Effect of coating thickness on the friction properties of rubber-sphere on rubber-coated-plane contacts

Nous présentons une étude expérimentale du frottement d'un contact entre une sphère caoutchouteuse et une lame de verre revêtue d'un film de caoutchouc d'épaisseur variable. Nous montrons que le dépôt joue un rôle clé dans les propriétés de rupture de l'interface de contact : des variations d'un facteur trois du coefficient de frottement statique sont observées lorsque l'épaisseur est modifiée. Certaines interprétations sont discutées pour expliquer le phénomène impliquant notamment le rôle de la viscoélasticité du caoutchouc

Potentiels des surfaces modelées dans la nanoscience des polymères

International audienc

Démouillage des films minces viscoélastique sur substrats glissants et déformables

Dewetting of thin polymer films supported on solid substrates is a common phenomenon with a crucial impact on various technological processes. Our understanding of the origin of some unexpected properties of thin polymer films in the nanometre range is still not satisfactory, despite enormous experimental and theoretical efforts over the past decade. Several approaches were employed to investigate and quantify the mechanical relaxation, and calorimetric properties. A better understanding of the glass transition and other properties of polymer surfaces and interfaces is expected from the dynamic studies such as dewetting.We mainly carried out dewetting experiments under the optical microscope in real time. Such experiments represent an attractive possibility due to of their simplicity, sensitivity, and rapidity. Dewetting allows us to link the molecular and interfacial properties with macroscopically observable parameters such as dewetting velocity and shape of the rim. These studies were completed by AFM images, which gave information on the shape of the rim related to the relaxation of the polymer chains and the dynamic behaviour.We focused on the understanding of the residual stresses, the influence of molecular weight, dewetting temperature, elasticity of film as well as the dependence on thickness and its relationship with the residual stresses. The influence of the substrate had also its place in our studies. The case of a deformable substrate was treated in detail.Le démouillage des films minces de polymère supportés par un substrat est un phénomène quotidien avec l'impact crucial sur divers procédés technologiques. Notre compréhension de l'origine de certaines propriétés inattendues des films minces nanométriques de polymère n'est toujours pas satisfaisante, malgré les énormes efforts expérimentaux et théoriques effectués la décennie passée. Plusieurs approches ont été utilisées pour étudier et quantifier la relaxation mécanique, et les propriétés calorimétriques. Une meilleure compréhension de la transition vitreuse et d'autres propriétés des surfaces et des interfaces de polymère pourrait également venir des études dynamiques telles que le démouillage. Nous avons effectué principalement des expériences de démouillage simples, attractives, rapides et efficaces par microscopie optique en temps réel, permettant de relier les propriétés moléculaires et interfaciales avec des paramètres macroscopiquement observables tels que la vitesse du démouillage et la forme du bourrelet. Ensuite, ces études sont complétées par des imageries en Microscopie à Force Atomique (AFM), qui donnent des informations sur la forme du bourrelet. Celle-ci est reliée à la relaxation des chaînes macromoléculaires et le comportement dynamique du polymère. Nous nous sommes concentrés sur la compréhension de la notion des contraintes résiduelles, de l'effet de la masse molaire, de la température du démouillage, de l'élasticité du film ainsi que l'influence de l'épaisseur et ses relations avec les contraintes résiduelles. L'influence du substrat a aussi sa place dans nos études. Le cas d'un substrat déformable est traité en détail

Potentiels des surfaces modelées dans la nanoscience des polymères

International audienc

Design des surfaces texturées hétéro-chimiques pour le contrôle des propriétés de rupture des interfaces de contact

International audienc

Design des surfaces texturées hétéro-chimiques pour le contrôle des propriétés de rupture des interfaces de contact

International audienc

Photo-crosslinked fluorinated thin films from azido-functionalized random copolymers

International audienceRandom copolymers of styrene, p-azidomethylstyrene and 1H,1H,2H,2H-perfluorodecyl methacrylate were prepared in two steps involving nitroxide-mediated radical copolymerization and azidation reaction and further characterized by 1H and 19F NMR, size exclusion chromatography, differential scanning calorimetry, and thermal gravimetric analysis. Ultrathin films of these azidomethyl-functionalized fluorinated random copolymers, with thicknesses ranging from 20 to 100 nm, were spin coated onto Si substrates and then crosslinked by ultraviolet irradiation resulting in smooth and insoluble crosslinked fluorinated polymer mats. The surface properties of the supported thin films were investigated by X-ray photoelectron spectroscopy and water contact angle measurements. These tailored photo-crosslinked coatings afford a versatile control and homogenization of the wetting properties of different organic and inorganic substrates

Etude et optimisation des interfaces fibre-matrice : cas de composites verre-PA6,6 à renfort continu

International audienc

Crosslinked PDMS Elastomers and Coatings from the Thermal Curing of Vinyl-Functionalized PDMS and a Diazide Aliphatic Crosslinker

International audienceThe crosslinking of poly(dimethylsiloxane) elastomers and coatings by the thermal curing of poly(dimethylsiloxane-co-methylvinylsiloxane) and 1,12-diazido-dodecane was studied. This crosslinking pathway relies on the cycloaddition of azides and alkenes as well as the thermal generation of nitrene transient radicals, which react with alkenes, yielding respectively 1,2,3-triazoline and aziridine crosslinking knots. The influence of temperature and the ratio of azide and vinyl functionalities has been investigated by rheological, swelling, and insoluble fraction measurements for materials crosslinked in bulk and by comparison of the thickness before and after extraction of the soluble materials by soxhlet extraction for the crosslinked coatings. The preparation of highly crosslinked PDMS-based elastomers and coatings has been demonstrated, even if the fraction of elastically effective crosslinks in bulk remained below 160 mol/m(3). Advantageously, this system does not require additional initiator or catalyst, is not sensitive to moisture or oxygen, and can be extended to a wide range of unsaturated polymers as well as different organic or inorganic solid substrates

The influence of progressive cross-linking on dewetting of polystyrene thin films

International audienceWe present dewetting experiments on thin polymer films as a function of cross-linking density. Covalent cross-links were obtained in the glassy state on the basis of azide photochemistry of linear random copolymers of styrene and p-(azidomethyl)styrene, i.e., 106 and 2500 kg/mol with 7% and 1% azide functionality among the polymer backbone, respectively. Upon ultraviolet radiation, azides generate highly unstable nitrene radicals which react with the surrounding polymer backbone, yielding covalent cross-links. We determined the probability for film rupture, defined by the number of holes formed per unit area, and the relaxation time (τw) of residual stresses which resulted from the film preparation process. For the lower molar mass polymer studied and for azide conversion rates lower than 60%, only partial cross-linking occurred. The effective molar mass of the polymer increased, and consequently, an increase in τw was observed. The increase in τw was accompanied by a decrease in hole density, indicating that the still present residual stresses in the films were not able anymore to rupture the films at the high probability of un-cross-linked polymers. For high conversion (>60%), cross-linking was significant enough to lead to the formation of a three-dimensional rubbery network which, in turn, generated an elastic force that counteracted the driving forces. This elastic force eventually inhibited dewetting and the relaxation of residual stresses. Thus, at high conversions, the relaxation time τw grew exponentially and the number of holes tended toward zero. For the higher molar mass polymer, no changes in the relaxation time τw were observed for low conversion (<30%). However, at a higher conversion rate, τw increased drastically, suggesting an almost infinitely long relaxation time at 100% conversion. Consequently, to successfully stabilize thin polymer films by cross-linking, it is preferable to use long polymer chains