Physical Chemistry III
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Universität Bielefeld > Department of Chemistry > Research Groups > Physical Chemistry III

Physical und Biophysical Chemistry

Foto Arbeitsgruppe

Prof. Dr. Thomas Hellweg

Secretary: S. Gericke, F3-112
phone.: +49 521-106-6888
fax: +49 521-106-2981

Bielefeld University, Department of Chemistry
Physical and Biophysical Chemistry (PC III)
Universitätsstr. 25, 33615 Bielefeld                                               How to Get to Bielefeld and its University

Recent Research Topics

Smart microgels are characterized by their reversible volume phase transition (VPT) induced by a change of an external stimulus like temperature, pH or ionic strength. In the case of cross-linked N-isopropylacrylamide (NIPAM) the phase transition is triggerd by temperature and occurs at ~32°C. The transition behaviour can be analysed by a wide varitiy of different techniques, like light scattering, fluorescence measurements or neutron scattering experiments.
The latter is gerenerally used to study the microgel network morphology on a local length scale. Using small angle neutron scattering (SANS) the network correlation lenght ξ which corresponds to the average mesh size between the entanglements in the internal network of the microgel, can be determined as a function of temperature. Approaching the VPT temperature of the microgel, the correlation length ξ is a measure for the network fluctuations and not directly connected to a physical mesh size. Close to the critical point the ξ value, according to theory, should diverge and the transition behaviour can be described by a scaling law with the exponent ν.
Our aim is to study the behaviour of the correlation length at the critical point in more detail and to analyse ξ as a function of the chemical and structural composition of the microgel.
Recently, we started to work on non NIPAM based microgels using a variety of different acrylamides or methacrylamides. For studies of the VPT and the critical behaviour N-n-propylacrylamide based microgels are very promising since they exhibit an exceptionally sharp transition.

Karg, M., Prévost, S., Brandt, A., Wallacher, D., von Klitzing, R., & Hellweg, T. "Poly-NIPAM Microgels with different cross-linder densities" Intelligent Hydrogels, Progress in Colloid and Polymer Science, 2013, 140, 63-76

Wedel, B., Hertle, Y., Wrede, O., Bookhold, J. & Hellweg, T. "Smart Homopolymer Microgels: Influence of the Monomer Structure on the Particle Properties" Polymers, 2016, 8 (4), 162