Inspiring the scientists of tomorrow with fascinating experiments

Sixty children were looking in awe at those ten weird persons, dressed in white robes and strange glasses: Were these aliens invading their kindergarten Auf dem Backenberg (Bochum) on that morning of the 11th of October? The reality, they were about to discover, was more down to Earth than that, but fascinating nonetheless.


The JCF Bochum at work ©JCFBochum2016

We, the men and women in white, were chemists of the JungChemikerForum Bochum – the 1998 founded local group of young members of the GDCh. And we had brought several intriguing chemical experiments that encouraged them to participate and solve some of nature’s mysteries.

Why don’t water and oil get along?

Ranging from only two-year-olds up to fourth graders, our audience was very mixed. Still, fascination unified them from the very beginning. In their first experiment they had to mix water with oil – but wait, they don’t want to mix?!? That result was quite unexpected for most of our little experimentalists, but we soon explained:


Water and else ©JCFBochum2016

The difference in polarities and intermolecular forces between water and oil makes them like cats and dogs – they form small groups of one kind, but simply don’t get along with each other because of their differences. But what if we take a drop of ink and let it fall into the mixture (of course after multiple attempts with these tricky pipettes)? Ink seems to prefer the company of the polar water molecules, making for a nice visualization of the underlying principles of solute-solvent interactions.

Is brushing your teeth really necessary?

The little explorers then switched to the next experiment: We had to convince them that brushing your teeth in the morning and evening wasn’t just a huge waste of time – a challenge indeed! As model for their teeth a hard-boiled egg was chosen that first had to be properly coated on one half with tooth paste. The children performed this task with vigor and enthusiasm (though maybe not as diligently as we had expected, so we cheated by secretly coating the eggs some more).


Brush the egg ©JCFBochum2016

Next, the egg was lowered into a glass full of vinegar, symbolizing everyday’s assortment of acids passing our teeth. Also the young participants understood the aggressive properties of this vile liquid after putting their noses over the glass as could be told from the grimaces they made. Having put the egg into the vinegar they observed that bubbles were only formed on the uncoated side of the egg. This being probably the first time these children had ever consciously perceived a chemical reaction our JCF instructors very slowly explained: They carefully introduced the concepts of acids and bases to them, how the stuff that had attacked their noses earlier would react with the egg shell (i. e. calcium carbonate, see below) and produce carbon dioxide, the same gas they knew from soda or lemonade.

2 CH3COOH + CaCO3 –> CO2 + H2O + Ca(CH3COO)2
Acetic acid + Calcium carbonate –> Carbon dioxide + Water + Calcium acetate

However, how come the side they had coated with tooth paste earlier did not show any bubbles? This, we explained, was because the tooth paste contained fluoride, a special ion that helps to prevent damage to teeth by reacting with the hydroxylapatite contained therein and making them more acid-resistant:

Ca5(PO4)3(OH) + F– –> Ca5(PO4)3F + OH
Hydroxylapatite + Fluoride –> Fluorapatite + Hydroxyde

What magical substance surrounds us all?


Chemical tools ©JCFBochum2016

Finally, the children arrived at their last experimental setup, the sight of gummy bears having magically attracted them there. But before they could find out what to do with the sweets (and possibly how they tasted) they had to perform a deceptively easy experiment by submerging an empty glass upside down in a bowl of water. When asked to get out the glass and feel the bottom of it surprise crossed their faces: How could it be that the inside stayed dry? There had been nothing in the glass to prevent water from coming in… or had there been? Could it be that something surrounds all of us at any given time and thus is also inside seemingly empty glasses? When asked these questions the children got thinking: “Nothing”, some children pouted, “the environment” was another cute attempt at solving this riddle. “The sun” was actually an answer that showed quite a lot of insight since light is of course an entirely valid answer.

