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Investigation of the Osmotic Deswelling of Polystyrene Microgels by Polymer Addition

Jeudi 25 avril 14:00 - Duree : 1 heure
Lieu : ILL4, seminar room, first floor - 71 avenue des Martyrs - Grenoble

Orateur : M. WERNER (University of Freiburg, Institue of Macromolecular Chemistry, Freiburg, Germany)

Polystyrene (PS) microgel colloids are of particular interest as convenient atom analogous model systems for the investigation of fundamental questions of the glass transition. Introducing attractive forces and thus utilising the depletion effect by adding linear polymer chains to colloid suspensions one can observe the so called re-entrant melting effect. Mode coupling theory predicts an increase of the thus created fluid pocket with decreasing attraction length . Recent studies of our group showed experimentally that the theories’ predictions can be realized qualitatively for PS microgel colloids using free PS as depletion polymer – but the extent of the fluid pocket was found to be dramatically larger than predicted and observed for other colloidal systems. One explanation for reaching such high fluid volume fractions is osmotic deswelling of the colloidal particles on polymer addition. Therefore we studied the effect of osmotic deswelling in highly concentrated PS microgel suspensions by monitoring the influence of polymer addition on the particle size for two polymer-colloid size ratios =0.03 and 0.06 and three different colloid-tracer systems. This was achieved by performing SANS experiments employing contrast variation techniques with host-tracer-mixtures of our colloidal systems. We improved the resolution of the experiments to monitor even size changes on the order of 1 nm and observed a clear reduction of the particle size for =0.03, whereas only a slight reduction (<1%) could be resolved for =0.06. These results imply that while osmotic deswelling occurs for small attraction lengths , it is not sufficient to explain the occurrence of fluid states up to volume fractions of =0.74 found for =0.06.

Contact : lugiez@ill.fr

Discipline évènement : (Biologie / Chimie)
Entité organisatrice : (ILL)
Nature évènement : (Séminaire)
Evènement répétitif : (General ILL Seminar - College 9)
Site de l'évènement : Polygone scientifique

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