2019 |
Dabo, M., Roland, T., Dalongeville, G., Gauthier, C., & Kekicheff, P. (2019). Ad-hoc modeling of closed-cell foam microstructures for structure-properties relationships. European Journal Of Mechanics A-Solids, 75, 128–141.
Abstract: During the formation of open-cell foams the relevant driving force besides gas pressure comes from surface tension which controls area minimization of the topology. Accordingly, the Surface Evolver software expressly developed to shape liquid surface by minimizing their energy given various constraints such as bubble volumes allows computing very realistic models of equilibrium foam microstructures. However, when considering non equilibrium foam (dense foam) or the formation of closed-cell foams where films between adjacent cells are thick, a more complete model would have to consider the expansion process as a whole and include the viscous flow of the suspending fluid, which eventually solidifies to form the solid phase of the foam. This situation has not been investigated computationally because the problem size is too large and despite several attempts there remain significant challenges to integrate the foaming process knowledge into mathematical formulas. In a continuing effort to establish structure-properties relationships, an ad-hoc model is detailed to generate numerical closed-cell foam microstructures that resemble the real ones for a medium to a high porosity range. Inspired from a physical description of the manufacturing process making use of chemical blowing agent, a dynamic approach taking into account the influence of the temperature on the physical material characteristics is proposed. It allows the nucleation of cells, their growth through gas expansion, and the interactions between growing cells to be taken into account simultaneously. The large variety of generated microstructures with porosities spanning the few to 95 percents range is compared to real polymeric closed-cell foams whose microstructures were determined by X-ray microtomography at high spatial resolution. These structures are then used as templates to generate realistic finite element models and study the mechanical properties.
|
|
2018 |
Lejeune, J., Le Houerou, V., Chatel, T., Pelletier, H., Gauthier, C., & Muellhaupt, R. (2018). Creep and recovery analysis of polymeric materials during indentation tests. European Journal Of Mechanics A-Solids, 68, 1–8.
Abstract: The present study describes comparative results obtained experimentally on two polymeric surfaces during contacts with a rigid spherical indenter. An experimental setup specifically dedicated to transparent materials has been used to analyze the creep phenomenon over long holding time segments (10(5) s) and to study the recovery process once contact has been removed. As a function of imposed contact time, a normalized value of representative strain is defined to quantify creep and recovery steps. Experimental results indicate that the recovery of the deformed surface after contact is mainly dependent on the initial contact time. Finite Elements Modeling will be used to discuss further the time-depending behaviors of the materials.
|
|
2017 |
Chapuis, P., Montgomery, P. C., Anstotz, F., Leong-Hoi, A., Gauthier, C., Baschnagel, J., et al. (2017). A novel interferometric method for the study of the viscoelastic properties of ultra-thin polymer films determined from nanobubble inflation. Review Of Scientific Instruments, 88(9).
Abstract: Glass formation and glassy behavior remain as the important areas of investigation in soft matter physics with many aspects which are still not completely understood, especially at the nanometer size-scale. In the present work, we show an extension of the ânanobubble inflationâ method developed by OâConnell and McKenna [Rev. Sci. Instrum. 78, 013901 (2007)] which uses an interferometric method to measure the topography of a large array of 5 mu m sized nanometer thick films subjected to constant inflation pressures during which the bubbles grow or creep with time. The interferometric method offers the possibility of making measurements on multiple bubbles at once as well as having the advantage over the AFM methods of OâConnell and McKenna of being a true non-contact method. Here we demonstrate the method using ultra-thin films of both poly(vinyl acetate) (PVAc) and polystyrene (PS) and discuss the capabilities of the method relative to the AFM method, its advantages and disadvantages. Furthermore we show that the results from experiments on PVAc are consistent with the prior work on PVAc, while high stress results with PS show signs of a new nonlinear response regime that may be related to the plasticity of the ultra-thin film. Published by AIP Publishing.
|
|
Divry, V., Jacomine, L., Le Houerou, V., Collin, D., Gauthier, C., & Holl, Y. (2017). Influence of formulation on friction properties of latex films. Progress In Organic Coatings, 113, 189–199.
