Self-Assembled Monolayers Derived from a Double-Chained Monothiol Having Chemically Dissimilar Chains

Abstract

The structure and conformation of self-assembled monolayers (SAMs) derived from the adsorption of a specifically designed double-chained partially fluorinated thiol having the formula 12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,19-heptadecafluoro-2-tetradecylnona-decane-1-thiol (2) onto the surface of evaporated gold were examined by ellipsometry, contact angle goniometry, polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS), and X-ray photoelectron spectroscopy (XPS). The results were compared to those of SAMs generated from normal hexadecanethiol (1) and a structurally related single-chained partially fluorinated thiol having the formula 12,12,13,13,14,14,15,15,16,16,17,17,18,18,19,19,19-heptadecafluorononadecane-1-thiol ( 3). Collectively, the studies demonstrate that the double-chained adsorbate 2 forms SAMs on gold in which the alkyl chains are less densely packed and less conformationally ordered than those in the SAMs derived from each of the single-chained adsorbates. Furthermore, the fluorocarbon moieties in the SAMs derived from 2 are more tilted from the surface normal than those in the SAMs derived from 3. The low values of contact angle hysteresis suggest, however, that the double-chained adsorbate 2 generates homogeneous monolayer films on the surface of gold.