Potential control characteristics of short-chain thiols of thioctic acid and mercaptohexanol self-assembled on gold

In this article we systematically investigated self-assembly of short-chain thiols of thioctic acid (TA) and mercaptohexanol (MCH) on gold under potential control, Edc (−0.4, +0.4 and +0.7 V) and compared the results obtained with open circuit potential (EOCP). Effect of Edc on thiol self-asembly was inspected based on the changes in electrochemical parameters including interfacial capacitance (C), phase angle (Φ1Hz), current density difference (Δi), charge transfer resistance (Rct) through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Experimental results showed that Edc could not obtain stable short-chain self-assembled monolayers (SAMs) (TA and MCH) in a short time. Both TA and MCH had slow self-assembly dynamics and needed a long time (> 24 h) to achieve adsorption equilibrium. Furthermore, the negative potential Edc (−0.4 V) did not facilitate the ordering of SAMs. The ordering of TA-SAMs was found to be the best when assembled under Edc (+0.4 V), whereas that of MCH-SAMs was almost the same when assembled under either EOCP or Edc (+0.4, +0.7 V). We considered that permeation of ions and water molecules perhaps dominated the slow self-assembly dynamics of short-chain thiols (TA and MCH) under Edc and mutual interaction between adjacent chains of thiols played an important role in the ordering of SAMs.