Effect of Substrate Morphology on the Odd–Even Effect in Hydrophobicity of Self-Assembled Monolayers

Thumbnail Image
Supplemental Files
Wang, Zhengjia
Chen, Jiahao
Gathiaka, Symon
Oyola-Reynoso, Stephanie
Major Professor
Committee Member
Journal Title
Journal ISSN
Volume Title
Research Projects
Organizational Units
Organizational Unit
Materials Science and Engineering

The Department of Materials Science and Engineering teaches the composition, microstructure, and processing of materials as well as their properties, uses, and performance. These fields of research utilize technologies in metals, ceramics, polymers, composites, and electronic materials.

The Department of Materials Science and Engineering was formed in 1975 from the merger of the Department of Ceramics Engineering and the Department of Metallurgical Engineering.

Dates of Existence

Related Units

Journal Issue
Is Version Of

Surface roughness, often captured through root-mean-square roughness (Rrms), has been shown to impact the quality of self-assembled monolayers (SAMs) formed on coinage metals. Understanding the effect of roughness on hydrophobicity of SAMs, however, is complicated by the odd-even effect-a zigzag oscillation in contact angles with changes in molecular length. We recently showed that for surfaces with Rrms > 1 nm, the odd-even effect in hydrophobicitycannot be empirically observed. In this report, we compare wetting properties of SAMs on Ag and Au surfaces of different morphologies across the Rrms similar to 1 nm limit. We prepared surfaces with comparable properties (grain sizes and Rrms) and assessed the wetting properties of resultant SAMs. Substrates with Rrms either below or above the odd-even limit were investigated. With smoother surfaces (lower Rrms), an inverted asymmetric odd-evenzigzag oscillation in static contact angles (?s) was observed with change from Au to Ag. Asymmetry in odd-even oscillation in Au was attributed to a larger change in ?s from odd to even number of carbons in the n-alkanethiol and vice versa for Ag. For rougher surfaces, no odd-even effect was observed; however, a gradual increase in the static contact angle was observed. Increase in the average grain sizes (>3 times larger) on rough surfaces did not lead to significant difference in the wetting properties, suggesting that surface roughness significantly dominated the nature of the SAMs. We therefore infer that the predicted roughness-dependent limit to the observation of the odd-even effect in wetting properties of n-alkanethiols cannot be overcome by creating surfaces with large grain sizes for surfaces with Rrms > 1 nm. We also observed that the differences between Au and Ag surfaces are dominated by differences in the even-numbered SAMs, but this difference vanishes with shorter molecular chain length (=C3).


Reprinted with permission from Wang, Zhengjia, Jiahao Chen, Symon M. Gathiaka, Stephanie Oyola-Reynoso, and Martin Thuo. "Effect of Substrate Morphology on the Odd–Even Effect in Hydrophobicity of Self-Assembled Monolayers." Langmuir 32, no. 40 (2016): 10358-10367, doi:10.1021/acs.langmuir.6b01681. Copyright 2016 American Chemical Society.

Fri Jan 01 00:00:00 UTC 2016