Basic science in evaporating droplets

Apr 18, 2013

What happens if you slowly evaporate a droplet containing dissolved particles? The question sounds simple, but it involves a surprising amount of basic physics and mathematics. Hanneke Gelderblom of the University of Twente devoted a full four years of research to this problem, looking into a variety of aspects including the physics behind coffee stains. "I found this study to be particularly interesting because of the combination of theory and experimentation." Gelderblom will defend her doctoral dissertation on 19 April.

Coffee drinkers know the problem all too well: drops of spilled coffee leave a dark ring on the outside, while the inside of the stain dries up much lighter. PhD candidate Hanneke Gelderblom says that ever since a researcher at the University of Chicago published on the coffee stain problem in 1997, there has been mounting interest in this topic in academic circles. She explains the reason for this interest: "Many can benefit from the coffee stain effect. In addition, there are many fields where these kinds of stains must be avoided, for example in printing or in the coatings industry. In both cases you need to know exactly how the stains are formed."


The system Gelderblom researched is in fact very simple: a drop of water containing micrometre () on a surface. Gelderblom looked at what happens when the droplet slowly evaporates.

"A simple basis like this is ideal for experimentation, because everything can be modelled reasonably well. There were many unknowns. Basic research is like a journey of understanding where you really get down to the fundamentals. I enjoy that, and theory and experimentation went hand in hand in this research."


Gelderblom and her fellow researchers discovered quite a bit in the past few years. "For example, I was surprised to find that the rings that remain after feature neatly arranged particles around the edges, while there is significantly less order in the middle." Gelderblom found a conclusive explanation for this phenomenon in the interplay of three factors: droplet evaporation, fluid flow and particle transport.

In another experiment Gelderblom and her colleagues evaporated the particle-infused droplets on a super-hydrophobic surface (a material that is extremely water-repellent). After the droplets had evaporated, the particles were neatly arranged in a ball shape. "This arrangement of the particles approached that of a dense sphere, which is theoretically the most ideal arrangement for particulate matter."

Another breakthrough stemming from this research is the accurate mathematical model that Gelderblom was able to construct to express flow in the edge of the droplet. The model shows that flow is dependent on the angle of the droplet with the surface.

Explore further: The hemihelix: Scientists discover a new shape using rubber bands (w/ video)

More information: Hanneke Gelderblom conducted her PhD research at the Department of Physics of Fluids. This research group is part of the University of Twente's MESA+ Institute for Nanotechnology. Gelderblom was supervised by Detlef Lohse and Jacco Snoeijer. She will defend her dissertation in the Waaier Building on the University of Twente campus on 19 April at 16:45.

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User comments : 8

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1 / 5 (1) Apr 19, 2013
Just another useless research of trivial phenomena... Apparently we have not enough much more important problems of solve in the time of energetic crisis. At the moment when many people are dying of starvation, some others are studying drying of droplets. Isn't it decadent or even amoral approach?
5 / 5 (1) Apr 19, 2013
Just another useless research of trivial phenomena...

I think you don't appreciate how complex the 'seemingly trivial' can be.
Certainly not in the light of how you pass off naively trivial explanations in your posts as a solution to complex phenomena.

Do some (any) work with math and physics and you'll VERY quickly discover that the naive approach is just that - naive.
1 / 5 (1) Apr 19, 2013
I'm not doubting the complexity and difficulty of this scientific work but its priority. Actually I'm worrying of such large intellectual effort wasted into description of essentially useless phenomena. Why these guys don't try to model the EM-drive or something more useful, for example? We should value such research like the art, which isn't financed until sufficient number of people isn't willing to buy/invest into it (i.e. like the crowdfunding applied for cold fusion research with more responsible people). Why the hell the extremely important research is crowdfunded, whereas the useless nonsenses are payed from mandatory fees of tax payers? This is just one of examples, how/why the modern science is rooting being corrupted with its own support.
not rated yet Apr 20, 2013
c work but its priority.

The more fundamental the greater the value in science.
If you think building gadgets/machines/drives is of more priority then you're missing the point of science. By a LOT. .
1 / 5 (1) Apr 20, 2013
The more fundamental the greater the value in science.
The science is payed with people and these people may have different ideas about priorities in human civilization. The scientific community is just social artifact embedded into it - and "its priorities" (actually the priorities of scientists involved) may differ significantly. The priority of scientists is the continuation of research by itself - even at the moment, when there is nothing useful to find already. These guys are looking for their neverending jobs - not for benefits of human society, which is paying this research and whole their existence. At the moment, when they could research some concept which would allow them to produce more publications, they will always study it first. BTW I'm trying to develop very fundamental perspective of observable reality and I don't think, I'm facing huge interest of science in this matter.
1 / 5 (1) Apr 20, 2013
If we will not put the priorities of human society before the priorities of science, it could become possible quite easily, we will research only weapons and useless if not dangerous stuffs, whereas we will die out because of energetic/environmental crisis, or rather from nuclear wars for the rest of resources. Whereas we will have the libraries full of complex, but essentially useless results of "basic research". Our survival is the highest priority at this piece of Universe, not the survival of science.

For me such an understanding is so natural, that I cannot really understand the thinking of my opponents here, until they're not directly engaged into scientific research. The research itself isn't the highest priority for human society - the useful research is. Just after we cover our basic needs as a civilization, we can invest into careless basic research needs of close group of scientists embedded into it.
1 / 5 (1) Apr 20, 2013
BTW I'm perfectly aware of the importance of basic research as a causal background for applied research. We really cannot have the successful applied research without sufficiently extensive basis of basic research. But - what the "sufficiently extensive basis" of basic research is? Could we ignore the applied research on behalf of basic research?
IMO it's similar decision like the most effective building of pyramid: if you invest too many resources into construction of grounds, you'll have no money for building of higher levels of it. And vice-versa: without robust foundations we cannot raise the higher floors of this building.
IMO the scientists have absolutely no idea, how to balance these two components of research "scientifically". They naturally tend to expand the safe and irresponsible basic research until the money are going. After years of ignorance of basic research applications they're getting very surprised, that the human society has no money for their games anymore.
1 / 5 (1) Apr 20, 2013
The usual objection of scientists in this connection is "but, but.. the national security and defense consumes way more money, than the scientific research as a whole". Such an objection is completely off topic, because i do consider wars as the natural consequence of imbalance between dynamics of growth between different countries. Just the scientists should motivate the countries into exploitation of human thinking instead of blind looting resources, because if we would remain dependent on resources, we will always fight for their access. The best way, how to remove the need of wars and mutual arms race is simply the remove the reasons of war: when the attacker will get no apparent profit from the attack of foreign country, then he will not spend the money into armament naturally. Why we still have no science about effective and peaceful design of human society itself? We are like the blind ants, who have absolutely no control about the future of their own colony.

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