Abstract: Friction coefficients (called mu) versus contact pressure or confinement (maximum indentation depth over film thickness) were measured together with bulk mechanical properties of waterborne, partially formulated, acrylic coatings. It was shown that the initial, unformulated latex film was significantly plasticized by humidity in air thanks to the presence of the acrylic acid hydrophilic monomer, resulting in an increase of the friction coefficient. However, the plasticizing effect of a coalescing agent (Texanol (TM)) was much stronger and therefore much more increased the friction coefficient, which only slowly decreased upon film aging. The film containing 10% of Texanol was used as the reference system for the remainder of the study. To this reference, different classical formulation ingredients were successively added (reference plus ethanol, reference plus thickener, plus cross linker, plus pigment). Curiously, the presence of ethanol in the aqueous phase, often added in order to speed up evaporation, had an increasing effect, although slight, on the friction coefficient of the dry film. The opposite was observed with the thickener, result interpreted in terms of a marked lubrication phenomenon. Crosslinking or pigment addition significantly decreased the friction coefficient. A positive correlation between friction and film softness could be observed (increase of p. when film softness increased and inversely), except when lubrication was dominating. These results should be helpful to formulators of waterborne films in several application areas.
|
|
Ponzio, F., Le Houerou, V., Zafeiratos, S., Gauthier, C., Gamier, T., Jierry, L., et al. (2017). Robust Alginate-Catechol@Polydopamine Free-Standing Membranes Obtained from the Water/Air Interface. Langmuir, 33(9), 2420–2426.
Abstract: The formation of polydopamine composite membranes at the water/air interface using different chemical strategies is reported. The use of either small molecules (urea, pyrocatechol) or polymers paves the way to understand which kind of compounds can be used for the formation of PDA-composite free-standing membranes produced at the water/air interface. On the basis of these screening results, we have found that alginate grafted with catechol groups allows the formation of robust free-standing films with asymmetric composition, stimuli-responsiveness, and self healing properties. The stickiness of these membranes depends on the relative humidity, and its adhesion behavior on PDMS was characterized using the JKR method. Thus, alginate-catechol polydopamine films appear as a new class of PDA composites, mechanically robust through covalent cross-linking and based on fully biocompatible constituting partners. These results open the door to potential applications in the biomedical field.
|
|
2016 |
Al-Kawaz, A., Rubin, A., Badi, N., Blanck, C., Jacomine, L., Janowska, I., et al. (2016). Tribological and mechanical investigation of acrylic-based nanocomposite coatings reinforced with PMMA-grafted-MWCNT. Materials Chemistry And Physics, 175, 206–214.
Abstract: The chemical functionalization of carbon nanotubes (CNTs) could improve their chemical compatibility. Poly(methyl methacrylate) (PMMA)-functionalized multi-walled carbon nanotubes (MWCNTs) are prepared by in situ atom transfer radical polymerization (ATRP) using a âgrafting fromâ approach. It allows the control of the thickness of the polymer layer grafted on MWCNTs from two parameters: the feed ratio of MMA to MWCNT, the volume fraction of solvent to MMA. This work compared the effect of several PMMA-grafted-MWNCT fillers embedded into a PMMA matrix, PMMA-grafted-MWCNT/PMMA, and obtained by solution mixing technique. We studied the tribological performances of 20 mu m coatings of these nanocomposites deposited on neat PMMA. The percentage of embedded fillers is kept low to maintain the transparency of the PMMA. The coefficient of friction was found to relatively decrease with the increase of the weight fraction of polymer grafted to the surface of MWCNT. Moreover the elastic modulus also increased with increasing the weight fraction of PMMA coated MWCNT. (C) 2016 Elsevier B.V. All rights reserved.
|
|
Chemtob, A., De Paz-Simon, H., Sibeaud, M., El Fouhali, B., Croutxe-Barghorn, C., Jacomine, L., et al. (2016). An orthogonal, one-pot, simultaneous UV-mediated route to thiol-ene/sol-gel film. Express Polymer Letters, 10(6), 439–449.
Abstract: We describe a novel combination of orthogonal reactions based on UV-driven thiol-ene and alkoxysilyl condensation reactions to form a single-step route toward thioether-bridged silsesquioxane films. Our chemical strategy consists of using two bifunctional (meth) acrylate (E) and propanethiol (T) trimethoxysilyl precursors containing two complementary functional moieties for thiol-ene coupling and sol-gel process. The reaction kinetics revealed that c.a. 85% of thiol and ene conversions were consumed concomitantly. Meanwhile, a complete hydrolysis was accomplished, affording ultimately a high degree of condensation (81%). Emphasis was placed on differences of mechanical properties between sol-gel hybrids resulting from thiol-ene reaction (E-T mixture) and ene homopolymerization (E only) using scratch test measurements. For the methacrylate system, the formation of thioether linkages within a vitreous silica network emerged as a useful strategy for the formation of a uniform, low-stress and flexible crosslinked hybrid structure. Enhanced mechanical properties were manifested by an expanded elastic domain, and better resistance to cracking. Moreover, there are clear indications that mechanical properties can be easily tuned upon varying the ratio of the two hybrid precursors.
|
|
Fu, L., Favier, D., Charitat, T., Gauthier, C., & Rubin, A. (2016). A new tribological experimental setup to study confined and sheared monolayers. Review Of Scientific Instruments, 87(3).
