In this research area we focus on the functionalisation of surfaces using polymeric materials such as polymer brushes, adsorbed microgels, responsive PE multilayers, and co-polymer networks. In addition, we investigate their internal structure and dynamics and how they interact with cellulose fibres.

Research topics

Picture: AG von Klitzing

Polymer brushes

Polymer brushes (PBes) are polymer chains densely grafted onto a substrate in the form of a planar surface or a particle, as shown in the figure on the left.

Our Research

Such polymer brushes enable the coating of surfaces with organic thin films. Depending on the polymeric material, the properties of the polymer brush can be tailored for specific applications. This includes sensitivity to external stimuli, to which the PBes may respond (e.g. temperature, pH, …).

Furthermore, PBes can be used to immobilize small particles introducing additional properties to the so-called composite material. One of many existing examples is the attachment of inorganic nanoparticles (e.g. gold or cobalt nanoparticles) to the PBes.

The group synthesizes PBs via Surface-Initiated Atom Transfer Radical Polymerization (SI-ATRP) reaction. Frequently used analysis methods for the polymer brushes are ellipsometry, AFM, X-ray (XRR), and neutron reflectometry (NR).

Contacts:

Elias Hallenbach
Philipp Ritzert

Selected publications:

  • Boyaciyan, Dikran; von Klitzing, R (2019): Stimuli-responsive polymer/metal composites: From fundamental research to self-regulating devices, Current Opinion in Colloid & Interface Science, 442019. pp. 193-207
  • Boyaciyan, Dikran; Braun, Larissa; Löhmann, Oliver; Silvi, Luca; Schneck, Emanuel; von Klitzing, Regine (2018): Gold nanoparticle distribution in polyelectrolyte brushes loaded at different pH conditions, The Journal of Chemical Physics, 149 (16), p. 163322.
  • Christau, Stephanie; Moeller, Tim; Genzer, Jan; Koehler, Ralf; von Klitzing, Regine (2017): Salt-Induced Aggregation of Negatively Charged Gold Nanoparticles Confined in a Polymer Brush Matrix, Macromolecules 2017, 50, 18, pp. 7333-7343
Picture: AG von Klitzing

Adsorbed microgels

Stimuli-responsive microgels at surfaces are of great interest for applications as surface coatings. They show differences in their swelling and shrinking behaviour compared to bulk systems, which can be studied by AFM measurements.

Our Research

Static AFM measurements can be used to get the apparent elastic modulus. Dynamic experiments provide the storage moduli (E’, G’) and loss moduli (E’’, G’’).

The combination of such stimuli-responsive microgels with adhesive properties, would further increase their usability, especially for medical purposes. In this project, the mussel-protein 3,4-dihydroxyphenyl-L-alanine (DOPA) is combined with the temperature-sensitive PNIPAM microgel. Mussels show strong adhesion to various substrates due to the DOPA molecule, which can be incorporated into the microgel structure. Nanoparticles will be used to enhance the microgels' mechanical strength. So the project aims for (bio)adhesive and mechanically stable microgels. The structure of the microgel, its adhesive properties and mechanical/rheological behaviour are studied at surfaces.

Contact person:

Joanne Zimmer

Selected publications:

  • Backes, S. and von Klitzing, R.: Nanomechanics and Nanorheology of Microgels at Interfaces. Polymers. 2018, 10, 978
  • Burmistrova, A., Steitz, R. and von Klitzing, R.: Temperature Response of PNIPAM Derivatives at Planar Surfaces: Comparison between Polyelectrolyte Multilayers and Adsorbed Microgels. ChemPhysChem. 2010, 11, 35771-3579
  • Burmistrova, A., Richter, M., Eisele, M., Üzüm, C. and von Klitzing, R.: The Effect of Co-Monomer Content on the Swelling / Shrinking and Mechanical Behaviour of Individually Adsorbed PNIPAM Microgel Particles. Polymers. 2011, 3, 1575-1590
  • Wang, W., Xu, Y., Backes, S., Li, A., Micciulla, S., Kayitmazer, A.B., Li, L., Guo, X. and von Klitzing, R. Langmuir. 2016, 32, 3365-3374

Acknowledgment:

Thanks to the Funding of the DFG and our cooperation partners from the Group of Prof. Guo at the ECUST in Shanghai.

Picture: AG von Klitzing

Responsive polyelectrolyte multilayer films/composites

Polyelectrolyte multilayer films are easy to prepare by simple layer-by-layer adsorption of anionic and cationic polyelectrolytes. Careful choice of the polyelectrolytes allows the tuning of film properties and their responsivity to external stimuli such as temperature, relative humidity or excess ions. The approach can be generalized by using all kinds of multiple charged molecules and allows incorporating charged particles.

Our Research

In our labs we investigate these multilayer films as potential candidates for functional application, such as biosensors and bioreactors, by (i) alternating preparation conditions and materials and/or (ii) incorporating colloids, nanoparticles and biomolecules. The feasibility of applying these films depends on their permeability and stability under relevant conditions. Using our in-house equipment like XRR, Ellipsometry, AFM and QCM-D we characterize film thickness, density, topology and viscoelasticity under varying outer stimuli. Additionally, we make use of neutrons at large scale facilities to reveal the inner structure and dynamics of these films.

