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General chemistry, physical chemistry, Chimie générale, chimie physique, Crystallography, Cristallographie cristallogenèse, Atomic molecular physics, Physique atomique et moléculaire, Sciences exactes et technologie, Exact sciences and technology, Chimie, Chemistry, Chimie generale et chimie physique, General and physical chemistry, Théorie des réactions, cinétique générale. Catalyse. Nomenclature, documentation chimique, informatique chimique, Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry, Généralités. Nomenclature, documentation chimique, informatique chimique, General. Nomenclature, chemical documentation, computer chemistry, Assemblage moléculaire, Molecular assembly, Ensamble molecular, Congrès, Congress, Congreso, Membrane, Membrana, Phénomène transport, Transport process, and Fenómeno transporte

General chemistry, physical chemistry, Chimie générale, chimie physique, Crystallography, Cristallographie cristallogenèse, Atomic molecular physics, Physique atomique et moléculaire, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Physicochimie des polymeres, Physicochemistry of polymers, Polymères minéraux et organominéraux, Inorganic and organomineral polymers, Propriétés et caractérisation, Properties and characterization, Conformation, Conformación, Cristal liquide, Liquid crystals, Cristal líquido, Diffraction neutron, Neutron diffraction, Difracción neutrónica, Diffusion neutron centrale, Small angle neutron scattering, Difusión neutrón central, Etude expérimentale, Experimental study, Estudio experimental, Siloxane copolymère, Siloxane copolymer, Siloxano copolímero, Structure état mésomorphe, Mesomorphic state structure, Estructura estado mesomorfo, Transformation nématique smectique, Nematic smectic transformation, Transformación nemático esméctico, Transition phase, Phase transitions, Transición fase, and Etat smectique C

Un polymorphisme de type nématique - smectique C a été pour la première fois révélé dans les polymères cristaux liquides en haltère. Des résultats structuraux et conformationnels obtenus par diffusion cohérente de neutrons sont présentés pour les deux mésophases. Une inversion de la conformation de la chaîne polymère est observée de la phase nématique à la phase smectique C. Ce comportement original est comparé au cas de la transition N - SA pour des polymères cristaux liquides en peigne.

General chemistry, physical chemistry, Chimie générale, chimie physique, Crystallography, Cristallographie cristallogenèse, Atomic molecular physics, Physique atomique et moléculaire, Sciences exactes et technologie, Exact sciences and technology, Physique, Physics, Domaines classiques de la physique (y compris les applications), Fundamental areas of phenomenology (including applications), Mécanique des fluides, Fluid dynamics, Ecoulements laminaires, Laminar flows, Suspensions laminaires, Laminar suspensions, Ecoulements non homogènes, Nonhomogeneous flows, Ecoulements polyphasiques et suspensions de particules, Multiphase and particle-laden flows, Sciences biologiques et medicales, Biological and medical sciences, Sciences biologiques fondamentales et appliquees. Psychologie, Fundamental and applied biological sciences. Psychology, Biophysique des tissus, organes et organismes, Tissues, organs and organisms biophysics, Biomécanique. Biorhéologie, Biomechanics. Biorheology, Laminar flows in cavities, Appareil circulatoire, Circulatory system, Aparato circulatorio, Coefficient portance, Lift coefficient, Coeficiente sustentador, Ecoulement cisaillé, Shear flow, Ecoulement conduite, Pipe flow, Ecoulement diphasique, Two-phase flow, Effet paroi, Wall effects, Ellipsoïde, Ellipsoid, Elipsoide, Erythrocyte, Erythrocytes, Excentricité, Eccentricity, Hémodynamique, Blood circulation, Modélisation, Modelling, Nombre Reynolds faible, Low Reynolds number, Número Reynolds débil, Particule non sphérique, Non spherical particle, Partícula no esférica, Suspension particule, Particle suspension, Suspensión partícula, Vaisseau sanguin, Blood vessels, Viscosité effective, Effective viscosity, and Viscosidad efectiva

The lift on a strongly non-spherical vesicle in a bounded shear flow is studied in the case the membrane moves with a velocity, which is a linear function of the coordinates. The magnitude of the induced drift is calculated as a function of the axes lengths, of the distance from the wall, and of the ratio of the cell to the solvent viscosity. It appears that the main mechanism for lift, in the presence of tank-treading motions, is the fixed orientation of the vesicle with respect to the flow. Tank-treading vesicles in suspensions, flowing through narrow gaps under small Reynolds number conditions: Re = L/ν < 1 (with L the gap width, the flow velocity and ν the viscosity) migrate away from the walls, with a velocity that is O(Re-1) larger than predicted by inertia.

