sedimentation is a ubiquitous phenomenon across many fields of science, such
as geology, astrophysics, and soft matter. Sometimes, sedimentation leads to
unusual phenomena, such as the Brazil-nut effect, where heavier (granular)
particles reside on top of lighter particles after shaking. We show
experimentally that a Brazil-nut effect can be realised in a binary colloidal
system of long-range repulsive charged particles driven purely by Brownian
motion and electrostatics without the need for activity. Using theory, we argue
that not only the mass-per-charge for the heavier particles needs to be smaller
than the mass-per-charge for the lighter particles, but that at high overall
density, the system can be trapped in a long-lived metastable state, which
prevents the occurrence of the equilibrium Brazil-nut effect. Therefore, we
envision that our work provides valuable insights into the physics of strongly
interacting systems, such as partially glassy and crystalline structures.
Finally, our theory, which quantitatively agrees with the experimental data,
predicts that the shapes of sedimentation density profiles of multicomponent
charged colloids are greatly altered when the particles are charge regulating
with more than two ion species involved. Hence, we hypothesise that
sedimentation experiments can aid in revealing the type of ion-adsorption
processes that determine the particle charge and possibly the value of the
corresponding equilibrium constants.Comment: 13 pages, 4 figures. In ancillary files: SI and 2 SI videos,
published manuscript with improved explanation on quantification of
parameter
Speed-Dispersion Induced Alignment : a 1D model inspired by swimming droplets experiments
We investigate the collective dynamics of self-propelled droplets, confined
in a one dimensional micro-fluidic channel. On one hand, neighboring droplets
align and form large trains of droplets moving in the same direction. On the
other hand, the droplets condensates, leaving large regions with very low
density. A careful examination of the interactions between two "colliding"
droplets demonstrates that local alignment takes place as a result of the
interplay between the dispersion of their speeds and the absence of Galilean
invariance. Inspired by these observations, we propose a minimalistic 1D model
of active particles reproducing such dynamical rules and, combining analytical
arguments and numerical evidences, we show that the model exhibits a transition
to collective motion in 1D for a large range of values of the control
parameters. Condensation takes place as a transient phenomena which
tremendously slows down the dynamics, before the system eventually settles into
a homogeneous aligned phase.Comment: 5 pages, 5 figure
О финансово-экономическом кризисе
У статті для визначення позиції молодих учених, стосовно фінансово-економічної кризи 2008–2010 р. використаний метод нечіткої кластеризації даних, що працює в режимі паралельної їхньої обробки. Наведено заходи щодо зниження наслідків кризи для України.В статье для определения позиции молодых ученых, применительно к финансово-экономическому кризису 2008—2010 гг. использован метод нечеткой кластеризации данных, который работает в режиме параллельной их обработки. Приведены мероприятия по снижению последствий кризиса для Украины.In an article for determining the position of young scientists, in relation to financial and economic crisis, 2008— 2010. used the method of fuzzy clustering, which operates in parallel processing. Shows the measures to reduce the impact of the crisis in Ukraine
Ring-shaped colloidal patterns on saline water films
Hypothesis: Electrostatically stabilised colloidal particles destabilise when brought into contact with cations causing the particles to aggregate in clusters. When a drop with stabilised colloidal partices is deposited on a liquid film containing cations the delicate balance between the fluid-mechanical and physicochemical properties of the system governs the spreading dynamics and formation of colloidal particle clusters. Experiments: High-speed imaging and digital holographic microscopy were used to characterise the spreading process. Findings: We reveal that a spreading colloidal drop evolves into a ring-shaped pattern after it is deposited on a thin saline water film. Clustered colloidal particles aggregate into larger trapezoidally-shaped ‘supraclusters’. Using a simple model we show that the trapezoidal shape of the supraclusters is determined by the transition from inertial spreading dynamics to Marangoni flow. These results may be of interest to applications such as wet-on-wet inkjet printing, where particle destabilisation and hydrodynamic flow coexist.</p
Formation of dodecagonal quasicrystals in two-dimensional systems of patchy particles
The behaviour of two-dimensional patchy particles with 5 and 7
regularly-arranged patches is investigated by computer simulation. For higher
pressures and wider patch widths, hexagonal crystals have the lowest enthalpy,
whereas at lower pressures and for narrower patches, lower-density crystals
with five nearest neighbours and that are based on the (3^2,4,3,4) tiling of
squares and triangles become lower in enthalpy. Interestingly, in regions of
parameter space near to that where the hexagonal crystals become stable,
quasicrystalline structures with dodecagonal symmetry form on cooling from high
temperature. These quasicrystals can be considered as tilings of squares and
triangles, and are probably stabilized by the large configurational entropy
associated with all the different possible such tilings. The potential for
experimentally realizing such structures using DNA multi-arm motifs are
discussed.Comment: 12 pages, 12 figure
Realization of the Brazil-nut effect in charged colloids without external driving
Sedimentation is a ubiquitous phenomenon across many fields of science, such as geology, astrophysics, and soft matter. Sometimes, sedimentation leads to unusual phenomena, such as the Brazil-nut effect, where heavier (granular) particles reside on top of lighter particles after shaking. We show experimentally that a Brazil-nut effect can be realized in a binary colloidal system of long-range repulsive charged particles driven purely by Brownian motion and electrostatics without the need for activity. Using theory, we argue that not only the mass-per-charge for the heavier particles needs to be smaller than the mass-per-charge for the lighter particles but also that at high overall density, the system can be trapped in a long-lived metastable state, which prevents the occurrence of the equilibrium Brazil-nut effect. Therefore, we envision that our work provides valuable insights into the physics of strongly interacting systems, such as partially glassy and crystalline structures. Finally, our theory, which quantitatively agrees with the experimental data, predicts that the shapes of sedimentation density profiles of multicomponent charged colloids are greatly altered when the particles are charge-regulating with more than one ion species involved. Hence, we hypothesize that sedimentation experiments can aid in revealing the type of ion adsorption processes that determine the particle charge and possibly the value of the corresponding equilibrium constants
Evaporation of binary liquids from a capillary tube
Evaporation of multi-component liquid mixtures in confined geometries, such
as capillaries, is crucial in applications such as microfluidics, two-phase
cooling devices, and inkjet printing. Predicting the behaviour of such systems
becomes challenging because evaporation triggers complex spatio-temporal
changes in the composition of the mixture. These changes in composition, in
turn, affect evaporation. In the present work, we study the evaporation of
aqueous glycerol solutions contained as a liquid column in a capillary tube.
Experiments and direct numerical simulations show three evaporation regimes
characterised by different temporal evolutions of the normalised mass transfer
rate (or Sherwood number, ), namely , , and . Here
is a normalised time. We present a simplistic analytical model
which shows that the evaporation dynamics can be expressed by the classical
relation . For small and medium , this expression
results in the first and second of the three observed scaling regimes,
respectively. This analytical model is formulated in the limit of pure
diffusion and when the penetration depth of the diffusion front is
much smaller than the length of the liquid column. When , finite length effects lead to , i.e.
the third regime. Finally, we extend our analytical model to incorporate the
effect of advection and determine the conditions under which this effect is
important. Our results provide fundamental insight into the physics of
selective evaporation from a multi-component liquid column