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Diving Into Surfaces

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Diving Into Surfaces Sylvie Roke cycles in the foyer of the Max Planck Institute for Metals Research for demonstration purposes only, but she loves cycling in the Swabian hills and dales around Stuttgart. xxxxxxxxxxxx MATERIAL & TECHNOLOGY_Personal Portrait Diving into Surfaces The experiments for her doctoral studies did not work out quite as planned the first time around. After switching gears and continued work, however, Sylvie Roke opened up a completely new perspective on soft matter. At the Max Planck Institute for Metals Research, she also uses this method to investigate potential new drugs and biological materials. A PORTRAIT BY UTA DEFFKE ometimes it is the small, ev- many more charges, which have an at- In spite of her delicate appearance and eryday things that still hide tractive or repulsive effect on each oth- her mere 32 years, it does not sound as big secrets. Take some oil, for er and on their surroundings. But what if Sylvie Roke is intimidated by this. On example, and pour it into a exactly do these molecules look like? the contrary. The young researcher bowl of water. The two liq- How are they arranged and why? Is loves such challenges and knows what S uids won’t mix, as everyone knows there a difference between a curved she can do and what she wants. When from an oil and vinegar vinaigrette. surface and a planar interface? she talks about her work and her plans, Only a vigorous shake makes the oil she makes vivid gestures, demonstrates floating on top disperse into the water CHALLENGING TEXTBOOK the motion of molecules with the aid in the form of fine droplets. Chemists WISDOM IS FUN of a slinky and sketches formulas and call this an emulsion. We encounter pictures on the board. She also demon- these everywhere in daily life, for exam- Initial speculations about this were al- strates comic talent when talking, as ple in the form of milk, butter, sham- ready circulating in specialist literature she imitates other people’s intonation poo and vaccines. But what deter- a century ago. “There are lots of theo- and facial expressions. mines the size of the droplets, their ries on droplet interfaces,” says Roke, Sylvie Roke sits in her office on the stability, or their interaction with the “but so far there have not been any di- sixth floor of a new building on the surrounding liquid? Why does every- rect measurements.” There were sim- outskirts of Stuttgart. Glass facade, con- thing change if certain substances are ply no suitable methods that would crete core – the Max Planck Institute for added? And how can this be influ- have enabled the researchers to access Metals Research. Since 2005, she has enced for a specific purpose? the interfaces of tiny droplets. Sylvie been heading her own, open-topic Max The answers to these questions are Roke has developed an optical meth- Planck Research Group, which now hidden at the interface of the droplets. od that makes this possible for the first comprises seven scientists from Brazil, Sylvie Roke draws a black circle on the time. “We can now jettison a large Spain, the US, France, the Netherlands whiteboard and another one around number of old ideas,” she says. “This and Germany. She is often asked just it. “This interface is only about one is fun, of course; but it is also quite dif- how she came to be at an institute for nanometer thick, but it is fundamen- ficult to carry out research that goes metals research, of all places. Historical- tally different from the rest of the liq- against textbook wisdom, because we ly, the institute was indeed dedicated uid,” explains the physicist. The liquid are viewed with a particularly critical strictly to research on metals, but now- Photo: Frank Vinken there is rather viscous and contains eye, of course.” adays one finds behind the doors of the 1 | 10 MaxPlanckResearch 69 MATERIAL & TECHNOLOGY_Personal Portrait » The curved surfaces of small particles scatter light in different directions. Sylvie Roke pursues the idea that these scattering effects can be used specifically to gain insight into the surface properties of the particles. institute offices and laboratories where that electrons cannot reach them. ciently strong signals. And because they researchers work on a broad spectrum Moreover, the particles are very small are so short, they are also suitable of materials and topics. And soft mat- and their surfaces are thus curved, for observing the temporal behavior ter, which cannot unequivocally be as- with the result that reflection experi- of the excited molecular oscillations signed to solid or liquid matter, is also ments are impossible. in a quick sequence of snapshots, as in the latest trend here – including biolog- The most promising tool for inves- a stroboscope. ical materials. tigating soft matter is light, because