<p>In order to extend the applications of aluminium, organic coatings may be applied on sheet materials, for instance for corrosion protection or aesthetic surface finish purposes in the automotive and construction industries, or on foil materials in the flexible packaging industry.</p><p>The most common mechanisms for deterioration and structural failure of organically coated aluminium structures are triggered by exposures to the surrounding environment. Despite the great importance to elucidate the influence of exposure parameters on a buried aluminium/polymer interface, there is still a lack of knowledge regarding the mechanisms that destabilise the structure. It is generally believed that a detailed <i>in situ</i> analysis of the transport of corroding species to the buried interface, or of surface processes occurring therein, is most difficult to perform at relevant climatic and real-time conditions.</p><p>In this work, Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) in the Kretschmann-ATR configuration was successfully applied to <i>in situ</i> studies of the transport of water and ionic species through polymer films to the aluminium/polymer interface upon exposure to ultra pure deionised water and to a 1 M sodium thiocyanate (NaSCN) model electrolyte. Other main processes distinguished were the formation of corrosion products on the aluminium surface and swelling of the surface-near polymer network. Hence, <i>in situ</i> ATR-FTIR was capable to separate deterioration-related processes from each other.</p><p>To perform more unambiguous interpretations, a spectro-electrochemical method was also developed for<i> in situ</i> studies of the buried aluminium/polymer interface by integrating the ATR-FTIR technique with a complementary acting technique, Electrical Impedance Spectroscopy (EIS). While transport of water and electrolyte through the polymer film to the aluminium/polymer interface and subsequent oxidation/corrosion of aluminium could be followed by ATR-FTIR, the protective properties of the polymer as well as of processes at the aluminium surface were simultaneously studied by EIS. The integrated set-up provided complementary information of the aluminium/polymer sample investigated, with ATR-FTIR being sensitive to the surface-near region and EIS being sensitive to the whole system. While oxidation/corrosion and delamination are difficult to distinguish by EIS, oxide formation could be confirmed by ATR-FTIR. Additionally, while delamination and polymer swelling may be difficult to separate with ATR-FTIR, EIS distinguished swelling of the polymer network and also identified ultimate failure as a result of delamination.</p><p>The capability of the integrated ATR-FTIR / EIS <i>in situ</i> technique was explored by studying aluminium/polymer systems of varying characteristics. Differences in water and electrolyte ingress could be monitored, as well as metal corrosion, polymer swelling and delamination.</p>

In order to extend the applications of aluminium, organic coatings may be applied on sheet materials, for instance for corrosion protection or aesthetic surface finish purposes in the automotive and construction industries, or on foil materials in the flexible packaging industry. The most common mechanisms for deterioration and structural failure of organically coated aluminium structures are triggered by exposures to the surrounding environment. Despite the great importance to elucidate the influence of exposure parameters on a buried aluminium/polymer interface, there is still a lack of knowledge regarding the mechanisms that destabilise the structure. It is generally believed that a detailed in situ analysis of the transport of corroding species to the buried interface, or of surface processes occurring therein, is most difficult to perform at relevant climatic and real-time conditions. In this work, Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) in the Kretschmann-ATR configuration was successfully applied to in situ studies of the transport of water and ionic species through polymer films to the aluminium/polymer interface upon exposure to ultra pure deionised water and to a 1 M sodium thiocyanate (NaSCN) model electrolyte. Other main processes distinguished were the formation of corrosion products on the aluminium surface and swelling of the surface-near polymer network. Hence, in situ ATR-FTIR was capable to separate deterioration-related processes from each other. To perform more unambiguous interpretations, a spectro-electrochemical method was also developed for in situ studies of the buried aluminium/polymer interface by integrating the ATR-FTIR technique with a complementary acting technique, Electrical Impedance Spectroscopy (EIS). While transport of water and electrolyte through the polymer film to the aluminium/polymer interface and subsequent oxidation/corrosion of aluminium could be followed by ATR-FTIR, the protective properties of the polymer as well as of processes at the aluminium surface were simultaneously studied by EIS. The integrated set-up provided complementary information of the aluminium/polymer sample investigated, with ATR-FTIR being sensitive to the surface-near region and EIS being sensitive to the whole system. While oxidation/corrosion and delamination are difficult to distinguish by EIS, oxide formation could be confirmed by ATR-FTIR. Additionally, while delamination and polymer swelling may be difficult to separate with ATR-FTIR, EIS distinguished swelling of the polymer network and also identified ultimate failure as a result of delamination. The capability of the integrated ATR-FTIR / EIS in situ technique was explored by studying aluminium/polymer systems of varying characteristics. Differences in water and electrolyte ingress could be monitored, as well as metal corrosion, polymer swelling and delamination. / QC 20101124

