Influence de tensioactifs sur l'hydratation du ciment à l'interface béton/coffrage

National audienceLa microstructure des principaux hydrates du ciment dans les premiers microns de la surface du béton affecte les propriétés de surface telles que porosité, dureté, résistance aux taches, etc. En particulier, des variations dans la quantité et la taille des cristaux d'hydroxyde de calcium peuvent faire apparaître des propriétés de surface intéressantes. Malgré cela, les paramètres et les mécanismes qui gouvernent la croissance de la Portlandite ne sont pas encore bien connus. Cette étude s'intéresse à l'utilisation de solutions composées d'eau et de tensioactifs non ioniques à l'interface béton/coffrage. Dans certains cas, la présence d'un tensioactif favorise la nucléation et la croissance de Portlandite en surface du béton. La quantité de Portlandite, mesurée par analyse d'image, semble augmenter avec l'hydrophobie du tensioactif utilisé. Des observations MEB montrent que les cristaux induits par les tensioactifs présentent une structure atypique composée de fines couches superposées. Enfin, des essais de calorimétrie montrent que les tensioactifs ne modifient pas la cinétique d'hydratation du ciment

Influences of freeze-drying and UV-irradiation on the microstructured morphology and on the wetting properties of PS41-PAA(271)coating

Influences of freeze-drying process and of UV-irradiation are studied on morphology, surface composition and wetting properties of polystyrene-b-poly(acrylic acid) (PS41-PAA(271)) diblock copolymers (dip-coated on the substrate made of stainless steel). Observations by scanning electron microscopy (SEM) and measurements of static water contact angles highlight that morphology of non-UV-irradiated PS41-PAA(271) is re-organised after steps of immersion/emersion in water and freeze-drying. These both processes modify PS41-PAA(271) surface in a microstructured layer of polymer that covers a part of the stainless-steel substrate. Moreover, analyses by X-ray photoelectron spectroscopy (XPS) and measurements of dynamic wetting angles with the Wilhelmy plate method demonstrate that stimuli-responsive properties Of PS41-PAA(271), whose wetting properties depend on the environment, are enhanced after using a step of UV-irradiation for 20 min. This process influences the composition of the coating in order to stabilise the smart material. Consequently, repeated cycles of immersion/emersion in water showed that a maximum gap of 20-25 degrees is obtained between the hydrophobic state (after drying at air for 90 min) and the hydrophilic state (after immersion in water). (c) 2008 Elsevier B.V. All rights reserved

Polymeric microstructures induced by freeze-drying process: Comparative study of PS41-PAA(271) morphologies after impregnations in water and in an alkaline solution

Surface of polymeric coating can be modified after being submitted to treatment based oil freeze-drying. Morphology of polystyrene-b-poly(acrylic acid) (PS41 -PAA(271)) diblock copolymers was investigated by using scanning electron microscopy (SEM). After clip-coating oil stainless steel substrate, influences of the nature and the pH of the immersing liquid, used before freeze-drying, were established. If water has impregnated the polymer in order to form a hydrogel, the surface could acquire a cellular monolayer structure after freeze-drying while stretched polymeric nodules, affected by the conditions of sublimation, cover some other parts of the surface. The porous monolayer happens when freeze-drying occurs in a homogenous and well-crystallised icy material. Observations of nucleation sites linked by polymeric filaments could be considered as the first step of growth of this regular network. In the other hand, if a KOH alkaline Solution has impregnated the polymer before freeze-drying, ionic species affect the morphology by inducing specific lamellar structures that close the porous Structure. XPS analyses highlight that the carboxylic functions of PS-PAA coating could be deprotonated during the immersion in the alkaline solution. This deprotonation induces polyacrylate-based compounds that Could disturb the growth of the cellular polymeric network. This phenomenon Should be avoided by using a neutral immersing solution in order to obtain a homogenous and Porous monolayer of PS-PAA after freeze-drying. (C) 2009 Elsevier B.V. All rights reserved

