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Investigation of Osmotic Deswelling of Polystyrene Microgels on Polymer Addition

Vendredi 12 septembre 2014 10:30 - Duree : 1 heure
Lieu : ILL - Seminar Room, 71 avenue des Martyrs - Grenoble

Orateur : E. BARTSCH (Institut für Physikalische Chemie, Univ. Freiburg, Germany)

In colloid science the interplay of theory and experiment often enables creating and customizing novel soft materials. Theory predicts that introducing short-ranged attractive inter­actions by adding linear polymer chains to colloid suspensions leads to mel­ting of the repulsive glassy state. On further increasing the attrac­tion strength (i.e. the polymer concentration) the colloidal particles form a novel glassy state, the attractive glass. According to theory this fluid region grows when the attraction length d shrinks. Experi­mentally, this amounts to reducing the ratio Rg/Rc of the radius of the added polymer coils to the radius of colloidal particles. Recently our group showed that this re-entry effect can be indeed found in real colloidal systems, polystyrene (PS) microgel colloids with added linear PS, in qualitative accord with theory. However, the extent of the refluidization, generating fluid dispersions up to volume fractions of 0.69, was much stronger than predicted and then found for PMMA hard sphere colloids. One possible reason for this unexpected behaviour could be the osmotic deswelling of the PS microgels on polymer addition. To evaluate whether or how far osmotic deswelling occurs in our PS microgel – PS polymer mixtures we performed SANS ex­periments on D11 at ILL, employing contrast variation techniques in toluene/toluene-D8 mixtures with host-tracer-mixtures of our colloidal system. We measured the dependence of the particle form factor P(q) of fully deuterated PS microgel tracers in colloid polymer mixtures for several colloid volume fractions in the reflui­dized region of the phase diagram. Within experimental error no change of P(q) and, thus, of particle size was observed. However, already a radius decrease of 2 nm which was beyond experimental resolution could explain most of the anomalously high fluid vo­lume fractions. Thus, SANS experiments on a system where fluid volume fractions of up to 0.715 have been observed and where deswelling effects should be stronger, are needed to give a definite answer on the role of osmotic deswelling.

Contact : tellier@ill.fr

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

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