A New Method to Evaluate the Surface Dipole Potential of Thiol and Disulfide Self-Assembled Monolayers and Its Application to a Disulfidated Tetraoxyethylene Glycol

• Published in: Langmuir 2009-02, Vol.25 (3), p.1828-1835
• Main Authors: Becucci, Lucia, Schwan, Adrian L, Sheepwash, Erin E, Guidelli, Rolando
• Format: Article
• Language: English
• Subjects: Chemistry; Colloidal state and disperse state; Electrochemistry; Electrochemistry: Charge Transfer, Electrocatalysis, Kinetics, Bioelectrochemistry; Exact sciences and technology; General and physical chemistry; Surface physical chemistry
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la803282w

A procedure to evaluate the surface dipole potential χ of thiol and disulfide self-assembled monolayers (SAMs) is described. The procedure consists of self-assembling the monolayers on a hanging mercury drop electrode and of measuring the charge involved in a progressive expansion of the mercury drop. This measurement is then combined with an estimate of the charge density q experienced by diffuse layer ions, obtained by measuring the diffuse layer capacitance of the SAM at different electrolyte concentrations by electrochemical impedance spectroscopy. These χ measurements, combined with chronocoulometric measurements of the total charge density σM against potential, indicate that SAMs of tetraoxyethylene glycol-d,l-α-lipoic acid ester (TEGL), 2,3-di-O-phytanyl-sn-glycerol-1-tetraoxyethylene glycol-d,l-α-lipoic ester (DPTL), and trioxyethyleneoxythiol (EO3) on mercury may undergo a reversal in the surface dipole potential of their polyoxyethylene chain with a change in the interfacial electric field. Moreover, TEGL and EO3 form stable SAMs without electron transfer to the metal, while no such conclusion can be drawn for DPTL.