Diving Into Surfaces

dales around Stuttgart. she loves cycling intheSwabian hillsand for demonstration purposes only, but Max PlanckInstitutefor Metals Research Sylvie Rokecycles in the foy er ofthe

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 hurry 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. The method she developed provides vibrational Mathematics appeared to her to be a spectroscopic information on the surfaces of cells and emulsion droplets. The scattering very natural way of thinking, and she of light discloses the surface structure and the size and shape of the particles. also found physics and chemistry easy. She began to read trade journals and enjoyed the idea of ending up doing something like that. So it was that she found her niche – in her family, as for her bachelor’s degree, one of them physics and chemistry. When the re- well, as both of her parents are in the simply recommended that she switch search group moved to Leiden Univer- legal profession. And her sister? “She to physics. So that is what she did. Af- sity and the chance was offered to en- became a psychiatrist and is responsi- ter another two and a half years, Roke ter the discipline of laser physics, Roke ble for the social side,” says Roke with not only completed her physics de- moved with them to write her doctor- a wink of an eye. gree, but also her chemistry degree, al thesis. At the university in Utrecht, close both with highest honors. While work- At first, this didn’t work out quite as to her little home town, she started to ing on her master’s thesis at the Insti- planned – the experiments weren’t suc- study chemistry. But when her ques- tute for Atomic and Molecular Physics cessful. Sylvie Roke started brooding tions as to why things happened got in Amsterdam, she became engrossed and thought of three possible causes: on the nerves of the university lectur- for the first time in the investigation “One: I am a lousy scientist; two: the

Photos: Frank Vinken (2) ers time and again during the lectures of surfaces – a classic interface between whole idea is wrong; or three: the cause

1 | 10 MaxPlanckResearch 71 MATERIAL & TECHNOLOGY_Personal Portrait

» The overall view of something was important to her, even as a student. That is why she participated in the “Universiteit Vrij van Nut”, the “University of Uselessness”.

is the bad signal-to-noise ratio.” In or- open-topic Max Planck Research Group der to find out whether the only really program and encouraged the young re- alarming hypothesis – the first one – searcher to apply. was correct or not, she decided to sim- Sylvie Roke confesses that, at that ply start a new project. And she already time, she didn’t really know very much had one in mind. about the Max Planck Society and its possibilities. While in Heidelberg, how- “IF YOU WANT SOMETHING, ever, she got to know Joachim Spatz, THERE IS ALWAYS A WAY” who was in the process of joining the Max Planck Institute for Metals Re- During the third year of her doctoral search. He was working with nano- studies, she spent a few weeks at structured surfaces and with biological Columbia University in New York. materials, and he advised her to apply There she met people who combined there as well. She was successful: her nonlinear optics in the visible spec- idea and the initial results of her new trum with light scattering. So why not method convinced not only the jurors combine light scattering with spectros- of the Max Planck Society, but also the copy in the infrared range, which is Board of Directors in Stuttgart. particularly suited to the analysis of This promised her a great opportu- molecular structures? nity, not only in scientific terms. Her Within a few months, she had con- boyfriend had declared that he was structed a laser system on the basis prepared to move from the Nether- of this idea, and showed that it was lands to Stuttgart if she got the job Stuttgart offers no opportunity to possible, in principle, to use it to with the research group. “It is very im- skate on ice, but with inline skates, determine the surface properties of portant to me that we don’t have to she can train without it. particles. “In retrospect, I was very have a long-distance relationship,” lucky there,” she says, “because my says Roke. “I know that many people test particles were of just the right size do this, but I could not and did not to enable me to measure them with want to. And if you want something, relative ease.” there is always a way ….” She had thus restored her “scientif- And how does it feel being Dutch ic honor,” and after completing her in Germany? And even more so in the doctoral studies, again with highest heart of Swabia, the almost mountain- honors, she left Holland to take up a ous, model region of German orderli- postdoc position. “As these things hap- ness? “Well,” she groans slightly, “it’s pen, I met Michael Grunze at a confer- different. And this takes some getting ence. We had a nice conversation, he used to at first.” She has since grown had an interesting position in physical somewhat apart from her home coun- chemistry available, and I ended up in try, however: “When I go back to the Heidelberg with an Alexander von Netherlands now, I often get irritated Humboldt fellowship.” The hosting and think: Can’t this work ‘normally’

professor also drew her attention to the for once? I don’t really belong here Photo: Frank Vinken

72 MaxPlanckResearch 1 | 10 Photos: Frank Vinken (2) While drinkinghercupoftea atbreak- using thelatesttechnologyfor reading. translates thisformyeyesand legs.” put onAlpesd’Huezandthe trainer with DVDandcomputer. “Icansimply reach, thereisalwaysthehome-trainer or apropermountainisnotwithin And whentheweatheroutsideisnasty, tain oftheTour deFrance,eleven times. Ventoux, thenotorious,bleakmoun- ride: shehasalreadyconqueredMont er bynature,shealsoenjoysaclassic cycling uphill,”sheconfesses.Afight- hills anddalesaroundStuttgart.“Ilike phere andabignationalparty. specialatmos- there is,ofcourse,avery the fantasticviewsofoldtowns, be enchantedbytheicylandscapeand people canskatefromtowntoand rather rare,eveninHolland.Butwhen few andfarbetween.Frozencanalsare and alternativespeedskatingrinksare Kornwestheim burneddownlastyear, the icerinkinneighboringtownof like flying,”shegushes.Unfortunately, ing. “Ilovethespeedonice,it’s almost favorite sports:cyclingandspeedskat- wasn’t already, whenshetalksabouther Netherlands becomesobvious,ifit The factthatSylvieRokeisfromthe AS WELL COMPETITIVE ON THE BIKE, parked there.” cle parking,’youwon’t seeanybikes keep totherules:“Ifitsays:‘Nobicy- live amuchmoreorderlylifeandalso she says,isprobablythattheGermans anymore.” Thebiggestdifference, The physicistisalsonotaverse to Sylvie Rokeenjoyscyclinginthe studies. Butsheandhercoworkers continuetobuildbetterdevices. The physicist constructedherfirstlasersystemduringdoctoral want to extend the theory to different- ly shaped particles as well, to enable the study of deformations (of cells) or of vi- ruses. The theory makes a significant contribution to interpreting the meas- urement results correctly, and to further optimizing the experimental setup.

