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Thèmes de recherche de l'Equipe CPCP

Projet 5 : Propriétés de surface et d’interfaces des systèmes macromoléculaires

Ce champ thématique concerne l’étude et la compréhension des mécanismes gouvernant les propriétés superficielles des polymères, des mécanismes fondamentaux du contact entre deux matériaux jusqu’aux propriétés tribologiques, en relation avec l’architecture, la microstructure des polymères et la chimie de surface. Ainsi, sur la base d’expériences originales telles que la spectroscopie PM-IRRAS, la mesure de forces locales d’adhésion par AFM ou encore les expériences de friction et de nano-friction, les résultats obtenus ont contribué à accroître la reconnaissance de l’équipe dans les champs disciplinaires portants sur les phénomènes de structuration, d’organisation et de cristallisation d’entités organiques et macromoléculaires à architecture contrôlée au voisinage d’une interface, les aspects fondamentaux du contact et les transitions d’échelle nano-macro, les phénomènes dissipatifs au voisinage d’une interface en relations entre la chimie de surface et les propriétés nanomécaniques, les mécanismes de frottement dans les systèmes polymères et carbonés, l’élaboration de revêtements carbonés ou encore l’étude des phénomènes de restructuration sous contrainte de glissement de chaînes macromoléculaires.

Les études suivantes ont ainsi été réalisées durant la période 2005-2009 :
- La modification chimique de surface de réseaux polymères modèles (PDMS) en relation avec les phénomènes dissipatifs locaux, à l’aide de la microscopie à force atomique en mode contact.
- L’adhésion et la friction d’élastomères modèles : mécanismes moléculaires interfaciaux.
- La modification chimique de surfaces métalliques par des molécules organiques fonctionnelles, modèles d’agents de couplages, en relation avec les propriétés d’adsorption, d’interaction et de conformation.
- La friction et l’adhésion sur des substrats modèles fonctionnalisés par greffage de molécules organiques : influence des interactions interfaciales
- La modification chimique de substrats dans le but de reproduire les interactions et les mécanismes hiérarchiques d’association entre biopolymères, pour conduire à la formation d’édifices supramoléculaires d’ordre et de mobilité déterminés, en particulier dans le cas de glucosides. Ce travail a été réalisé dans le cadre d’une ACI Nanosciences « Biosyami : système biomimétique pour la synthèse de l’amidon ».
- Les phénomènes de structuration, d’organisation et de cristallisation d’entités macromoléculaires à architectures contrôlées au voisinage d’une surface.
- La modification de la cristallinité des polymères induite par la friction
- L’anisotropie de films minces d’élastomères induite par la friction : étude conformationnelle par PM-IRRAS.
- L’orientation moléculaire du transfert induit par le frottement du polystyrène contre des substrats modèles.
- L’influence de la chimie de surface sur la friction et le transfert du graphite
- Les adhésifs crash en collage automobile.

Figure 2 : Film de transfert lors d’un contact hydrophobe (a) et analyse conformationnelle (PM-IRRAS) (b)


Influence of the surface chemistry on the nanotribological behaviour of (AFM tip/graphite) couples

The development of the nanotechnology has made essential the knowledge of the tribological behaviour of carbonaceous materials, and more particularly of graphite. Atomic force microscopy (AFM) is thus used to study the friction properties at this nanoscopic scale. In this work, results concerning the friction of AFM tips against graphite pins are presented, with a particular emphasis on the effect of the chemical modification of these tips on the tribological behaviour of graphite.

Personnel: Jradi Khalil; Schmitt Marjorie; Bistac Sophie
Source: APPLIED SURFACE SCIENCE, 2012, Volume: 258 Issue: 10 Pages: 4687-4697

Mechanisms of Interfacial Degradation of Epoxy Adhesive/Galvanized Steel Assemblies: Relevance to Durability

This study reports on the durability of galvanized steel joints bonded with toughened epoxy adhesive formulations under the influence of temperature and moisture aging. The influence of hydrothermal aging on the substrate and adhesive properties was first determined and then correlated to the durability of bonded joints.
The mechanical properties of the adhesively bonded joints were assessed by a shear stress-strain analysis on single lap joints. Experimental results have shown a loss of adherence during aging. Scanning electron microscopy, fourier transform infra-red spectroscopy, and differential scanning calorimetry were conducted to analyze precisely the locus of failure and the failure faces after separation of the interface. Consequently, physical and chemical modifications of the adhesive and surface corrosion of the substrate were observed. A three-step mechanism has been proposed to explain the loss of adhesion during aging.
The first step was attributed to adhesive and interface hydrolysis of the lap-shear sample's Highly stressed zones, the second step to hydrolysis of the centre of the bonded joint and initiation of corrosion. The last one is due to an important growth of corrosion products which favours rupture in a weak boundary layer at the metal/polymer interphase. The aging model proposed bears out that the higher the corrosion resistance of the metal surface the lower the loss of adhesion under a wet environment.

