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martedì 22 ottobre 2019
# gst: the transition from quiescent spherical cap states to self-piloted motile states of volatile droplets
mercoledì 21 febbraio 2024
# gst: when volatile droplets dance across a surface erratically (along random trajectories)
giovedì 23 novembre 2017
# gst: levitation in a temperature gradient: the two liquids don't mix
<< A drop or two of cold cream in hot coffee can go a long way toward improving one's morning. But what if the two liquids didn't mix? >>
AA << have now explained why under certain conditions a droplet of liquid should not coalesce with the liquid surface below. If the droplet is very cold, and the bath sufficiently hot, then the droplet should "levitate" on the bath's surface, as a result of the flows induced by the temperature difference >>
<< If you study that process mathematically, you can show the way in which temperature is changing in the droplet over time is exactly with this power law of 2/3 that we observed in our experiments >> Michela Geri.
Jennifer Chu. Study explains how droplets can 'levitate' on liquid surfaces. Nov 15, 2017
https://m.phys.org/news/2017-11-droplets-levitate-liquid-surfaces.html
Michela Geri, Bavand Keshavarz, et al. Thermal delay of drop coalescence.
Journal of Fluid Mechanics. 2017; 833 doi: 10.1017/jfm.2017.686 Nov 8, 2017.
giovedì 9 settembre 2021
# gst: apropos of unexpected thresholds, the minimum temperature for levitating a droplet
sabato 21 maggio 2022
# gst: apropos of transitions, two aspects of intermittency
giovedì 8 ottobre 2020
# gst: observing the crystallization process in a droplet
sabato 6 marzo 2021
# gst: the dynamics of a collective bubble (in a foam) that collapse in a droplet
mercoledì 15 febbraio 2023
# gst: when a soliton juggles ('catches' and 'throws') droplets
martedì 11 giugno 2019
# gst: apropos of bubbles, how simple foams collapse
<< When a bubble breaks, (AA) found that a collapse event propagates via impact with the receding film and tiny scattered droplets breaking other bubbles. >>
<< A key finding was that changing the viscosity of the fluid did not lead to a significant change in the number of bubbles broken. Methods to stabilize foams commonly rely on changing the viscosity, yet the team's findings clearly show how both the number of bubbles collapsed and the velocity of the receding film are unaffected. >>
Two distinct physical mechanisms identified for how simple foams collapse. Tokyo Metropolitan University. June 10, 2019.
https://m.phys.org/news/2019-06-distinct-physical-mechanisms-simple-foams.html
Naoya Yanagisawa, Rei Kurita. In-situ observation of collective bubble collapse dynamics in a quasi-two-dimensional foam. Scientific Reports 9, Article number: 5152. March 26, 2019
sabato 25 settembre 2021
# gst: ️apropos of spontaneous active matter, the active droploids.
venerdì 15 marzo 2024
# gst: multi-component droplets may exhibit self-lubricating effects
lunedì 10 luglio 2023
# gst: myriad of complex dynamics from the atomization of acoustically levitated droplets
martedì 2 luglio 2019
# gst: apropos of freezing bubbles ...
<< Droplets or puddles tend to freeze from the propagation of a single freeze front. In contrast, videographers have shown that as soap bubbles freeze, a plethora of growing ice crystals can swirl around in a beautiful effect visually reminiscent of a snow globe. >>
AA << characterize the physics of soap bubbles freezing on an icy substrate and reveal two distinct modes of freezing. The first mode, occurring for isothermally supercooled bubbles, generates a strong Marangoni flow that entrains ice crystals to produce the aforementioned snow globe effect. The second mode occurs when using a cold stage in a warm ambient, resulting in a bottom-up freeze front that eventually halts due to poor conduction along the bubble. >>
S. Farzad Ahmadi, Saurabh Nath, et al. How soap bubbles freeze. Nature Communications. volume 10, Article number: 2531. Jun 18, 2019.
https://www.nature.com/articles/s41467-019-10021-6
Rosaire Bushey. Freezing bubbles viral video inspired research now published. Virginia Tech. Jun 19, 2019.
lunedì 21 maggio 2018
# gst: the intricate dynamics of a splashing droplet
<< at all times, the rim thickness is governed by a local instantaneous Bond number equal to unity, defined with the instantaneous, local, unsteady rim acceleration. This criterion is found to be robust and universal for a family of unsteady inviscid fluid sheet fragmentation phenomena, from impacts of drops on various surface geometries to impacts on films >>
Wang Y, Dandekar R, et al. Universal Rim Thickness in Unsteady Sheet Fragmentation. Phys. Rev. Lett. 120, 204503. doi: 10.1103/PhysRevLett.120.204503. May 16, 2018.
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.204503
<< Because all these features change constantly over a short period of time, extracting high-accuracy, unbiased measurements in the data is quite tricky (..) Classical algorithms are unable to capture all of these details >> Lydia Bourouiba.
<< In contrast, her team’s algorithms can automatically discern a splashing droplet’s rim and distinguish it from the smaller droplets that spray out from the rim, and the ligaments that form around the rim >>
Jennifer Chu. New theory describes intricacies of a splashing droplet. MIT. May 17, 2018.
http://news.mit.edu/2018/new-theory-describes-intricacies-splashing-droplet-0516
https://m.phys.org/news/2018-05-theory-intricacies-splashing-droplet.html
lunedì 19 febbraio 2018
# chem: how to quickly wrap droplets with a splash to stabilize emulsions
<< Whether an object has a regular or irregular shape, wrapping it with a thin film can be challenging >>
Deepak Kumar, Joseph D. Paulsen, et al. Wrapping with a splash: High-speed encapsulation with ultrathin sheets. Science. 2018; 359 (6377): 775 - 8. doi: 10.1126/science.aao1290. Feb 16, 2018.
http://science.sciencemag.org/content/359/6377/775
<< The quick and simple solution Kumar [Deepak Kumar] has found is a huge advance, and once he mastered it and identified the most important parameters, he found he could get adventurous and make different shapes. "We show that we have made cubes and a tetrahedron, for example" >>
<< If you want to add complexity, you could put a layer or a pattern on the inside of the wrapping, or you could add a window to make it slightly leaky. Once you know how to do the technique, it's not fussy. >>
University of Massachusetts Amherst. Physicists speed up droplet-wrapping process. Feb 15, 2018.
https://m.phys.org/news/2018-02-physicists-droplet-wrapping.html