General chemistry, physical chemistry, Chimie générale, chimie physique, Crystallography, Cristallographie cristallogenèse, Atomic molecular physics, Physique atomique et moléculaire, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Industrie des polymeres, peintures, bois, Polymer industry, paints, wood, Technologie des polymères, Technology of polymers, Formes d'application et semiproduits, Forms of application and semi-finished materials, Alvéolaires, Cellular, Adhésif, Adhesive, Adhesivo, Essai adhérence, Adhesion test, Ensayo adherencia, Etat fondu, Molten state, Estado fundido, Etude expérimentale, Experimental study, Estudio experimental, Mécanisme, Mechanism, Mecanismo, Pouvoir collant, Tack, Poder pegante, Propriété surface, Surface properties, Propiedad superficie, Siloxane(diméthyl) polymère, Dimethylsiloxane polymer, and Siloxano(dimetil) polímero

We present an experimental study of the tack of a model polymer melt by the probe tack test coupled with an optical observation of the fracture profile. This set-up allowed us to study the different processes involved in tack and to estimate their importance. We distinguished three different regimes that can be correlated to the rheological properties of the adhesive. In particular, the regime where viscoelastic losses in the bulk of the polymer are important is discussed in detail, in the frame of a recent model by de Gennes. We found, in this case, an enhancement of the energy of adhesion and put into evidence peculiar fracture profiles similar to the trumpet profile predicted by the model. We also studied the influences of surface roughness and polymer adsorption on the formation of the bond.

General chemistry, physical chemistry, Chimie générale, chimie physique, Crystallography, Cristallographie cristallogenèse, Atomic molecular physics, Physique atomique et moléculaire, Sciences exactes et technologie, Exact sciences and technology, Physique, Physics, Domaines classiques de la physique (y compris les applications), Fundamental areas of phenomenology (including applications), Optique, Optics, Optique quantique, Quantum optics, Propriétés non classiques du rayonnement; états comprimés, dégroupement de photons, statistiques subpoissoniennes; définitions opérationnelles de la phase du champ; mesures de la phase, Nonclassical field states; squeezed, antibunched and sub-poissonian states; operational definitions of the phase of the field; phase measurements, Transitoires optiques: battements quantiques, échos de photons, déclin d'induction libre, déphasages et revivals, nutation optique, transparence auto-induite, Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation and self-induced transparency, Nonclassical field states; squeezed, antibunched, and sub-Poissonian states; operational definitions of the phase of the field; phase measurements, Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency, Atome 2 niveaux, Two level atom, Atomo 2 niveles, Etude théorique, Theoretical study, Modèle Jaynes Cummings, Jaynes Cummings model, Modelo Jaynes Cummings, Optique quantique, Quantum optics, Traitement information, Information processing, and Procesamiento información

We study the possibility of producing disentangled states in the Jaynes-Cummings model when the input field is a superposition of two Fock states, |M) and |M + 1), and the atom is initially in a superposition of its two stationary states. In the case of large M, we show that Jaynes-Cummings interaction provides quantum state swapping between the two qubits (atom and field).

General chemistry, physical chemistry, Chimie générale, chimie physique, Crystallography, Cristallographie cristallogenèse, Atomic molecular physics, Physique atomique et moléculaire, Sciences exactes et technologie, Exact sciences and technology, Physique, Physics, Etat condense: structure, proprietes mecaniques et thermiques, Condensed matter: structure, mechanical and thermal properties, Propriétés mécaniques et acoustiques de l'état condensé, Mechanical and acoustical properties of condensed matter, Anélasticité, frottement interne, relaxation des contraintes et résonances mécaniques, Anelasticity, internal friction, stress relaxation, and mechanical resonances, Composé organique, Organic compounds, Effet milieu, Medium effect, Efecto medio, Etude expérimentale, Experimental study, Milieu poreux, Porous medium, Medio poroso, Module conservation, Storage modulus, Módulo conservación, Module perte, Loss modulus, Módulo pérdida, Polyol, Poliol, Propriété mécanique, Mechanical properties, Relaxation anélastique, Anelastic relaxation, Solution aqueuse, Aqueous solutions, Solution électrolyte, Electrolyte solution, Solución electrólito, Température transition vitreuse, Glass transition temperature, and Temperatura transición vítrosa

A procedure yielding to the determination of the low-frequency dynamical behavior of glass-forming systems with low glass transition temperature is presented in this paper. The liquids are injected in an inorganic porous medium and the mechanical response of the heterogeneous composite samples is studied. It is shown that the dynamic behavior of the liquid is poorly affected by the presence of the substrate. This enables to build the long-time relaxation diagram for maltitol, sorbitol and LiCl, 6H2O. The mechanical measurements are interpreted in the framework of a model based on the assumptions of localized disorder (defects) and hierarchically constrained dynamics in the glass transition region.

