Dresden 2014 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 36: Colloids and Complex Liquids II

CPP 36.6: Vortrag

Mittwoch, 2. April 2014, 16:15–16:30, ZEU 114

New fitting model for structural oscillation forces — •Sebastian Schön — Technische Universität Berlin Strasse des 17. Juni 124 D-10623 Berlin

Structural forces are a well known phenomenon in surface science. They arise due to the layering of particles in the vicinity of a confining wall. The layered structure has an oscillatory density profile in normal direction. Overlap with a second interfacial region results in an attractive or repulsive force acting on the surfaces, depending on the separation of the walls. These forces can be fitted via following formula:

f(x)=-A*e^(-x/ξ)*cos(2π(x-Δx)/λ),

where f is the force, x is the separation between the walls, A is the amplitude of the oscillations, ξ is the decay length, λ signifies the wavelength of the oscillation and Δx is the phase shift. This common fit formula can be extended by introducing an additional term of exponential decaying nature. The additional term is able to describe deviations between the common fit and data measured for aqueous suspensions of silica nanoparticles, especially at small wall to wall separations and larger concentrations. Furthermore, it is shown that neglecting this term leads to an oscillatory behaviour depending on the starting point of the fit region of the three important fit parameters: amplitude, wavelength and decay-length. The extension enables a large increase of the data range accessible for accurate fitting, especially towards small separation and leads to the removal of the oscillatory behaviour of the fit parameters. Therefore, resulting in a strong increase of accuracy for all fit parameter in the system studied here.