Understanding and optimization of local electrografting – COPEL

With the present project, we propose to face the challenge of understanding the local electrografting situation arising in the case of a highly polarized microelectrode moved closer to a substrate. Combining theoretical and experimental work, and starting from very simple situations to increase the complexity gradually, we propose to construct a realistic theoretical model for high voltage localized electrografting by SECM. It will be made extensive use of numerical simulations with Comsol Multiphysics, a commercially available user friendly software, especially devoted to multiphysics coupling.
The work will be divided into five main steps. First, a suitable model for the conventional SECM direct mode of surface transformation under mild conditions will be provided. Secondly, the complex chemical reactivity associated with the presence of diazonium salts and vinylic monomers in solution will be studied. In a third step, the specific impact on mass transport of bubbles formed in the vicinity of a microelectrode will be investigated. Models and results developed in those three preliminary steps will then be brought together to propose a general model for high voltage local electrografting, taking into account the entire complexity of the problem. After a necessary step of validation by confrontation against experiment, the model proposed will be exploited for several purposes, some more technical some more fundamental.

Theoretical and Experimental results are under acquisition, interpretation and valorization.

This work will represent a convenient framework to optimize the experimental protocol for the synthesis of diazonium salts and vinylic polymers grafted films whose experimental feasibility by localized electrografting has already been established in the literature. But it will also be exploited to investigate the feasibility of new coatings. It is also expected that the model can be re-invested in more general situations than localized electrografting, for example in the context of corrosion.

Nunige, S ; Cornut, R; Hazimeh; Hauquier, F; Lefrou, C; Combellas, C; Kanoufi, F. ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Volume: 51 Issue: 21 Pages: 5208-5212 DOI: 10.1002/anie.201201083 Published: 2012

Organic coatings on surfaces are present everywhere in today’s life, from paints used in car industry to medical devices. Among the different coating techniques, electrografting which is based on the electro-induced polymerization of dissolved electro-active monomers on metallic or semiconducting surfaces leads to coatings strongly attached to the surface. Itis a powerful and versatile technique which finds applications in various fields including biocompatibility, corrosion, lubrication, soldering, and adhesion.

These last decades, due to an increasing technological demand for miniaturization, there has been a growing interest for modified surfaces containing functionalities with micrometer or nanometer spatial definitions. Scanning Electrochemical Microscopy (SECM), often used as an analytical technique, has also been shown to be an interesting tool for local surface modification. In particular, using SECM, localized electrografting of vinylic monomers and diazonium salts on various substrates has been demonstrated.

Unfortunately, the specific conditions that are necessary for the process to occur with vinylic monomers are extreme in comparison to conventional surface transformation with SECM. Among others, combination of high current densities and high electric potentials generates bubbles, leading to turbulences and temporary insulating layers at the electrode-solution interface. In addition both the local electric potential and the chemical content of the solution underneath the probe are observed to play a role in the transformation. Up to now, the contribution of each is still not well identified, making a complete control of the procedure still out of reach.With the present project, we propose to face the challenge of understanding the local electrografting situation arising in the case of a highly polarized microelectrode moved closer to a substrate. Combining theoretical and experimental work, and starting from very simple situations to increase the complexity gradually, we propose to construct a realistic theoretical model for high voltage localized electrografting by SECM. It will be made extensive use of numerical simulations with Comsol Multiphysics, a commercially available user friendly software, especially devoted to multiphysics coupling.

The work will be divided into five main steps. First, a suitable model for the conventional SECM direct mode of surface transformation under mild conditions will be provided. Secondly, the complex chemical reactivity associated with the presence of diazonium salts and vinylic monomers in solution will be studied. In a third step, the specific impact on mass transport of bubbles formed in the vicinity of a microelectrode will be investigated. Models and results developed in those three preliminary steps will then be brought together to propose a general model for high voltage local electrografting, taking into account the entire complexity of the problem. After a necessary step of validation by confrontation against experiment, the model proposed will be exploited for several purposes, some more technical some more fundamental. Among other, it will represent a convenient framework to optimize the experimental protocol for the synthesis of diazonium salts and vinylic polymers grafted films whose experimental feasibility by localized electrografting has already been established in the literature. But it will also be exploited to investigate the feasibility of new coatings. It is also expected that the model can be re-invested in more general situations than localized electrografting, for example in the context of corrosion.