General chemistry, physical chemistry, Chimie générale, chimie physique, Crystallography, Cristallographie cristallogenèse, Atomic molecular physics, Physique atomique et moléculaire, Sciences exactes et technologie, Exact sciences and technology, Physique, Physics, Etat condense: structure, proprietes mecaniques et thermiques, Condensed matter: structure, mechanical and thermal properties, Structure des liquides et des solides; cristallographie, Structure of solids and liquids; crystallography, Etude de structures de liquides particuliers, Studies of specific liquid structures, Solutions de macromolécules et de polymères; polymères fondus, gonflements, Macromolecular and polymer solutions; polymer melts, swelling, Sciences appliquees, Applied sciences, Physicochimie des polymeres, Physicochemistry of polymers, Polymères organiques, Organic polymers, Propriétés et caractérisation, Properties and characterization, Propriétés des solutions et des gels, Solution and gel properties, Macromolecular and polymer solutions; polymer melts; swelling, Confinement, Confinamiento, Diffusion neutron centrale, Small angle neutron scattering, Difusión neutrón central, Dynamique conformationnelle, Conformational dynamics, Dinámica conformacional, Milieu poreux, Porous medium, Medio poroso, Solution semidiluée, Semidilute solution, Solución semidiluada, Structure solution, Solution structure, Estructura solución, Styrène polymère, Styrene polymer, Estireno polímero, Vycor, and Vicor

Nous observons par diffusion de neutrons aux petits angles la structure de chaînes de polystyrène en solution semi-diluée confinées dans un milieu poreux modèle, le Vycor. La taille des chaînes en solution à l'état libre est toujours supérieure au diamètre des pores, 70 Å. L'utilisation d'un mélange adéquat de solvants et de polymères hydrogénés et deutérés nous permet de mesurer directement le facteur de forme d'une seule chaîne au milieu des autres. La pénétration des chaînes dans le milieu poreux est presque totale pour la concentration (Φ = 20%) et la gamme de poids moléculaire (35 000 < Mw < 800 000) utilisées. Le rayon de gyration des chaînes confinées est toujours inférieur au rayon de gyration des chaînes libres dans la solution équivalente. Nos mesures sont en accord avec les prédictions théoriques établies par Daoud et de Gennes pour des chaînes confinées dans un pore cylindrique quand les chaînes sont enchevêtrées et comprimées transversalement mais restent idéales à grande échelle dans la direction du cylindre à cause de l'écrantage du volume exclus (régime dit de cigares semi-dilués). Les valeurs des coefficients de partage des chaînes entre le milieu poreux et la solution libre ainsi que le comportement asymptotique des facteurs de structure montrent que le polystyrène s'adsorbe sur la surface nue du Vycor. Nous montrons que la silanisation du Vycor supprime cette adsorption.

General chemistry, physical chemistry, Chimie générale, chimie physique, Crystallography, Cristallographie cristallogenèse, Atomic molecular physics, Physique atomique et moléculaire, Sciences exactes et technologie, Exact sciences and technology, Physique, Physics, Etat condense: structure, proprietes mecaniques et thermiques, Condensed matter: structure, mechanical and thermal properties, Equations d'état, équilibres de phases et transformations de phases, Equations of state, phase equilibria, and phase transitions, Transformations de phases particulières, Specific phase transitions, Transformations dans les cristaux liquides, Transitions in liquid crystals, Composé organique, Organic compounds, Cristal liquide, Liquid crystals, Diagramme phase, Phase diagrams, Equilibre phase, Phase equilibria, Etude expérimentale, Experimental study, Phase bleue, Blue phase, Fase azul, Structure isotrope, Isotropic structure, Estructura isótropa, Transformation phase cristal liquide, and Liquid crystal phase transformations

Static and dynamic light scattering measurements, all using circularly polarized light, are used to investigate the third blue phase to isotropic liquid critical point in a mixture of S, S-4 (methylbutyl)phenyl-4'- (methylbutyl)biphenylcarboxylate (S,S-MBBPC) and its racemate. The intensity of light scattering and the relaxation time for the most strongly fluctuating chiral mode are found to be significantly greater than in a supercritical mixture of S,S-MBBPC. While the increase is substantial, there is no indication that any true divergence in these quantities is present. The results can qualitatively be explained by the simple phenomenological theory of Lubensky and Stark [3], which places this transition in the same universality class as the liquid-gas transition.

