Control of surface modification via the use of radical scavenger – RADICAL

The project deals with the functionalization of conductive surfaces via the reduction of diazonium precursors. This efficient process is booming but classically leads to the non reproducible elaboration of structurally disorganized multilayers, which are very difficult to characterize. The objective is to develop a methodology allowing the grafting control of the organic entities on the substrate in terms of thickness and organization. The main idea is to control the polymerization which represents a major barrier for obtaining reproducible and organized layers. Instead of playing with the molecular structure of the grafts as reported by recent works, the project proposes to directly act on the mechanism via the use of radical traps. This approach allows, in one hand, to avoid the synthesis of complex sterically hindered precursors, and in the other hand, to extend the control of the layers to every kind of structures without resorting to the post-functionalization

The project aims a significant progress in the control of the two main functionalization methods using diazonium precursors : electrografting and spontaneous grafting. Those two methods experimentally differ by the use of an electrochemical assistance in the first case, whereas the second exploits the intrinsic reducing character of the substrate to be modified. A common radicalar mechanism is admitted until now to explain the generation of polymeric layers, but recently acquired knowledge tends to differentiate the two ways. This fact commands to separately consider the grafting problematic depending on whether electro-induction is used or not.
The first part of the project will be dedicated to the validation and development of the control strategy for electrografting and spontaneous grafting on various substrates via the adding of radical scavengers. This way will allow to knock down the scientific barriers identified (nature of the substrate, structure of radical scavengers) and optimize the condition of the grafting control in order to get close to near monolayer materials. The impact of the diazonium precursor substitution on the organic film growth in the presence of radical scavenger will be of special interest. The second part of the project will deal with the comprehension of the grafting control and with the development of mechanistic aspects. This approach will bring to a new point of view on the key factors that lead to uncontrolled polymerization of diazoniums. The last part of the project will take advantage of the scientific knowledge acquired during the two first parts to study the properties and reactivity of the organic layers. The aim is to quantify the gain obtained by the radicalar control strategy and extend the knowledge to the accessibility of the confined species on the surface. The establishment of structure/properties relationships will be investigated on nanomaterials functionalized by absorbent and/or fluorescent moieties, whereas studies of the interfacial reactivity will be focused on electrocatalytic surfaces incorporating nitroxyl radicals, whose behaviour is known by the team.

The multidisciplinary team will be composed of three physico-chemists, one organic chemist, and one physicist, all located at the MOLTECH-Anjou laboratory.