Abstract: We have developed an original experimental setup, coupling tribology, and velocimetry experiments together with a direct visualization of the contact. The significant interest of the setup is to measure simultaneously the apparent friction coefficient and the velocity of confined layers down to molecular scale. The major challenge of this experimental coupling is to catch information on a nanometer-thick sheared zone confined between a rigid spherical indenter of millimetric radius sliding on a flat surface at constant speed. In order to demonstrate the accuracy of this setup to investigate nanometer-scale sliding layers, we studied a model lipid monolayer deposited on glass slides. It shows that our experimental setup will, therefore, help to highlight the hydrodynamic of such sheared confined layers in lubrication, biolubrication, or friction on solid polymer. (C) 2016 AIP Publishing LLC.
|
|
Rubin, A., Favier, D., Danieau, P., Giraudel, M., Chambard, J. - P., & Gauthier, C. (2016). Direct observation of contact on non transparent viscoelastic polymers surfaces: A new way to study creep and recovery. Progress In Organic Coatings, 99, 134–139.
Abstract: This work presents a new instrumentation dedicated to the study of contact creep and recovery of non transparent polymeric samples. The aim is to be able to analyze viscoelastic properties of polymeric surfaces recording the apparent contact area for the contact creep phase and the residual imprint area for the recovery phase. This gives valuable information not to be model dependant in the analysis compared to classical techniques. Indeed, for the creep phase many methods have been proposed to estimate the contact area, but rarely perform direct vizualisation as we propose. For the recovery phase two main challenges arise: avoid contact probe not to influence on recovery kinetics; get recording at early times to have information before recovery is quite finished. This study focus on indentation problems to prove the concept of viscoelastic analysis directly from experimental data without modeling. But the problematic is more larger than that and widen to more complicated rheological surface studies including indentation and scratching. (C) 2016 Elsevier B.V. All rights reserved.
|
|
2015 |
Eap, S., Keller, L., Schiavi, J., Huck, O., Jacomine, L., Fioretti, F., et al. (2015). A living thick nanofibrous implant bifunctionalized with active growth factor and stem cells for bone regeneration. International Journal Of Nanomedicine, 10, 1061–1074.
Abstract: New-generation implants focus on robust, durable, and rapid tissue regeneration to shorten recovery times and decrease risks of postoperative complications for patients. Herein, we describe a new-generation thick nanofibrous implant functionalized with active containers of growth factors and stem cells for regenerative nanomedicine. A thick electrospun poly(epsilon-caprolactone) nanofibrous implant (from 700 mu m to 1 cm thick) was functionalized with chitosan and bone morphogenetic protein BMP-7 as growth factor using layer-by-layer technology, producing fish scale-like chitosan/BMP-7 nanoreservoirs. This extracellular matrix-mimicking scaffold enabled in vitro colonization and bone regeneration by human primary osteoblasts, as shown by expression of osteocalcin, osteopontin, and bone sialoprotein (BSPII), 21 days after seeding. In vivo implantation in mouse calvaria defects showed significantly more newly mineralized extracellular matrix in the functionalized implant compared to a bare scaffold after 30 daysâ implantation, as shown by histological scanning electron microscopy/energy dispersive X-ray microscopy study and calcein injection. We have as well bifunctionalized our BMP-7 therapeutic implant by adding human mesenchymal stem cells (hMSCs). The activity of this BMP-7-functionalized implant was again further enhanced by the addition of hMSCs to the implant (living materials), in vivo, as demonstrated by the analysis of new bone formation and calcification after 30 daysâ implantation in mice with calvaria defects. Therefore, implants functionalized with BMP-7 nanocontainers associated with hMSCs can act as an accelerator of in vivo bone mineralization and regeneration.
|
|
Merindol, R., Diabang, S., Felix, O., Roland, T., Gauthier, C., & Decher, G. (2015). Bio-Inspired Multiproperty Materials: Strong, Self-Healing, and Transparent Artificial Wood Nanostructures. Acs Nano, 9(2), 1127–1136.