General chemistry, physical chemistry, Chimie générale, chimie physique, Crystallography, Cristallographie cristallogenèse, Atomic molecular physics, Physique atomique et moléculaire, Sciences exactes et technologie, Exact sciences and technology, Physique, Physics, Generalites, General, Physique statistique, thermodynamique, et systèmes dynamiques non linéaires, Statistical physics, thermodynamics, and nonlinear dynamical systems, Thermodynamique, Thermodynamics, Thermodynamiques hors équilibre et irréversible, Nonequilibrium and irreversible thermodynamics, Domaines classiques de la physique (y compris les applications), Fundamental areas of phenomenology (including applications), Mécanique des fluides, Fluid dynamics, Stabilité hydrodynamique, Hydrodynamic stability, Non linéarité (incluant la théorie des bifurcations), Nonlinearity (including bifurcation theory), Sélection de mode; formation de mode, Pattern selection; pattern formation, Equation évolution, Evolution equation, Ecuación evolución, Instabilité oscillatoire, Oscillatory instability, Inestabilidad oscilatoria, Onde stationnaire, Standing waves, Stabilité non linéaire, Non linear stability, Estabilidad no lineal, Sélection mode, and Mode selection

Stable standing wave localized solutions of square symmetry are possible for a quintic Swift-Hohenberg type equation with complex coefficients. We point out that these localized solutions, which are surrounded by a pattern-free state exist for a range of values for the external stress parameter subcritically. We discuss similarities to recent experimental observations of standing wave localized squares in granular materials.

General chemistry, physical chemistry, Chimie générale, chimie physique, Crystallography, Cristallographie cristallogenèse, Atomic molecular physics, Physique atomique et moléculaire, Sciences exactes et technologie, Exact sciences and technology, Physique, Physics, Etat condense: structure, proprietes mecaniques et thermiques, Condensed matter: structure, mechanical and thermal properties, Structure des liquides et des solides; cristallographie, Structure of solids and liquids; crystallography, Cristaux liquides, Liquid crystals, Déterminations expérimentales des structures smectiques, nématiques, cholestériques et autres, Experimental determinations of smectic, nematic, cholesteric, and other structures, Surfaces et interfaces; couches minces et trichites (structure et propriétés non électroniques), Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties), Structure et morphologie de couches minces, Thin film structure and morphology, Structure et morphologie; épaisseur, Structure and morphology; thickness, Composé minéral, Inorganic compounds, Métal Composé, Metals Compounds, Compuesto, Composé binaire, Binary compounds, Couche mince, Thin films, Cristal nématique, Nematic crystals, Etude expérimentale, Experimental study, Orientation moléculaire, Molecular orientation, Silicium oxyde, Silicon oxides, Structure surface, Surface structure, TEM, Topographie, Topography, O Si, and SiO

We present transmission electron microscopy micrographs of SiO films obliquely evaporated on indium-tin oxide coated glass surfaces. To study the growth mechanism of these SiO films, we present film cross sections in the evaporation plane. Varying the evaporation angle, we observe a column to needle transition, with increasing surface roughness. This transition corresponds to the planar to oblique nematic liquid crystal orientation transition, through the bistable one. The SiO surface roughness is estimated to induce a nematic surface order decrease (surface melting). The azimuthal nematic orientation on these plates corresponds to the direction of minimum surface melting. This confirms the predictions of the Barbero-Durand model.

General chemistry, physical chemistry, Chimie générale, chimie physique, Crystallography, Cristallographie cristallogenèse, Atomic molecular physics, Physique atomique et moléculaire, Sciences exactes et technologie, Exact sciences and technology, Physique, Physics, Physique atomique et moleculaire, Atomic and molecular physics, Structure électronique des atomes, des molécules et de leurs ions: théorie, Electronic structure of atoms, molecules and their ions: theory, Corrections aux calculs de structure électronique, Corrections to electronic structure, Interactions hyperfines et effets isotopiques, effet jahn-teller, Hyperfine interactions and isotope effects, jahn-teller effect, Hyperfine interactions and isotope effects, Jahn-Teller effect, Atome, Atoms, Etude théorique, Theoretical study, Hafnium, Paramétrisation, Parametrization, Parametrización, Structure fine, Fine structure, Structure hyperfine, Hyperfine structure, Structure électronique, and Electronic structure

The fine structure of the low configurations of the atomic hafnium has been analysed by simultaneous parametrization of one and two body interactions for the model space (5d + 6s)4. Using the calculated eigenfunctions the magnetic-dipole A and electric-quadrupole B hyperfine constants were predicted to stimulate the experimental work concerning the energy level structure of 179Hf.