REACTIVITE DE SURFACE ET FONCTIONNALISATION DES MATERIAUX DE CONSTRUCTION

Ce document synthétise mon parcours professionnel et détaille les travaux scientifiques réalisés depuis mon doctorat en Sciences et Génie des Matériaux obtenu en 2004 (laboratoire CEMEF, Mines Paristech) jusqu’à mes activités actuelles de chargé de recherche au Centre R&D de LafargeHolcim (un des leaders mondiaux de matériaux de construction) et au Département de Construction Architectonique (Université de Burgos, Espagne). Mes travaux de recherche se répartissent entre d’une part, le management de projets de recherche en lien avec la caractérisation, la fonctionnalisation et la réactivité des surfaces ; et d’autre part, l’élaboration de matériaux innovants en lien avec le développement durable (par ex. : dépollution de l’air, incorporation de matériaux recyclés). Ces activités effectuées dans un contexte international me permettent d’être le tuteur industriel de nombreux étudiants et de collaborer avec des laboratoires universitaires et partenaires extérieurs.La 1ère partie de ce manuscrit présente une notice de mon parcours professionnel, détaillant mes activités de recherche (sous la forme d’une liste de publications, communications et brevets réalisés), de management d’équipe et d’encadrement scientifique. La 2ème partie de ce document expose les principaux résultats obtenus au cours de ces différentes années afin de reconstituer ma trajectoire scientifique et d’établir les perspectives scientifiques liées à mes thématiques de recherche. Enfin, la 3ème et dernière partie présente certaines des publications les plus représentatives de mes activités

Adhésion et adhérence entre les peintures automobiles et des adhésifs sensibles à la pression : influence du nettoyage sur la physico-chimie et la tenue mécanique des interfaces

Automotive topcoats are constituted of basecoat/clearcoat system or lacquer. Analyses of their outermost surface point out that polysiloxane additives are detected on the clearcoats and oxygenated compounds are detected on the lacquer, these compounds cover partially the polyacrylate-polyurethane network. The segregation of siloxane additives to the clearcoat surface decrease the adhesion of pressure-sensitive adhesives. The slight adhesion is explained by calculation of solubility parameters : the interaction between siloxane additives and PSA is lower than the interaction between polyacrylate network and adhesive. Analyses point out that an ethanol cleaning can remove additives from the topcoat surface and improve considerably adhesion to clearcoats. Moreover, this study characterizes the mechanical behaviours of two PSA families, which are composed of elastomer or acrylic copolymers. The local peel strength is correlated to the adhesive deformation. The majority of peel strength is dissipated when elongation is maximum. Adhesives behaviours depend on the composition (elastomer or acrylic) and peel strength is proportional to the contact area with the substrate.Les finitions de peintures automobiles sont constituées par un vernis ou par une laque. Leur analyse montre une migration de tensioactifs à base de polysiloxane vers la surface des vernis et de composés oxygénés vers la surface de la laque, ces composés recouvrant partiellement le réseau polyacrylate-polyuréthane. Cette migration d'additifs est la cause de la faible adhérence mesurée lors du pelage d'adhésifs sensibles à la pression sur le vernis. Le calcul des paramètres de solubilité explique cette faible adhérence : les PSA interagissent beaucoup plus avec le réseau polyacrylate qu'avec les additifs siliconés. Le nettoyage à l'éthanol enlève les composés siliconés ou oxygénés de la surface des peintures, ce qui améliore l'adhérence des PSA sur le vernis. De plus, nous étudions le comportement mécanique lors du pelage de deux PSA (à base élastomère ou acrylique) en corrélant la dissipation locale de l'énergie avec la déformation des PSA. La majorité de l'énergie est dissipée lorsque la déformation des PSA est maximale. L'allure des courbes de comportement dépend du caractère élastomère/acrylique de l'adhésif et l'énergie dissipée est proportionnelle à l'aire de contact avec le substrat

Study of siloxane additives migration to the surface of polyester-(melamine)-polyurethane coatings: Aging effects after ethanol cleaning

International audienceThis study determines the influences of siloxane flow agents' migration on the outermost surface composition of clearcoats, before and after ethanol cleaning. This evaluation is undertaken to improve adhesion of pressure-sensitive adhesives (PSAs) on automotive paint systems. Most of the siloxane flow agents segregate from the bulk to the clearcoat outermost surface during curing. These additives can cover until 50% of the surface area but X-ray photoelectron spectroscopy (XPS) and time of flight-secondary ion mass spectrometry (ToF-SIMS) analyses indicate that they can be removed by ethanol cleaning. Composition of the cleaned clearcoats surfaces are similar as the composition of clearcoat formulated without siloxane additives: the polyester-(melamine)-polyurethane network is more detected than before cleaning. However, outermost surface analyses show that several aging weeks increase the siloxane additives segregation. This post-cleaning migration modifies the clearcoat surface composition and cancels the chemical modifications due to the ethanol cleaning. XPS analyses show that silicon concentrations after cleaning and aging are inversely proportional to the initial silicon concentrations measured after curing. It highlights that aging has to be controlled to improve adhesion of PSAs on clearcoats. A second ethanol cleaning on aged clearcoats is not effective to remove these new siloxane additives. Their formulation should be different from the flow agents and it could modify their solubility in ethanol. This result could also indicate that these new siloxane additives are not located on the last molecular layer of surface and they would not be soluble in ethano

