The role of viscosity on drop impact forces on non-wetting surfaces
Alright. Let's, dive into something that I think we all see every day, but probably don't think twice about.
Speaker 2:Oh, yeah.
Speaker 1:Drop impact.
Speaker 2:Mhmm.
Speaker 1:So, you know, raindrops hitting your window.
Speaker 2:Yeah.
Speaker 1:Ink jets spitting out these tiny little dots.
Speaker 2:Yeah.
Speaker 1:Yeah. Even just a drop of water falling from your faucet.
Speaker 2:Sure.
Speaker 1:It turns out there's this whole hidden world of complexity behind these everyday events.
Speaker 2:Well, and what's fascinating here is that it drops impact. You know? It isn't just a simple splat. You know? It's this dynamic process with these distinct phases Mhmm.
Speaker 2:Spreading, retracting, and sometimes even bouncing. Yeah. And the forces involved are far more intricate than you might imagine.
Speaker 1:And get this. Okay. There's a recent research paper
Speaker 2:Oh, wow.
Speaker 1:By Sanjay and their team
Speaker 2:Okay.
Speaker 1:Published in the Journal of Fluid Mechanics.
Speaker 2:Nice.
Speaker 1:It actually made the cover
Speaker 2:Wow. Okay.
Speaker 1:For revealing some pretty mind blowing findings about these forces.
Speaker 2:So what did they, what did they find?
Speaker 1:So they discovered that when a drop hits a surface, especially one that doesn't easily get wet Mhmm. There are actually two distinct force peaks, not just the one you'd intuitively expect.
Speaker 2:Two peaks.
Speaker 1:Two peaks.
Speaker 2:I'll admit that threw me for a loop a little bit.
Speaker 1:Yeah.
Speaker 2:I mean, the first peak okay. That makes sense. Right? That initial slam when the drop first makes contact. Right.
Speaker 2:But a second one, what's the story there?
Speaker 1:Yeah. I mean, that threw me for a loop too.
Speaker 2:Yeah.
Speaker 1:The first peak makes sense, that initial slam.
Speaker 2:Right.
Speaker 1:But a second one, what's going on?
Speaker 2:Yeah. So the second peak is directly linked to something called the Worthington jet.
Speaker 1:Okay.
Speaker 2:So picture this. Right before the drop might bounce back up
Speaker 1:Okay.
Speaker 2:A thin column of liquid shoots straight upwards, almost like a tiny geyser erupting from the drop.
Speaker 1:Okay. Now that's just cool.
Speaker 2:Yeah.
Speaker 1:But wouldn't you think all the force would be directed downwards?
Speaker 2:Right.
Speaker 1:If the drop is about to bounce? Yeah. Why an upward jet at that moment?
Speaker 2:It does seem counterintuitive. Right? Yeah. But remember, the drop isn't static. Right.
Speaker 2:Spreading out, then trying to pull back in on itself. Mhmm. All this movement creates these intricate internal flows within the droplet. Yeah. And at a very specific
Speaker 1:jet is like the grand finale. Exactly. Yeah. Upward jet is like the grand finale.
Speaker 2:Exactly. Exactly. And it's this upward motion that contributes to that second force peak. Alright. What's even more surprising is that sometimes the second peak driven by the Worthington jet Yeah.
Speaker 2:Can actually be stronger than the initial impact force.
Speaker 1:No. Stronger than the initial slam.
Speaker 2:Stronger.
Speaker 1:That's really unexpected. Yeah. I'm starting to see why this research is getting so much attention. Yeah. So how do they even begin to untangle all of this?
Speaker 2:Well, they started by looking at two key players. The Weber number Okay. Which measures the drop's kinetic energy upon impact, and the anosaurage number Okay. Which measures its viscosity. Okay.
Speaker 1:So the Weber number tells you how much oomph the drop has when it hits.
Speaker 2:Yeah. Yeah.
Speaker 1:And the anisort number tells you how resistant it is to flow.
