Tessera
Folgen

Vatsal Sanjay

@comphy-lab.org

Fluid dynamicist | Assistant Professor, Physics Department, Durham University | ex-PoF (Univ. Twente) | IITR alum | soft-matter & non‑Newtonian flows (drops, bubbles, jets, sheets) | #FluidDynamics #SoftMatter #Drops #Bubbles #DNS

23 Posts207 Follower244 Folgt
Adam Squires@adsquires.bsky.social · 11mo ago

New paper by Jamie McLauchlan, working with Anton Souslov in Cambridge, and Jim Walker and Jonathan Reid in Bristol (and others, including us) - with a very cool combination of state-of-the-art experiments with theory: what happens when aerosol droplets hit surfaces? www.pnas.org/doi/10.1073/...

Why tiny droplets stick or bounce: The physics of speed and size

When a droplet of liquid the size of a grain of icing sugar hits a water-repelling surface, like plastics or certain plant leaves, it can meet one of two fates: stick or bounce. Until now, scientists ...

phys.org

Vatsal Sanjay@comphy-lab.org · last yr.

So inspiring to hear my mentor, Detlef Lohse (@poftwente.bsky.social), share his scientific journey in this @thelhseries.bsky.social! His thoughts on curiosity, mentorship, and the "puzzle solving" joy of science resonate deeply. A must-watch! Always so much to learn. bit.ly/3DXBixh

"Living Histories". Detlef Lohse | #TheLivingHistoriesSeries

The Living Histories series: https://tinyurl.com/TheLHSeries Very brief "trajectory talks" on personal histories leading to the becoming of biological physicists / quantitative biologists / neuroscientists / mathematicians/ complexity scientists. Series concept: Srividya Iyer-Biswas Series organizers: Srividya Iyer-Biswas, Tapa Bhattacharjee, Jasmine Nirody, and Charlie Wright Series website: https://tinyurl.com/TheLHSeries

bit.ly

Markus Deserno@markusdeserno.bsky.social · last yr.

📣 Heads up! During 2025 #BiophysicsWeek the Membrane Structure and Function Subgroup is hosting a Webinar about “Milestones and Future Directions” in our field! It’s intended to be pedagogically accessible, and if you don’t mind me also presenting, then please consider signing up and logging in! 🧪🧬

Bild
Babak Vajdi Hokmabad@babakvh.bsky.social · last yr.

It was fun to uncover this story—bridging microbial physiology, biological pattern formation, & active matter physics. The results may even have implications for controlling microbes in applications. We'd love your feedback. Please report/share with whoever might be interested! [8/8]

Babak Vajdi Hokmabad@babakvh.bsky.social · last yr.

Many biological fluids are polymer solutions, whose viscoelasticity can enhance cell swimming and promote large-scale mixing. We showed that the core-shell organization also arises in polymer solutions, but with fascinating additional flow fluctuations. [7/8]

Babak Vajdi Hokmabad@babakvh.bsky.social · last yr.

We then developed a biophysical model describing this interplay quantitatively. The model recapitulates the experiments, and also yields criteria for predicting the different ways in which confined bacterial populations self-organize under different conditions. [6/8]

Bild
Babak Vajdi Hokmabad@babakvh.bsky.social · last yr.

Cells consume O2, creating a gradient that alters motility: (i) They move up the gradient toward the droplet boundary via aerotaxis, & (ii) They stop swimming in the anoxic droplet core and accumulate. These motility variations in turn reshape O2 fluxes. A feedback loop! [5/8]

Babak Vajdi Hokmabad@babakvh.bsky.social · last yr.

By simultaneously measuring cell distributions, oxygen concentration, and swimming-generated fluid flow, we figured out that this spatial organization is driven by the interplay between cell metabolism-generated oxygen gradients and collective motility. [4/8]

Babak Vajdi Hokmabad@babakvh.bsky.social · last yr.

Surprisingly, when the droplets are big and concentrated, the cells self-organize into a concentrated inner "core" of immotile cells surrounded by a more dilute outer "shell" of highly motile cells. (See movie in 1st tweet.) In some cases, the core shrinks and disappears. [3/8]

Babak Vajdi Hokmabad@babakvh.bsky.social · last yr.

Bacteria often inhabit confined spaces, such as biological tissues/gels & soils/sediments, where metabolites are scarce. What influence does confinement have on a population of motile bacteria? We addressed this question by studying quasi 2D droplets of swimming E. coli. [2/8]

Bild
The Royal Society@royalsociety.org · last yr.

