Rhéologie et Adhésion de polymères supramoléculaires fonctionalisés en leur milieu

Les adhésifs sensibles à la pression (PSAs) sont constitués de matériaux polymères mous qui collent presque instantanément sur presque tout type de surface. Les propriétés adhésives de ces matériaux sont principalement contrôlées par leurs propriétés rhéologiques et ainsi, par la structure moléculaire des polymères utilisés dans leur formulation. La nature des monomères, la distribution des masses molaires et le degré de réticulation sont des exemples de paramètres habituellement définis par les ingénieurs pour l’optimisation des adhésifs commerciaux. La singularité de notre projet est d’étudier les propriétés adhésives de matériaux polymères modèles fonctionnalisés par des groupements urée.Ces groupements fortement interactifs par liaison hydrogène renforcent les propriétés élastiques et dissipatives de la matrice polymère constituée de chaînes non enchevêtrées, tout en gardant une très faible viscosité dans les solvants non polaires. Inspiré de l’étude récente sur le PIBUT (Courtois et al, Adv .Func. Mater. 2010), nos systèmes modèle sont constitués de chaînes linéaires polybutylacrylate fonctionnalisées en leur milieu. La méthode de synthèse utilisée dans notre projet permet un très bon contrôle de la longueur des chaînes, tout en permettant d’utiliser une grande diversité de groupements interactifs. La caractérisation systématique de nos matériaux nous a permis d’identifier les paramètres structuraux qui gouvernent la rhéologie et l’adhésion. Des structures supramoléculaires plus complexes ont aussi été explorées dans notre projet et montrent clairement le fort potentiel de la chimie supramoléculaire pour le domaine de l’adhésion.Pressure Sensitive Adhesives (PSA) are soft polymer materials which stick on almost any surface due to their particular rheological properties. Engineers adjust polymers molecular structure to optimize adhesion properties for each application. The nature of the monomers, molecular weight distribution and degree of crosslinking are classical tunable parameters for acrylic adhesives. The specificity of our project is to investigate the adhesive properties of model polymers functionalized by urea groups. The presence of strong hydrogen bonds inside the polymeric matrix allows to dramatically increase the viscosity and dynamic modulus of short polymer chains (M<20kg/mol) reducing the need for crosslinking while reducing dramatically the viscosity when dissolved in polar solvents. Inspired by the recent study on PIBUT (Courtois et al, Adv .Func. Mater. 2010), our model systems are linear center-functionalized polybutylacrylate chains synthesized with a highly controlled but versatile synthesis method. In our work, the extensive characterization of these materials allowed us to identify the key structural parameters governing their rheology and their adhesive properties. More complex structures were also investigated and showed clearly the potential of the supramolecular chemistry for the science of adhesion

Viscoelasticity of Supramolecular Center-functionalized Polymer: Effect of the strength of Hydrogen Bonding Stickers

International audienceDuring the last decade, supramolecular chemistry (1) showed its great potential for the elaboration of innovative materials, with features such as self-healing or stimuli-responsiveness. Supramolecular materials are composed of polymer chains functionalized by strongly interacting moieties. These moieties, called “stickers”, can associate by non covalent interactions (hydrogen bonds, ionic…) and thus, form a transient network in the polymer matrix. While the self-assembly of stickers favors elastic behavior in the case of telechelic polymer chains (2), our group focused on the control of dissipative properties of center-functionalized polymers at small and large deformation (3), an important property for soft adhesives.The specificity of our project is to adjust the viscoelastic properties of non or lightly entangled center-functionalized polymers by varying the supramolecular parameters, such as the strength and the density of stickers. Monodisperse poly(butylacrylate) chains below and above their average molecular weight between entanglements, center-functionalized by multiple hydrogen bonding stickers were synthesized by ATRP. Their structure (by AFM and SAXS) and linear viscoelastic properties in the melt state were systematically characterized. Stickers are observed to self-assemble into cylindrical aggregates packed into a hexagonal structure. This supramolecular structure gives a gel-like character at low molecular weight and high sticker density while the entanglements’ dynamics makes them highly dissipative over a large frequency range (5 decades) for higher Mw and lower sticker density. The transition from one regime to another is easily adjusted by varying independently the length of the side chains and the nature of stickers. Such a fine control of the dissipative properties via chemical non random structures makes the supramolecular center-functionalized polymers promising to target fine-tuned innovative soft materials.(1)Seiffert, S. et al, J. Chem. Soc. Rev. 2012 (2) Folmer, B. J. B. et al, Adv. Mater. 2000 (3) Courtois, J. et al Adv. Funct. Mater. 2010

Supramolecular Chemistry for Pressure Sensitive Adhesives ?

