Search

A versatile method based on electrografting of aryldiazonium salts was used to introduce covalently attached initiators for atom transfer radical polymerization (ATRP) on glassy carbon surfaces. Polymer brushes of ferrocenylmethyl methacrylate were prepared from the surface-attached initiators, and these films were thoroughly analyzed using various techniques, including X-ray photoelectron spectroscopy (XPS), infrared reflection-absorption spectroscopy (IRRAS), ellipsometry, and electrochemistry. Of particular interest was the electrochemical characterization of the electron transfer through the diazonium-based initiator layer to the redox centers in the polymer brush films. It was found that the apparent rate constant of electron transfer decreases exponentially with the dry-state thickness of this layer. To investigate the electron transfer in the brushes themselves, scanning electrochemical microscopy (SECM) was applied, thereby allowing the effect from the initiator layer to be excluded. The unusual transition feature of the approach curves recorded suggests that an initial fast charge transfer to the outermost-situated ferrocenyl groups is followed by a slower electron transport involving the neighboring redox units.

The reaction between a nucleophilic 4-(2-aminoethyl)phenyl-tethered glassy carbon surface and various para-substituted aryl isocyanates [ONC-PhX; X = NO(2), COPh, Cl, H, and NMe(2)] has been studied in toluene. It is demonstrated that the nucleophilic addition reaction is relatively fast occurring within two hours while providing an efficient and versatile route for derivatizing alkylamine-functionalized surfaces. An often overlooked issue in surface reactions is the possibility for competing physisorption processes. In such cases, the solution-based reactants become adsorbed to the surface or embedded in the grafted layer rather than chemically bonded to the surface. It is shown that for two of the aryl isocyanates (X = NO(2) and COPh) this physical adhesion can be so strong that even prolonged ultrasonic treatment cannot remove the adsorbant. However, a single potential excursion is capable of desorbing most of the physisorbed layers. The isocyanate-based method is also compared with the well-known approaches involving diazonium salts for assembling similar chemical systems directly. It is concluded that the method can be used advantageously not only in cases, where such approaches should fall short, but also if the goal is to achieve better control of the positioning of, e.g., redox active molecules in a well-defined layer with the ultimate goal of obtaining distinct electrochemical responses.