Doctoral students seminar (July 17, 2018)

Erik Schreck on “Individual polymer analysis on the example of P3HT on Ag(111)”

and Sebastian Belau on “Nanomechanical Investigation of Polymer Folding”

Martin-Luther-Universität Halle-Wittenberg 
Von-Danckelmann-Platz 3, SR 1.04
06120 Halle (Saale) 

Time: 3.30pm - 5.00pm 

Link to Google-Maps


Individual polymer analysis on the example of P3HT on Ag(111)

Erik Schreck

The interactions between polymers and surfaces are hard to investigate and poorly understood. Investigations of individual P3HT molecules on Ag(111) without solvents give insights to the polymer/surface interaction. Electrospray deposition is used to distribute individual polymers on a adsorbate free single crystal under ultra-high vacuum conditions. The polymers are measured with scanning tunneling microscopy and spectroscopy revealing informations about the local and electronic structure at the subnanometer scale. The analysis of end-to-end distances depending on chain length show 2D self-avoiding random walk behavior. A persistence length of 5 nm and a bandgap of around 3 eV is found. The influence of a surface is discussed by comparing the results on silver with former results on gold indicating a weaker interaction for the first.

Nanomechanical Investigation of Polymer Folding

Sebastian Belau

The crystallization of polymers is typically investigated by cooling of a melt and characterizing the process or the finally formed structure with different methods (e.g. DSC, SAXS, NMR spectroscopy). Here we want to follow a different approach and investigate the crystallization at ambient conditions by using mechanical stress. Herby single polymer chains shall be stretched and the structure formation process will be induced by lowering the applied force. This way crystallization as well as structure disruption could be studied. To this end we focus on short polyethylene oxide (PEO) chains of approximately 5-20 kDa. The application of force to the PEO will be carried out in an optical tweezers setup as well as in a magnetic tweezer setup. For the convenient manipulation as well as for a precise length determination, we started to synthesize PEO-DNA hybrids consisting of a single polymer chain with dsDNA attached to both ends. Herby the reaction of thiol with maleimide, click chemistry with an azide-alkyne reaction and copper free click chemistry between azide and DBCO is exploited. The successful coupling of DNA to the polymer could be shown.

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