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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 12: Confined Fluids

CPP 12.3: Vortrag

Dienstag, 26. Februar 2008, 11:30–11:45, C 230

Broadening of solid-liquid phase transitions due to influence of surrounding interfaces — •Ralf Köhler and Hans Riegler — MPI KGF, Abt. Grenzflächen, 14424 Potsdam, Germany

In objects with reduced dimensionality (films, particles), surfaces and interfaces become important for their physical behaviour like phase transitions. Despite its importance for fundamental and applied science (nucleation, sintering, etc.) relatively little is known about the influence of the surrounding interfaces on the phase behaviour due to the lack of quantitative experimental data. With Contrast Enhanced Interference Microscopy (1) we investigate long-chain alkanes which form two-dimensional aggregates (domains) of nanometer thickness on planar silicon oxide surfaces. Thus, we quantify the influence of the surrounding interface on the liquid-solid phase transition of the domains. The domains melt gradually below the bulk phase transition temperature, forming a coexisting liquid film, which wets the adjacent substrate surface. The film thickness varies with temperature i.e., the liquid and solid phases exchange reversibly alkanes, whereby converting melting enthalpy into interfacial energy. The melting behaviour is quantitatively described in a thermodynamic approach. The behaviour is universal for the phase behaviour of any adsorbed material, which wets surrounding interfaces.

1) R.Köhler, P.Lazar, and H.Riegler, Appl.Phys.Lett. 89, 241906 (2006) 2) H.Riegler and R.Köhler, Nature Physics, 754 (2007)