# gst: apropos of evaporation, puncturing of active drops

<< By virtue of self-propulsion, active particles impart intricate stresses to the background fluids. (..) this active stress can be utilized to greatly control evaporation dynamics of active drops. >>

AA << discover a new phenomenon of puncturing of the active drops, where the air-liquid interface of the drop undergoes spontaneous tearing and there occurs a formation of a new three-phase contact line due to the liquid-air interface hitting the liquid-solid interface through evaporation-driven mass loss. Post puncturing, (AA) see an inside-out evaporation of the drop, where the new contact line sweeps towards the pinned outer contact line of the drops, contrasting regular drops that straightaway shrink to zero volume with self-similar shape. >>

<< Furthermore, (..) the activity inside the drops can manipulate the three-phase contact-line dynamics, which for contractile drops can result in an up to 50% enhanced lifetime of the drop and 33% quicker evaporation for extensile drops. By analyzing the flux distribution inside the drop, (AA) gain insights on nonintuitive deposition patterns (e.g., ring galaxy type deposits that demonstrate controllable spatial gradients in the concentrations of the deposited particles) of active particles, which are oftentimes biological substances or bimetallic nanoparticles of interest. >>

Ghansham Rajendrasingh Chandel, Vishal Sankar Sivasankar, Siddhartha Das. Evaporation of active drops: Puncturing drops and particle deposits of ring galaxy patterns. Phys. Rev. Fluids 9, 033603. Mar 27, 2024. 

https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.9.033603

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

Keywords: gst, drop, particle, evaporation, transition, drop interactions, droplet, droploid

# gst: multi-component droplets may exhibit self-lubricating effects

<< Over the past decade, there has been a growing interest in the study of multicomponent drops. These drops exhibit unique phenomena, as the interplay between hydrodynamics and the evolving physicochemical properties of the mixture gives rise to distinct and often unregulated behaviors. >>

<< Of particular interest is the complex dynamic behavior of the drop contact line, which can display self-lubrication effect. The presence of a slipping contact line in self-lubricating multicomponent drops can suppress the coffee-stain effect, conferring valuable technological applications. >>

Huanshu Tan, Detlef Lohse, Xuehua Zhang. Self-Lubricating Drops. arXiv: 2403.01207v1 [physics.flu-dyn]. Mar 2, 2024

https://arxiv.org/abs/2403.01207

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

Keywords: drop, droplet, droploid, multicomponent drops, drop contact line, self-lubrication

# gst: droplets scoot like caterpillars.

<< From swells in an ocean to ripples in a puddle, the shearing effect of wind blowing over a liquid is visible at all scales. This shear determines the interactions between Earth’s atmosphere and its surface water and, researchers now explain, the movement of liquid droplets that crawl up and down the window of a moving car in the rain. In a series of experiments, (AA) show that airflow triggers surface waves that cause such droplets to crawl like caterpillars before they break apart. >>️

<< At first, the airflow across the droplet’s surface caused the droplet to extend into an oval shape. The droplet also began to tilt, with the liquid piling up at the droplet’s downwind edge. When the drag force exerted by the airflow overcame the capillary force between the glycerin and the glass, the droplet began to slide and to stretch out even more. Surface waves then developed on the elongated droplet and traveled toward its leading edge. The waves induced a stable caterpillar-like motion, with the droplet stretching and contracting along its length. Eventually, beyond a threshold length that depended on the droplet’s volume, the caterpillar was no longer able to withstand the shearing force and broke into several droplets. >>️

AA << say that the behavior follows the same pattern as that of an elongated droplet sliding along an incline. >>

️

Rachel Berkowitz. Droplets Scoot Like Caterpillars. Physics 16, s110. Sep 1, 2023.

https://physics.aps.org/articles/v16/s110  

A. Chahine, J. Sebilleau, R. Mathis, D. Legendre. Caterpillar like motion of droplet in a shear flow. Phys. Rev. Fluids 8, 093601. Sep 1, 2023.

