Art meets science filter: Do you recognize this phenomenon?

February 20, 2022 2:02 PM

I have an art/design project in which I combine sediments and liquids in jars, in order to explore and visualize natural phenomena. There's a recurring phenomenon that I find captivating, and it surely happens out in the world. But where, and how?

Droplets like the ones here often show up in my art works. When I put certain sediments into a jar that contains a variety of liquids, they fall down from the surface and through the layers. As they do, they pull air and less dense liquids down into denser liquids. The resulting composites sometimes find temporary stasis based on the relative density/mass of the cluster as a whole. Some droplets last in suspension for mere seconds, until the components separate and rise/fall accordingly. Other droplets find an equilibrium and remain suspended longer, sometimes for several days.

What happens in the jar certainly happens outside the jar too. (This is, in fact, my overall interest - to catch an imaginative glimpse of atmospheric, geological, hydrological etc. phenomena that are typically too small or large for humans to easily see). Do you know of examples of this kind of aggregate rising/falling/suspension phenomenon in the natural world?

posted by marlys to Science & Nature (16 answers total)

I think this is the same phenomena: Sometimes I make hot chocolate by first putting hot water in a mug, then adding spoons of hot chocolate mix. The hot cocoa mix sometimes doesn't want to get 'wet', and it just sits on the surface of the water. Sometimes even forming its own pockets of dry mix with water all around. Stirring gently doesn't help - only vigorous stirring will make the cocoa pockets small enough that they can get saturated.
posted by hydra77 at 2:28 PM on February 20, 2022 [2 favorites]

Best answer: Carrying bubbles of air down is really interesting! It could make a lot of difference in swamp microbiology, for instance. Maybe flocculation covers it? Maybe this is something septic engineers know about?
posted by clew at 3:06 PM on February 20, 2022

I’ve heard of this in the context of the dancing raisins science experiment for kids.
posted by mekily at 3:13 PM on February 20, 2022 [2 favorites]

Dry pasta in carbonated water, as the carbonation decreases, will often hang in the middle with neutral buoyancy.

I'm reminded of Millikan's oil drop experiment, though that's electrostatic force rather than buoyancy.
posted by away for regrooving at 3:14 PM on February 20, 2022

Raisin/pasta jinx.
posted by away for regrooving at 3:14 PM on February 20, 2022

I think it's the varying density of the liquid influencing the surface tension of air trapped inside the particles. The escaping air forced out by a bit of incoming water (I assume) gets trapped around the particle depending on the density of the solution at different heights. As it fully settles you'll get the floaters and the sinkers and the surface tension that keeps the bubble around the particle will slowly go away. And it's just some bits from the top are heavy enough to sink some and maybe hang out for a while and some of the lighter bits that got caught at the bottom do the same but going up instead of down. So density gradient influencing surface tension.

Or something like that...
posted by zengargoyle at 5:01 PM on February 20, 2022

Response by poster: These are interesting, thanks! Flocculation and dancing raisins are particularly similar to this phenomenon, in that the physical combining of different materials is what creates movement or suspension.

I’m struck that these are both human-made scenarios (as are, obviously, my jars). If anyone has more thoughts re: manifestations in natural phenomena, especially atmospheric, I’d be particularly excited to hear about those. (Swamp microbiology is an interesting lead that I nothing about - time to read a bit more about swamp gases…)
posted by marlys at 7:52 PM on February 20, 2022

Best answer: Rising/falling/suspension sounds similar to how hail forms. (We were previously told that a hailstone went through several cycles of rising and falling, but Wiki is telling me that the latest understanding is that it initially grows in an updraft and then, when it gets heavy enough, starts falling while continuing to grow. I guess it's not likely to go through several cycles of that.)
posted by polecat at 9:38 PM on February 20, 2022 [1 favorite]