International audiencePressure Sensitive Adhesives (PSA) are soft polymer materials which instantly stick on almost any surface. The adhesives properties of these materials are mainly based on their rheological behavior and, thus on the chemical architecture of the polymer chains. Commercial PSAs are usually composed of lightly crosslinked and highly entangled polymer chains, the molecular structure of which is adjusted to get a good peeling and shear resistance (Creton, C. MRS Bulletin, 2003). The specificity of my project is to investigate the rheological and adhesive properties of short polymer chains functionalized by urea groups. The strong hydrogen bonding interactions between these urea moieties increase strongly the dissipative properties upon deformation, while keeping a low viscosity in non polar solvents (Courtois, J. et al, Adv. Funct. Mater., 2010).The viscoelastic and adhesive properties of linear poly(butylacrylate) chains center-functionalized by bis- or tri-urea stickers were systematically studied. The molecular mechanisms, which govern the rheological behavior at small and large deformation, were identified by modifying the chemical structure of the polymer chains in a systematic way. Based on these results, more complex molecular architectures were then synthesized in order to improve the adhesive properties. The promising results from these new systems highlight the high potential of the supramolecular chemistry for the elaboration of new PSAs

Effects of Multifunctional Cross-linkers on Rheology and Adhesion of Soft Nanostructured Materials

International audienceWe investigate the nanostructure, the rheology and the adhesion of soft supramolecular materials elaborated by blending monofunctional and multifunctional poly(isobutene) (PIB) chains. Monofunctional PIB chains (PIBUT) are linear and unentangled polymer chains (Mn ≈3kg/mol) functionalized in the middle by a bis-urea interacting moiety, able to self-associate by four hydrogen bonds. Covalent coupling of monofunctional PIB allows us to synthesize longer chains bearing two or three interacting moieties. These chains are then added to monofunctional PIB to prepare blends containing up to 10% of multifunctional PIB (M-PIBUT). The influence of M-PIBUT on the supramolecular nanostructure, which results from the self-assembly of stickers, is studied by Atomic Force Microscopy and Small Angle X-ray Scattering at room temperature. Multifunctional and monofunctional chains are shown to interact with each other to form bundles of rod-like aggregates. The consequences of these interactions on the rheology of the blends were studied by shear tests in the linear and non linear regimes, below and above the order-disorder transition temperature. A pronounced strengthening effect of M-PIBUT is observed at room temperature: the supramolecular blends become more elastic and are more resistant to creep with increasing concentration of M-PIBUT. The effects of M-PIBUT on the nanostructure and the rheology suggest that M-PIBUT, which can link with more than one supramolecular aggregate, plays the role of a physical cross-linker. The impact of these supramolecular cross-linkers on the adhesion of the blends is studied by probe-tack tests and discussed by analyzing the in-situ deformation through the debonding images

Combined Effect of Chain Extension and Supramolecular Interactions on Rheological and Adhesive Properties of Acrylic Pressure-Sensitive Adhesives

A new approach for the elaboration of low molecular weight pressure-sensitive adhesives based on supramolecular chemistry is explored. The synthesis of model systems coupled with probe-tack tests and rheological experiments highlights the influence of the transient network formed by supramolecular bonds on the adhesion energy. The first step of our approach consists of synthesizing poly­(butyl acrylate-<i>co</i>-glycidyl methacrylate) copolymers from a difunctional initiator able to self-associate by four hydrogen bonds between urea groups. Linear copolymers with a low dispersity (<i>M</i>_n = 10 kg/mol, Ip < 1.4) have been synthesized via atom transfer radical polymerization. Films of the copolymers were then partially cross-linked through reaction of the epoxy functions with a diamine. The systematic variation of the average ratio of glycidyl methacrylate and diamine per copolymer shed light on the respective role played by the supramolecular interactions (between bis-urea groups and with the side chains) and by the chain extension and branching induced by the diamine/epoxy reaction. In this strategy, the adhesive performance can be optimized by modifying the strength of “stickers” (via the structure of the supramolecular initiator, for instance) and the polymer network (e.g., via the length and level of branching of the copolymer chains) in order to approach commercial PSA-like properties (high debonding energy and clean removal)

