Berlin 2015 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 46: P11: Wetting, Micro and Nano Fluidics
CPP 46.11: Poster
Wednesday, March 18, 2015, 10:00–13:00, Poster A
Spontaneous Formation of Nanopatterns in Velocity-Dependent Dip-Coated Organic Films: From Dragonflies to Stripes — Tomas P. Corrales1, Mengjun Bai2, Valeria del Campo1, Maria Retamal1, Moshe Deutsch3, Haskell Taub2, Klaus Knorr1, Ulrich G. Volkmann1, and •Patrick Huber1,4 — 1Fac. de Fisica, Pont. U. Santiago, 7820436 (Chile) — 2Physics and Astronomy Dep., U. of Missouri, Columbia, Missouri 65211 (USA) — 3Physics Dep., Bar-Ilan U., Ramat-Gan 52900 (Israel) — 4Materials Physics, Hamburg U. of Technology, D-21073 Hamburg (Germany)
We present a study of thin, n-alkane films on the native oxide layer of a silicon surface, prepared by dip-coating in a n-C32H66/n-heptane solution. Electron micrographs reveal two distinct adsorption morphologies depending on the substrate withdrawal speed v. For small v, dragonfly-shaped molecular islands are observed. For a large v, stripes parallel to the withdrawal direction are observed. These have a few hundred micrometer lengths and a few-micrometer lateral separation. Grazing incidence X-ray diffraction and atomic force microscopy show that both patterns are monolayers of surface-normal-aligned C32 molecules. With increasing v, the surface coverage first decreases, then increases for v > vcr ∼ 0.15 mm/s. The critical vcr marks a transition between the evaporation regime and the entrainment regime. The stripes’ strong texture and the well defined separation are due to an 2D crystallization in narrow liquid fingers, which result from a hydrodynamic instability in the dip-coated films, akin to the tears of wine phenomenology, see also T. Corrales et al., ACS Nano 8, 9954 (2014).