Relationship between the fracture energy and the mechanical behaviour of pressure-sensitive adhesives

International audienceMechanical behaviours of two pressure-sensitive adhesives (PSAs) families, composed of elastomer copolymers or polyacrylate/acrylic copolymers, are characterised by peel tests. Fracture energy varies linearly according to the applied contact force between two levels, which depends on tackiness and cohesion of the PSA. Local fracture energies are measured by an original peeling system and they are related with the adhesive deformation. Mechanical behaviours of PSAs depend on their composition but majority of fracture energy is dissipated on the first millimetre near the bending zone where fibrils elongation is maximum. Observations of interfaces between PSAs and glass substrate underline that fracture energy varies linearly according to the contact area

Adhesion of pressure-sensitive adhesives to automotive coatings: influence of topcoat composition

International audienceThis study characterizes the influence of automotive coating composition on the adhesion of pressure-sensitive adhesives (PSA). Automotive topcoats are generally constituted of a basecoat/clearcoat system, but a layer of lacquer is used for white colour coating. X-ray Photoelectron Spectroscopy (XPS) and Secondary Ion Mass Spectrometry (SIMS) are used to study the topcoat surface composition. Siloxane additives are detected on the clearcoat surface but not on the lacquer surface. Peel tests show that the adhesion of PSA to the lacquer is higher than to the clearcoat. Moreover, study of clearcoat formulated without additives confirms that the siloxane additives are unfavourable to the adhesion of PSA. When the PSA is peeled from a clearcoat, analyses of failure surfaces indicate that the failure seems to propagate within the PSA near the interface. On the contrary, the failure seems to propagate within the bulk of the lacquer during peeling. This difference is explained by XPS analysis of lacquer: the outermost surface is constituted of a layer of oxygenated unidentified compounds, which are detected on the failure surface of PSA. Chemical bonds between these compounds and the lacquer network seem to be weaker than the bonds between these compounds and the PSA. Analyses point out that the ethanol cleaning can remove the additives from the topcoat surface and improve considerably the adhesion to the clearcoat. If the topcoat is cleaned before applying the PSA, the failure propagates deeper within the PSA than if the topcoat is not cleaned

Influence of additives segregation on surface composition of automotive coatings: Effects of an ethanol cleaning

International audienceThe automotive topcoat is constituted of a pigmented basecoat, covered by a transparent and shiny clearcoat. This layer protects the basecoat from the environment damage and determines the paint appearance. For white plain colour, the basecoat/clearcoat system is replaced by a layer of lacquer. The surface analyses are used to determine the influence of the topcoat composition on the adhesion of pressure-sensitive adhesives. X-ray photoelectron spectroscopy (XPS) and secondary ions mass spectrometry (ToF-SIMS) study the automotive topcoats chemistries. These analyses point out that polysiloxane additives are detected on the clearcoats but not on the lacquers. The impact of the different additives families (anti-UV agents and surface levelling additives) on the topcoat surface chemistry is identified. Moreover, the aluminium pigments do not appear on the metallic basecoat surface because of a siloxane additives layer, which also covers the polyester-polyurethane network. XPS studies on the basecoats covered by a clearcoat formulated without additive bring to the fore that the basecoat siloxane additives segregate towards the clearcoat/air interface during the curing process. The clearcoats additives can be removed with an ethanol cleaning according to the XPS analyses but this solvent cleaning is not able to remove all the additives from the basecoat surface, which seem to be partly cross-linked with the basecoat polyurethane networ

Characterisation of the variations of tint and the adhesion of pigments onto the surface of mortar

International audienceA method, coupling Particle-Induced X-ray Emission (PIXE) and colorimetry, is proposed to determine the amount of pigments transferred from the casting mould and to quantify their adhesion onto the surface of coloured mortar about 4 weeks after demoulding. PIXE analyses allow the quantification of the amount of pigments anchored onto the hardened mortars, even if the observations by Scanning Electron Microscopy (SEM) remain necessary to study the near-surface microstructure, especially for the rough samples. The optical parameters deduced from the colorimetry measurements are more interesting to establish the homogeneity of the perceived tint. Indeed, a protocol is proposed to evaluate the adhesion of the pigments by relating the amount of pigments (detected by PIXE analyses) and the coordinates measured in the CIE (L∗, a∗, b∗) colour space, before and after a water washing test