Abstract: Nanocomposite films possessing multiple interesting properties (mechanical strength, optical transparency, self-healing, and partial biodegradability) are discussed. We used Layer-by-Layer assembly to prepare micron thick wood-inspired films from anionic nanofibrillated cellulose and cationic poly(vinyl amine). The film growth was carried out at different pH values to obtain films of different chemical composition, whereby, and as expected, higher pH values led to a higher polycation content and also to 6 times higher film growth increments (from 9 to 55 nm per layer pair). In the pH range from 8 to 11, micron thick and optically transparent LbL films are obtained by automated dipping when dried regularly in a stream of air. Films with a size of 10 cm(2) or more can be peeled from flat surfaces; they show tensile strengths up to about 250 MPa and Youngs moduli up to about 18 GPa as controlled by the polycation/polyanion ratio of the film. Experiments at different humidities revealed the plasticizing effect of water in the films and allowed reversible switching of their mechanical properties. Whereas dry films are strong and brittle (Youngs modulus: 16 GPa, strain at break: 1.7%), wet films are soft and ductile (Youngs modulus: 0.1 GPa, strain at break: 49%). Wet film surfaces even amalgamate upon contact to yield mechanically stable junctions. We attribute the switchability of the mechanical properties and the propensity for self-repair to changes in the polycation mobility that are brought about by the plastifying effect of water.
|
|
Rubin, A., Favier, D., Danieau, P., Chambard, J. - P., & Gauthier, C. (2015). In situ analysis of viscoelastic contact on glassy polymer surfaces. Materiaux & Techniques, 103(6).
Abstract: The aim of this study is to understand time-dependant behaviour of polymeric surfaces and to characterize corresponding rheological mechanisms. One way to study this behaviour is by means of creep (including followed recovery) experiments. The first key point is the experimental characterization of the recovery phase. One of the specificity of the group is to develop original devices which allow us to record some mechanical and physical information on transparent polymers without being model dependant. The current step is to be able to study non transparent polymers with a new set-up where the normal load is applied by an UMT apparatus (Bruker) and the imprint recovery is measured by a deflectometry technique instrument developed by HOLO3. This new set-up allow to study voscoelastic and viscoplastic recovery kinetics.
|
|
2014 |
Moreno-Couranjou, M., Blondiaux, N., Pugin, R., Le Houerou, V., Gauthier, C., Kroner, E., et al. (2014). Bio-Inspired Nanopatterned Polymer Adhesive: A Novel Elaboration Method and Performance Study. Plasma Processes And Polymers, 11(7), 647–654.
Abstract: The objective of this work is to investigate a novel top-down synthesis route toward the elaboration of nanopatterned polymer surfaces by combining thin polymer structuring (polymer-demixing) and plasma etching techniques. Thanks to this original approach, the adjustment of the parameters during the wet chemical and plasma steps allows independent tuning of the lateral dimension of the polymer structures (diameter) and the height of the pillars. The nanopatterning description of two different polymers, namely polyethylene naphthalate and polyimide, is reported. Johnson-Kendall-Roberts (JKR) adhesion tests are carried out to compare the adhesive property of the patterned and non-patterned polymer surfaces. These measurements allow highlighting the importance of the polymer viscoelasticity for future development of bioinspired polymer-based dry adhesives.
|
|
Rubin, A., Rebutin, N., Gerard, P., & Gauthier, C. (2014). Mechanical properties of a rubber-reinforced block copolymer PMMA: Effect of the nanostructuration on tribological performances. Materials Letters, 135, 184–187.
Abstract: The effect of a nanostructured architecture of a rubber-reinforced block copolymer PMMA on both volume and surface mechanical properties is studied. The rubber inclusions ordered at the nanoscale enhance the ductile behavior of the triblock copolymer. This acrylic glass can therefore be easily thermoformed even. Besides, polymeric surfaces are sensitive to scratches which have direct influence on optical transparency. Scratches, which left irreversible grooves on the surface, appear at higher strains with rubber inclusion ordered at the nanoscale compared to classical PMMA or high impact cast PMMA. Eventually, the studied rubber-reinforced block copolymer PMMA is a good candidate to acrylic glass dedicated to automotive glazing. (C) 2014 Elsevier B.V. All rights reserved.
|
|
Shishkan, O., Zamfir, M., Gauthier, M. A., Boerner, H. G., & Lutz, J. - F. (2014). Complex single-chain polymer topologies locked by positionable twin disulfide cyclic bridges. Chemical Communications, 50(13), 1570–1572.
