Phase Separation of Alkanethiol Self-Assembled Monolayers during the Replacement of Adsorbed Thiolates on Au(111) with Thiols in Solution

Abstract

Replacement of self-assembled monolayers (SAM) of hexadecanethiol (HDT) on the Au(111) surface with 12-mercaptododecanoic acid (MDDA) in ethanol solution has been studied using voltammetry of the reductive desorption and scanning tunneling microscopy (STM). The exchange of adsorbed HDT molecules with MDDA dissolved in ethanol proceeds domainwise, that is, not in a random fashion. Two well-separated peaks, corresponding to the desorption of MDDA-rich domains and HDT-rich domains, appear in a voltammogram over the replacement process. The peak potential associated with the desorption of HDTrich domains remains unchanged in the course of the replacement, indicating that the solubility of MDDA in HDT-rich domains is very small. STM imaging of the substrate shows that domains whose sizes are greater than 15 nm 2 are predominant and occupy 85% of the area of HDT-rich domains. The entire exchange process is pseudo-first-order with the rate constant being 9.1 × 10 -3 h -1 in 1 mmol dm -3 MDDA in ethanol at 31 °C. The reverse process, i.e., the replacement of adsorbed MDDA with dissolved HDT in ethanol, is much slower, suggesting the stabilization of MDDA monolayers by lateral hydrogen bonding. A significant shift in the peak potential of MDDA-rich domains during the replacement indicates the considerable dissolution of HDT in MDDA domains.

Formation of viologen radical cation condensed phase through two-dimensional molecular organization process on an HOPG electrode surface in binary viologen solutions

“…In the binary systems, intermolecular hetero-interaction joins the important factors. Elucidation of interplay of these interaction modes, together with the molecule-surface interactions, is a fundamental issue to understand the 2D molecular organization processes at a molecular level [19][20][21][22][23][24][25][26][27]. The 2D molecular organization processes of viologen binary systems may provide us with the opportunity to shed light in depth on the interplay of interactions.…”

Mixed poly (ethylene glycol) and oligo (ethylene glycol) layers on gold as nonfouling surfaces created by backfilling

“…1(a)] where the mechanism of addition is similar to that of the replacement phenomena observed for short alkane thiol SAMs when they are exposed to longer alkane thiol molecules. 16 Here, replacement of short alkane thiol by longer alkane thiols begins at grain boundaries and is followed by gradual replacement of entire domains, resulting in phase separated arrangement. 16,17 The replacement of shorter alkane thiols with longer alkane thiols in SAMs is thermodynamically favored due to the higher number of intermolecular van der Waals interactions formed with longer alkane thiol molecule.…”

Dependence of the redox reaction of cytochromecon the mixing state of binary self-assembled monolayers composed of 11-aminoundecanethiol and 10-mercaptoundecanoic acid on Au(1 1 1)

“…1B are CVs for the reductive desorption of the SAMs of AUTe-MUAe prepared with the selective replacement method [33,48] from the corresponding template binary SAMs in Fig. 1A.…”

“…The selective replacement method [33,48] was used to form the phase separated SAMs of AUTe-MUAe. MELerich domains were removed from the template binary SAMs by applying a potential of À0:65 V for 20 min in a 0:5 mol dm À3 KOH solution.…”