Dresden 2020 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 26: Brownian Motion, Transport and Anomalous Diffusion

DY 26.8: Talk

Tuesday, March 17, 2020, 12:00–12:15, HÜL 186

Entropic contribution to surface diffusion barriers of oligophenyls — •Mila Miletic¹, Karol Palczynski^{1, 2}, and Joachim Dzubiella^{1, 2} — ¹Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin, Germany — ²Physikalisches Institut, Albert-Ludwigs-Universität, Freiburg, Germany

Surface diffusion is usually described by Arrhenius laws, with a diffusion energy barrier in the exponent and a prefactor. The prefactor contains not only the jump length and attempt frequency but also contributions of the system's entropy to the diffusion. However, the decomposition into these three contributions is often unclear, which hampers the interpretation of the prefactor. We successfully perform such a decomposition for single oligophenyl molecules of different length on an amorphous silica surface using atomistic molecular dynamics simulations, and find meaningful values for the jump length, attempt frequency and entropy of the adsorbates. We systematically increase the molecular length, from a single phenyl ring, up to six phenyl rings and study the influence of the increase in length on surface diffusion and binding. First, we find a substantial difference in entropy of about one order of magnitude between the shortest and longest adsorbates and entropy contributions to the diffusion barrier of about 20-30%. Second, as for the binding to the surface, we find that longer molecules display higher binding free energies with substantial entropic contributions coming from the increase in internal degrees of freedom with the molecular length. Our results demonstrate that it is essential for investigations of surface diffusion to consider entropic effects.