IMPORTANT CLUES FOR THE DRUGS OF THE FUTURE

A medical project with the University of Utrecht has just been completed. “I literally met the researcher in the elevator and he told me about the problem he had,” remembers Sylvie Roke. The medical researchers had developed tiny spheres of biodegradable plastic to pos- sibly fight secondary liver cancer. These When Roke first came to Stuttgart, she was keenly aware of the microspheres contain small quantities differences between the Nether- of holmium that is radioactivated to lands and her new home. Since emit beta radiation to destroy tumors. then, however, her home country In order to optimize the therapy, they has become almost foreign to her. wanted to find out more about the biodegradable plastic microspheres: where exactly the holmium was located in them and how they were interact- ing with the body fluids. The Max Planck researchers were initially confused by the results of their measurements on the particles. The scattering phenomena they observed could not be explained by the surfaces of the plastic spheres. Instead, all indi- cations suggested that the plastic molecules within the sphere formed crys- fast, she likes to use her e-book reader. sor Frits Bienfait. In two-week summer talline regions. Roke found that the It has the feel of a real book and is very camps without television or computer, holmium located inside these regions practical, she says – it saves a lot of bag- she met students from all faculties is in a configuration that is so stable gage, especially when traveling. In who came together to discuss diverse that it doesn’t get released even after an terms of content, however, she prefers and controversial subjects. A boxers’ activation process of several hours. Syl- history: Persian Fire by Tom Holland, responsibility for his (or her) own vie Roke believes that this is an impor- for example, on the war between the brain, for example. “These were very tant finding for the design of future Persians and the Greeks. She also thinks important experiences for me, oppor- drugs. “It is very satisfying to discover Bill Bryson’s “A Short History of Nearly tunities to consider things so intense- something fundamental that, at the Everything” is particularly good. What ly and from very different perspec- same time, is also very useful, isn’t it?” she values about this sweeping broad- tives,” sums up Roke. The holmium-loaded microspheres are side of popular science is that it makes She also tries to implement this in- now being tested in clinical studies. the bigger picture clear. tegrated approach in her Max Planck Sylvie Roke does not spend much Bryson does not simply list discov- Group. Here, chemists and physicists time in the lab these days. She is writ- eries chronologically. He thus does work together on both the experiment ing publications and planning for the much more justice to the course of sci- and the corresponding theories. Just re- future – planning to publish her ideas ence, Roke thinks. The overall view of cently they published a complete theo- and results further, also in talks, be- something was important to her even ry for their scattering method, the so- cause her group is the only one in the as a student. That is why she partici- called nonlinear Mie theory. This world taking this approach to particle pated in the “Universiteit Vrij van enables them to describe the scattering and droplet surfaces. And you cannot Nut,” the “University of Uselessness,” process on spherical particles for any bump into everyone who could be in-

which was founded by biology profes- type of medium. In the future, they terested in that in an elevator. Photo: Frank Vinken

74 MaxPlanckResearch 1 | 10 MATERIAL & TECHNOLOGY_Personal Portrait

And her personal future? There are no The next big project has already begun ed with work, she and her fellow scien- plans for any children, Sylvie Roke and anyway: In 2009 she was awarded one tists can investigate the smallest struc- her partner agree on that. “I like being of the coveted ERC grants from EU re- tures of soft matter and resolve the an aunt and I Skype a lot with my search support in the amount of 1.1 mil- processes very well as a function of time nephew and niece. But children de- lion euros to study emulsions. This will and thus contribute to developing ma- mand a lot of energy, I can see this keep her busy until the end of 2014. Syl- terials with new properties. “There are so with my sister. I enjoy what I do very vie Roke is not worried about her long- many questions to be answered that we much. Not many people have such an term future: “There was a certain risk in- will certainly be occupied with this for opportunity, and I think I should take volved in starting work on my idea the next 20 years. The Max Planck Soci- advantage of it.” here.” But now, since all ideas she start- ety offers ideal conditions for that.”

GLOSSARY

Soft matter Colloids Nonlinear vibrational spectroscopy Light scattering Matter that is neither unequivocally Small particles In contrast to linear spectroscopy, this is Light that strikes a particle from one di- solid nor liquid. Soft matter undergoes with a diameter operated with not one, but two lasers for rection is scattered in different directions. changes easily. It is characterized by the in the size range irradiation. The first one excites a mole- The incident light then temporarily con- fact that small temperature changes of nanometers cule to vibrate. The molecules react to verts the particle into an electric dipole, in the vicinity of a system produce major to microns. different frequencies depending on their which oscillates and thus emits light. The changes in the system itself. Biological structure. The second laser excites the direction of the scattered light depends materials are soft. Milk, for example: molecule to emit a photon itself. on the size and shape of the particles. In without a refrigerator, it quickly turns This method works only with molecules the case of nonlinear light scattering, the sour. In solid materials, the associated in an asymmetrical environment, so for molecular surface structure also deter- temperature increase has no such effect. example on surfaces. mines the direction of light.

1 | 10 MaxPlanckResearch 75