https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.8.093601

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

Keywords: gst, drop, droplet, droploid, bubble, transition

# gst: analogy between quasi-2D and 3D liquid drops.

<< Liquid drops are everywhere around us and important in numerous technological applications. Here, (AA) demonstrate a quasi-two-dimensional (Q2D) analogy to the regular, often close to axisymmetric, three-dimensional (3D) drops. >>️

<< The Q2D drops are created by confining liquids between vertical walls, leading to formation of low aspect ratio capillary bridges that are deformed by gravity. When stationary, the Q2D drops adopt projected shapes that are analogous to 3D sessile drops, ranging from circular drops to puddles. >>️

<< When moving, the Q2D drops exhibit capillary and fluid mechanical behaviours analogous to 3D drops, including impacts and sliding on pseudo-surfaces. The Q2D drops also exhibit considerably more complex phenomena such as levitation, instabilities and pattern formation when subjected to external electric, magnetic and flow fields -- all seen also in regular 3D drops. >>️

<< 3D-Q2D analogy suggests that the diverse and often complicated phenomena observed in 3D drops can be studied in the Q2D geometry, >>

️

Tytti Kärki, Into Pääkkönen, et al. Quasi-Two-Dimensional Drops. arXiv: 2401.11845v1 [physics.flu-dyn]. Jan 22, 2024.

https://arxiv.org/abs/2401.11845

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

Keywords: gst, drop, droplet, droploid, analogy

# gst: nonmonotonic appearance- disappearance behaviors of two unequal-sized miscible liquid drops

<< the coalescence process of two miscible liquid drops exhibits a nonmonotonic behavior of partial coalescence from appearance to disappearance and then reappearance with decreasing surface tension ratio. The strong lifting force of the intense Marangoni flow causes the reappearance of partial coalescence at higher surface tension difference between two drops. When the Ohnesorge number increases, high viscous forces restrict the propagation of Marangoni flow and do not favor the pinch-off, even in the presence of a significant surface tension difference. The generation of secondary drops at a considerable surface tension difference is also prevented for small parent drop size ratio. >>️

Swati Singh, Arun K. Saha. Effect of surface tension gradients on coalescence dynamics of two unequal-sized drops. Phys. Rev. Fluids 8, 053604. May 24, 2023. 

https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.8.053604

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

Keywords: gst, behavior, drop, drop breakup, drop coalescence, drop interactions, droplet, droploid

# gst: apropos of transitions, droplet trajectories during single and collective bursting bubbles

<< Mechanisms of droplet production from bursting bubbles have been extensively studied for single bubbles, but remain sparsely investigated in more complex collective settings. >>️

<< In the collective bubbling experiment, subsurface quasimonodisperse bubbles are rising up to the surface where, depending on the surfactant concentration, they can either merge or assemble in rafts of monodisperse bubbles. Drop trajectories are recorded, analyzed, and shown to exhibit uniquely distinctive features for the different production mechanisms: centrifuge film drops are ejected sideways, and jet drops are ejected vertically. Different single-burst scalings are finally compared to the experimental size-velocity relationships, and reveal that drops coming from collective bubble bursting appear slower and more scattered than when coming from single bursting bubbles. >>️

B. Neel and L. Deike. Velocity and size quantification of drops in single and collective bursting bubbles experiments. Phys. Rev. Fluids 7, 103603. Oct 5, 2022. 

https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.7.103603

Also: 'when a superbubble can generate trains of shock waves'. Mar 6, 2019.

https://flashontrack.blogspot.com/2019/03/gst-astro-when-superbubble-can-generate.html

Also: 'transition', 'droplet', 'droploid', 'bubble', in: https://www.inkgmr.net/kwrds.html

Keywords: gst, transition, drop, droplet, droploid, bubble, collective dynamics,  fluid dynamics

PS: << they can either merge or assemble in rafts of monodisperse bubbles >> ; this is poetry, without unnecessary adjectives, anzicheforse ... FonT. Wed June 14, 2023 16:58 (cest)