Relation entre la concentration et le coefficient d'autodiffusion de solutions aqueuses de xanthane
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Le coefficient de friction entre un polymere liquide et une surface solide depend fortement des interactions entre les deux parties. Dans le cas d'un ecoulement de polymere sur des surfaces de silice modifiees lorsque le taux de... more
Le coefficient de friction entre un polymere liquide et une surface solide depend fortement des interactions entre les deux parties. Dans le cas d'un ecoulement de polymere sur des surfaces de silice modifiees lorsque le taux de cisaillement augmente la friction d'abord forte devient ensuite tres faible avec un fort glissement a la surface. Dans le cas du test de pelage d'un adhesif liquide, selon le substrat solide utilise, il est possible de passer d'un regime ou la dissipation par friction est importante a un regime ou la dissipation par cisaillement est preponderante.
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Research Interests: Mathematics, Photochemistry, Fluorescence, Biology, Medicine, and 12 moreBiological Sciences, Lasers, Diffusion, Animals, Brownian Motion, Photobleaching, Membrane, Macromolecule, Bovine Serum Albumin, fluorescence recovery after photobleaching (FRAP), fluorescent dyes, and Medical and Health Sciences
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We have used the “Forced Rayleigh scattering” technique with spiropyran dyed polystyrene spheres in aqueous suspension, to measure the self diffusion as a function of the strength of interaction between the particles. The latter quantity... more
We have used the “Forced Rayleigh scattering” technique with spiropyran dyed polystyrene spheres in aqueous suspension, to measure the self diffusion as a function of the strength of interaction between the particles. The latter quantity was modified both by adding electrolyte and by changing the particle concentration, as well as by using spheres with different diameters and charges. We find that the diffusion constant decreases monotonically from the Stokes value as the repulsive interaction is increased, until the interactions are sufficiently strong to form a colloidal crystal. At this point there is a first order transition indicated by the decrease of the diffusion constant by ~ four orders of magnitude and the presence of Bragg reflections. These measurements are compared with viscosity measurements done in the liquid and solid states, with quasielastic light scattering measurements and with models for diffusion and viscosity in interacting systems.
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Publisher Summary This chapter introduces a reptation model in its simplest version. It discusses the interest of complementary self diffusion and viscoelastic measurements, and presents the currently available methods for measuring... more
Publisher Summary This chapter introduces a reptation model in its simplest version. It discusses the interest of complementary self diffusion and viscoelastic measurements, and presents the currently available methods for measuring diffusion in entangled polymer systems. Results obtained on polydimethylsiloxane (PDMS), a model liquid polymer well above its glass temperatured at room temperature are described, and the consequences on the limits of the entangled regime as seen from diffusion measurements, compared to what is observed in rheometry, are discussed. The chapter presents the dynamics of linear chains that could be described by simple reptation arguments, assuming that each chain essentially sees a frozen environment during its reptation time, as soon as the number of entanglements per chain is larger than 10. Below this value, the dynamics is strongly accelerated mainly through the constraint release mechanism: a simple reptation behavior is recovered when the matrix is frozen down, indicating that the fluctuations of the chains inside their tube are not dominant in this acceleration of the motion.
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We present experimental investigations of the spreading of nonvolatile liquids (polydimethylsiloxane drops) on smooth horizontal silicon wafers. We distinguish the macroscopic part of the drop, which can be seen by bare eye (or through a... more
We present experimental investigations of the spreading of nonvolatile liquids (polydimethylsiloxane drops) on smooth horizontal silicon wafers. We distinguish the macroscopic part of the drop, which can be seen by bare eye (or through a microscope) from the microscopic part, or precursor film, which progressively develops, like a liquid tongue (thickness smaller than 1000 A) all around the drop. The spreading kinetics of the macroscopic drop appears independent of the spreading parameter, in contrast to the precursor film which is deeply influenced by the surface energies. We have characterized this precursor film (both its profile and its evolution) by optical techniques. The results are compared with the recent de Gennes and Joanny’ theoretical predictions, and specific polymeric effects are pointed out.