Science advances our economic, physical, and social and cultural wellbeing, and is key to a sustainable future. However, we live in times of great change, and the values that have driven science for the benefit of humanity are under threat. Read our statement here: royalsociety.org/news/2025/02...

Science under threat | Royal Society

The Royal Society will use its voice and the expertise of our Fellows to resist the various challenges to science.

royalsociety.org

Vatsal Sanjay@comphy-lab.org · last yr.

To get an executive summary, have a look at our blog post: blogs.comphy-lab.org/Blog/2025-JF... and/or an `AI` generated general summary at bit.ly/4ifVrxg

2025-JFM-viscous-drop-impact - CoMPhy-Lab blogs

The role of viscosity on drop impact forces on non-wetting surfaces: From Raindrops to Inkjet Printing When a liquid drop hits a surface, the impact creates fascinating fluid dynamics that are crucia…

blogs.comphy-lab.org

Vatsal Sanjay@comphy-lab.org · last yr.

📢 Checkout our work in J. Fluid Mech. (bit.ly/3QuxMgE) on how viscosity alters drop-impact forces. Together with Bin Zhang, Cunjing Lv, & Detlef Lohse. The first and second force peaks emerge from distinct flow mechanisms—one at impact, another at take-off. @poftwente.bsky.social bit.ly/4gUvD8P

Vatsal Sanjay@comphy-lab.org · last yr.

📢 Checkout our work in J. Fluid Mech. (bit.ly/3QuxMgE) on how viscosity alters drop-impact forces. Together with Bin Zhang, Cunjing Lv, & Detlef Lohse. The first and second force peaks emerge from distinct flow mechanisms—one at impact, another at take-off. @poftwente.bsky.social bit.ly/4gUvD8P

[SM1]: The role of viscosity on drop impact forces

The case shown here is We = 40, Oh = 0.0025. Paper: https://doi.org/10.48550/arXiv.2311.03012 Full description: Comparison of the drop impact force $F(t)$ obtained from experiments and simulations for the three typical cases with impact velocity $V_0 = 1.2\,\si{\meter}/\si{\second}, 0.97\,\si{\meter}/\si{\second}, 0.96\,\si{\meter}/\si{\second}$, diameter $D_0 = 2.05\,\si{\milli\meter}, 2.52\,\si{\milli\meter}, 2.54\,\si{\milli\meter}$, surface tension $\gamma = 72\,\si{\milli\newton}/\si{\meter}, 61\,\si{\milli\newton}/\si{\meter}, 61\,\si{\milli\newton}/\si{\meter}$ and viscosity $\eta_d = 1\,\si{\milli\pascal\second}, 25.3\,\si{\milli\pascal\second}, 80.2\,\si{\milli\pascal\second}$. These parameter give $Oh = 0.0025, 0.06, 0.2$ and $We = 40$. For the three cases, the two peak amplitudes, $F_1/(\rho_dV_0^2D_0^2) \approx$ 0.82, 0.92, 0.99 at $t_1 \approx 0.03\sqrt{\rho_dD_0^3/\gamma}$ and $F_2/(\rho_dV_0^2D_0^2) \approx$ 0.37, 0.337, 0.1 at $t_2 \approx 0.42\sqrt{\rho_dD_0^3/\gamma}$, characterize the inertial shock from impact and the Worthington jet before takeoff, respectively. The drop reaches the maximum spreading at $t_{\text{max}}$ when it momentarily stops and retracts until $0.8\sqrt{\rho_dD_0^3/\gamma}$ when the drop takes off ($F = 0$). The black and gray dashed lines in panel (a) mark $F = 0$ and the resolution $F = 0.5\,\si{\milli\newton}$ of our piezoelectric force transducer, respectively. We stress the excellent agreement between experiments and simulations without any free parameters. The left part of each numerical snapshot shows (on a $\log_{10}$ scale) the dimensionless local viscous dissipation function $\tilde{\xi}_\eta \equiv \xi_\eta D_0/\left(\rho_dV_0^3\right) = 2Oh\left(\boldsymbol{\tilde{\mathcal{D}}:\tilde{\mathcal{D}}}\right)$, where $\boldsymbol{\mathcal{D}}$ is the symmetric part of the velocity gradient tensor, and the right part the velocity field magnitude normalized with the impact velocity.

bit.ly