pH Induced Conformational Change of Self Assembled Monolayers

Self-Assembled Monolayers (SAMs) are molecules that organize themselves onto a surface. SAMs can passivate an electrochemical surface as well as functionalize a surface to carry out REDOX reactions. The pH of the solution can affect the structure and orientation of the monolayer. An understanding of SAMs self-assembly and structure can provide insight into the effectiveness of SAM coverage and contact angle on passivating a gold surface. A gold electrode was incubated in an 11-amino-1-undecanethiol SAM(AUT SAM) for 48 hours, rinsed and placed in various buffer solutions at pH 5.0, 7.0, and 8.0 with ferrocene methanol. Cyclic voltammetry and impedance measurements were used to monitor the surface coverage and thickness of the tunneling layer of the SAM. Multiphysics simulations were also ran on COMSOL for cyclic voltammetry and impedance measurements the surface coverage, theta was calculated to be 2.5 x 10-6 < 3.0 x 10-6 < 4.5 x 10-6, 0.7 x 10-6 < 3.0 x 10-6 < 7.0 x 10-6, 3.0 x 10-6 < 1 x 10-5, for pH 5.0, 7.0, 8.0 respectively. Were also able to calculate the thickness of the tunneling layer to be1.34 nm < 1.37 nm < 1.39 nm, 1.13 nm < 1.15 nm < 1.18 nm, and 0.99 nm < 1.01 nm < 1.04 nm for pH 5.0, 7.0, 8.0 respectively.