Cold Atmospheric Plasmas in interactions with materials and liquids for biological applications

International audienceCold Atmospheric Plasmas (CAPs) are now currently used for numerous applications concerning the surface treatment of solid materials at the macro-, micro- and nano- scales. Surface modifications produced lead to new functionnalities induced by the interactions of the materials with the different energy components (electrons, ions, photons, reactive species) of these partially ionised gases, produced at atmospheric pressure and temperature closed to the room one. Another large area of applications is related to the treatment of liquids in which it is possible to increase the chemical reactivity, thus allowing nanoparticles synthetisis or bacterial decontamination. In this presentation we will first discuss on the physical and chemical properties of these specific plasmas. Their principles of manufacturing will be summarized and particular attentions will be indicated on the environment around the plasma-surface interaction zone. A non-exhaustive state of the art will provide a better understanding of the physical mechanisms associated with their propagation up to the material to be treated. A large biological applications field will be then shown, illustrated by the analyses of modifications produced on steels, polymers but also on physiological liquids and living cells. Methods of the interactions characterizations are numerous and we will present some known techniques but with an innovative approach as for instance the IR-ATR spectroscopy for tracking of modifications of polymers surface. The insitu electrochemistry1 has been also developed during the plasma exposure of liquids and results obtained will be given, showing that it is possible to measure very low current in the nA range and in the presence of high electric fields used for the plasma formation. Bio-chemically Reactive Oxygen and Nitrogen Species (RONS) production (H2O2, NO2-) can thus be followed and quantified, as well as the detection of short-living species

Cardiopulmonary resuscitation in adults over 80 : outcome and the perception of appropriateness by clinicians

OBJECTIVES: To determine the prevalence of clinician perception of inappropriate cardiopulmonary resuscitation (CPR) regarding the last out‐of‐hospital cardiac arrest (OHCA) encountered in an adult 80 years or older and its relationship to patient outcome. DESIGN: Subanalysis of an international multicenter cross‐sectional survey (REAPPROPRIATE). SETTING: Out‐of‐hospital CPR attempts registered in Europe, Israel, Japan, and the United States in adults 80 years or older. PARTICIPANTS: A total of 611 clinicians of whom 176 (28.8%) were doctors, 123 (20.1%) were nurses, and 312 (51.1%) were emergency medical technicians/paramedics. RESULTS AND MEASUREMENTS: The last CPR attempt among patients 80 years or older was perceived as appropriate by 320 (52.4%) of the clinicians; 178 (29.1%) were uncertain about the appropriateness, and 113 (18.5%) perceived the CPR attempt as inappropriate. The survival to hospital discharge for the “appropriate” subgroup was 8 of 265 (3.0%), 1 of 164 (.6%) in the “uncertain” subgroup, and 2 of 107 (1.9%) in the “inappropriate” subgroup (P = .23); 503 of 564 (89.2%) CPR attempts involved non‐shockable rhythms. CPR attempts in nursing homes accounted for 124 of 590 (21.0%) of the patients and were perceived as appropriate by 44 (35.5%) of the clinicians; 45 (36.3%) were uncertain about the appropriateness; and 35 (28.2%) perceived the CPR attempt as inappropriate. The survival to hospital discharge for the nursing home patients was 0 of 107 (0%); 104 of 111 (93.7%) CPR attempts involved non‐shockable rhythms. Overall, 36 of 543 (6.6%) CPR attempts were undertaken despite a known written do not attempt resuscitation decision; 14 of 36 (38.9%) clinicians considered this appropriate, 9 of 36 (25.0%) were uncertain about its appropriateness, and 13 of 36 (36.1%) considered this inappropriate. CONCLUSION: Our findings show that despite generally poor outcomes for older patients undergoing CPR, many emergency clinicians do not consider these attempts at resuscitation to be inappropriate. A professional and societal debate is urgently needed to ensure that first we do not harm older patients by futile CPR attempts. J Am Geriatr Soc 68:39–45, 201