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L’adhesion d’assemblages coextrudes Polypropylene (PP) – Polyamide 6 (PA6) renforces par des copolymeres dibloc PP/PA6 formes in situ a ete etudiee en fonction des conditions d’extrusion. Nous montrons que la densite de copolymeres formes... more
L’adhesion d’assemblages coextrudes Polypropylene (PP) – Polyamide 6 (PA6) renforces par des copolymeres dibloc PP/PA6 formes in situ a ete etudiee en fonction des conditions d’extrusion. Nous montrons que la densite de copolymeres formes a l’interface reste tres inferieure a la valeur de saturation et apparait peu sensible aux parametres d’outillage a structure geometrique finale donnee. Les vitesses de migration des especes reactives vers l’interface et les cinetiques de reaction de formation des copolymeres en l’absence d’ecoulement ont ete caracterisees, ainsi que la creation de surface d’interface pendant l’etirage du film lie a la coextrusion. La densite finale de copolymeres depend de ces deux parametres. Nous montrons par ailleurs que l’adhesion depend des conditions d’extrusion a densite de copolymeres donnee. Une simulation numerique de l’etape de refroidissement permet de correler l’adhesion et la contrainte exercee sur la section du film lors de la cristallisation.
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The sodium dodecyl sulfate (or SDS)/ n-butanol/toluene/ brine system has been selected for investigation in the low surfactant concentration range. For a 6.5% NaCl salinity and the following proportions of the other components: brine... more
The sodium dodecyl sulfate (or SDS)/ n-butanol/toluene/ brine system has been selected for investigation in the low surfactant concentration range. For a 6.5% NaCl salinity and the following proportions of the other components: brine 65.74%, toluene 31.90%, n-butanol 2.30% and SDS 0.04%, the sample is composed of a transparent upper oily region, an intermediate turbid microemulsion region, and a lower transparent one. The oil-microemulsion interface is sharp; the intermediate and lower regions are separated by a diffuse interface, a few millimeters thick. Index of refraction and gas chromatographic analyses plus quasielastic light scattering (QELS) characterize the sample as composed of a non uniform vertical composition aqueous domain of microemulsion type and an excess oily solution. In the aqueous domain, two regions with constant but different index of refraction (n) and mutual diffusion coefficient (D) correspond approximately to the intermediate and lower regions and are separated by a region with progressive n and D variation. The composition and structure results at a given temperature suggest an alcohol-rich composition of the microemulsion interfacial film, the n-butanol/SDS ratio becoming larger than for usual SDS/n-butanol/toluene/brine systems. Due to this fact, an unusually low value of the rigidity constant of the interfacial film is expected. Preliminary experimental results define the thermal range in which the sample displays a diffuse interface, and show that the surfactant is near its solubilization limit for the given proportions of the other components.
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The structure of layers of poly(dimethylsiloxane) terminally grafted on silica has been studied by small angle neutron scattering. The authors have observed the influence of the polymer molecular weight, the grafting density and the... more
The structure of layers of poly(dimethylsiloxane) terminally grafted on silica has been studied by small angle neutron scattering. The authors have observed the influence of the polymer molecular weight, the grafting density and the solvent quality. At a high grafting density, in good and in bad solvents, the chains are stretched and the thickness of the layers is proportional to the polymer mass. In a good solvent the inner structure of the layers is similar to that of a semi-dilute solution of free polymer at the same local concentration, in agreement with the description of Alexander.
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ABSTRACT Direct measurements of the velocity of a high-molecular-weight polydimethylsiloxane melt in the immediate vicinity of a solid wall (100 nm from the interface) have been conducted, using a novel optical technique based on... more
ABSTRACT Direct measurements of the velocity of a high-molecular-weight polydimethylsiloxane melt in the immediate vicinity of a solid wall (100 nm from the interface) have been conducted, using a novel optical technique based on evanescent wave induced fluorescence and pattern photobleaching. On silica, quite distinct behaviours are observed: (i) for weak polymer-surface interactions (silica modified by grafting of C18 hydrocarbon chains), a sharp transition between almost no and strong slippage at the wall appears for high enough shear rate, in good agreement with a recent model that ascribes the onset of slippage to a stretching transition of a few chains attached to the surface; (ii) for strong polymer-surface interactions (bare silica) chains irreversibly adsorbed build a pseudo-brush; only weak slippage develops with b (the length under the surface where the velocity extrapolates to zero) independent of the shear rate. No sharp transition appears within the explored shear rate range.