After some coaxing and hinting the small researchers indeed arrived at air as the substance we were searching for, but as true scientists were very skeptic about it. An invisible substance that is everywhere? We clearly had to visualize this mystical air to convince them. So we let them produce some bubbles by slightly tilting the submerged glass and thus see the otherwise invisible air. As crowning experiment we asked the children to let two gummy bears inside a small boat (made from aluminum foil) take a dive to the bottom of the water bowl without letting them get wet! The kindergartners soon figured out that they could use the same protective hull of air inside the glass to achieve this task and received some sweets for their accomplishment.

We were very delighted by the children’s remarkable enthusiasm to experiment and eagerness to learn about nature’s secrets. Although they probably did not realize it, they had experienced some of the fundamental principles of Solvation Science: The interactions of and interfaces between hydrophilic and hydrophobic solvents (water and oil), the preference of a polar molecule (ink) for water as polar solvent, acid-base reactions in aqueous media (egg shell plus vinegar), water as “tool” in experiments to probe and visualize certain effects (air bubbles). Besides teaching the children these important principles from physics and chemistry, another goal was to inform about them the puzzling work of chemists. Most of them had never even heard of us before and found our alien coats and safety-glasses very interesting. All in all, a very fascinating and instructive day for these small explorers!

This event has been organized in cooperation with the Young Spirits program of Evonik. Please contact us if you are also interested in teaching science to children, so we can supply you with contact to Evonik’s Young Spirits program or the actual procedures of the experiments described in this blog entry.

About the authors
dsc00024_aTim Schleif is a PhD student in the group of Prof. Sander working on matrix isolation experiments at the Ruhr-University Bochum since 2015. He is also the speaker of the JungChemikerForum Bochum that organizes talks and excursions for the students of the faculty.



Christoph Schran is a PhDstudent in the group of Prof. Marx working on nuclear quantum effects at the Ruhr-Univeristy Bochum since 2016. As an active member of the JungChemikerForum Bochum, he organized the event at the kindergarten.

Ultrafast lasers will help us understand the matrix of life.


Clara Saraceno

Born in Argentina, university studies in France, an experience in the industry in the US and a PhD in Switzerland: The 32 year old physicist Clara Saraceno has literally followed her passion for lasers around the world. Since June, the 2015 Sofja Kovalevskaja Award winner (a prize of the The Alexander Von Humboldt Foundation) has started a W2 tenure track professorship at RUB. In RESOLV she will build the ultrafast lasers that Martina Havenith (speaker of the cluster) will use to investigate the role of water in biological processes. Similar to the lasers she works with, Saraceno is a powerful and resolute scientist. Her driving force, as she tells us in this interview, is fun.

Q: RESOLV is essentially about understanding how water works and why is water the matrix of life. Why exploit lasers in the THz field to study water?

Water shows extremely strong absorption in the THz regime, hence we can apply light sources in that field to investigate water dynamics. For example this could help us follow how water behaves around a protein while the molecule is functioning, making reactions and so on.

Q: How do you want to study water dynamics?

In general, the more short laser pulses you have per second the more information per second you get. Hence, to study fast dynamics we need lasers that deliver very short pulses at very high repetition rate, which means reaching high average power.

Q: How simple is that?

That’s exactly the ongoing challenge in ultrafast laser research! There are several ways to do this: You could pump the power by amplifying a regular ultrafast oscillator output or you can aim for simple compact source by trying to push the oscillator itself. I actually prefer the second option: I could reach an average 275 W power with 600 femtoseconds pulse duration and 17 MHz repetition rate in the near infrared range – a record that I actually achieved in 2012. My challenge here at RUB is to use these sources and convert them into high-power sources into the 1-10 THz range: We would like to reach an average power close to 1 W and a repetition rate bigger than 1 MHz.


The THz gap in the electromagnetic radiation spectrum © Martin Saraceno

Q: What are the main hurdles along the way and how can you overcome them?