General chemistry, physical chemistry, Chimie générale, chimie physique, Crystallography, Cristallographie cristallogenèse, Atomic molecular physics, Physique atomique et moléculaire, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Physicochimie des polymeres, Physicochemistry of polymers, Polymères organiques, Organic polymers, Propriétés et caractérisation, Properties and characterization, Propriétés des solutions et des gels, Solution and gel properties, Approximation phase aléatoire, Random phase approximation, Aproximación fase aleatoria, Chaîne semiflexible, Semiflexible chain, Cadena semiflexible, Conformation, Conformación, Etude théorique, Theoretical study, Estudio teórico, Modélisation, Modeling, Modelización, Polymère, Polymer, Polímero, Solution chimique, Chemical solution, Solución química, Solution semidiluée, Semidilute solution, Solución semidiluada, and Fonction diffusion

We study the scattering function of semiflexible polymer chains within the framework of a rigid Gaussian model for polymers first introduced by Harris and Hearst. The tractability of this model allows for a computation of the most relevant physical properties for any value of the chain rigidity. We also explore at the level of the Random Phase Approximation some of the bulk and surface behaviour of semidilute solutions of semiflexible polymers.

General chemistry, physical chemistry, Chimie générale, chimie physique, Crystallography, Cristallographie cristallogenèse, Atomic molecular physics, Physique atomique et moléculaire, Sciences exactes et technologie, Exact sciences and technology, Physique, Physics, Etat condense: structure, proprietes mecaniques et thermiques, Condensed matter: structure, mechanical and thermal properties, Equations d'état, équilibres de phases et transformations de phases, Equations of state, phase equilibria, and phase transitions, Transformations de phases particulières, Specific phase transitions, Transformations dans les cristaux liquides, Transitions in liquid crystals, Etat condense: structure electronique, proprietes electriques, magnetiques et optiques, Condensed matter: electronic structure, electrical, magnetic, and optical properties, Propriétés et matériaux diélectriques, piézoélectriques et ferroélectriques, Dielectrics, piezoelectrics, and ferroelectrics and their properties, Matériaux diélectriques, piézoélectriques, ferroélectriques et antiferroélectriques, Dielectric, piezoelectric, ferroelectric and antiferroelectric materials, Liquides et cristaux liquides, Liquids and liquid crystals, Propriétés optiques, spectroscopie et autres interactions de la matière condensée avec les particules et le rayonnement, Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation, Propriétés optiques des matériaux massifs et des couches minces, Optical properties of bulk materials and thin films, Pouvoir rotatoire optique, Optical rotatory power, Liquids, emulsions, and suspensions; liquid crystals, Optical activity, Composé chiral, Chiral compound, Compuesto quiral, Cristal liquide antiferroélectrique, Antiferroelectric liquid crystals, Propriété optique, Optical properties, Spectre Raman, Raman spectra, Théorie phénoménologique, Phenomenological theory, Teoría fenomenológica, Transformation phase, and Phase transformations

Optical rotatory power and Raman scattering experiments on chiral liquid crystals belonging to a series which exhibits one or two ferrielectric phases have been performed. The results of these non-perturbative techniques show that, depending upon the aliphatic chain length, a first order transition with a jump in sign and value of the helical pitch, or a divergence and sign reversal of the pitch with no transition can occur in these systems. These observations are in agreement with a generalized Landau-de Gennes phenomenological model predicting that the ferrielectric phases, when both exist, should be isostructural.

