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Polymer Brushes in Restricted Geometries

Jeudi 24 janvier 2013 14:00 - Duree : 1 heure
Lieu : Seminar Room ILL4 - 6 rue Jules Horowitz - Grenoble

Orateur : Tonya KUHL (University of California at Davis, USA)

Polymer molecules at solid or fluid interfaces have an enormous spectrum of applications in a wide variety of technologies from lubrication of mechanical surfaces to the synthesis of biocompatible interfaces. Over the past two decades, neutron reflectivity measurements have become a powerful tool for measuring the conformations of ultra-thin polymer layers at interfaces, however the structure of solvated polymer brushes under confinement and/or shear has remained elusive due to the inherent difficulties in measuring thin-film properties.

In this talk, I will present novel neutron reflectivity measurements of the structure of opposing polymer brushes as a function of confinement. I will compare these results to the structure of polymer brushes at a single interface as well as to high precision surface force apparatus measurements of the force required to compress polymer brushes. In the second half of the talk, I will discuss recent results on the forces measured between two brush polymer layers and between a brush and a hard wall for moderately polydisperse copolymers and for low polydispersity copolymers. Molecular dynamics simulations of the compressive forces, for both monodisperse and polydisperse brushes, match the experimental data. The theory of Milner-Witten-Cates (MWC), corrected for polydispersity, accurately predicts the force data at moderate polymer density but fails to describe the repulsions for strong compressions when the polymer volume fraction between the surfaces is larger than a few percent. A modification to the MWC theory that reconciles the discrepancies between experiment, simulation and theory will be presented.

Contact : campbell@ill.eu

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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