it Interfaces play a key role in many can penetrate liquids and solid bodies. MAJOR AWARDS FOLLOW THE processes. They determine the electron- Furthermore, light is already being FIRST PUBLICATIONS ic properties of computer chips and the used to investigate surface structures, mechanical stability of solid bodies. specifically in the form of second- The researchers headed by Sylvie Roke They affect transport processes through order nonlinear optical spectroscopy. have used this method to prove, for ex- cells, when medication is administered, In a nutshell, this method shows ample, that a suspension of colloidal for example, and the interaction of how the molecules vibrate at surfaces, glass particles – small spheres in a liq- particles with their environment. The which in turn can be used to derive uid – takes on a gel-like consistency if physical and chemical properties of their structure. the molecular chains, which sit like nanomaterials are based almost ex- But the sophisticated method works hairs on the colloidal surface, arrange clusively on the properties of their sur- in this form only with planar surfaces, themselves alternately with molecules faces, because the smaller the dimen- because a reflected light beam is neces- of the liquid. The molecular hairs thus sions of a body are, the more dominant sary for detection and analysis. Howev- influence the properties of the materi- is the contribution of its surface, and the er, the curved surfaces of small particles al, in this case the material to gel. The more important it is to understand it. scatter light in different directions, so researchers also showed that the surface that no reflected beam can be meas- of soap sitting on small oil droplets in CELL WALLS AND DROPLETS ured. Sylvie Roke uses the idea that one water is fundamentally different from IN A NEW LIGHT can nevertheless use the scattered light soap sitting on the planar interface be- to gain information about the surface tween bulk oil and bulk water. More- There are several established methods molecules. She uses the scattering effect over, the Max Planck scientists are con- for investigating planar surfaces, rang- for the specific purpose of gaining in- tinuously working on improving the ing from scanning probe techniques to sight into, for example, the molecular sensitivity of their apparatus and inte- imaging with electrons to optical spec- surface composition, chirality or charge grating new optical effects. troscopic methods. These methods that is present in the interfacial region. In 2008, Sylvie Roke was awarded have contributed decisively to the con- In order to realize nonlinear light- the Hertha Sponer Prize of the German tinuous miniaturization of microelec- scattering spectroscopy, Sylvie requires Physical Society (DPG) for her devel- tronics. However, these techniques are a sound knowledge of the particle scat- opment. And back in 2006, she re- of very limited use in investigating the tering processes. Only then can she cor- ceived the Dutch Minerva Prijs, which surfaces of soft matter, such as cells rectly interpret the data. In the labora- is a biannual prize for a scientific pa- and emulsions. There are several prob- tory, lasers are set up on a large table per. “This is something quite special lems at once: quite a few of the meth- with many mirrors and lenses that for me,” says Roke with some pride. ods require vacuum conditions, where shape the variously colored light “Some researchers have been honored liquids immediately evaporate; and beams. Ultrashort intense flashes of for their lifetime achievements with the interesting surfaces are often hid- light are required for the oscillations of this award, and I received it after only den in liquids or in solid materials so the surface molecules to generate suffi- a few publications.” 70 MaxPlanckResearch 1 | 10 Sylvie Roke was already in a bit of a hur- ry at the very beginning of her life. Maybe in slightly too much of a hurry, because she was born three months pre- mature, and initially had to fight for survival. Even later in life, she was more occupied than other children with growing up and getting stronger. Luck- ily she had her sister, who was one year older and served as a great example. “Being one year older, she was always taller and better than I was, but she took me along nevertheless. She learned how to play soccer, so I had to learn, too. When she wanted us to run through the forest, I ran with her. And when she wanted to climb trees, we climbed trees. Following her around was very important for my develop- ment. And it was fun.” At some point, when she was 15 or 16, Sylvie Roke found her own way in life. And it was at this time that she also became interested in science. When Sylvie Roke explains nonlinear scattering spectroscopy, she uses her hands, simple models and, of course, a whiteboard.
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