Research Description

Volkswagenstiftung
DFG SPP 1726 ("Microswimmers")
DFG SPP 1369
IMPRS
Helmholtz Graduate School for Macromolecular Bioscience
G-RISC

• Nanomanipulation of absorbed particles
• Interaction of single nano-particles and macromolecules with surfaces and its application in nanotechnology and life science
• Global/coordinated coupling of optical energy by nano-structured metal gratings: surface plasmon interference nanolithography (SPINAL)
• Photochemically induced processes
• Magnetic-particle filled polymer films (MPFPF)
• Ordering phenomena at interfaces
• Microscopy and spectroscopy of macromolecules and nano-objects at interfaces (AFM, STM, SEM, SPR)

The general focus of our research is on fundamental phenomena in the field of soft matter at surfaces and on measurements and quantitative description of interactions between nano-particles and polymer surfaces.

Manipulation of adsorbed nano-objects: We suggested that it should be possible to move or reposition also strongly adsorbed objects with relative ease, in large number and simultaneously. The essential idea is not to put more effort in fighting against the prevailing surface forces but rather to utilize them – in clear contrast to current techniques of nano-manipulation with atomic force microscopy (AFM).

1. Santer, S.; Kopyshev, A.; Donges, J.; Yang, H.-K.; Rühe J. «Dynamically Reconfigurable Polymer Films: Impact on Nano-Motion» Advanced Materials, 18, 2359 (2006).
2. Santer (Prokhorova), S.A.; Rühe, J. «Motion of nano-objects on polymer brushes» Polymer 45, 8279 (2004).

Polymer brushes that can undergo pronounced topographical changes on a nano meter length scale, occurring during phase transitions induced by changing the environmental conditions. We were able to show that these topography changes generate fluctuations in the surface forces on the same scale as the topography, and consequently drag suitably sized adsorbed objects along. Our stunning finding was although the particles could be relocated by considerable distances after only a few switching cycles (i.e., changing the environmental conditions periodically), they remain firmly adsorbed on the surface at any stage which is of great practical importance for the development of robust devices and products using this principle. We discovered that brushes that were not able to initiate motion had the peculiar property to exactly recover the previous morphology after a switching cycle – a feature that we coined domain memory effect and that has meanwhile sparked the interest of established theorists that we are in collaboration with.

1. Santer, S.; Kopyshev, A.; Yang, H.-K.; Rühe J. «Local Composition of Nanophase Separated Mixed Polymer Brushes» Macromolecules 39, 3056 (2006).
2. Santer, S.; Kopyshev, A.; Donges, J.; Yang, H.-K.; Rühe J. «Domain Memory of Mixed Polymer Brushes» Langmuir 22, 4660 (2006).
3. Santer, S.; Kopyshev, A.; Donges, J.; Rühe, J.; Jiang, X.; Zhao, B.; Müller, M. «Memory of Surface Pattern in Nanophase Separated Mixed Brushes: Simulation and Experiment» Langmuir 23 (2007) 279.
4. Filimon, M.; Kopf, I.; Schmidt, D. A.; Bründermann, E.; Rühe, J.; Santer, S.; Havenith, M. M. «Local chemical composition of nanophase-separated polymer brushes» Physical Chemistry Chemical Physics, 13 (2011) 3764.
5. Filimon, M.; Kopf, I.; Ballout, F.; Schmidt, D.A.; Bründermann, E.; Rühe, J.; Santer, S.; Havenith, M. «Smart polymer surfaces: mapping chemical landscapes on the nanometre scale» Soft Matter, 6 (2010) 3764.

Photosensitive polymer brushes: the topography of the azobenzene containing polymer brushes shows a strong reaction upon irradiation with UV light resulting in formation of surface relief gratings (SRG). The SRG pattern can be erased through solvent treatment when the periodicity of the stripe pattern is less than the length of the fully stretched polymer chains. In the opposite case, photo-mechanical scission of receding polymer chains is observed during SRG formation and the inscribed patterns are permanent.

1. Schuh, Ch.; Lomadze, N.; Ruhe, J.; Kopyshev, A.; Santer, S. «Photomechanical Degrafting of Azo-Functionalized Poly(methacrylic acid) (PMAA) Brushes» The Journal of Physical Chemistry B, 115 (2011) 10431.
2. Lomadze, N.; Kopyshev, A.; Ruhe, J.; Santer, S.«Light-Induced Chain Scission in Photosensitive Polymer Brushes» Macromolecules, 44 (2011) 7372.

Reversible structuring of photosensitive polymer films by surface plasmon near field radiation: azobenzene-polymer thin films with integrated optically active elements supposed to support and steer the response of polymer films to external illumination by acting as nano-scale antennas. During irradiation surface plasmon polarizations (SPP) are generated on a metallic mask. The interaction of the SPP with azo polymers results in printing of near field intensity distributions into topography with the pattern size below the diffraction limit. The topography can be driven reversible, this allows us to analyze different patterns by changing polarization or wavelength at the same position.

1. König, T.; Sekhar, Y. N.; Santer, S. «Surface plasmon nanolithography: impact of dynamically varying near-field boundary conditions at the air–polymer interface» J. Mater.Chem., 22 (2012) 5945 - 5950.
2. König, T.; Sekhar, Y. N.; Santer, S. «Near-Field Induced Reversible Structuring of Photosensitive Polymer Films: Gold Versus Silver Nano-antennas» Plasmonics (2012) DOI 10.1007/s11468-012-9339-3
3. König, T.; Santer, S. «Stretching and distortion of a photosensitive polymer film by Surface Plasmon generated near fields in the vicinity of a nanometer sized metal pin hole» Nanotechnology, 23 (2012), 155301.
4. König, T.; Goldenberg, L.M.; Kulikovska, O.; Kulikovsky, L.; Stumpe, J.; Santer, S. «Reversible structuring of photosensitive polymer films by surface plasmon near field radiation» Soft Matter, 7 (2011) 4174.

Magnetic particle filled polymer films (MPFPF): a thin double layer membrane (less than 100nm thick) is constructed containing a certain volume fraction of magnetic nanoparticles. The membrane’s elastic properties are thus made responsive to external magnetic fields, and the interplay of adhesive, elastic and magnetic forces changes the forces acting on an adsorbed nano object.

1. Schlemmer, Ch.; Betz, W.; Bertchold, B.; Santer S.A «Design of thin polymer membranes filled with magnetic particles on a microstructured silicon surface» Nanotechnology, 20 (2009) 255301

Reversible light-controlled DNA compaction by azobenzene containing surfactant: we study the interaction of DNA molecule with cationic azobenzene-containing surfactant, the properties of which can be controlled with light by reversible switching of the azobenzene unit, incorporated into the surfactant tail, between a hydrophobic trans (visible irradiation) and a hydrophilic cis (UV irradiation) configuration.

1. Zakrevskyy, Y.; Kopyshev, A.; Lomadze, N.; Morozova, E.; Lysyakova, L.; Kasyanenko, N.; Santer, S. «DNA compaction by azobenzene-containing surfactant» Phys Rev E, 84 (2011) 021909.