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Roughness, optical and wetting properties of nanostructured thin films

: Schröder, Sven; Coriand, Luisa; Duparré, Angela


Mackay, T.G. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Nanostructured Thin Films VI : 25.-29.8.2013, San Diego, CA, USA
Bellingham, WA: SPIE, 2013 (Proceedings of SPIE 8818)
ISBN: 978-0-8194-9668-3
Paper 88180S
Conference "Nanostructured Thin Films" <6, 2013, San Diego/Calif.>
Fraunhofer IOF ()
thin film coatings; functional surfaces; hydrophobic; self cleaning; roughness; light scattering

Roughness structures are essential for a variety of functional surfaces, for example surfaces with extreme wetting behavior like superhydrophobicity or superhydrophilicity. On the other hand, roughness also gives rise to light scattering, and thus limits the usability of such surfaces for optical applications. Our approach is based on using small-scale intrinsic roughness components of thin film coatings to achieve the desired functional properties while keeping the light scattering at acceptable levels. A comprehensive measurement and analysis methodology for effectively predicting, defining and controlling the structural and wetting properties of stochastically rough superhydrophobic surfaces is presented. Power Spectral Density (PSD) functions determined from atomic force microscopy data are used for thorough roughness analysis as well as to predict the wetting and light scattering properties. Dynamic contact angle analysis is performed by measuring advancing, receding, roll-off, and bounce-off angles. Examples of natural and technical superhydrophobic surfaces like the Lotus leaf and thin film coatings with stochastic nanoroughness are given. These surfaces reveal high advancing contact angles, low contact angle hysteresis, low roll-off angles, and, consequently, the effect of self-cleaning.