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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 13: Polymer Physics IV: Thin Films

CPP 13.5: Vortrag

Dienstag, 27. März 2007, 15:30–15:45, H40

Molecular-dynamics simulations of thin films with a free surface — •Simone Peter, Hendrik Meyer, and Joerg Baschnagel — Institut Cahrles Sadron, Strasbourg, France

We present results [1,2] from molecular-dynamics simulations for a model of non-entangled short polymer chains in a free standing and a supported film geometry. We investigate the influence of confinement on static and dynamic properties of the melt. We find that the relaxation at the surfaces is faster in comparison to the bulk. We perform a layer-resolved analysis of the dynamics and show that it is possible to associate a gradient in critical temperatures Tc(y) with the gradient in the relaxation dynamics. This finding is in qualitative agreement with experimental results on supported polystyrene (PS) films [Ellison et al, Nat. Mater. 2, 695 (2003)].

Furthermore we show that the y-dependence of Tc(y) can be expressed in terms of the depression of Tc(h), the global Tc for a film of thickness h, if we assume that Tc(h) is the arithmetic mean of Tc(y) and parameterize the depression of Tc(h) by Tc(h)=Tc/(1+h0/h), a formula suggested by Herminghaus et al [Eur. Phys. J E 5, 531 (2001)] for the reduction of the glass transition temperature in supported PS films. We demonstrate the validity of this formula by comparing our simulation results to results from other simulations and experiments.

[1] S. Peter, H. Meyer and J. Baschnagel, J. Polym. Sci. B, 44, 2951 (2006)

[2] S. Peter, H. Meyer, J. Baschnagel and R, Seemann, J. Phys: Condens. Matter (2007)