My first academic publication came out a few weeks ago. Since then I found out that it was promoted as a featured article by the journal that published it, and this prompted me to write something about it. Unfortunately, if you’re not at a university or a company with a scientific research arm, you’re not going to be able to access the paper as it’s behind a paywall. What’s more, it is entitled “Wavefront kinetics of plasma oxidation of polydimethylsiloxane: limits for sub-μm wrinkling”, and that should give you an idea of the type of language used. The requirement for both detail and brevity in research articles necessitates that every one-word technical term that could save ten words of explanation must be used wherever possible. Brevity is fine, but it means that only experts familiar with the field can really understand it. So it’s behind a paywall, and it’s behind a language wall. That’s why I’ve written this.
The article talks about what happens when you take an ordinary piece of silicone rubber (a.k.a. silicone, different from silicon) and put it in contact with a super-reactive version of oxygen known as oxygen plasma. Unlike normal oxygen, which is stable and does nothing interesting when put next to silicone, oxygen plasma reacts with the surface and turns it into glass (yep!).
The oxygen plasma only touches the surface, so only the part very close to the surface changes. The bulk of it stays the same. This happens to be a pretty useful effect for scientists who use this material. It turns out that the thin glassy layer that is created by the plasma oxidation of the surface is very reactive for the first few minutes after touching the plasma. The surface will chemically bond to other surfaces upon contact meaning that you wouldn’t need glue if you wanted to stick it to other surfaces (for example). Also, water can spread out on the surface of the silicone rubber more easily after plasma treatment (before plasma treatment water doesn’t spread out on the surface at all), meaning you can deposit thin layers of inks or other water soluble materials on top if you want to. Sometimes scientists want to do things like this.
All this has been known for a few decades but nobody has really understood all of the details of how it happens. People have tried however, and each attempt has unlocked a new piece of the puzzle. In the nineties, scientists noticed that the glassy surface layer thickens over time:
Other scientists realised that the idea of a definite interface between the glassy layer and the silicone was simplistic. They saw that there was a gradient in the ‘completeness’ of the reaction that converts silicone to glass at the interface, and this results in a more gradual change from glass to silicone as you go deeper below the surface:
Our work looked at the implications of these two observations when combined. We thought about what the interface between the glassy layer and the unreacted silicone could look like as it grew, then did several sets of measurements to help aid the discussion. We found that the position of the gradient shifts with time:
On its own this is quite a trivial finding, but what is important about is is the implication for what happens in the initial moments of the reaction. This is, that in the initial moments the top layer thickens and stiffens simultaneously, gradually changing from a soft silicone to a stiff glassy material. This contrasts with what people have previously assumed about this topic.
This new understanding goes some way to providing an explanation for past disagreements between different scientists’ data, and should help other scientists use this technique more reproducibly in the future.
Most of the times I’ve described this work to non-scientists, people are surprised at the level of detail with which we have been looking at a seemingly arbitrary question. Naturally, people ask why. That’s an important question to be able to answer, and two of the reasons are as follows.
The first is that it could have immediate practical benefits. Knowing how this process affects the surface of silicone rubber tells us new things we didn’t know about how we can expect silicone rubber to behave after plasma oxidation. As an example, there is currently emerging interest in the physical process of wrinkling, because it has been shown that microscopic wrinkles can be used to make materials behave in different, more useful ways. There are many methods for making wrinkles, but the cheapest involves plasma oxidation of silicone. Knowing about how the silicone/plasma reaction works actually helps us understand what the limitations of using this method are and helps us identify ways to circumvent those limitations. The bottom line is that in the future this may be able to lead to more widespread availability of more useful materials at lower costs.
The second reason for doing this work is that it might one day have some indirect practical benefit that we can’t predict just yet. When scientists and engineers try to solve problems, they often find they need to know the answer to scientific questions they didn’t predict they would need to know when they started. Fortunately for them, there’s a huge collection of searchable scientific literature they can call upon to find the answer to their question. My paper contributes to this collection, so it is possible that some time in the distant future some scientist will reach a bottleneck in his or her work that relies on the knowledge obtained through my investigation. It’s a long shot to assume this will happen, but it generally holds that the more fundamental and seemingly arbitrary scientific questions that have been publicly answered, the quicker future scientists and engineers can get on with their work.
There is a third reason too. That is: it’s fun to understand things.
But I’ll cover that one in another post someday.