Abstract: Oligomers containing the peptide sequence cysteine-any-cysteine (CXC) were attached, at specific locations, to a linear chain of polystyrene. The polymer-bound peptide motifs were then oxidized under dilute conditions to afford a complex bio-hybrid bi-cyclic topology via intramolecular twin disulfide bridge formation.
|
|
2013 |
Chatel, T., Le Houerou, V., Pelletier, H., & Gauthier, C. (2013). Numerical analysis of the creep of the contact and recovery of the imprint on amorphous polymer surfaces. Mechanics Of Time-Dependent Materials, 17(4), 581–595.
Abstract: This article attempts to analyze the viscoelastic behavior of an amorphous polymer during a microindentation test. The viscoelastic behavior of an amorphous polymer (poly(methyl methacrylate), PMMA) is derived from different relaxation tests performed under different applied true strains. A generalized Maxwell model is then used to identify the mechanical parameters of the viscoelastic behavior. The numerical results display good correlation with experiments during the creep phase. The uniaxial relaxation test used to identify the viscoelastic behavior is chosen in relation to the experimental conditions of indentation. The results obtained for the recovery phase allow a first analysis of the strain and von Mises equivalent stress fields during indentation test. The recovery of the imprint left on the surface seems to depend on the location of the strain maxima. If a strain level of 10 % or more reaches the surface of the deformed volume, a permanent imprint is obtained. Otherwise the residual imprint may be considered to be completely healed even if the subsurface has partially yielded during the loading phase or creep time.
|
|
Hisler, V., Palmieri, M., Le Houerou, V., Gauthier, C., Nardin, M., Vallat, M. - F., et al. (2013). Scale invariance of the contact mechanics of micropatterned elastic substrates. International Journal Of Adhesion And Adhesives, 45, 144–149.
Abstract: This paper describes the conditions for contact formation between soft elastic hemispheres and soft elastic substrates micropatterned with pillars. These microstructured substrates were often proposed in the two past decades for the control of adhesion. In this study the hexagonal micropillars are arranged in hexagonal arrays and the width L of the pillars as well as the distance D between the pillars (with L=D for a sample) are both varied from one sample to another in order to keep the overall planar surface fraction of the pillars constant. Additionally, two pillars of heights h=4 mu m and h=16 mu m are considered here. As expected from previous studies different contact morphologies are found as a function of the aspect ratio and the contact pressure. The contact may be formed (i) only at the top of the pillar, (ii) both at the top and between the pillars, or (iii) simultaneously at the top of the pillars and in between the pillars at the centre of the contact for which the pressure is the highest. Unexpectedly it is shown in this last case that the same contact morphology is obtained with the same pressure if the surface pattern aspect ratio L/h is varied homothetically, suggesting a scale invariant behaviour of the contact formation between the hemisphere and the soft elastic micropatterned substrate. (C) 2013 Elsevier Ltd. All rights reserved.
|
|
Klein, G., Le Houerou, V., Gauthier, C., & Holl, Y. (2013). Friction properties of acrylic-carboxylated latex films. 2: Effect of post added surfactant. Tribology International, 57, 257–265.
Abstract: The second part of this work aiming at investigating how specificities of thin films prepared from aqueous polymer colloids (latexes) influence their friction properties is devoted to the role of surfactants. Two acrylic latexes containing either 1 wt% or 4 wt% of acrylic acid were used, to which 0 to 9 wt% of sodium dodecyl sulfate (SDS) was post added before film formation by drying. Bulk mechanical properties were also studied in order to improve interpretation of friction results. Increasing the amount of SOS in the films has the effect of increasing Youngâs and shear storage moduli and decreasing tan delta. SOS, forming crystallized aggregates in the bulk of the films, behaves like a reinforcing filler, except at 9 wt% where the SDS phase percolates under stress and allows film deformation by shear bands at very low stress. Friction coefficients dramatically decrease with increasing SDS concentration, especially at high strain rate. Surface shear stress is strongly decreased due to lubrication by SDS having migrated to the film surface. In order to gain more insight in the lubrication mechanisms, SOS layers were deposited on glass in increasing amounts. This part of the study seemed to indicate that organization of the SOS surface layers has more impact than their amount. (C) 2012 Elsevier Ltd. All rights reserved.
|
|
Rubin, A., Gauthier, C., & Schirrer, R. (2013). Analysis of the effect of nano-roughness on the friction of a vitreous polymer. Wear, 303(1-2), 40–48.