General chemistry, physical chemistry, Chimie générale, chimie physique, Crystallography, Cristallographie cristallogenèse, Atomic molecular physics, Physique atomique et moléculaire, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Physicochimie des polymeres, Physicochemistry of polymers, Polymères organiques, Organic polymers, Propriétés et caractérisation, Properties and characterization, Propriétés des solutions et des gels, Solution and gel properties, Propriété mécanique, Mechanical properties, Propiedad mecánica, Elasticité, Elasticity, Elasticidad, Equation variationnelle, Variational equation, Ecuación variacional, Etude théorique, Theoretical study, Estudio teórico, Loi échelle, Scaling law, Ley escala, Marche autoévitante, Self avoiding walk, Marcha autoevitante, Modèle mathématique, Mathematical model, Modelo matemático, Méthode approchée, Approximate method, Método aproximado, Polyélectrolyte, Polyelectrolyte, Polielectrolito, Solution chimique, Chemical solution, Solución química, Théorie champ, Field theory, and Teoría campo

This paper discusses the elastic behavior of a single polyelectrolyte chain. A simple scaling analysis as in self avoiding walk chains are not possible, because three interplaying relevant length scales are involved, i.e., the Debye screening length and the Pincus blob size. Therefore a self-consistent computation of an effective variational propagator is employed. It is shown that the elastic force as a function f of the distance R behaves as f R for small f. For larger forces we find a new regime, characterized by deformations larger than a computed electrostatic blob size. These results are supported by simulations and intuitive physical arguments.

General chemistry, physical chemistry, Chimie générale, chimie physique, Crystallography, Cristallographie cristallogenèse, Atomic molecular physics, Physique atomique et moléculaire, Sciences exactes et technologie, Exact sciences and technology, Physique, Physics, Domaines interdisciplinaires: science des materiaux; rheologie, Cross-disciplinary physics: materials science; rheology, Rhéologie, Rheology, Types de matériaux, Material types, Mélanges de polymères, Polymer blends, Techniques et appareillage, Techniques and apparatus, Calcul d'écoulement (par exemple, méthode des éléments finis), Flow computation (e.g. Finite element), Computational methods in fluid dynamics, Kinematics of deformation and flow, Ecoulement visqueux, Viscous flow, Effet milieu, Medium effect, Efecto medio, Effet paroi, Wall effects, Etude expérimentale, Experimental study, Etude théorique, Theoretical study, Force centrifuge, Centrifugal force, Force gravitationnelle, Gravitational force, Fuerza gravitacional, Hydrodynamique, Hydrodynamics, Propriété rhéologique, Rheological properties, and Propiedad rheológica

The viscosity of a fluid can be measured by observing the motion of a probe sphere (or ball) in a centrifuge tube filled with this fluid. The hydrodynamic behavior of the probe ball moving in the centrifuge tube has been solved theoretically. We have got the universal relationship (for balls of a given material and size in a given tube) between the terminal ball velocity, the fluid viscosity and the centrifuge acceleration using the only adjustable parameter - the rotational friction coefficient between the ball and the tube. The rotation of the centrifuge tube in the horizontal plane induces an inertia force which is counterbalanced by the friction force acting on the ball. As a result, the ball moves along the tube with some characteristic speed, which is a measure of the viscosity of the fluid. This speed was calculated in the lubrication approximation. The gravitational acceleration causes the ball to move very close to the bottom of the centrifuge tube. In this situation, the gravity is balanced by a levitation force introduced and calculated in the present paper. The origin of this force is the formation of the bubble behind and below the moving ball. The theoretical development on the terminal velocity for the ball moving very near the bottom of the horizontal centrifuge tube is tested by using a specially designed centrifuge for two types of balls and a wide set of viscosity standards. Excellent agreement between theory and experiment suggests that we have developed a new approach to measure high viscosities of fluids at low shear rates which might be especially useful for the investigation of polymer melts.

General chemistry, physical chemistry, Chimie générale, chimie physique, Crystallography, Cristallographie cristallogenèse, Atomic molecular physics, Physique atomique et moléculaire, Sciences exactes et technologie, Exact sciences and technology, Physique, Physics, Etat condense: structure, proprietes mecaniques et thermiques, Condensed matter: structure, mechanical and thermal properties, Equations d'état, équilibres de phases et transformations de phases, Equations of state, phase equilibria, and phase transitions, Transformations de phases particulières, Specific phase transitions, Transformations dans les cristaux liquides, Transitions in liquid crystals, Surfaces et interfaces; couches minces et trichites (structure et propriétés non électroniques), Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties), Propriétés physiques non électroniques de couches minces, Physical properties of thin films, nonelectronic, Propriétés mécaniques et acoustiques, Mechanical and acoustical properties, Constante élasticité, Elastic constants, Couche mince, Thin films, Cristal smectique, Smectic crystals, Equilibre thermodynamique, Thermodynamic equilibrium, Equilibrio termodinámico, Etude expérimentale, Experimental study, Propriété mécanique, Mechanical properties, Transformation phase cristal liquide, and Liquid crystal phase transformations

