# gst: when volatile droplets dance across a surface erratically (along random trajectories)

<< When a drop of a volatile liquid is deposited on a uniformly heated wettable, thermally conducting substrate, one expects to see it spread into a thin film and evaporate. >>️

<< Contrary to this intuition, due to thermal Marangoni contraction, the deposited drop contracts into a spherical-cap-shaped puddle, with a finite apparent contact angle. Strikingly, this contracted droplet, above a threshold temperature, well below the boiling point of the liquid, starts to spontaneously move on the substrate in an apparently erratic way. >>️

Pallav Kant, Mathieu Souzy, et al. Autothermotaxis of volatile drops. Phys. Rev. Fluids 9, L012001. Jan 31, 2024. 

https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.9.L012001

Rachel Berkowitz. Hot Surfaces Make Droplets Move Erratically. Physics 17, s14. Jan 31, 2024. 

https://physics.aps.org/articles/v17/s14 

Also: drop, bubble, erratic

in https://www.inkgmr.net/kwrds.html

Keywords: gst, drop, bubble, erratic, thermotaxis, autothermotaxis

# gst: rearrangements of a jammed 2-D emulsion (during slow compression).

<< As amorphous materials get jammed, both geometric and dynamic heterogeneity are observed. (AA)  investigate the correlation between the local geometric heterogeneity and local rearrangements in a slowly compressed bidisperse quasi-two-dimensional emulsion system. The compression is driven by evaporation of the continuous phase. >>

<< droplets in heterogeneous local regions are more likely to have local rearrangements. These rearrangements are generally T1 events where two droplets converge toward a void, and two droplets move away from the void to make room for the converging droplets. Thus, the presence of the voids tends to orient the T1 events. >>️

<< The presence of a correlation between the structural quantities and the rearrangement dynamics remains qualitatively unchanged over the entire range of packing fractions observed. >>️

Xin Du, Eric R. Weeks. Rearrangements during slow compression of a jammed  two-dimensional emulsion. Phys. Rev. E 109, 034605. Mar 20,  2024.

https://journals.aps.org/pre/abstract/10.1103/PhysRevE.109.034605

Also: drop, in https://www.inkgmr.net/kwrds.html 

Keywords: drops, droplets, droploids 

# 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