Personnel: Calvez P.; Bistac S.; Brogly M.; et al.
Source: JOURNAL OF ADHESION, 2012, Volume: 88 Issue: 2 Pages: 145-170

Contributions of chemical and mechanical surface properties and temperature effect on the adhesion at the nanoscale

The atomic force microscope (AFM) is a powerful tool to investigate surface properties of model systems at the nanoscale. However, to get semi-quantitative and reproducible data with the AFM, it is necessary to establish a rigorous experimental procedure. In particular, a systematic calibration procedure of AFM measurements is necessary before producing reliable semi-quantitative data. In this paper, we study the contributions of the chemical and mechanical surface properties or the temperature influence on the adhesion energy at a local scale. To reach this objective, two types of model systems were considered. The first one is composed of rigid substrates (silicon wafers or AFM tips covered with gold) which were chemically modified by molecular self-assembling monolayers to display different surface properties (methyl and hydroxyl functional groups). The second one consists of model polymer networks (cross-linked polydimethylsiloxane) of variable mechanical properties. The comparison of the force curves obtained from the two model systems shows that the viscoelastic contributions dominate for the adhesion with polymer substrates, whereas, chemical contributions dominate for the rigid substrates. The temperature effect on the adhesion energy is also reported. Finally, we propose a relation for the adhesion energy at the nanoscale. This relation relates the energy measured during the separation of the contact to the three parameters: the surface properties of the polymer, the energy dissipated within the contact zone and the temperature.

Personnel: Awada Houssein; Noel Olivier; Hamieh Tayssir; et al.
Source : THIN SOLID FILMS, 2011, Volume: 519 Issue: 11 Pages: 3690-3694

Surface characterizations of poly(ethylene terephthalate) film modified by a carbohydrate-bearing photoreactive azide group


Grafting of a carbohydrate UV-reactive molecule, the β-d-galactopyranosyl-(1–4)-1-N-[2-(4-azidophenyl amino)-ethylamino]-1-deoxy-d-glucitol (AzPhLac), has been achieved on poly(ethylene terephthalate) film. The dependence of surface density and yield of grafted AzPhLac have been studied versus the number of moles of UV-treated AzPhLac via the deposit of a drop of solution with a known volume and concentration. A nearly complete grafting of initial AzPhLac molecules was reached for the lowest concentration and lowest volume of solution deposit conditions. Grafting density values in the range of 29–181 nmol/cm2 confirm the polymeric nature of the grafted layer. FTIR–ATR demonstrated the heterogeneity in thickness of the grafted surface due to the drop-deposit method and solvent evaporation process. AFM (imaging) allowed us to find a correlation between grafting density and rms roughness. Water-contact angle and AFM (contact mode) gave further evidence of the hydrophilic nature of the extreme surface.

Personnel: Roger Philippe; Renaudie Laetitia; Le Narvor Christine; et al.
Source: EUROPEAN POLYMER JOURNAL, 2010, Volume: 46 Issue: 7 Pages: 1594-1603

Hydroxypropyl methylcellulose (HPMC) formulated films: Relevance to adhesion and friction surface properties

Cellulose derivatives constitute one of the most dedicated polymers used in the production of film coatings (tablets, capsules ...). The effect of the composition of hydroxypropyl methylcellulose (HPMC)-stearic acid films on the surface physico-chemical properties was investigated. Incorporation of stearic acid into HPMC films induces strong changes on surface structure, hydrophobic/hydrophilic character, adhesion and friction characteristics. The variations observed suggest an accumulation of stearic acid on film surfaces, resulting a decrease of its roughness and surface free energy. The nano-adhesion and nano-friction experiments were evaluated by using AFM/FFM. while the macro-adhesion and macro tribological studies were performed on tack test and pin-on-disk tribometer respectively. In all the cases, it was found that the hydrophobic character of stearic acid leads to decrease adhesion and friction at the two scales. The surface capillary force plays a key role in these properties. In addition, the study indicates the interplay of adhesion in friction property of HPMC films and the role of stearic acid as lubricant.

Personnel: Fahs Ahmad; Brogly Maurice; Bistac Sophie; et al.
Source: CARBOHYDRATE POLYMERS, 2010, Volume: 80 Issue: 1 Pages: 105-114

Atom transfer radical polymerization of styrene from different poly(ethylene terephthalate) surfaces: Films, fibers and fabrics

Poly(ethylene terephthalate) (PET) is a semi-crystalline thermoplastic polyester used in many fields. For a variety of applications, however, it is necessary to impart desired properties by introducing specific functional groups on the surface. A simple method for growing polymer brushes by atom transfer radical polymerization (ATRP) on PET films, fibers and fabrics was devised. The different PET surfaces were first reacted with 1,2-diaminoethane by aminolysis reaction to incorporate primary amino and alcohol functions on the surface. Then, in a second step, ATRP initiator was grafted by reaction with bromoisobutyryl bromide. The efficiency of these reactions was confirmed by using colorimetric titration and X-ray photoelectron spectroscopy (XPS). Surface-initiated ATRP was performed in bulk using styrene monomer with CuBr/PMDETA catalytic system in the presence of a sacrificial initiator (ethyl 2-bromoisobutyrate). Good control of the polymerization was obtained as attested by comparison of polystyrene molar masses obtained in solution from sacrificial initiator with those obtained from the surface after cleavage. Wetting properties were found to vary systematically depending to the type of functionalization and grafting. Evolution of surface morphology according to reaction steps was investigated using atomic force microscopy (AFM).

Personnel: Bech Loic; Elzein Tamara; Meylheuc Thierry; et al.
Source: EUROPEAN POLYMER JOURNAL, 2009, Volume: 45 Issue: 1 Pages: 246-255