Résumé du travail L’étude des modifications de surfaces, et plus particulièrement des matériaux d’électrodes est un domaine en plein essor. Les modifications d’électrodes par voie organique ont des applications potentielles dans des domaines aussi variés que l’inhibition de la corrosion, l’électronique moléculaire, l’optoélectronique ou encore les biosenseurs. Dans ce travail, nous nous sommes intéressés à l’électrode d’Au (111) modifiée par du 2-mercaptobenzimidazole. Dans un premier temps, l’adsorption du MBI sur électrode d’Au (111) sous contrôle du potentiel a été examinée par des mesures de capacité, de voltampérométrie cyclique, de chronocoulométrie et de spectroscopie SNIFTIR in situ. Les mesures de capacité révèlent qu’en milieu neutre, la molécule de MBI s’adsorbe en un film compact à des potentiels supérieurs à -0,3 V (vs. ECS). En deçà de cette valeur, le film se dilue progressivement lorsque le potentiel est rendu plus négatif, jusqu’à une valeur de -0,9 V où les molécules de MBI sont totalement désorbées de la surface. La morphologie des voltampérogrammes subit des variations significatives au cours du temps. Ces changements montrent que l’adsorption du MBI s’accompagne d’une levée de reconstruction de la surface, qui passe d’une structure initiale (√3 x 22) à une structure (1 x 1). Une estimation de la quantité de MBI adsorbée est obtenue par intégration des courbes de densité de courant. La courbe de densité de charge interfaciale a été extraite des mesures de chronocoulométrie. Cette courbe de densité de charge fournit des informations quant à l’évolution de l’excès superficiel en fonction du potentiel. La qualité des spectres infrarouges relevés in situ nous a permis d’effectuer des analyses qualitatives et quantitatives. Celles-ci montrent une bonne corrélation avec les résultats électrochimiques et apportent une signature moléculaire du film adsorbé et des espèces issues de sa désorption. Des calculs basés sur la Théorie de la Fonctionnelle de la Densité (DFT) ont permis une bonne interprétation des spectres infrarouges du MBI et de certains de ses dérivés. En outre, nous avons pu déterminer l’orientation des molécules à la surface, et montré que celle-ci varie peu avec le potentiel. Dans un second temps, nous nous sommes focalisés sur les propriétés de la monocouche auto-assemblée de MBI sur électrode d’Au (111), déterminées par voltampérométrie cyclique et spectroscopie infrarouge in situ. La monocouche est stable lorsque le potentiel est maintenu dans un domaine d’environ 800 mV. La monocouche auto-assemblée de MBI subit un processus de désorption réductive, influencé par le temps d’immersion de l’électrode dans la solution de surfactant ainsi que par le pH du milieu. Deux mécanismes de désorption réductive sont proposés, l’un valable en milieu neutre et basique, l’autre en milieu acide. Les résultats des mesures de spectroscopie infrarouge in situ apportent une preuve moléculaire de la validité des mécanismes proposés sur base des résultats électrochimiques. Un rapide examen des potentialités de cette monocouche a été réalisé à l’aide de réactions sondes. / Abstract Studies on surface modifications, and particularly of electrode material, are a growing field of interest. Organic modifications of electrode surfaces have potential applications in domains such as corrosion inhibition, molecular electronics, optoelectronics or biosensors. In the present work, we focussed on the modification of Au(111) electrodes by 2-mercaptobenzimidazole (MBI). In the first part, the adsorption, under potential control, of the MBI molecule onto the Au(111) electrode was studied by means of capacitance measurements, cyclic voltammetry, chronocoulometry and in-situ SNIFTIR spectroscopy. Capacitance measurements indicate that in neutral solution, the MBI molecule is adsorbed as a compact film at potentials higher than -0.3 V (vs. SCE). Below this value, the film becomes progressively less dense when the potential is made more negative, until a value of -0.9 V where MBI molecules are totally desorbed from the surface. The shape of the voltammograms evolves significantly with time. These changes show that a lift of the surface reconstruction occurs concomitantly to the adsorption of MBI. The initial (√3 x 22) reconstructed structure is lifted to the (1 x 1) unreconstructed one. The amount of adsorbed MBI is estimated by integration of the current density curves. The interfacial charge density curve was obtained by chronocoulometry measurements. This curve provides useful data regarding the evolution of the surface concentration with the potential. The quality of the infrared spectra obtained in situ allowed us to perform quantitative as well as qualitative analyses of the results. These analyses show a good correlation with the electrochemical results and provide molecular information on the adsorbed layer and on the species formed during the desorption process. Density Functional Theory (DFT) calculations were helpful in the interpretation of the infrared spectra of MBI and some of its derivatives. Additionally, we were able to determine the orientation of the molecules on the surface, and demonstrated that this orientation is slightly affected by the potential. In the second part of the work, we investigated the properties of the self-assembled monolayer of MBI on Au(111) electrode by cyclic voltammetry and in situ infrared spectroscopy. The monolayer is stable within an 800 mV potential range. The self-assembled monolayer undergoes a reductive desorption process, which is affected by the pH of the medium and by the immersion time of the electrode into the surfactant solution. Two mechanisms were proposed for the reductive desorption, one being valid in neutral and basic media, the other in acidic conditions. The in situ infrared spectroscopic results provide molecular evidences supporting the mechanisms proposed on an electrochemical basis. An exploratory examination of the potentialities of the monolayer is made by means of electrochemical probe reactions.