Abstract: The theological behavior at the interface between a polymer surface and a rigid indenter during dry friction is linked to the local pressure and the roughness of the surface of the indenter. This study analyzed experimental results for the friction coefficient mu versus the mean contact pressure p(mean) obtained at ambient temperature on polycarbonate. The rigid indenters consisted of spherical glass tips of several radii having surfaces of two types: polished to tight tolerance (optical lenses) or nano-roughened (chemical etching). Below the yield stress (p(mean) < 100 MPa), the intrinsic friction coefficient followed a master curve for smooth indenters whereas nano-roughnesses reduced the friction (from 5.5 to 140 nm Rrms). To explain these experimental results an original model based on the classical laws of contact mechanics was developed and provides a basis to study the rheology of confined polymer layers. (c) 2013 Elsevier B.V. All rights reserved.
|
|
Solar, M., Meyer, H., & Gauthier, C. (2013). Analysis of local properties during a scratch test on a polymeric surface using molecular dynamics simulations. European Physical Journal E, 36(3).
Abstract: This work demonstrates a possible route to connect a particle (chain) based understanding with continuum mechanical questions about contact mechanics. The bond orientation, chain conformation and stress field of a polymer film were analyzed during scratch tests (tangential contact) using a molecular dynamics (MD) simulation approach. Scratch tests with a conical tip at constant scratching velocity were simulated on linear amorphous polymer surfaces at various temperatures and roughnesses of the tip and for various interactions between the tip and the particles of the polymer chains. The second Legendre polynomial (computed for small domains around the tip) gave the bond orientation inside the polymer film during sliding of the tip. The gyration tensor (layer-resolved in the direction of the polymer film thickness) provided information about the conformation of the polymer chains. These results allowed us to argue in favor of Briscoeâs hypothesis (thin film sheared vs. âbulkâ compressive behavior) concerning the friction properties of the polymer surfaces. Finally, the first stress measurements of the virial stress tensor (in sub-boxes placed in the MD cell) revealed a complex combination between compressive hydrostatic pressure and shear stress, which may be interpreted as a complex sheared domain at the interface.
|
|
2012 |
Klein, G., Le Houerou, V., Muller, R., Gauthier, C., & Holl, Y. (2012). Friction properties of acrylic-carboxylated latex films-1: Effects of acrylic acid concentration and pH. Tribology International, 53, 142–149.
Abstract: The aim of this work was to investigate how specificities of thin films prepared from aqueous polymer colloids (latexes) influence their friction properties, tested with a sliding stainless steel spherical tip. Two acrylic latexes containing either 1 wt% or 4 wt% of acrylic acid (AA) were used at pH 2 or 10. Bulk mechanical properties were also studied in order to improve the interpretation of friction results. Increasing AA concentration and pH increases the overall film rigidity, pH being more effective than AA concentration. Contact pressures are directly correlated to bulk mechanical properties whereas surface shear stresses are also strongly influenced by molecular interactions with the sliding tip. Friction coefficients are rather high, peaking at 5, because of important viscoelastic dissipation in the films as well as strong polar interactions introduced by AA, especially at high pH. The paper also addresses the question of the relevant characteristic length in this kind of friction study. (C) 2012 Elsevier Ltd. All rights reserved.
|
|
Rubin, A., Gauthier, C., & Schirrer, R. (2012). The friction coefficient on polycarbonate as a function of the contact pressure and nanoscale roughness. Journal Of Polymer Science Part B-Polymer Physics, 50(8), 580–588.
Abstract: During dry friction the rheological behavior at the interface between a polymer surface and a rigid indenter is linked to the local pressure and the roughness of the surface of the indenter. This study on polycarbonate reports experimental results obtained at ambient temperature using rigid, spherical glass indenters of various radii. In a first step, a plot of the experimental friction coefficient mu versus the mean contact pressure pmean showed that below the yield stress (pmean < 100 MPa) the intrinsic friction coefficient follows a master curve for smooth indenters. In a second step, roughened indenters were prepared by chemical etching, which allowed the monitoring of nanoscale roughness parameters. From 5.5 to 140 nm Rrms, the friction coefficient mu progressively fell to a plastic-like constant value, indicating that the nanoroughness mediates the friction. These results form the basis for a study of the rheology of confined polymer layers. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012
|
|
Solar, M., Meyer, H., Gauthier, C., Fond, C., Benzerara, O., Schirrer, R., et al. (2012). Mechanical behavior of linear amorphous polymers: Comparison between molecular dynamics and finite-element simulations. Physical Review E, 85(2, 1).
