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| Hauptseite > Publikationsdatenbank > Dynamics of spherical particles in a crowded suspension of colloidal rodsDynamic information from TIRM revisited |
| Hauptseite > Publikationsdatenbank > Dynamics of spherical particles in a crowded suspension of colloidal rodsDynamic information from TIRM revisited |
| Conference Presentation (After Call) | FZJ-2017-05782 |
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2017
Abstract: Total internal reflection microscopy (TIRM) enables measuring the interaction energy between a flat glass wall and a colloidal probe sphere as a function of separation distance.In an earlier contribution [1] we showed that depletion potentials induced by the rod-like fd-virus follow the classical low density approximation [2] at concentration, at which this is expected to fail. At even higher concentrations, we observed deviations from the idel gas behaviour, which however show a trend opposite to theoretical prediction [3]. In this presentation we are discussing wheter this observation may be caused by the systems dynamics, which are usually disregarded in TIRM experiments The standard approach to analyse the dynamic information inherent to TIRM data is extracting the probe particle’s diffusion coefficient normal to the wall from the mean square displacement (MSD) vs. time curves [4]. However, in the course of our investigation we discovered that a more reliable method is to determine the particle’s drift velocity from the mean displacement (MD) vs. time curves.The analysis of the probe particles’ drift velocity data reveals a dynamic fingerprint of the finding from static data that for the large spheres and high fd-concentrations the apparent depletion potential is significantly deeper than expected from the classical theoretical prediction.Further we observe that there is potential to measure local viscosities with TIRM, by measuring position dependent drift velocities and fit the experimental data with the appropriate theoretical expression, where the viscosity is the only free parameter.Finally, we identified the reason why drift velocities can be determined more reliably than diffusion coefficients from the initial slope of the time dependence of the mean displacement and mean square displacement, respectively.[1] S. De Sio and P. R. Lang, Z. Phys. Chem. 229, 1161–1175 (2015).[2] S. Asakura and F. Oosawa, J. Polym. Sci. 33, 183 (1958) and J. Chem. Phys. 22, 1255 (1954).[3] Y. Mao, M.E. Cates and H.N.W. Lekkerkerker J. Chem. Phys. 106, 3721 (1997).[4] R. J. Oetama and J. Y. Walz, J. Coll. Interf. Sci. 284, 323 (2005).
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