Dresden 2009 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 21: Topical Session Nanoporous Functional Materials - Poster

MM 21.6: Poster

Tuesday, March 24, 2009, 14:45–16:30, P4

Phase Transitions and Molecular Dynamics of n-Alcohols Confined in Mesoporous Silicon — •Rene Berwanger and Rolf Pelster — Universität des Saarlandes, Saarbrücken, Germany

We have studied phase transitions and molecular dynamics of several n-alcohols in their bulk state and confined into nanotubes with a diameter of 8 nm (mesoporous silica). For this purpose we have combined x-ray, infrared and dielectric measurements. Under confinement the transition temperatures are lowered by up to approximately 30 K. In addition, there is a fundamental structural difference in the crystalline phase. While the bulk alcohols exhibits a polycrystalline mixture of orthorhombic β- and monoclinic γ-forms, geometrical confinement favors the more simple β-form: only crystallites are formed, where the chain axis are parallel to the layer normal. However, the γ-form, in which the chain axis are tilted with respect to the layer normal, is suppressed. A reason for this might be the irregular shape of the nanotubes, into which the crystallites have to fit, favoring the formation of the geometrically more simple and less bulky form. The β-crystallites form bi-layers, that are not randomly orientated in the pores. The molecules are arranged with their long axis perpendicular to the pore axis and parallel to the plane normal of the respective silicon facets (the [011] and [0-11] direction of the silicon matrix).