Like for every high power, solid-state laser, we would need to minimize heat and maximize cooling, by choosing the right materials and the right geometry. The one geometry that I favor implies a gain medium, the main source of heat, shaped like a pancake. The disks that we use are just a few hundred microns thin, allowing for better dissipation of the heat and better-shaped short pulses.

Q: How do you cool down the discs?

The disks are actually glued on diamonds! They dissipate heat very well. We don’t use the pretty polished ones, just synthetic, but they are still expensive. The diamonds are then water-cooled.

Q: So much for hard science. What led you to work with lasers?

It was during my university studies on optics in France, there was this lecture on lasers technology. It was so cool! And then the school was offering an internship at Coherent, an American laser manufacturing company set in California. I thought: “Sunny California, for one year, lasers are cool, why not?”. But I applied too late.


Inside of a laser © Clara Saraceno

I contact them anyway after my master for an engineer trainee, and they got me. There I learned everything about lasers and I really got the ultrafast laser bug. It was real fun!

Q: How did it happen that you then went back to academia?

I soon found out that in the laser industry you need a PhD to make interesting things. So I was looking for an opportunity and it happened that my ex boyfriend was in Europe and that my cubicle-colleague at Coherent knew Prof. Ursula Keller at ETH in Zurich, Switzerland. He suggested I should apply there. They wanted me, and I really had a great time in Zurich, it’s a fantastic group!

Q: You’ve mentioned it already three times, what do you mean with fun?

I really enjoy manipulating stuff, go to lab and turn knobs. I love making nice devices and lasers. And I really marvel at the German way of making good functioning devices based on sound engineering.

Q: And now you are here at RUB?

Again there were coincidences. Martina Havenith once came to Zurich to give a talk. In her last slide she said “we need to increase the resolution, we need more powerful sources”. And my boss, Keller, goes “take Clara, she is looking for a job!”. So I applied for the Kovalevskaja prize and here I am.

Q: How was moving from the green, mountain-rich Switzerland to the concrete-rich Bochum?

Switzerland is super-nice, but with a family and a small baby, my priority was to move forward in science. I’m impressed by the scientific excellence that I’ve found here. I think there’s really room for good collaborations and for my own activity to grow. And the environment is a nice too! If I look at the right side I see green hills.

Q: Who do you see yourself collaborating with?

A natural collaboration would be with Janne Savolainen. He knows a lot about the right ways to generate THz light. And here I come, with some of the most powerful ultrafast lasers in the world!

2_schematic THz gen_water

Simplified scheme of the project idea: Disk (on diamond) generates near infrared pulse; conversion to THz pulse, which is used to study water molecules © Martin Saraceno

Q: What are your next steps at RUB? When will you do research on water?

First, we need to build up a lab, a good one. It will take around 6 months. Then I will start to tinker with laser to near the short pulses-high power in the THz domain. Soon, I would guess in some 18 month, we’ll do some experiments on water in parallel with the laser development.

Q: Becoming a professor at 32 is an outstanding achievement, especially for a woman, given the gender gap that still exists in science. What are your suggestions to young students and young women in science?

I always had so much fun with my work, so I would say: feel the passion! And don’t over think! If you see an opportunity give it a shot, what can you lose? Throw yourself in the pool, then things will work out.

Q: Clara, will we ever have the lightsabers of Star Wars?

Unfortunately laser swords make little sense physically. For the beam to suddenly ‘stop’ propagating, this would somehow imply that the laser beam is ‘trapped’ in a similar way to a resonator. However then, when something would intercept the beam the resonator would automatically stop, and the laser light would not be there anymore.

About the Author

EF3Emiliano Feresin is a science journalist, currently responsible for the outreach activities within the RESOLV cluster at RUB. Born and raised in Italy, he holds a Diploma and a PhD degree in chemistry. Driven by an innate curiosity for scientific stories, he completed his education with a master degree in science communication. Along the path he has written for outlets like Nature and Chemistry World and learned that the reader has always the last word.