Sekretariat: S. Gericke, F3-112
Tel.: +49 521-106-6888
Fax: +49 521-106-2981
Universität Bielefeld, Fakultät für Chemie
Physikalische und Biophysikalische Chemie (PC III)
Universitätsstr. 25, 33615 Bielefeld Anreise
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