Abstract: This paper studies the rheology of weakly entangled polymer melts and films in the glassy domain and near the rubbery domain using two different methods: molecular dynamics (MD) and finite element (FE) simulations. In a first step, the uniaxial mechanical behavior of a bulk polymer sample is studied by means of particle-based MD simulations. The results are in good agreement with experimental data, and mechanical properties may be computed from the simulations. This uniaxial mechanical behavior is then implemented in FE simulations using an elasto-viscoelasto-viscoplastic constitutive law in a continuum mechanics (CM) approach. In a second step, the mechanical response of a polymer film during an indentation test is modeled with the MD method and with the FE simulations using the same constitutive law. Good agreement is found between the MD and CM results. This work provides evidence in favor of using MD simulations to investigate the local physics of contact mechanics, since the volume elements studied are representative and thus contain enough information about the microstructure of the polymer model, while surface phenomena (adhesion and surface tension) are naturally included in the MD approach.
|
|
2011 |
Baietto, M. C., Rannou, J., Gravouil, A., Pelletier, H., Gauthier, C., & Schirrer, R. (2011). 3D crack network analysis during a scratch test of a polymer: A combined experimental and multigrid X-FEM based numerical approach. Tribology International, 44(11), 1320–1328.
Abstract: The scratch behavior of a thermoset solid polymer exhibiting brittle behavior in tension is investigated. The surfaces are scratched and an imaging system is used to record real time photographs. The 3D crack pattern is analyzed using fluorescence confocal laser scanning microscopy. A finite element simulation is performed to determine the indenter/specimen contact conditions. They are used as input data for the 3D crack network analysis based on combined 3D localized multigrid and X-FEM/level set techniques. The computed stress distributions within the 3D cracked specimen are of great interest to understand the crack network formation observed during the experiments. (C) 2010 Elsevier Ltd. All rights reserved.
|
|
Belon, C., Chemtob, A., Croutxe-Barghorn, C., Rigolet, S., Le Houerou, V., & Gauthier, C. (2011). A Simple Method for the Reinforcement of UV-Cured Coatings via Sol-Gel Photopolymerization. Macromolecular Materials And Engineering, 296(6), 506–516.
Abstract: A difunctional methacrylate oligomer was mixed with a variable amount of a MAPTMS precursor in the presence of both a radical and a cationic photoinitiator. The simultaneous photolysis of both photosensitive molecules upon UV irradiation allowed the single- step generation of a type-II polymethacrylate/ polysiloxane nanocomposite film. Methacrylate and methoxysilyl conversions during irradiation were efficiently monitored by FTIR spectroscopy. The inorganic structure of the resulting silica-based hybrid films was characterized using 29 Si solid-state NMR. Finally, the reinforcement ability of the resulting hybrid films was also assessed by using a unique range of characterization techniques: DMA, scratch test, and nanoindentation.
|
|
Chatel, T., Gauthier, C., Pelletier, H., Le Houerou, V., Favier, D., & Schirrer, R. (2011). Creep of the contact with a spherical tip and recovery of the imprint on amorphous polymer surfaces. Journal Of Physics D-Applied Physics, 44(37).
Abstract: This paper is devoted to an analysis of the creep and recovery occurring on the surface of an amorphous polymer during indentation, a characteristic of the self-healing performance of the material. Creep and recovery were studied using a home made experimental device which allows one to record in situ the evolution of the imprint created by a probe. The influence of the temperature, the initial imposed strain and the creep duration were analysed. The evolution of the true contact area with time was followed during micro-indentation. We demonstrate the non-linear behaviour of the amorphous polymer studied during the creep and recovery phases. The results obtained allow calculation of the activation energy and activation volume of the polymer. These results are also compared with the predictions of the viscoelastic model of Lee and Radok and viscoplasticity is demonstrated for a reasonable initial mean contact strain as defined by Tabor. Nevertheless, it is still difficult to quantify the recovery and to define the conditions for the appearance of plasticity.
|
|
Mansha, M., Gauthier, C., Gerard, P., & Schirrer, R. (2011). The effect of plasticization by fatty acid amides on the scratch resistance of PMMA. Wear, 271(5-6), 671–679.