Speaker 2:Right? Exactly.
Speaker 1:Like a massive raindrop falling from a rooftop Yeah. Would have a high Weber number.
Speaker 2:Exactly.
Speaker 1:A honey would have a high anisort number.
Speaker 2:You got it.
Speaker 1:Okay.
Speaker 2:And by using these numbers, they were able to create a sort of map of different drop impact regimes
Speaker 1:Okay.
Speaker 2:Each with its own unique characteristics. Right. This allows them to predict the resulting behavior and forces depending on the fluid and forces depending on the fluid and the conditions.
Speaker 1:Oh, cool.
Speaker 2:For instance, for those low viscosity drops like water
Speaker 1:Yeah.
Speaker 2:They found that the first impact force is primarily driven by inertia, that initial momentum. Yep. They even derived an equation to describe it. The force is proportional to the density of the liquid, the velocity of the drop squared, and the diameter of the drop squared.
Speaker 1:So, basically, the bigger, faster, and denser the drop Yeah. The harder that initial slam
Speaker 2:Exactly.
Speaker 1:Makes sense to me. Yeah. But what about those high viscosity drops
Speaker 2:Right.
Speaker 1:Like our honey example?
Speaker 2:Exactly.
Speaker 1:I'm guessing it's not so straightforward.
Speaker 2:You're right about that. You're right about that. Yeah. Here's where things get really interesting and counterintuitive.
Speaker 1:Yeah.
Speaker 2:The research found that high viscosity drops actually create a larger first peak force than you'd expect based on inertia alone.
Speaker 1:Hold on. Wouldn't you think a thicker, stickier fluid Yeah. Would actually cushion the impact a bit?
Speaker 2:You would think. Right? Yeah.
Speaker 1:Why would it lead to a bigger force?
Speaker 2:That's what's so fascinating about this. Yeah. It all comes down to that resistance to deformation we talked about. Right. Because viscous fluids like honey resist spreading out.
Speaker 1:Okay.
Speaker 2:They experience a much higher pressure right at the point of impact. Uh-huh. And that translates to a surprisingly strong force. Think of it like trying to flatten a ball of dough versus a drop of water. Yeah.
Speaker 2:The dough pushes back much harder.
Speaker 1:Okay. That analogy really helps.
Speaker 2:Right.
Speaker 1:So you've got these two force peaks.
Speaker 2:Yeah.
Speaker 1:And the first one can be influenced by both inertia and viscosity
Speaker 2:Right.
Speaker 1:Depending on the fluid.
Speaker 2:Exactly.
Speaker 1:And then there's that mesmerizing Worthington jet
Speaker 2:Right.
Speaker 1:Tied to the second peak.
Speaker 2:Exactly.
Speaker 1:My brain is already working overtime trying to picture all of this.
Speaker 2:It's definitely complex. Yeah. But what's remarkable is that despite all these intricacies, there's an underlying elegance to it.
Speaker 1:Okay.
Speaker 2:For example, the second force peak, the one linked to the Worthington jet Yeah. Always appears at a remarkably consistent time Mhmm. Tied to a very specific shift in the drop's internal flow.
Speaker 1:So it's like the drop is going through this choreographed routine
Speaker 2:Uh-huh.
Speaker 1:And the Worthington jet is this perfectly timed move always appearing at the same beat.
Speaker 2:Exactly. Exactly. And the strength of that second peak, the power behind that jet Yeah. Is influenced by both the viscosity and the impact speed.
Speaker 1:Okay.
Speaker 2:Think of it as a spectrum.
Speaker 1:Right.
Speaker 2:On one end, you have a low viscosity, high speed impact where inertia dominates, and on the other end, a slower impact where surfant tension plays a bigger role.
Speaker 1:So it's like this delicate balance
Speaker 2:Yeah.
Speaker 1:Between these different forces.
