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Control of surface properties of self-assembled monolayers by tuning the degree of molecular asymmetry |
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| Authors: | Susana Moreno Flores Andrey Shaporenko |
| Institution: | a Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany b Applied Physical Chemistry Department, University of Heidelberg, Im Neuenheimer Feld 253, 69120 Heidelberg, Germany c Center of Micro and Nanochemistry and Engineering, Organic Chemistry I, University of Siegen, Adolf-Reichwein-Str. 3, 57068 Siegen, Germany |
| Abstract: | We have studied self-assembled monolayers (SAMs) of asymmetric dialkyldisulfide derivatives of the form CH3-(CH2)11+m-S-S-(CH2)11-OH with m = −4, −3, 0, +2 and +4 on gold. Sub-nanoscale changes in the length of the CH3-terminated alkylchain have been used to selectively protrude one particular end group in the resulting film. The alteration of the chain length in only two methylene units already results in changes of surface properties, which have been detected with local (chemical force microscopy) and macroscopic (contact angle) techniques. In particular, advancing contact angles can be adjusted between 40° and 80°. The adhesion between a hydrophobic tip and these SAMs in water is determined by the chemical nature of the protruding end group. Chemical force microscopy, X-ray photoelectron spectroscopy and infrared reflection absorption spectroscopy have shown that these SAMs are composed of mixed, well-packed CH3- and OH-alkylthiolate branches. The surface composition ratio is close to 1:1 for all investigated SAMs. |
| Keywords: | Self-assembly Asymmetric dialkyldisulfide derivatives Scanning probe techniques Chemical force microscopy Wetting X-ray photoelectron spectroscopy Infrared reflection absorption spectroscopy |
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