Characterization of self-assembled Bis[2-(2-bromoisobutyryloxy) undecyl] disulphide (DTBU) on gold surfaces suitable for use in surface-initiated atom transfer radical polymerization (SI-ATRP)

Abstract

Bis[2-(2-bromoisobutyryloxy) undecyl] disulphide (DTBU) is an initiator for surface-initiated atom transfer radical polymerization (SI-ATRP) able to functionalize metal surfaces through formation of self-assembled monolayers (SAM). The goal of this work is the making monolayers with the DTBU initiator on gold polycrystalline electrodes and their study by electrochemical methods as cyclic voltammetry (CV), capacity-potential curves (C-E), electrochemical impedance spectroscopy (EIS), and angle contact measurements for their characterization. Information of the integrity and permeability of the monolayers has been obtained by capacitancepotential measurements and impedance spectra. Also, the blocking effect of the physical barrier that SAM can produce to different redox probes is explored by using voltammetry and impedance. DTBU forms a compact monolayer whose main features are related with heterogeneous chain structures, having a non-polar hydrocarbon internal part and a polar head group. This is confirmed by X-ray photoelectron spectroscopy (XPS) which shows the presence of the elements of the DTBU adsorbate of SAM. Moreover, mixed monolayers of DTBU and 6-mercaptopurine (6MP) have been prepared and characterized, to check if the thiol facilitates electron exchange through monolayers. On this approach, different DTBU:6MP ratios have been employed and characterized studying IRRAS spectra, electrochemical properties, and contact angle on the modified surface. These mixed monolayers provide optimal conditions for adaptation and use in e-ATRP.