Berlin 2015 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 11: Colloids and Complex Liquids II (joint session CPP/ DY)

DY 11.2: Talk

Monday, March 16, 2015, 15:15–15:30, C 130

Short Ranged Repulsive Energy in Oscillatory Structural Forces — •Sebastian Schön and Regine von Klitzing — Technische Universität Berlin Strasse des 17. Juni 124 D-10623 Berlin

Oscillatory structural forces are a genuine feature observed for simple and complex fluids in the vicinity of smooth wall. The origin of these forces is related to the characteristic quality of molecules or nanoparticles to form well-ordered layers in the vicinity of a confining wall. These forces can be described by the following function as proposed by Israelachvilli: f(x)=-A*e^(-x/ξ)*cos(2π(x-Δx)/λ), with f the force as a function of x, the separation. The Amplitude A describes the strength of the particle interaction, the decay length ξ is a measure of how fast the order decays and the wavelength λ is directly related to the inter-particle distance. Structural oscillation forces are long ranged compared to the common DLVO forces and can be used in a variety of applications e.g. oil removal or separation of bidisperse particle suspensions For both it is important to know the strength of the oscillatory forces at very small separations. An additional repulsive term is introduced to describe deviations observed between experimental data and the common fit function, this allows accurate fitting of experimental data down to very small separations and removes systematic deviations in A, λ and ξ depending on the starting point of the fit. The short ranged repulsive energy described by the new term is investigated at different particle concentrations, measurement speed and under the addition of NaOH, HCl and NaCl at different concentrations.