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ABSTRACT
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ABSTRACT The final stages of the spreading of nonvolatile polymer droplets on smooth solid surfaces have been studied by the technique of x-ray reflectivity. Clean and silanated silicon wafers which are substrates corresponding,... more
ABSTRACT The final stages of the spreading of nonvolatile polymer droplets on smooth solid surfaces have been studied by the technique of x-ray reflectivity. Clean and silanated silicon wafers which are substrates corresponding, respectively, to high and low positive spreading parameters S, have been investigated. In both cases the equilibrium state has been characterized and compared with recent theoretical predictions. We show that for a high S value, the final state cannot be viewed as a dense homogeneous film, whereas for a low S value, the theoretical "pancake" picture could be appropriate.
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We have investigated the shear flow of a polydimethylsiloxane (PDMS) melt on a PDMS brush of well-controlled density. As the shear rate, dot gamma, is increased, we show the existence of a slip transition from a weak slip regime, where... more
We have investigated the shear flow of a polydimethylsiloxane (PDMS) melt on a PDMS brush of well-controlled density. As the shear rate, dot gamma, is increased, we show the existence of a slip transition from a weak slip regime, where the extrapolation length of the velocity profile, b, is a constant b0, to a strong one, where dot gamma sticks
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Abstract Using the forced Rayleigh light scattering technique, the self-diffusion coefficient, D s , of polystyrene chains included in tridimensional structures was measured as a function of the molecular characteristics of the host... more
Abstract Using the forced Rayleigh light scattering technique, the self-diffusion coefficient, D s , of polystyrene chains included in tridimensional structures was measured as a function of the molecular characteristics of the host polystyrene network, swollen at equilibrium. Photochromic linear polystyrenes were prepared anionically by deactivation of the living polymer with a spiropyran molecule. Polystyrene networks were obtained by copolymerization of living polystyrene with divinylbenzene. From swelling experiments, it was concluded that the addition of 8% labelled polystyrene to the network does not modify the elastic properties of the gel. We present preliminary results which demonstrate the feasibility of self-diffusion measurements on such systems, and reveal two different diffusion processes: a fast one that we attribute to chains free to move inside the network defects; and a slow one, corresponding to chains effectively entangled in the gel.
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The slip behavior of polydimethylsiloxane (PDMS) polymer melts flowing on non-adsorbing surfaces made of short non-entangled PDMS chains densely end-grafted to silica has been characterized. For high enough shear rates, constant slip... more
The slip behavior of polydimethylsiloxane (PDMS) polymer melts flowing on non-adsorbing surfaces made of short non-entangled PDMS chains densely end-grafted to silica has been characterized. For high enough shear rates, constant slip lengths proportional to the bulk fluid viscosity have been observed, in agreement with Navier's interfacial equation, and demonstrating that the interfacial Navier's friction coefficient is a local quantity, independent of the polymer molecular weight. Comparing the interfacial shear stresses deduced from these measured slip lengths to available friction stress measured for crosslinked PDMS elastomers, we directly compared the interfacial melt or elastomer friction coefficient to the monomer-monomer friction.
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The slippage of polymer solutions on solid surfaces is often attributed to a depletion layer whose origin, thickness, and interaction with the flow are poorly understood. Using a Dynamic Surface...
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Two important questions on the validity of the mechanical analysis commonly used to deduce adhesion strength from a Johnson, Kendall and Roberts (JKR) test are investigated in detail, based on systematic experiments conducted on a JKR... more
Two important questions on the validity of the mechanical analysis commonly used to deduce adhesion strength from a Johnson, Kendall and Roberts (JKR) test are investigated in detail, based on systematic experiments conducted on a JKR machine which allows the relations between the contact area and the load, and between the deformation in the centre of the contact area and
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Nous etudions l'interface entre polyamide 6 et polypropylene isotactique, renforcee par un copolymere dibloc forme in situ. Nous avons observe la structure cristalline de cette interface par diffraction des rayons X sur des films... more
Nous etudions l'interface entre polyamide 6 et polypropylene isotactique, renforcee par un copolymere dibloc forme in situ. Nous avons observe la structure cristalline de cette interface par diffraction des rayons X sur des films minces de ces polymeres et observe une orientation specifique du iPP en presence de PA6. D'autre part nous faisons varier la nature du bloc PP du copolymere de facon a mieux comprendre le role de celui-ci tant dans l'orientation cristalline de l'interface que dans l'adhesion du systeme.