Les effets d'une perturbation mécanique appliquée parallèlement au plan des couches smectiques d'un film librement suspendu sont étudiés à partir d'un nouveau dispositif expérimental. Les expériences sont réalisées sur des films de différentes épaisseurs dans les phases smectiques dites liquides, hexatiques et cristallines. Nous montrons que la phase thermodynanique du ménisque est un paramètre crucial car il détermine le régime de perturbation que subit le film. En s'appuyant sur un modèle phénoménologique, nous distinguons deux régimes de perturbation : le régime d'écoulement et le régime élastique. Les mesures effectuées dans ce dernier cas nous permettent d'extraire la valeur de la constante élastique dans les phases cristallines smectique B et smectique G. La forte variation du coefficient de compressibilité observée entre ces deux phases indique que l'angle d'inclinaison des molécules apporte au film une variable macroscopique supplémentaire pour répondre à la perturbation mécanique imposée.

General chemistry, physical chemistry, Chimie générale, chimie physique, Crystallography, Cristallographie cristallogenèse, Atomic molecular physics, Physique atomique et moléculaire, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Physicochimie des polymeres, Physicochemistry of polymers, Polymères organiques, Organic polymers, Propriétés et caractérisation, Properties and characterization, Structure, morphologie et analyse, Structure, morphology and analysis, Effet matrice, Matrix effect, Efecto matriz, Etude expérimentale, Experimental study, Estudio experimental, Groupe hydrophobe, Hydrophobic group, Grupo hidrófobo, Interface gaz solide, Gas solid interface, Interfase gas sólido, Modélisation, Modeling, Modelización, Mélange, Mixture, Mezcla, Polymère téléchélique, Telechelic polymer, Polímero telechélico, Recuit, Annealing, Recocido, Silane organique, Organic silane, Silano orgánico, Structure interface, Interface structure, Estructura interfaz, Styrène polymère, Styrene polymer, Estireno polímero, and Distribution fonctionnalité

Deuteropolystyrene has been functionalised at each end by fluorosilane groups, the polymer obtained had a relative molar mass of 98 x 103. Thin films of this polymer mixed with unfunctionalised hydrogenous polystyrene have been prepared and the blends annealed to equilibrium at 413 K. The distribution of the end functionalised deuteropolymer was obtained by neutron reflectometry and a range of molecular weights of the hydrogenous polystyrene matrix has been used. In all cases the deutero polystyrene was preferentially located at the air-polymer interface to an extent which was far greater than that for unfunctionalised deutero polystyrene in the same hydrogenous matrices. From the near surface depth profiles obtained, the surface excess, surface volume fraction and thickness of the end functionalised deuteropolystyrene rich layer have been obtained as a function of the equilibrium concentration of end functionalised deuteropolystyrene. These parameters have been compared with the predictions of scaling theory for brush like layers of polymers attached to a surface. The surface layer thickness and average volume fraction of the surface layer display stretched wet brush behaviour which is not expected for end functionalised polymers on the basis of the molecular weights explored. The possibility that local grafting densities are significantly higher than the average value is discussed. The shape of the near surface depth profile has been fitted using a self consistent field theory using the sticking energy of the fluorosilane groups as the only adjustable parameter. Fits of reasonable quality were obtained and using this sticking energy the surface volume fractions and normalised surface excess parameters have been calculated and compared with those obtained experimentally. Good agreement between surface volume fractions is obtained, but the agreement between normalised surface excess values becomes increasingly worse as the relative molar mass of the hydrogenous matrix increases.

General chemistry, physical chemistry, Chimie générale, chimie physique, Crystallography, Cristallographie cristallogenèse, Atomic molecular physics, Physique atomique et moléculaire, Sciences exactes et technologie, Exact sciences and technology, Chimie, Chemistry, Chimie generale et chimie physique, General and physical chemistry, Etat colloïdal et états dispersés, Colloidal state and disperse state, Membranes, Agent surface, Surfactant, Agente superficie, Composé amphiphile, Amphiphilic compound, Compuesto anfifílico, Copolymère biséquencé, Diblock copolymer, Copolímero bisecuencia, Cristal liquide, Liquid crystals, Cristal líquido, Etat smectique, Smectic state, Estado esméctico, Etude théorique, Theoretical study, Estudio teórico, Inclusion, Inclusión, Membrane, Membrana, Particule colloïdale, Colloid particle, Partícula coloidal, Protéine, Protein, and Proteína

