Regensburg 2016 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 8: Hydrogels and Microgels

CPP 8.2: Vortrag

Montag, 7. März 2016, 15:30–15:45, H40

Impact of the cononsolvency effect on the temperature response of PNIPAM microgels in water/ethanol-mixtures — •Sebastian Backes and Regine von Klitzing — Technische Universität Berlin, Stranski-Laboratorium für Physikalische und Theoretische Chemie, Berlin, Germany

Microgels made of N-isopropylacrylamide (NIPAM) are of great interest because of their pronounced temperature response in solution. They possess a volume phase transition temperature (VPTT) below which they are swollen. When the VPPT is exceeded, the gels expel the solvent and shrink. Both pure water and several pure organic solvents like ethanol are good solvents for PNIPAM. In mixtures of water and ethanol however the solubility is significantly decreased, with the microgels showing a minimum volume at a certain mixing ratio of ca. 20% (cononsolvency effect).

After adsorption on a solid substrate the mixing ratio for the minimum value increases from 20% to about 40-50%. Therefore the volume of microgels has been examined both in bulk using dynamic light scattering and on silica wafers using atomic force microscopy for several water/ethanol mixtures and a temperature range from 10 to 50°C.

The volume phase transition temperature has been shown to decrease from 32°C in pure water to values below the measuring range (i.e. <10°C) for intermediate mixing ratios. At higher ethanol content the VPTT reappears in a broadened form rather than a sharp transition.