Structure and Wettability of Methoxy-Terminated Self-Assembled Monolayers on Gold

Abstract

This manuscript describes the structure and wettability of self-assembled monolayers (SAMs) derived from the adsorption of a series of ω-methoxyalkanethiols (CH3O(CH2)nSH, where n = 9−14) onto the surface of gold. Using ellipsometry, polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), and contact angle measurements, the interfacial properties were examined as a function of chain length. Analysis by ellipsometry revealed a progressive increase in the thickness of the films as the chain length of the adsorbate was increased. Similarly, analysis by PM-IRRAS revealed a progressive increase in the conformational order of the methylene chains of the films. Moreover, the frequency and intensity of two characteristic C−H stretching bands of the methoxy groups were observed to vary systematically as a function of odd- versus even-numbered chain length, reflecting an alternating structural change in the films (i.e., an “odd−even” effect). Studies of contact angle wettability revealed tha...