Dresden 2006 – scientific programme

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O: Oberflächenphysik

O 21: Phase transitions

O 21.2: Talk

Tuesday, March 28, 2006, 11:30–11:45, WIL C207

Submonolayer coverage of long chain alkanes at SiO2/air interfaces: Molecular mobility, phase transition, and structure formation — •Ralf Köhler and Hans Riegler — MPI für Kolloid- und Grenzflächenforschung, Abt. Grenzflächen, 14424 Potsdam, Germany

The ordering behavior of submonolayers of long chain alkanes at SiO2/air interfaces is a surprisingly complex phenomenon. Below the surface melting point two-dimensional nucleation and structure formation occurs. The observed fractal crystallites (1,2) can be related to a process analogous to diffusion-limited aggregation (3). One can distinguish three growth scenarios depending on the initial thickness of the liquid alkane film, i.e., due to different supply conditions to the growth front. The system also shows a reversible (equilibrium)-coexistence of solid domains and remaining fluid film in between. The melting temperature of the two-dimensional domains depends on the total amount of alkane at the surface and follows the liquid-drop model for melting of low-dimensional systems (4) if one introduces a critical length, i.e., a critical film thickness, into this model. On-line optical microscopy observations are presented and analyzed. 1) A.Holzwarth et al., Europhys.Lett. 52, 653 (2000) 2) H.Schollmeyer et al., Langmuir 19, 5042 (2003) 3) L.Knüfing et al., Langmuir 21, 992 (2005) 4) K.K.Nanda et al., PRA 66, 013208 (2002)