Inspired by Helen Czerski’s post about bubbles in paper straws, we decided to try some experiments to see if paper straws are the only ones to create bubble rings. We recorded all the videos here using super slow-mo mode on a Galaxy S8 plus. The frame rate (480fps) and picture quality is good but the autofocus had an itchy trigger finger and delighted in switching to focus on something a few inches away just as we started filming. Just because I’m filming glass and water under fluorescent light doesn’t mean I need a back seat video taker. More override controls please!
Iteration one: Paper straws with fizzy water
This worked pretty well, and we were quickly able to reproduce Helen’s results. Go reproducible science! We played around with different ways of filming and got some nice videos.
Iteration two: The peristaltic pump
This is the point where @edrosten suggested it would be ‘really easy’ to do this using a peristaltic pump. And I was like:
Usually when either of us say something will be really easy, it usually means a 3-5 year research program. Anyway, we got the pump down from the attic and worked out that electrical tape was airtight enough to seal a straw to the tubing.
The peristaltic pump was very cute and could pump water fine, but rarely produced bubble rings except very occasionally at the beginning (results not shown). A constant flow of water did not produce bubble rings, just a little stream of bubbles. Maybe we just needed a bigger pump.
Iteration three: Just add everything except water
To see if viscosity might have any effect, we created a sugar syrup to increase the viscosity. To hydrolyse the sugar and ensure that the syrup would be miscible in water, we added citric acid.
Concentration was lost for a while as I was trying to use an inverted camera tripod to film the process from under the glass. The syrup ended up caramelising a bit. Mixed with sparkling water, it produced a taste I would definitely quaff while eating a burger and fries.
It also produced very nice bubble rings. Difficult to say if the viscosity had any effect. More experiments are needed.
The next obvious step after sugar was to really crank up the viscosity, so we decided to try adding xanthan gum. This is a standard storecupboard ingredient with anyone obsessed with changing the texture of food. We had two packs. Mixed with water, it produces something that basically looked like snot.
The bubbles slowed down beautifully in this mix. We didn’t capture any good rings, but we had a lot of fun. This is definitely the part of the experiment I would do more of if I had time.
Iteration four: Paper and plastic, with a cleaner container
It occurred to us that ten year old glasses might possibly not be the smoothest surface. This turned out to very definitely be the case, as we discovered when we got a new jar and tried the experiment in that. Lower background! Easier to detect the signal! Hurrah!
We also decided to purchase some plastic straws. These seem to have almost disappeared (which is a good thing). After some hunting we were able to get some reusable plastic straws.
The first thing that we noticed was that the bubble profile was very different on the plastic and paper straws. Like, really different. The paper straw has lots of little bubbles and the plastic straw had (to my eye) a bigger range of sizes and, on average, larger bubbles. Could this be due to different numbers of nucleation points? Or are the bubbles more motile on the surface of the plastic and so aggregate? I have no idea. I know nothing about bubbles except that I have consumed far too many of them during these experiments. Seriously, I had no idea what drinking this amount of gassy water does to a person.
First we tried to get bubble rings with the plastic straws. This was definitely much, much harder than with the paper straws. We only saw a ring once:
And that was out of a lot of tries. More often it looked like this:
As you can see, there is one absolutely honking bubble that comes out at the end like Jabba the Hutt. That happened a lot with the plastic straws, and it’s one of the things that made us think maybe the bubbles were more motile on plastic and could be joining forces.
Iteration five: MOAR NUCLEATIONS
So anyway, then we started thinking about the issue of nucleation points. Could we add nucleation points to plastic straws by roughening the surface? I grabbed some sandpaper.
As you can see, the bubble profile changed a bit if we compare paper, plastic, and sandpapered plastic. The sandpapered plastic has more bubbles and the paper has more small bubbles, something that was particularly noticeable when the straws were initially inserted into the water.
And the sandpapered plastic produced bubble rings pretty reliably!
Plastic straws rarely produce bubble rings, but can be induced to produce them by roughening the surface. I met a friend this afternoon and we were discussing teflon coated tubing that minimises bubbles. Suddenly, bubbles are everywhere!
I’m sure that the differences are fundamentally down to the material properties, and that makes me both happy and nostalgic for the good old days when I used to do materials science.
For me it’s time to go back to microscopy, but I hope you enjoyed our bubble journey. I had a lot of fun, and it was nice to actually do some experiments at home. And if I ever end up in a bubble-off with an Instagram celebrity or Bond supervillain, I now know which straw to choose.