Speaker 2:Precisely. Precisely. And right in the middle of this viscosity energy map at a very specific point, we find this fascinating singular jet phenomenon.
Speaker 1:A singular jet. Yeah. Now I'm really intrigued. Yeah. What makes it so special?
Speaker 2:Well, this jet occurs at a very specific combination of a high Weber number and a very low honor source number.
Speaker 1:Okay.
Speaker 2:It's incredibly thin and fast. But here's the kicker.
Speaker 1:Yeah.
Speaker 2:It often forms with a tiny bubble entrapped right at its base.
Speaker 1:Wait. A bubble trapped in a jet.
Speaker 2:A bubble trapped in a jet. That's wild. Yeah.
Speaker 1:It's amazing that there's this specific recipe, this perfect blend of viscosity and impact speed that creates this unique phenomenon.
Speaker 2:Right.
Speaker 1:I'm starting to see why this research is making waves.
Speaker 2:It really highlights the level of detail and precision present in even the simplest natural events.
Speaker 1:Yeah.
Speaker 2:And we're only beginning to uncover all the nuances.
Speaker 1:Wow. It really does make you wonder what else we're missing. You know? Yeah. Because we don't have the tools to see it yet.
Speaker 2:Right.
Speaker 1:Reminds me of that saying, we don't know what we don't know.
Speaker 2:Yeah. But now, thanks to this research, we know a little bit more.
Speaker 1:Exactly. Exactly. And the really exciting part is that understanding these fundamental forces at play in a tiny droplet can have huge implications across a wide range of fields.
Speaker 2:Okay. Let's unpack that. Yeah. So the paper itself specifically mentions inkjet printing.
Speaker 1:Okay.
Speaker 2:I can see how knowing the precise force of a droplet impact would be crucial for getting those tiny dots of ink exactly where they need to be.
Speaker 1:Absolutely. Absolutely. Ink chip printing is all about precision.
Speaker 2:Yeah. You
Speaker 1:know? Yeah. Depositing incredibly precise amounts of ink onto paper.
Speaker 2:Right.
Speaker 1:This research could lead to optimizing print quality, ink usage, and even printing speed. Yeah. Imagine crisper images, less wasted ink, and faster printers
Speaker 2:Right.
Speaker 1:All thanks to a deeper understanding of drop impact.
Speaker 2:That would be a game changer for anyone who prints regularly. Yeah. And it's a great example of how, how, you know, seemingly esoteric research
Speaker 1:Right.
Speaker 2:Can have very practical applications. What other applications did they highlight?
Speaker 1:They also discussed agricultural sprays.
Speaker 2:Think about pesticides or fertilizers being applied to crops.
Speaker 1:Okay.
Speaker 2:The size and force of those droplets along with the viscosity of the liquid can significantly impact how effectively they coat the plants.
Speaker 1:So this research could lead to more efficient and targeted spraying techniques.
Speaker 2:Exactly.
Speaker 1:Which would be a huge win for sustainability in agriculture. Yeah. Minimizing waste and environmental impact is something we all care about these days.
Speaker 2:Absolutely. It's
Speaker 1:fascinating to think that something as seemingly simple as drop impact plays a role in that.
Speaker 2:It really highlights how fundamental physics principles underpin so much of our world Yeah. Even in areas we might not expect. And it's not just printing in agriculture.
Speaker 1:Right.
Speaker 2:The paper even touched on applications and understanding respiratory disease transmission.
Speaker 1:Now that's an area where even small improvements can have a big impact. Absolutely. Especially given everything we've learned in recent years about how these diseases spread. Yeah. How does drop impact factor into that?
Speaker 2:Well, when we cough or sneeze
Speaker 1:Yeah.
Speaker 2:We expel tiny droplets of saliva, and some of those droplets can carry pathogens. Right. Understanding how these droplets impact surfaces, how far they travel Mhmm. And how long they remain viable can help us develop more effective strategies for preventing disease transmission.