Contact person:

Olaf Soltwedel

Selected publications:

  • Regine von Klitzing, Internal structure of polyelectrolyte multilayer assemblies, Phys. Chem. Chem. Phys., 2006, 8, 5012-5033
  • Samantha Micciulla, Olaf Soltwedel, Oliver Löhmann and Regine von Klitzing, Temperature responsive behavior of polymer brush/polyelectrolyte multilayer composites, Soft Matter, 2016, 12, 1176-1183
  • Oliver Löhmann, Samantha Micciulla, Olaf Soltwedel, Emanuel Schneck and Regine von Klitzing, Swelling Behavior of Composite Systems: Mutual Effects between Polyelectrolyte Brushes and Multilayers, Macromolecules, 2018, 51, 2996-3005
Picture: AG von Klitzing

Amphiphilic co-polymer networks

Amphiphilic co-polymer networks (ACN) allow for the simultaneous transport of hydrophilic (e.g. water) and hydrophobic components (e.g. oxygen). These networks demonstrate a different swelling behavior depending on the type of solvent and environment they are exposed to. This behavior critically impacts the mechanical properties of the ACN gels and mass transport through these gels.

Our Research

As a result, our aim is to control the composition, structure, and homogeneity of the ACN gels to tailor their properties for future applications. In order to understand the underlying processes, we investigate model networks made of different “tetra-polymer stars.”

Our methods to characterize model networks and study their mechanical properties, particularly at the interface, include atomic force microscopy (AFM), small angle x-ray scattering (GISAXS), small angle neutron scattering (GISANS), quartz crystal microbalance (QCM) measurements and tensiometry.

Contact person:

Kevin Hagmann

Selected publications:

  • Lorenzo, F. D., Hellwig, J., von Klitzing, R., & Seiffert, S.: Macroscopic and Microscopic Elasticity of Heterogeneous Polymer Gels. ACS Macro Lett. 2015, 4, 698−703.
Picture: AG von Klitzing

Cross-scale characterization of the interaction of polymers on cellulose interfaces: Construction of a cellulose model surface

As a functional material, cellulose based paper has a high importance in a variety of sectors, such as packaging, print media and specialty papers. This is especially crucial with regard to reducing plastic use and waste and replacing it with renewable and biodegradable resources.

Our Research

The interactions of cellulose fibers with functional additives, such as the wet-strength increasing polymers PDADMAC and PAE, have been investigated in the past with respect to the mechanical properties of the resulting paper.[1-3]

Yet, a systematic understanding of the effects of the chemistry and structure of the polymer on the properties of the fibers is still missing and would lead to an exhaustive knowledge of the functionalization of paper. To allow for a comprehensive investigation of the interaction between cellulose and the functional additives, model surfaces of cellulose are prepared by dip, spin or spray coating. The cellulose model surfaces are then coated with functional additives and characterized by methods such as ellipsometry, AFM, contact angle, neutron reflectometry and QCM.

Literature:

[1] S. H. Lee, H. L. Lee, H. J. Youn, BioResources, 2015, 10, 851–865.

[2] E. L. Hult, J. Ropponen, K. Poppius-Levlin, T. Ohra-Aho, T. Tamminen, Industrial Crops and Products, 2013, 50, 694–700

[3] T. Obokata, M. Yanagisawa, A. Isogai, Journal of Applied Polymer Science, 2005, 97, 2249–2255

Funding:

Deutsche Forschungsgemeinschaft

Contact person:

Cassia Lux

Picture: AG von Klitzing

Internal structure and dynamics of polymer coatings

The general question addresses the correlation between structure, dynamics and swelling behavior of polymer coatings.

Our Research

While structure information perpendicular to the surface is obtained via reflectometry methods (ellipsometry, X-ray and neutron reflectometry) the structure lateral to the surface is gained under grazing incidence (GI): Small angle x-ray or neutron scattering under grazing incidence (GISAXS, GISANS). For studies of the internal dynamics neutron spin echo under grazing incidence (GINSE) is used.

X-ray studies are mainly carried out at our lab equipment. Neutron studies are done at the FRM II in Garching or at the Institut Laue-Langevin (ILL) in Grenoble (France).

Contact person:

Regine von Klitzing

Literature

  • S. Wellert, Y. Hertle, M. Richter, M. Medebach, D. Magerl, W. Wang, B. Deme, A. Radulescu, P. Müller-Buschbaum, T. Hellweg, R. von Klitzing (2014): „Inner structure of adsorbed ionic microgel particles“ Langmuir 30, 7168 – 7176
  • J. Witte, T. Kyrey, J. Lutzki, A. M. Dahl, J. Houston, A. Radulescu, V. Pipich, L. Stingaciu, Matthias Kühnhammer, M. U. Witt, R. v. Klitzing, O. Holderer, S. Wellert (2019): “A comparison of the network structure and inner dynamics of homogeneously and heterogeneously crosslinked PNIPAM microgels with high crosslinker content” Soft Matter 15, 1053 – 1064