Untersuchung der elektrophoretischen Mobilität blanker und funktionalisierter, sphärischer Kolloide mittels molekulardynamischer Simulationen

In this work, the electrophoretic mobility of colloids in salt solutions are studied by means of coarse-grained Molecular Dynamics simulations. Two different types of colloids are considered; bare colloids and polyelectrolyte-grafted colloids. A novel model for simulation of large bare colloids in the presence of explicit ions is developed. Comparison of the results with experimental data helps gain a better understanding of the mechanisms responsible for the interesting phenomenon of mobility reversal. Furthermore, a hitherto unknown electrokinetic behavior of polyelectrolyte-grafted colloids is found from simulations including full hydrodynamic interactions. The validity of the existing theories is verified via comparison with simulation results.Diese Arbeit beschäftigt sich mit Computersimulationen der Elektrophorese kolloidaler Teilchen in Salzlösungen. Zwei unterschiedliche Typen von Kolloiden sind betrachtet; nackte Kolliode und Polyelektrolyt-beschichtete Kolloide. Ein neues Modell ist entwickelt, das Simulationen von großen nackten Kolloiden in Gegenwart von expliziten Ionen ermöglicht. Dabei helfen Vergleiche mit unabhängigen Experimenten, die Simulationen mancher Phänomene, wie z.B. Mobilitätmkehr, besser zu verstehen. Außerdem, ist ein neues, bisher unbekanntes, elekrophoretisches Verhalten von Polyelektrolyt-beschichteten Kolloiden, durch Computersimulationen entdeckt, die eine vollständige Beschreibung der hydrodynamischen Wechselwirkungen einschließen. Dabei werden die Simulationsergebnisse mit bestehenden Theorien verglichen, deren Gültigkeit und Grenzen dadurch überprüft werden

Computing the Electrophoretic Mobility of Large Spherical Colloids by Combining Explicit Ion Simulations with the Standard Electrokinetic Model

The electrophoretic mobility of large spherical colloids in different salt solutions of varying valency and concentration is studied via a combination approach of numerically solving the standard electrokinetic model with a ζ potential that has been obtained from explicit ion simulations of the restricted primitive model, thus going beyond the standard mean-field treatment. We compare our theoretical mobility curves to two distinct sets of experimental results and obtain good agreement for monovalent and divalent salt solutions. For the case of the trivalent La³⁺ salt, the experimentally obtained mobility reversal at high ionic strengths can be obtained only by adding an additional attractive interaction of 4<i>k</i>_B<i>T</i> to the potential between the colloid and La³⁺, hinting at the presence of a nonelectrostatic binding term for this ion. It is also shown that, contrary to intuition, charge inversion does not necessarily result in mobility reversal