Speaker 1:So things like mask design, ventilation systems Yeah. Even social distancing guidelines
Speaker 2:Yeah. Things like that.
Speaker 1:Could potentially be informed by this type of research.
Speaker 2:Potentially. Yeah.
Speaker 1:It's incredible to think that something as seemingly mundane as a cough or a sneeze could hold such valuable information.
Speaker 2:Absolutely. It's all about understanding the mechanisms of droplet transport and impact. Wow. And last but not least, the paper mentioned industrial cooling.
Speaker 1:Industrial cooling.
Speaker 2:Industrial cooling.
Speaker 1:It's not one I would have guessed. Yeah. How do drops come into play there?
Speaker 2:It turns out that controlled droplet impact can be a very efficient way to transfer heat.
Speaker 1:Okay.
Speaker 2:Think about using sprays to cool down hot machinery or electronic components.
Speaker 1:Okay.
Speaker 2:This research can provide valuable insights into optimizing those cooling processes, making them more effective and energy efficient.
Speaker 1:So we've gone from everyday examples like, printers and raindrops
Speaker 2:Right.
Speaker 1:To these incredibly important fields like disease prevention and industrial processes.
Speaker 2:Absolutely.
Speaker 1:It seems like drop impact really is everywhere.
Speaker 2:It is. It really is.
Speaker 1:It's amazing how something so seemingly simple can have such widespread consequences.
Speaker 2:That's a perfect example of how even the most mundane phenomena can be a gateway to fascinating science with real world applications. And that's what makes this research so exciting. It's taking something we all see every day Yeah. And revealing its hidden depths and potential.
Speaker 1:It's a great reminder that there's always more to learn even in the most familiar things.
Speaker 2:Right.
Speaker 1:And I love how this, you know, deep dive approach
Speaker 2:Yeah.
Speaker 1:Lets us explore those hidden depths without getting bogged down in all the, you know Right. Technical details.
Speaker 2:Absolutely. We're highlighting those moments. You know? Right. Those surprising insights that make you appreciate the beauty and wonder of the science Yeah.
Speaker 2:Without overwhelming you with jargon.
Speaker 1:So if you had to sum it up Okay. What would you say is the key takeaway from this research? Sure. What's the big picture message for our listeners?
Speaker 2:I think the key takeaway is that drop impact is far more intricate and fascinating than we might assume. It's not just a single splat.
Speaker 1:Right.
Speaker 2:There's a whole symphony of forces at play, multiple peaks, complex internal flows Yeah. And those mesmerizing phenomena like the Worthington jet
Speaker 1:Right.
Speaker 2:All influenced by factors like viscosity and impact speed.
Speaker 1:And as we've seen, this deeper understanding has the potential to revolutionize a wide range of fields.
Speaker 2:It really does.
Speaker 1:Who'd have thought that studying something as simple as a drop hitting a surface Mhmm. Could unlock such groundbreaking applications? Right. It really is a testament to the power of scientific curiosity.
Speaker 2:Absolutely. Sometimes the most unexpected discoveries come from simply asking, what's really going on here? Yeah. And then diving deep into the science no matter how seemingly mundane the phenomenon might appear.
Speaker 1:Speaking of diving deeper, I'm curious about something. This research focused on rigid surfaces.
Speaker 2:Right.
Speaker 1:But what about surfaces that aren't rigid? Yeah. Like skin or fabric?
Speaker 2:Okay.
Speaker 1:What would happen if a drop hit something soft or elastic? How would the forces change?
Speaker 2:That's a fantastic question, and it's one of the avenues for future research that the paper highlights. How would the forces change on a surface that deforms on impact? Right. How would the drops spread, retraction, and bouncing be affected? It's a whole new layer of complexity to explore.
Speaker 1:And while we're on the topic of future research, there's one more thing I'm wondering about.
Speaker 2:Okay.
Speaker 1:We've been talking about Newtonian fluids like water and honey. Yeah. But what about non Newtonian fluids?
