Regensburg 2007 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 12: Polymer Physics III: Interfaces

CPP 12.3: Vortrag

Dienstag, 27. März 2007, 10:30–10:45, H40

Submonolayer coverage of long chain alkanes at SiO2/air interfaces: Nucleation, and phase behaviour - Molecular transportation, and structure formation — •Ralf Köhler and Hans Riegler — MPI of Colloids and Interfaces, Dept. Interfaces, 14424 Potsdam-Golm, Germany

The ordering behavior of submonolayers of long chain alkanes at SiO2/air interfaces is a surprisingly complex phenomenon with two-dimensional nucleation, surface flow and structure formation. On-line optical microscopy observations (1) show three growth scenarios depending on the overall alkane coverage. The observed fractal crystallites (2,3) can be related to a process analogous to diffusion-limited aggregation (4). At least two qualitatively and quantitatively different domain shapes can be distinguished which could also be reproduced by computer simulations. 2d-nucleation theory reveals reasonable values for line tension and activation energies. The 2d-geometry also allows the identification of active nucleation sites in comparison to quasi-homogenous nucleated domains. The system also shows the equilibrium coexistence of the solid domains and a fluid alkane film in between whose thickness depends on the temperature. The observed confinement-induced melting temperature shift is in agreement with thermodynamical calculations assuming an effective interface potential. (1) R.Köhler et al., Appl.Phys.Lett. 89, 241906 (2006); (2) A.Holzwarth et al., Europhys.Lett. 52, 653 (2000); (3) H.Schollmeyer et al., Langmuir 19, 5042 (2003); (4) L.Knüfing et al., Langmuir 21, 992 (2005)