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In order to understand the molecular mechanisms responsible for the adhesion between isotactic polypropylene (iPP) and polyamide 6 (PA6) in the presence of PPg-PA6 copolymer, thin films assemblies with a typical thickness of 110 nm have... more
In order to understand the molecular mechanisms responsible for the adhesion between isotactic polypropylene (iPP) and polyamide 6 (PA6) in the presence of PPg-PA6 copolymer, thin films assemblies with a typical thickness of 110 nm have been prepared. The crystalline orientation close to the interface has been investigated by X-Ray diffraction. An epitaxial crystallization of iPP on PA6 was observed. Similarly to what happens for adhesive strength, the epitaxy is enhanced when increasing the copolymer surface density or the length of the PP block and further enhanced when annealing the samples above the melting temperature of PA6.
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Nous avons etudie l'adhesion d'un assemblage Polyamide 6 (PA6) - Polypropylene isotactique (PP). La formation in situ de copolymere, par reaction des extremites NH 2 du PA6 6 et des groupes anhydride succinique portes par des... more
Nous avons etudie l'adhesion d'un assemblage Polyamide 6 (PA6) - Polypropylene isotactique (PP). La formation in situ de copolymere, par reaction des extremites NH 2 du PA6 6 et des groupes anhydride succinique portes par des chaines de PP modifiees, assure le renforcement de l'interface. Boucher et al. ont precedemment mis en evidence un fort accroissement de l'energie d'adhesion, a densite de copolymere donnee, en fonction de la masse moleculaire des blocs PP du copolymere et de la temperature ([1], [2]). Afin de comprendre cette augmentation d'energie d'adhesion, nous avons developpe des moyens d'observations qui nous ont permis de relier l'energie d'adhesion a la structure de l'interface (densite surfacique de copolymere forme Σ, morphologie et cristallinite interfaciales). Deux explications plausibles ont ete examinees de maniere systematique: la presence de la phase β du PP a l'interface et les phenomenes de co-cristallisation.
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The capillary bridge formed between a solid spherical surface and an infinite liquid bath is an efficient technique for characterizing the adhesion property of a solid surface. When the solid surface is pulled out of the liquid at a... more
The capillary bridge formed between a solid spherical surface and an infinite liquid bath is an efficient technique for characterizing the adhesion property of a solid surface. When the solid surface is pulled out of the liquid at a sufficiently high velocity, a thin liquid film is deposited on the solid and drains more slowly than the central capillary bridge. The retraction kinetics of this "pancake" and the critical velocity above which it appears are studied as a function of the viscosity of the liquid or the wettability of the solids. The dynamics of the liquid film follows the classical law of dynamic dewetting. This makes the capillary bridge test, used in the dynamical regime, a very efficient tool for discriminating between antiadhesive coatings.
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We have investigated simple shear flows of poly-dimethyl-siloxane (PDMS) melts on PDMS brushes with well controlled grafting density Σ, using optical techniques based on near field laser anemometry to measure the local velocity of a... more
We have investigated simple shear flows of poly-dimethyl-siloxane (PDMS) melts on PDMS brushes with well controlled grafting density Σ, using optical techniques based on near field laser anemometry to measure the local velocity of a polymer melt at a solid interface. We have observed a slip transition from a weak slip regime to a strong one as the shear rate crosses a critical value γ*. The influence of the molecular weight of the melt Mm, of the molecular weight of the brush chains Mb and of Σ on γ*, has been investigated to elucidate the molecular mechanisms. The results are compared with an existing molecular model.
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We study the friction of a poly(dimethylsiloxane) (PDMS) rubber network sliding, at low velocity, on a substrate on which PDMS chains are end-tethered. We thus clearly evidence the contribution to friction of the pull-out mechanism of... more
We study the friction of a poly(dimethylsiloxane) (PDMS) rubber network sliding, at low velocity, on a substrate on which PDMS chains are end-tethered. We thus clearly evidence the contribution to friction of the pull-out mechanism of chain-ends that penetrate into the network. This interfacial dissipative process is systematically investigated by probing the velocity dependence of the friction stress and its variations with the grafting density and molecular weight of the tethered chains. This allows us to confirm semi-quantitatively the picture of arm retraction relaxation of the grafted chains proposed in models of slippage at a network/brush interface.