Methods of slab-geometry molecular dynamics computer simulation were tested, compared, and applied to the prediction of activity coefficients, interfacial electrochemistry characterization, and ion transport through a model biological channel-membrane structure. The charged-sheets, 2-D Ewald, corrected 3-D Ewald, and corrected particle-particle-particle-mesh (P3M) methods were compared for efficiency and applicability to slab-geometry electrolyte systems with discrete water molecules. The P3M method was preferred for long-range force calculation in the problems of interest and was used throughout. The osmotic molecular dynamics method (OMD) was applied to the prediction of liquid mixture activity coefficients for six binary systems: methanol/n-hexane, n-hexane/n-pentane, methanol/water, chloroform/acetone, n-hexane/chloroform, methanol/ chloroform. OMD requires the establishment of chemical potential equilibrium across a semi-permeable membrane that divides the simulation cell between a pure solvent chamber and a chamber containing a mixture of solvent and solute molecules in order to predict the permeable component activity coefficient at the mixture side composition according to a thermodynamic identity. Chemical potential equilibrium is expedited by periodic adjustment of the mixture side chamber volume in response to the observed solvent flux. The method was validated and shown to be able to predict activity coefficients within the limitations of the simple models used. The electrochemical double layer characteristics for a simple electrolyte with discrete water molecules near a charged electrode were examined as a function of ion concentration, electrode charge, and ion size. The fluid structure and charge buildup near the electrode, the voltage drop across the double layer, and the double layer capacitance were studied and were found to be in reasonable agreement with experimental findings. Applied voltage non-equilibrium molecular dynamics was used to calculate the current-voltage relationship for a model biological pore. Ten 10-nanosecond trajectories were computed in each of 10 different conditions of concentration and applied voltage. The channel-membrane structure was bathed in electrolyte including discrete water molecules so that solvation, entry, and exit effects could be studied. Fluid structure, ion dynamics, channel selectivity, and potential gradients were examined. This work represents the first such channel study that does not neglect the vital contributions of discrete water molecules.

