Foamy frothy fun

Most of my days end with a long soak in a deliciously hot bubble bath. I don't need fancy scents, instead I enjoy the heat of the water and playful texture of the bubbles. Bubbles rise up as a mound ringing the stream of water from the faucet. Further away, bubbles slide into irregular shapes reminiscent of fictitious moon bases and futuristic homes. If it's really quiet, the muffled pops as multiple bubbles end their existence is audible. In addition to a relaxing end to a day, my bubble bath is an example of a foam.

Foams form when billions of tiny bubbles are packed together within a solid or a liquid. Irregular sized bubbles are common in all foams except the most idealized ones. Like what happens for individual bubbles (check out my bubble post), it's surface tension that helps keep a foam stable. Liquid foams break down eventually – there are even chemicals on the market to make this process go faster. Gas can diffuse from small bubbles into large ones and eventually out of the foam, or gravity can drain liquid out the bottom making bubbles so weak they pop on top.

A Belgian physicist, Joseph Plateau (1801-1883), figured out the basis of what we know about soap films and foams. His diverse interests also included spending time with moving image illusions like the action one sees when using a "flip-book". Back to soap film, Plateau came up with a series of laws to describe stable foam structures (foams that don't follow these laws tend to rearrange themselves until they do). They are:
1.Soap film surfaces are smooth.
2.The soap film curvature is continuous and constant along the entire a surface.
3.When three or more bubbles connect together, they will shift around until each line only contains three bubble-wall intersections – called a Plateau Border. With matching surface tensions all three angles are 120 degrees, the most efficient option.
4.Only four Plateau Borders can meet at a point.

Foams form in nature. Examples include: sea and river foams, and the foaming at the mouth of a rabid dog. There are fish, such as gourami and Siamese fighting fish, that blow a mass of bubbles coated in saliva to house their eggs. In the same spirit, some species of frogs make foam nests to lay their eggs in. These nests may be constructed in crevices, on the surface of water, or on forest floors.

Beyond bubble baths, soaps can be whipped to form a lather with bubbles so small they hardly can be seen. This idea was extended into modern shaving foams where a compressed gas is rapidly decompressed to expand a cream into a foam. Foams can also be hardened into permanent structures like insulation and flotation devices. Ceramic can be made into foams useful for acoustic insulation, absorption of environmental pollutants, and the filtration of molten metal alloys among other applications. Cement foams are used as a light-weight building material with good insulating capability. Even metals can be manipulated into becoming a foam. Metal foams are used in exhaust mufflers as they a great at dampening noise. They also make efficient materials for heaters and heat exchangers since they have so much surface area.

We eat a lot of foams: they can add a light texture to an angel food cake, or be tasty in the form of whipped cream and meringues. Breads are often a foam as the yeast produces tiny bubbles of gas which causes the dough to rise. One of the best foams is the head that forms when a beer is poured into a glass; this foam is made by which is made by carbon dioxide bubble rising to the surface. For the best head on your glass of beer, chose a wheat beer instead of a barley beer.

Note: there is an optimum foam combination of wheat beer consumed in a bubble bath – use with caution.

Tiny bubbles

Anyone remember the show “That's Incredible!”? It was on in the early 80's. I watched it as a kid (and yes I'm dating myself as the show went off the air in 1984). One episode I remember vividly: The hosts hyped how this man could make a square bubble, which I suppose what hosts are supposed to do. Since all the bubbles I had ever seen were round, I was really curious how a square bubble could be made (and I wasn't yet jaded about TV). I was expecting the square bubble to be free-floating by itself, so I was kinda disappointed in how it was done. The “performance artist” blew a bunch of connected bubbles (I forget how many). Next he took a long inhale from a cigarette, then stuck a straw between the connected bubbles and filled the space with the smoke. The filled space was in the form of a cube, and I felt tricked.

A short lived creation, soap bubbles hold a sphere of air with a thin film of soapy water which is formed by surface tension. Spherical shapes are preferred (really large bubbles can end up forming elongated shapes from air currents) because a sphere is the smallest surface area possible to contain a specific volume of air. The soap film surface tension is strong and flexible enough that waves can travel along the surface and is so thin the surface appears iridescent.

