Regensburg 2013 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 45: Colloids and Complex Liquids II

CPP 45.10: Talk

Thursday, March 14, 2013, 17:45–18:00, H40

Confinement induced repulsion in oscillatory structural forces — •Sebastian Schön and Regine von Klitzing — Stranski-Laboratorium, Department of Chemistry, TU Berlin, Straße des 17. Juni 124, D-10623 Berlin

Suspensions of nanoparticles show a layered ordering in the vicinity of surfaces. Overlap of these regions, as under confinement conditions, leads to oscillatory changes in the ordering behavior of the particles, dependent on the exact wall to wall distance. These changes originate from the entropic excluded volume effect and indicate a break in the translational symmetry of the bulk system.

Force measurements have been performed by Colloidal Probe Atomic Force Microscopy (CP-AFM), where the colloidal probe on the cantilever and the substrate act as confining surfaces. Forces can be extracted from the deflection signal of the cantilever and are normalized with the radius of the colloidal probe to get the corresponding force curves. These provide a direct means to the structural response of the nanoparticles during a gradual change of the confinement.

Investigation of suspensions with varying ionic strength and pH, invoked via addition of sodiumchloride, sodiumhydroxide or hydrochloric acid, show an additional repulsion underlying the normal structural force signal as described by Israelachvili. The key parameters of the oscillatory force signal, namely amplitude, wavelength and decay-length as well as the extra repulsion are compared for suspensions with different additives.