Résumé du travail<p><p>L’étude des modifications de surfaces, et plus particulièrement des matériaux d’électrodes est un domaine en plein essor. Les modifications d’électrodes par voie organique ont des applications potentielles dans des domaines aussi variés que l’inhibition de la corrosion, l’électronique moléculaire, l’optoélectronique ou encore les biosenseurs.<p>Dans ce travail, nous nous sommes intéressés à l’électrode d’Au (111) modifiée par du 2-mercaptobenzimidazole. <p><p>Dans un premier temps, l’adsorption du MBI sur électrode d’Au (111) sous contrôle du potentiel a été examinée par des mesures de capacité, de voltampérométrie cyclique, de chronocoulométrie et de spectroscopie SNIFTIR in situ.<p>Les mesures de capacité révèlent qu’en milieu neutre, la molécule de MBI s’adsorbe en un film compact à des potentiels supérieurs à -0,3 V (vs. ECS). En deçà de cette valeur, le film se dilue progressivement lorsque le potentiel est rendu plus négatif, jusqu’à une valeur de -0,9 V où les molécules de MBI sont totalement désorbées de la surface.<p>La morphologie des voltampérogrammes subit des variations significatives au cours du temps. Ces changements montrent que l’adsorption du MBI s’accompagne d’une levée de reconstruction de la surface, qui passe d’une structure initiale (√3 x 22) à une structure (1 x 1). Une estimation de la quantité de MBI adsorbée est obtenue par intégration des courbes de densité de courant.<p>La courbe de densité de charge interfaciale a été extraite des mesures de chronocoulométrie. Cette courbe de densité de charge fournit des informations quant à l’évolution de l’excès superficiel en fonction du potentiel.<p>La qualité des spectres infrarouges relevés in situ nous a permis d’effectuer des analyses qualitatives et quantitatives. Celles-ci montrent une bonne corrélation avec les résultats électrochimiques et apportent une signature moléculaire du film adsorbé et des espèces issues de sa désorption. Des calculs basés sur la Théorie de la Fonctionnelle de la Densité (DFT) ont permis une bonne interprétation des spectres infrarouges du MBI et de certains de ses dérivés. En outre, nous avons pu déterminer l’orientation des molécules à la surface, et montré que celle-ci varie peu avec le potentiel.<p><p>Dans un second temps, nous nous sommes focalisés sur les propriétés de la monocouche auto-assemblée de MBI sur électrode d’Au (111), déterminées par voltampérométrie cyclique et spectroscopie infrarouge in situ. La monocouche est stable lorsque le potentiel est maintenu dans un domaine d’environ 800 mV. La monocouche auto-assemblée de MBI subit un processus de désorption réductive, influencé par le temps d’immersion de l’électrode dans la solution de surfactant ainsi que par le pH du milieu. Deux mécanismes de désorption réductive sont proposés, l’un valable en milieu neutre et basique, l’autre en milieu acide. Les résultats des mesures de spectroscopie infrarouge in situ apportent une preuve moléculaire de la validité des mécanismes proposés sur base des résultats électrochimiques.<p>Un rapide examen des potentialités de cette monocouche a été réalisé à l’aide de réactions sondes.<p>/<p>Abstract<p><p>Studies on surface modifications, and particularly of electrode material, are a growing field of interest. Organic modifications of electrode surfaces have potential applications in domains such as corrosion inhibition, molecular electronics, optoelectronics or biosensors.<p>In the present work, we focussed on the modification of Au(111) electrodes by 2-mercaptobenzimidazole (MBI).<p><p>In the first part, the adsorption, under potential control, of the MBI molecule onto the Au(111) electrode was studied by means of capacitance measurements, cyclic voltammetry, chronocoulometry and in-situ SNIFTIR spectroscopy.<p>Capacitance measurements indicate that in neutral solution, the MBI molecule is adsorbed as a compact film at potentials higher than -0.3 V (vs. SCE). Below this value, the film becomes progressively less dense when the potential is made more negative, until a value of -0.9 V where MBI molecules are totally desorbed from the surface.<p>The shape of the voltammograms evolves significantly with time. These changes show that a lift of the surface reconstruction occurs concomitantly to the adsorption of MBI. The initial (√3 x 22) reconstructed structure is lifted to the (1 x 1) unreconstructed one. The amount of adsorbed MBI is estimated by integration of the current density curves.<p>The interfacial charge density curve was obtained by chronocoulometry measurements. This curve provides useful data regarding the evolution of the surface concentration with the potential.<p>The quality of the infrared spectra obtained in situ allowed us to perform quantitative as well as qualitative analyses of the results. These analyses show a good correlation with the electrochemical results and provide molecular information on the adsorbed layer and on the species formed during the desorption process. Density Functional Theory (DFT) calculations were helpful in the interpretation of the infrared spectra of MBI and some of its derivatives. Additionally, we were able to determine the orientation of the molecules on the surface, and demonstrated that this orientation is slightly affected by the potential.<p><p>In the second part of the work, we investigated the properties of the self-assembled monolayer of MBI on Au(111) electrode by cyclic voltammetry and in situ infrared spectroscopy. The monolayer is stable within an 800 mV potential range. The self-assembled monolayer undergoes a reductive desorption process, which is affected by the pH of the medium and by the immersion time of the electrode into the surfactant solution. Two mechanisms were proposed for the reductive desorption, one being valid in neutral and basic media, the other in acidic conditions. The in situ infrared spectroscopic results provide molecular evidences supporting the mechanisms proposed on an electrochemical basis.<p>An exploratory examination of the potentialities of the monolayer is made by means of electrochemical probe reactions.<p> / Doctorat en sciences, Spécialisation chimie / info:eu-repo/semantics/nonPublished