| AVS 60th International Symposium and Exhibition | |
| Thin Film | Wednesday Sessions |
| Session TF+AS+BI+EM+SE+SS-WeA |
| Session: | Applications of Self-Assembled Monolayers and Nano-Structured Assemblies |
| Presenter: | J. Knauf, Advanced Molecular Films GmbH and RWTH Aachen University, Germany |
| Authors: | J. Knauf, Advanced Molecular Films GmbH and RWTH Aachen University, Germany L. Reddemann, Advanced Molecular Films GmbH and Universität zu Köln, Germany A. Böker, RWTH Aachen University and DWI an der RWTH Aachen e.V., Germany K. Reihs, Advanced Molecular Films GmbH, Germany |
| Correspondent: | Click to Email |
The size of topographic surface structures that affect wetting can be as small as sub-nanometer dimensions. As a model system we prepare monolayer from binary mixtures of 1H,1H,2H,2H-perfluoroalkyl thiols of different chain lengths on gold. Detailed characterization by static secondary ion mass spectrometry and ellipsometry confirm binary monolayer of randomly mixed constituents. Owing to their stiff helical conformation such perfluoroalkyl chains create topographic features of well-characterized sub-nanometer dimensions. As a result, surface topographies of randomly distributed long and short chains of a height difference of 1.2 Å per CF2 group and a next neighbor distance of 5.8 Å are obtained.
We present comprehensive investigations of wetting properties of such binary monolayers of various molar fractions and chain length differences. As an example, a binary mixed monolayer from 1H,1H,2H,2H-perfluorodecyl and 1H,1H,2H,2H-perfluorododecyl thiols, thus differing by two CF2 groups increase the advancing water contact angle from 116.0° for either one of the single component monolayer by about 2° to 117.7° for a surface of an equimolar composition of the two constituents. Such increase is considerably less than expected from simple thermodynamic models. Wenzel´s equation of wetting on rough surfaces predicts an advancing angle difference of 7°. Results of contact angles of different liquids on various sub-nanometer size topographies will be presented and discussed assuming an apparent effective reduction of surface energy at short length scales similar to results obtained from grazing-incidence X-ray scattering experiments [1].
[1] S. Mora et al., Phys. Rev. Lett. 90, 216101 (2003)