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Elastic shells, capsules, and polymer networks

Elastic capsules and shells

Elastic shells are thin (quasi two-dimensional) elastic solids in a curved geometry. Of particular interest in soft matter theory and applications are closed spherical elastic shells, which can also be termed elastic capsules and which enclose a liquid of given volume or pressure. On the microscale, capsules have received a lot of attention as delivery systems and as biologically relevant model systems. Prominent examples of biological microcapsules are red blood cells or virus capsules; more generally, all biological cells where a thin layer of elastic cytoskeleton is surrounding the liquid cytosol and participating in deformations can be viewed as elastic capsules. If a coupling to the cytoskeleton is absent, a description of the membrane as a quasi two-dimensional liquid is more appropriate, and we obtain a vesicle rather than a microcapsule. Artificial capsules can be fabricated by various methods, for example, by interfacial polymerization at liquid droplets or by multilayer deposition of polyelectrolytes, and have numerous applications as delivery systems.

Usage as delivery systems requires that the mechanical behavior of capsule shells is understood and well characterized. In order to characterize microcapsules mechanically, their response to external forces and perturbations has to be explored quantitatively. For this purpose, we developed the method of “elastometry” for elastic capsules attached to a capillary, where we model the shape change of a hanging capsule during deflation, analogously to pendant drop tensiometry for liquid droplets.

Elastic instabilities such as buckling or wrinkling are relevant for the mechanical behavior of capsules as they give rise to stress concentration, for example, stress is concentrated in the rim of the indentation after buckling. Therefore, these instabilities represent potential pathways to failure of capsules in delivery applications. Moreover, elastic instabilities are fascinating from a theoretical point of view because they represent important shape bifurcations, which are characteristic for the polymorphism of many soft matter systems. The resulting buckled shapes of capsules can also be useful for colloidal self-assembly.

On the one hand, our research focuses on elastic instabilities such as the buckling instability and further post-buckling instabilities of spherical elastic shells. On the other hand, we are insterested in developing theoretical tools to enable the determination of elastic material parameters from analyzing experimental data on capsule shapes during a controlled capsule deformation.

Usage as delivery systems also requires controlled actuation of capsules. We investigated the manipulation of ferrofluid-filled capsules by magnetic fields and their deformation at liquid-liquid interfaces by surface tension.

Within the DFG Priority Programme SPP 1726 "Microswimmers" we also explore the use of elastic capsules as microswimmers.


Elasticity of polymer networks

Quasi two-dimensional networks built from stiff semiflexible polymers are a particular realization of an elastic shell, which is of biological importance for the mechanical properties of the cytoskeletal cell cortex. We are studying elastic instabilities such as wrinkling for such polymer networks.



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Location & approach

The campus of TU Dort­mund University is located close to interstate junction Dort­mund West, where the Sauerlandlinie A 45 (Frankfurt-Dort­mund) crosses the Ruhrschnellweg B 1 / A 40. The best interstate exit to take from A 45 is “Dort­mund-Eichlinghofen” (closer to South Campus), and from B 1 / A 40 “Dort­mund-Dorstfeld” (closer to North Campus). Signs for the uni­ver­si­ty are located at both exits. Also, there is a new exit before you pass over the B 1-bridge leading into Dort­mund.

To get from North Campus to South Campus by car, there is the connection via Vogelpothsweg/Baroper Straße. We recommend you leave your car on one of the parking lots at North Campus and use the H-Bahn (suspended monorail system), which conveniently connects the two campuses.

TU Dort­mund University has its own train station (“Dort­mund Uni­ver­si­tät”). From there, suburban trains (S-Bahn) leave for Dort­mund main station (“Dort­mund Hauptbahnhof”) and Düsseldorf main station via the “Düsseldorf Airport Train Station” (take S-Bahn number 1, which leaves every 20 or 30 minutes). The uni­ver­si­ty is easily reached from Bochum, Essen, Mülheim an der Ruhr and Duisburg.

You can also take the bus or subway train from Dort­mund city to the uni­ver­si­ty: From Dort­mund main station, you can take any train bound for the Station “Stadtgarten”, usually lines U41, U45, U 47 and U49. At “Stadtgarten” you switch trains and get on line U42 towards “Hombruch”. Look out for the Station “An der Palmweide”. From the bus stop just across the road, busses bound for TU Dort­mund University leave every ten minutes (445, 447 and 462). Another option is to take the subway routes U41, U45, U47 and U49 from Dort­mund main station to the stop “Dort­mund Kampstraße”. From there, take U43 or U44 to the stop “Dort­mund Wittener Straße”. Switch to bus line 447 and get off at “Dort­mund Uni­ver­si­tät S”.

The AirportExpress is a fast and convenient means of transport from Dortmund Airport (DTM) to Dortmund Central Station, taking you there in little more than 20 minutes. From Dortmund Central Station, you can continue to the university campus by interurban railway (S-Bahn). A larger range of international flight connections is offered at Düsseldorf Airport (DUS), which is about 60 kilometres away and can be directly reached by S-Bahn from the university station.

The H-Bahn is one of the hallmarks of TU Dort­mund University. There are two stations on North Campus. One (“Dort­mund Uni­ver­si­tät S”) is directly located at the suburban train stop, which connects the uni­ver­si­ty directly with the city of Dort­mund and the rest of the Ruhr Area. Also from this station, there are connections to the “Technologiepark” and (via South Campus) Eichlinghofen. The other station is located at the dining hall at North Campus and offers a direct connection to South Campus every five minutes.

The facilities of TU Dortmund University are spread over two campuses, the larger Campus North and the smaller Campus South. Additionally, some areas of the university are located in the adjacent “Technologiepark”.

Site Map of TU Dortmund University (Second Page in English).