What’s the best plasma to stir your morning coffee

PhD researcher Calum T. Ryan studied room temperature plasmas and showed that it could affect how you make your morning coffee.

The summer holidays are over, the kids are back to school, and everyone is heading back to the office. An integral part of the morning routine for most is coffee. So, what's the best plasma to stir your coffee? A peculiar question to ask, but for PhD researcher Calum T. Ryan - who happens to be a dedicated coffee drinker - it's a question worth answering. For his PhD research, Ryan explored the key physics of plasma-induced liquid flows, which could have implications for improving medicines and growing healthier crops, and yes - even for your morning coffee. He defended his PhD thesis on September 10^th.

If you add energy (in the form of heat for example) to matter it leads to a change of state. For instance, heating up a solid causes it to first melt into a liquid and then evaporate into a gas. Just think of the phases of water - ice blocks, liquid in a glass, and liquid turning to steam.

However, adding even more energy causes electrons to break free from their host atoms and then turn into a 'fluid' of charged particles. This is known as a plasma - the 4^th state of matter.

Plasmas can be found in lightning and in stars, but they also have industrial applications. You can meet plasmas in neon lights and fusion reactors. In addition, plasmas are used in microchip production, with ASML playing a leading role in harnessing the power of plasmas.

[Photo: iStockphoto]

Stirring towards chaos

In plasma-liquid interactions, the plasma creates a flow in the liquid, which stirs the RONS throughout the solution differently depending on the flow type.

If the flow is very turbulent, the RONS will mix more uniformly in the liquid. "But if the flow is focused to one point in the liquid, the RONS will collect at that point and they won't be spread throughout the liquid," says Ryan.

This can create a problem for the pharmaceutical and agricultural industries where specific RONS distributions in a liquid are needed.

"Controlling plasma-induced liquid flow can lead to the optimization of plasma-liquid interactions and therefore lead to better medicines and healthier crops," notes Ryan. "In agriculture, plasma-activated water is used to make better fertilizers and thus enhance plant health."

Plasma-based coffee machines?

But what does this all mean for your morning coffee? And what is the best plasma to stir your coffee?

"When comparing flows driven by plasmas with different polarities (positive or negative voltages), we found that positive plasmas drive faster flows in liquids in comparison to negative plasmas."

To visualize how positive and negative voltage plasmas stir liquids, Ryan added instant coffee to a plasma liquid mixture. "We discovered that the faster flow of the positive plasma mixed the instant coffee more uniformly, so we can expect the same behavior for a plasma-mixed liquid containing RONS."

While Ryan's discovery is a fundamental finding about plasma flows, does the researcher think that his work could revolutionize the coffee ritual in the morning?

"I'm not sure about that. I don't think that there'll be plasma-based coffee machines any time soon! I never drank any of the coffee though. The plasma adds nitrates to the liquid (which are very useful for fertilizer production), you could argue that it might taste like bad alcohol!"

Despite the bad taste, there could be valuable lessons here for anyone who wants to make a nice cup of uniformly mixed coffee every morning.

"These lessons would come at the cost of a nice, tasty cup of coffee though - at the moment anyway!" jests Ryan.

In June 2024, Calum T. Ryan won Talking Science - the science pitching competition for TU/e PhD and EngD researchers. In Talking Science, participants are asked to pitch for no longer than three minutes about their work. They cannot use slides, but props to support the pitch are allowed.

Ryan's winning pitch was entitled 'Going with the Flow Using 'Super-Water''. The jury deemed his pitch to be engaging, funny, and well-structured.

In addition to winning Talking Science 2024, Ryan also won an award for his oral presentation at the 25^th International Symposium on Plasma Chemistry (ISPC25) and an award for a poster at the 1^st NNV Plasma Symposium (Plasma Rolduc).

After his PhD, Ryan is looking to continue his passion for science communication, and he's currently exploring some opportunities related to this. In the meantime, he will be speaking as part of the programme for the Gala van de Wetenschap, which takes place at the International Theater Amsterdam on November 25 and is organized by New Scientist NL.

[Photo: Bart van Overbeeke]

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