Attachment of Organic Layers to Materials Surfaces by Reduction of Diazonium Salts

Grafting of 4-pyrrolyphenyldiazonium in situ generated on NiTi, an adhesion promoter for pyrrole electropolymerisation?

“…Furthermore, spontaneous grafting of Py-PD on NiTi after its surface polishing (to eliminate the titanium dioxide layer) in a controlled atmosphere is unsuitable to preserve its corrosion resistance and thus its biocompatibility. Nevertheless, as mentioned previously diazonium salt grafting with aryl cation intermediates is possible [14,24,32,33] when thermally activated [24,32]. For this purpose, the magnetic induction heating, based on physical phenomena (Faraday-Lenz law, Eddy currents, and Joule effect) commonly used to heat electrically conductive materials thanks to a time-varying magnetic field is a technique of choice.…”

“…Robust films result from the covalent carbon-metal [18][19][20] and/or carbon-metal oxide [20][21][22][23] bonds formed through the process. The diazonium salt grafting is generally achieved by electrochemical [14,[24][25][26][27][28][29] or chemical reduction [21,24,25]. In this last process, a chemical reductant such as hypophosphorous acid [25] can be used as source of electron.…”

“…Yet in situ generated diazonium grafting methods are generally reported using Generally, a large excess of acid (at least 8 eq.) which can be detrimental for active metal surface modification is used [14,29].…”

“…It is generally admitted that for both, chemical and electrochemical diazonium salt grafting, the process includes aryl radical formation and nitrogen loss resulting from the diazonium salt reduction [14,21,24,25,31]. However, if there is no electron source (no electrochemical grafting, no reducing agent and non-reducing substrate) for the dediazotation, a mechanism involving the grafting of a carbocation instead of a radical aryl is possible [14,24,[32][33][34]. Purification and especially storage of diazonium salts can be problematic given their the poor stability of these compounds.…”

“…Grafting diazonium salts on metal and alloy substrates is an attractive way for the surface modification of theses substrates and has been thoroughly studied in the past decades [13][14][15][16][17]. Robust films result from the covalent carbon-metal [18][19][20] and/or carbon-metal oxide [20][21][22][23] bonds formed through the process.…”