Regensburg 2004 – scientific programme
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CPP: Chemische Physik und Polymerphysik
CPP 16: POSTER: Computational Physics, Complex Systems
CPP 16.17: Poster
Tuesday, March 9, 2004, 17:00–19:00, B
Characterisation of water/hydrophobic interfaces — •Marco Maccarini1, Michael Himmelhaus1, Jörg Fick1, Michael Grunze1, and Roland Steitz2 — 1Ruprecht Karls Universität Heidelberg , Im Neuenheimer Feld 253, D-69120 Heidelberg — 2Berlin Neutron Scattering Center, Hans Meitner Institut, Glienicker St 100
Solid/liquid interfaces between water and hydrophobic surfaces are of great interest because of the crucial role they play in the stabilisation of supramolecular structures, mesoscopic assemblies, nanoparticles and micelles in chemical technology and in biological systems, and of proteins, membranes and cells in aqueous environment. Theoretical studies (Lum 1999,Pertsin 2002) predicted a depletion layer, i.e. a layer of water with reduced density, near the hydrophobic surface/water interface. This extends to a thickness in the order of nm into the bulk water and is thermodynamically less stable than the vapour phase. In order verify experimentally the density changes occurring on such a short length-scale, stable hydrophobic model surfaces, flat on a molecular scale, are needed. We assessed the stability of two different hydrophobic surfaces, passivated silicon and HDMS coated silicon (contact angle ∼ 90∘) with a roughness of the order of few Å, against water: changes in hydrophobicity and surface oxidation were determined by contact angle, ellipsometry, and XPS. Preliminary studies on on the water depletion layer have been carried out by Neutron Reflectometry on HMDS coated silicon, oxided silicon, self assembling monlayers (SAM) of alkanthiols on gold.