Berlin 2012 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 20: (Hydro)gels and Elastomers

CPP 20.2: Vortrag

Mittwoch, 28. März 2012, 09:45–10:00, C 264

Phase transition behaviour of different aqueous poly(N-isopropylacrylamide) systems monitored by dielectric spectroscopy — •Marieke Füllbrandt¹, Regine von Klitzing², and Andreas Schönhals¹ — ¹BAM Bundesanstalt für Materialforschung und -prüfung, Unter den Eichen 87, 12205 Berlin — ²Stranski-Laboratorium für Physikalische und Theoretische Chemie, Technische Universität Berlin, Strasse des 17. Juni 124, 10623 Berlin

Dielectric Relaxation Spectroscopy (DRS) is applied in a broad frequency range at temperatures between 15°C to 50°C to aqueous solutions of linear Poly(N-isopropylacrylamide)(pNIPAM) with different polymer concentrations and to aqueous dispersions of pNIPAM microgels with different crosslinking densities. In aqueous media thermosensitive pNIPAM shows a lower critical solution temperature (LCST) at about 32°C where it changes its properties from hydrophilic to hydrophobic. The phase transition of pNIPAM can be monitored by both the temperature dependence of the DC conductivity and the frequency dependence of the conductivity spectra. The latter one is due to a Maxwell/Wagner/Sillars polarization and can be related to the change in chain or particle structure at the LCST of pNIPAM. The frequency and temperature dependence of the conductivity was investigated in dependence on the polymer concentration for linear pNIPAM and on the crosslinking density for pNIPAM microgels. The dielectric measurements were accompanied by dynamic light scattering (DLS) and zeta potential measurements in order to relate the dielectric data with results obtained by well established methods.