Abstract: Scratch durability of polymer surfaces is becoming crucial for the growing use of these materials in innovative applications, replacing former materials with more resistant surfaces. A variety of physicochemical processes such as annealing and a range of ion plantation techniques, generally applied to improve surface properties, cannot be applied to transparent polymers like PMMA due to their darkening outcome. Enhancement of the scratch resistance must be investigated for the most part as a consequence due to decreasing the friction coefficient. The recovery of the groove left on the surface increases if the tip is smooth or if the local friction coefficient is low. The effect of three fatty acid amides namely Erucamide, Behenamide and Stearamide on both surface and bulk mechanical properties of PMMA was studied at a wide range of temperature. Experimental results show that a decrease in friction coefficient is possible by the introduction of appropriate plasticizer without having a significant effect on its bulk behaviour and this decrease in friction depends upon the nature and the content of plasticizer. Moreover, Erucamide has been proved more effective in decreasing friction of PMMA than Behenamide or Stearamide. The values of the rear contact angle and in situ photographs during scratching confirm that the decrease in friction is associated with the decrease of yielding of the contact between the tip and the polymer surface. The surface energy analysis shows that the decrease in friction coefficient is without any significant change in surface energy of PMMA. (C) 2011 Elsevier B.V. All rights reserved.
|
|
Solar, M., Meyer, H., Gauthier, C., Benzerara, O., Schirrer, R., & Baschnagel, J. (2011). Molecular dynamics simulations of the scratch test on linear amorphous polymer surfaces: A study of the local friction coefficient. Wear, 271(11-12), 2751–2758.
Abstract: This work presents a mechanical analysis of tangential contact using molecular dynamics simulations. Scratch tests with a conical tip on amorphous polymer surfaces were simulated at various temperatures, scratching velocities, roughnesses of the tip and with various interactions between the tip and the monomers. The local friction coefficient for the different contact conditions (temperature, tip roughness and scratching velocity) was calculated by studying the apparent friction and the contact asymmetry. The results are in good agreement with experimental data from tests on classical polymer surfaces on a microscopic scale. (C) 2011 Elsevier B.V. All rights reserved.
|
|
2010 |
Belon, C., Chemtob, A., Croutxe-Barghorn, C., Rigolet, S., Le Houerou, V., & Gauthier, C. (2010). Combination of Radical and Cationic Photoprocesses for the Single-Step Synthesis of Organic-Inorganic Hybrid Films. Journal Of Polymer Science Part A-Polymer Chemistry, 48(19), 4150–4158.
Abstract: Nanocomposite materials prepared from radically photocurable hybrid sol-gel precursors have been widely developed within the last decade, especially to devise novel optical devices and coatings. For their synthesis, a preferential route has involved in the successive sol-gel process of acrylate trialkoxysilane precursors followed by radical photopolymerization. In contrast, this work presents an original one-step synthesis based on the association of two different photoinitiators (PIs) in the same formulation: the photolysis of a hydroxyphenylketone (radical PI) affords polyacrylate chains while that of a diaryl iodonium salt (cationic PI) generates powerful superacids catalyzing the sol-gel reactions of the alkoxy functions. The behavior of methacrylate and acrylate trimethoxysilane precursors was compared to highlight the effect of the organic moiety functionality on the reaction kinetics (Fourier transform infrared spectroscopy) and the film microstructure (C-13 and Si-29 solid-state nuclear magnetic resonance). Interestingly, evidence of local organization in these hybrid films was also given by X-ray analysis. In a last part, their thermomechanical properties were discussed thoroughly using a range of techniques: DSC, scratch-resistance test, nanoindentation. (c) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4150-4158, 2010
|
|
Belon, C., Chemtob, A., Croutxe-Barghorn, C., Rigolet, S., Schmitt, M., Bistac, S., et al. (2010). Nanocomposite coatings via simultaneous organic-inorganic photo-induced polymerization: synthesis, structural investigation and mechanical characterization. Polymer International, 59(8), 1175–1186.
Abstract: Hybrid sol-gel films were prepared via a simultaneous organic-inorganic UV-curing process using a diaryliodonium salt as a superacid photogenerator. In this single-step procedure, an epoxy functionalized reactive resin mixed with a variable amount of either of two epoxy trialkoxysilane precursors was UV-irradiated, causing both the initiation of epoxy ring-opening copolymerization and the catalysis of trialkoxysilyl sol-gel reactions. The concomitant photo-induced sol-gel process was found to have a significant effect on the two related propagation mechanisms in competition for the oxirane ring-opening – the active chain-end and the activated monomer mechanisms – as proved by a systematic examination of the hybrid material microstructure through Si-29 and C-13 solid-state NMR spectroscopy. The effect of the oxo-silica network generation on the epoxy reaction kinetics was also evaluated using real-time Fourier transform infrared spectroscopy upon varying the epoxysilane structure and its concentration. Thermal and dynamic mechanical analyses were systematically performed on these hybrids, by studying thoroughly their structure-property interdependence. Other mechanical characterizations through tribological and scratch tests suggested that the present photopolymer-silica hybrid material provides a powerful tool to tailor mechanical property profiles. (C) 2010 Society of Chemical Industry
|
|