Response by poster: dancing leaves, sure, I’m happy to share more. In the first three images, the droplets are primarily colored sand, pulverized biochar, very tiny glass beads, and mineral oil, each with its bit of air at the top, suspended in a sugar syrup (there’s other stuff in the jar at present, but this mostly accounts for what you see in the droplets). The video is a couple years old so I don’t remember all the details - I do remember that syrup, oil, and sand were involved (and I believe a layer of vinegar had diluted the syrup some). Image/film-wise, it’s low tech - iPhone camera, tripod, macro lens for individual droplets. As for technique, my original ask more or less describes it - I drop materials in and their interactions do the rest. My interest is in what the materials themselves do together. When I train my lens into a jar, it all feels very much like an emergent world with its own phenomena, a tiny, strange corollary of the world in which we live. Hence this question - I often find myself wondering about correlations between the little worlds and our big one.
posted by marlys at 10:38 AM on February 21, 2022

Heh, totally thought this was just water with stuff settling out. The whole oil, sugar, vinegar puts a different spin on things.

Exploring the Density of Liquids with Salt - Buggy and Buddy
posted by zengargoyle at 1:52 PM on February 21, 2022

Lava Lamp Experiment (Chemistry) - YouTube. Guess that's more fluid dynamics. Not sure if there's an easy atmospheric thing. Your thing could also be the acidic vinegar reacting with something basic (think baking soda like) and producing CO2.
posted by zengargoyle at 2:09 PM on February 21, 2022

I think that the study of just WHY you can get these clumps of granular material together with captured air is related to "wettability". E.g., the abstract of this paper:

The efficient dispersion of powders in liquids is required in many fields. However, there are only a few studies on the physicochemical properties of the powders and the dispersion rate. The process of dispersing an agglomerated powder is mainly controlled by the forces acting between the primary particles, and between particles and liquid. In this paper, we present an experimental study of the dispersion kinetics of a hydrophobic powder (cocoa) in water. We firstly determined the surface free energy of the powder using several methods (static wettability, dynamic wettability). Interpretation of calculated values of spreading coefficients and interaction parameters revealed no energetically favoured cocoa–water interactions. A series of dispersion experiments were conducted in a stirred vessel to investigate the influence of stirring speed, temperature and concentration of powder in water. The dispersion concentration was measured using an optical scattering method, which was shown to give good information for evaluating the dispersion process. The experimental data fit an exponential mathematical model with two parameters (A, α): X(t) = A[1 – exp(–αt)]. It was found that the rate of dispersion depends on the agitation speed with a critical speed 630 rpm. All results are discussed as a function of the agitation speed and temperature.

posted by the antecedent of that pronoun at 5:25 PM on February 21, 2022

Best answer: Not the same substances as involved in your process, but featuring similar dynamics: salt fingers
posted by flabdablet at 10:26 PM on February 21, 2022

Response by poster: Thanks, all! You’ve offered some great suggestions here that I’ll explore further…
posted by marlys at 7:09 PM on February 22, 2022

Best answer: I'm in geology, and while there's certainly differences, rocks are aaallll about stuff mixing into different stuff with um....stuff happening.

So in a practical sense, I have the issue of wettability and agglomeration happen (I literally describe it as "the thing that happens with hot cocoa) when mixing fine powder samples into epoxy. They will also slowly separate by density as the heavier pieces sink through the epoxy faster - buuuut this effect gets whackadoo'd when the material is so fine that the cocoa thing happens since the particles are attracted to each other more than the wet epoxy.

In nature, you have this thing called "framboidal pyrite" - it's super pretty in microscope! Instead of forming normal crystals, they form little balls (a la raspberry - framboise!) of teeny tiny guys. When you grind up a rock with those in there, they'll actually float on top!

But on a GRAND scale, look at the whole field of petrology and igneous rock formation - different minerals form at different times (which then means the chemical constituents in the fluid magma changes, which means different minerals form) - this is called Bowen's reaction series at a basic level, but the "paragenesis" of a rock is looking at exactly how and which minerals formed in what sequence, by looking at how they grew into each other - i.e. was was fluid when this solidified, what came after, what changed when a mountain grew on top, then a fracture brought more water in...etc.etc.etc. The things you have in your material look a lot like "fluid inclusions" - little tiny, tiny space capsules of fluid in a rock that tell us an awful lot of what happened when it formed.

Petrology is a huge field! Also very fun!
posted by aggyface at 1:06 PM on February 25, 2022

Maybe this: How to Clean Sewage with Gravity - YouTube.
posted by zengargoyle at 12:49 PM on March 1, 2022