Theoretical Insights into the Solvent Polarity Effect on the Quality of Self-Assembled N-Octadecanethiol Monolayers on Cu (111) Surfaces.

ABSTRACT: The effect of solvent polarity on the quality of self-assembled n-octadecanethiol (C₁₈SH) on Cu surfaces was systematically analyzed using first-principles calculations. The results indicate that the adsorption energy for C₁₈SH on a Cu surface is -3.37 eV, which is higher than the adsorption energies of the solvent molecules. The higher adsorption energy of dissociated C₁₈SH makes the monolayer self-assembly easier on a Cu (111) surface through competitive adsorption. Furthermore, the adsorption energy per unit area for C₁₈SH decreases from -3.24 eV·Å^-2 to -3.37 eV·Å^-2 in solvents with an increased dielectric constant of 1 to 78.54. Detailed energy analysis reveals that the electrostatic energy gradually increases, while the kinetic energy decreases with increasing dielectric constant. The increased electrostatic energies are mainly attributable to the disappearance of electrostatic interactions on the sulfur end of C₁₈SH. The decreased kinetic energy is mainly due to the generated push force in the polar solvent, which limits the mobility of C₁₈SH. A molecular dynamics simulation also confirms that the -CH? site has a great interaction with CH?(CH?)?CH? molecules and a weak interaction with CH?CH?OH molecules. The different types of interactions help to explain why the surface coverage of C₁₈SH on Cu in a high-polarity ethanol solution is significantly larger than that in a low-polarity n-hexane solution at the stabilized stage.

SUBMITTER: Hu J 

PROVIDER: S-EPMC6017570 | biostudies-literature | 2018 Mar

REPOSITORIES: biostudies-literature