Graduate Student Fatema Amin

"Organosulfur Compounds at the Nexus of Solution Chemistry, Interfacial Properties and Applications"

A self-assembled monolayer (SAM) is formed by the adsorption of a monomolecular layer onto a substrate in a spontaneous and ordered manner. These molecules have a surface-active headgroup that binds to the substrate and a tail group carrying different functionalities that impart properties like corrosion resistance, anti-stiction, and bio-sensing. The ease of modification of these functionalities affords molecular-level control of the surface properties in microelectronics. The problem arises with many of these miniaturized devices (i.e., microelectrode arrays, diagnostic chips, etc.) requiring selective features in different regions of the same surface. While the deposition of a homogenous monolayer is straightforward, the integration of multiple functionalities within a monolayer to achieve regioselective properties is challenging. This study aims to understand the effectiveness of heterogeneous monolayers in selective control of surface features while addressing the challenges associated with molecular-level dilution of surface-active components. With a particular focus on organic thiosulfate and thiol compounds, our current work investigates the mechanistic processes in fabricating mixed monolayers on gold, where surface forces and hydrophobicity can be precisely controlled. Our findings confirm: 1) the spontaneous adsorption of thiosulfates on gold undergoes fast autocatalytic hydrolysis in a non-aqueous solvent; 2) the mixed thiol monolayers on gold enable a hydrophobic system where the droplet sliding angle is tunable by interfacial frictional drag.