Surprisingly, soapy water has less surface tension that water alone and is needed to keep the bubble stable. As a bubble is formed, the soap film stretches decreasing the concentration of soap which increases the surface tension. This mechanism is called the 'Marangoni Effect' and occurs when a surface tension gradient (that is regions of greater and lesser surface tension) causes liquid to move away from areas of low surface tension. The soap acts as a stabilizer by letting the thinnest parts of the film to have the strongest surface tension thus keeping the bubble together.

What happens when two bubbles stick together? Well, they will arrange themselves in such a way that minimizes the surface area. Bubbles of different sizes will end up with a bulging internal wall into the larger on as smaller bubbles have higher internal pressure. If they are the same size, the internal wall will be flat - a phenomenon exploited by the cube-making bubble performer.

So sneaky internal bubble-wall cubes aren't so impressive. How about antibubbles ….

Talking to politicians

I was volunteered to present a simplified version of my research to a group of visiting politicians yesterday. I was given exactly 3.5 minutes to present starting at 3:13 pm, I guess politicians live in a precise world (as we all expected they showed up somewhat late). So here is what I said:

The focus on my research in on how the tides interact with Fraser Ridge (a sub-surface bump in the Strait of Georgia). One really interesting effect is the formation of lee waves on the flood tide. Ocean waters tend to be stratified, which means the water is organized so the denser water sits lower than the less dense water. As tides move this water over an obstacle like Fraser Ridge, water is forced to speed up because of the constricted space and it gains momentum. On the lee side of the obstacle the momentum can carry less dense water down deep. Eventually, friction causes the water to slow and the less dense water bounces back up in a formation called a lee wave. Effects like these lee waves can provide an explanation why some coastal sites form productive ecosystems.

What is interesting about Fraser Ridge is that a rare glass sponge reef has made its home there. Glass sponge reefs were once common in the world's oceans at the same time that dinosaurs roamed the earth. Like the dinosaurs, we thought glass sponge reefs were extinct. In the 1990s, living glass sponge reefs were discovered in a few locations off the coast of BC and it turns out they make great habitat for young rock fish. Glass sponges are filter feeders fixed to the bottom so they need enough flow to bring in their food, remove their waste and keep them from being buried in sediment. Periodic formation of lee waves can provide the flow they need.

At my study site, a lee wave forms on each flood tide. The sponges have chosen to live on the steepest slope which corresponds to the strongest currents, turbulence and sharpest lee wave.

Working comfortably in remote places

I've been reading 'Packing for Mars' and enjoying it greatly. The author describes the ups and downs of working in space. I've never worked in space, but I certainly can relate to some of the difficulties of working in remote, confined and difficult places. Add on top of that sleep deprivation, situations can become really dangerous and/or hilarious (for some reason sleep deprivation can leave me giggly).

When I first started doing field work in the army I made the mistake of thinking that if I only had a short time to sleep, I should just lay down with my boots on and attempt to sleep anywhere – like on a pile of rocks (looked comfortable in the dark) or the main thoroughfare for an army of ants. It didn't take me long to realize taking the time to blow up an air mattress, pull out a sleeping bag, and take my boots off would make me so much more comfortable.

I've spent months working out of tents, which can be comfortable especially if I've brought a cot. I've even packed a pillow when heading out to these places. A large tented camp can be just like a small town – hot food and showers are often available. If the ground isn't frozen, mud always makes an appearance (I've never lived in a tented camp in the desert but I suspect the issue then would be sand). Everything can end up covered in mud and without running water it is hard to clean up. I've had mud fill all the treads on my boots to the point where I just slip slide around.

Working on small boats exposes one to the weather, which is okay with the proper clothing and a warm place to spend the night (or day if working on the boat at night). Open boats aren't my favorite; on a nasty day it is nice to get inside if only for a few moments.

By far, my favorite field work space are full sized ships – I like knowing there is a comfortable place to sleep nearby especially if my shift is long. Hot showers (even if they are short), clean clothes and hot food prepared by someone else are other pluses. There are always people around on a ship which I find to be a comfort if we are out in the middle of the ocean or up in the arctic. The downside to working on a ship is my tendency towards sea sickness which can be dealt with.

Where ever I go, being comfortable appears to be a choice. It's never that much harder to make oneself more comfortable – start with taking the boots off.

Water drops on kale

I was out in my garden this morning in the few moments of sun before more rain and I noticed beads of rain water had formed on the kale leaves. See how the veins on the leaf are moved when looked at through the water? See the sky reflection? If I had leaned close enough, my reflection would probably be visible too.