When we started up this blog I had hoped to post a bit more educational content on the workings of the sensors we develop and the research that we do. Sadly, however, I have been nowhere near a lab in what feels like months. Partly this is because I have Read more…
Open science and science communication is something I have come to slowly, over my career. I’ve always been passionate about science and many a trip to the pub results in my friends rolling their eyes when I begin to wax lyrical on some topical point. Over the last few years Read more…
As part of our subsurface oil spill project I have been working on the development of simulation rig to demonstrate the sensor in schools. At the moment the sensor is already stable is water and response well to localised oil in water so the kit is mostly about showing that Read more…
My project over the last 3 years could be summed up as “getting stuff to stick to fibre optic sensors”. The sensors were kindly prepared by various other members of the group (best ones were by Rebecca) and I was then responsible for finding the right material to coat on to the fibre to make it sensitive to X. Exciting stuff, I know. Most of my coating work was done using a technique called Langmuir Blodgett, the first stage of which is preparing monolayers of material spread on a large trough of water. These monolayers are explained in slightly more detail in my previous post about our Lego Brewster Angle microscope. Now, for reasons I can’t quite remember, I looked at a monolayer one day and thought to myself “What if I add food dye?”. The video below shows the result.
This video was shot using a small USB camera overlooking the surface of the water. The food dye is a 1:100 dilution in some water and as shown, the drop was simply touched to the surface of the water which then caused the formation of the ring. If the drop fell naturally from the tip of the syringe, it will still created a ring but these have a much greater variation in shape (more information on that effect is detailed here). The rings in the video were created using a monolayer of stearic acid but further work showed that these rings form in clean water as well. Although, without a monolayer, they were slower and more prone to simply dissipating as a blob of colour. The video below shows the comparison of rings formed with and without a monolayer.
Update: Video now available for download at FigShare
Vortex ring formation, arrows show the direction of flow
Although this model only explains why they form in water and not why the existence of a monolayer material accelerates them so significantly. This acceleration is explained by a more complex series of forces and is still not quite fully understood.
Now where this work gets even more interesting is that while making these rings, I found that if I used a multilayer (2-3 layers) insted of a monolayer, I occasionally got quite different rings that defy my knowledge of the vortex ring effect.
Update: Video now available for download at FigShare
The rings created here were made though a layer of calix[4]resorcinarene C11 but I have also made them using a stearic acid monolayer. For an as of yet unexplained reason these rings split into two (never more) at the point of formation. This split is not always equal and the later rings have only very small off shoots. They don’t always occur with a multilayer, a work experience student (Lucy Ackroyd) very kindly spent an entire morning making multi-layers trying to re-create these and managed to produce precisely zero (got loads of other good data though!). Honestly I can’t even being to wrap my head around what is causing these split vortex rings. I don’t know enough about fluid dynamics to tackle this problem. So this blog post is my way of reaching out to anyone who thinks they have a theory of what is causing this effect. Please post any suggestions either as to the cause of these split drops or for any further experiments that you think might help solve this problem. As it happens, it is relatively simple to make these rings yourself (described below) so I would be very interest to see if anyone can produce any other weird effects!
Steve, Fei and Thomas are attending the international conference on optical fibre sensors (OFS) this this week and are presenting a number of poster presentations of their work. If you are attending please go see them, they are only too happy to talk to people interested in the odd things Read more…
Brewster’s angle is the angle at which light of a certain polarisation won’t reflect off a surface. The resulting reflection will then be made up of only light from a single polarisation (p-polarised). This little optical quirk is how polarised lenses remove lots of scattered reflections in photographs and why Read more…