Speaker 2:Okay.
Speaker 1:Those strange liquids that don't follow the usual rules of viscosity Right. Like blood or ketchup.
Speaker 2:Now that opens up a whole new can of worms. How would the forces and dynamics change with a fluid whose viscosity can change depending on the forces applied to it? Right. Would we still see those two distinct force peaks? Would the Worthington jet behave the same way?
Speaker 1:Right. It's mind boggling to think about all the possibilities and unanswered questions. Yeah. It seems like the future of drop impact research is anything but dry.
Speaker 2:It really is. There's so much more to explore.
Speaker 1:It sounds like there's a whole universe of possibilities waiting to be explored.
Speaker 2:There really is. It's like this research has opened a door to a whole new realm of scientific inquiry.
Speaker 1:And the best part is that anyone can walk through that door. If you're as intrigued by this as we are Yeah. We highly encourage you to check out the full research paper by Sanjay and their team.
Speaker 2:Yes. Definitely.
Speaker 1:We'll include a link in the show notes. It's packed with fascinating details. And for those who love the nitty gritty
Speaker 2:Yeah.
Speaker 1:There are equations galore.
Speaker 2:And don't forget the visuals. The paper includes some incredible images and figures that really bring these concepts to life. If you're a visual learner, I highly recommend checking them out.
Speaker 1:Even if you just stick with the audio Yeah. I think you'll agree that this deep dive has given us a newfound appreciation for the hidden complexity of something as seemingly simple as a drop hitting a surface.
Speaker 2:It's a reminder that science is everywhere even in the most everyday occurrences. Occurrences. And sometimes, those everyday occurrences can lead to groundbreaking discoveries with far reaching implications.
Speaker 1:So the next time you see a raindrop splashing on your window or your printer spitting out a tiny dot of ink Yeah. Take a moment to appreciate the intricate dance of forces at play.
Speaker 2:And who knows? Maybe this deep dive has sparked an idea or a question in your own mind. Maybe you're wondering about the impact forces of a different type of fluid or how these principles might apply to a specific real world problem.
Speaker 1:That's the beauty of science. It's a never ending journey of discovery. So keep those questions coming, keep exploring, and keep diving deep into the world around you. Until next time, stay curious. Sounds like there's a whole universe of possibilities waiting to be explored.
Speaker 2:There really is. It's like this research has opened a door to a whole new realm of scientific inquiry.
Speaker 1:And the best part is that anyone can walk through that door. You know, if you're as intrigued by this as we are Yeah. We highly encourage you to check out the full research paper by Sanjay and their team. We'll include a link in the show notes. Great.
Speaker 1:It's packed with fascinating details.
Speaker 2:Uh-huh.
Speaker 1:And for those who love the, you know, the nitty gritty
Speaker 2:Right.
Speaker 1:There are equations galore.
Speaker 2:Oh, yeah. And don't forget the visuals. The paper includes some incredible images and figures that really bring these concepts to life. If you're a visual learner, I highly recommend checking them out.
Speaker 1:Yeah. Even if you just stick with the audio Yeah. I think you'll agree that this deep dive has given us a newfound appreciation for the hidden complexity of something as seemingly simple as a drop hitting a surface.
Speaker 2:It really is a reminder that science is everywhere, even in the most everyday occurrences. And sometimes those everyday occurrences can lead to groundbreaking discoveries with far reaching implications. So the
Speaker 1:next time you see a raindrops flashing on your window or your printer spitting out a tiny dot of ink, take a moment to appreciate the intricate dance of forces at play. You know, it's more than meets the eye.
Speaker 2:And who knows? Maybe this deep dive has sparked an idea or a question in your own mind. Maybe you're wondering about the impact forces of a different type of fluid or how these principles might apply to a specific real world problem.
Speaker 1:That's the beauty of science. It's a never ending journey of discovery. So keep those questions coming, keep exploring, and keep diving deep into the world around you. Until next time, stay curious.