We study theoretically the behaviour of inclusions in thin films of smectic-A liquid crystal consisting of a stack of regularly spaced membranes. Such membranes are frequently formed in thin diblock copolymer films or in solutions of amphiphilic surfactants. Inclusions, such as colloidal particles or large proteins, couple locally to the smectic and may deform the membranes over a large length scale. Using the Landau-de Gennes description of smectic liquid crystals we obtain the deformation field of the membranes for the two cases of a freely suspended film and a film on a rigid substrate. In the first case we compare and contrast with earlier work on inclusions confined between two membranes and in a lamellar phase of infinite thickness. We show that the existence of an overshoot in the deformation of the layers is intrinsically related to the finite size of the sample. This leads to qualitative differences in the interaction potential between two inclusions for finite and infinite systems. The interaction, monotonically attractive for infinite systems, becomes repulsive at large distance is the sample is finite. We show that the equilibrium position of the particle depends on the surface tension at the film boundary and give quantitative predictions for the particle-induced deformation of the membranes.

General chemistry, physical chemistry, Chimie générale, chimie physique, Crystallography, Cristallographie cristallogenèse, Atomic molecular physics, Physique atomique et moléculaire, Sciences exactes et technologie, Exact sciences and technology, Physique, Physics, Domaines classiques de la physique (y compris les applications), Fundamental areas of phenomenology (including applications), Mécanique des solides, Solid mechanics, Mécanique des structures et des milieux continus, Structural and continuum mechanics, Contact mécanique (frottement...), Mechanical contact (friction...), Etat condense: structure, proprietes mecaniques et thermiques, Condensed matter: structure, mechanical and thermal properties, Equations d'état, équilibres de phases et transformations de phases, Equations of state, phase equilibria, and phase transitions, Etudes générales des transformations de phases, General studies of phase transitions, Tribology and mechanical contacts, Appareillage essai, Test equipment, Contact mécanique, Mechanical contacts, Etude expérimentale, Experimental study, Frottement sec, Dry friction, Frotamiento seco, Hystérésis mécanique, Mechanical hysteresis, Histéresis mecánica, Surface rugueuse, Rough surface, and Superficie rugosa

We report an experiment on dry friction between two elastic surfaces made of millimetric steel spheres embedded in an elastic medium. We study the hysteresis cycle of the tangential force induced by a quasi-static cyclic displacement. At low velocities, hysteresis effects are fully characterized by a recovery length comparable to the size of the steel spheres. This length is independent of the velocity and of the normal load. We propose an interpretation for this recovery length with a simple model of discrete contacts.

General chemistry, physical chemistry, Chimie générale, chimie physique, Crystallography, Cristallographie cristallogenèse, Atomic molecular physics, Physique atomique et moléculaire, Sciences exactes et technologie, Exact sciences and technology, Sciences appliquees, Applied sciences, Physicochimie des polymeres, Physicochemistry of polymers, Polymères organiques, Organic polymers, Propriétés et caractérisation, Properties and characterization, Structure, morphologie et analyse, Structure, morphology and analysis, Chaîne semiflexible, Semiflexible chain, Cadena semiflexible, Dynamique moléculaire, Molecular dynamics, Dinámica molecular, Etude théorique, Theoretical study, Estudio teórico, Membrane, Membrana, Modèle reptation, Reptation model, Modelo reptación, Modélisation, Modeling, Modelización, Polymère, Polymer, and Polímero

The dynamics of semi-flexible polymers and membranes is discussed. The effect of thermal undulations on both the transversal and longitudinal Mean Square Displacement (MSD) of a tagged monomer is studied in free polymers and membranes. The two MSDs are found to be proportional to one another, and behave as ∼ t3/4 for polymers and ∼ t2/3 for membranes on the short time scale. The longitudinal motion is shown to be linked to the dynamics of fluctuations of the projected length (area) of the polymer (membrane). We demonstrate how, at long times, these fluctuations lead to reptation motion of the polymer (membrane) in the longitudinal direction. We generalize this approach to investigate the motion of a membrane between two plates and a polymer in a tube. The latter problem is used as a model for polymer motion in semi-dilute solutions in which the persistence length is longer than the entanglement length. Such systems are not suitable for the classical reptation model of de-Gennes and of Doi and Edwards, which was designed for chains that are flexible on the entanglement distance. The reptation diffusion coefficient and relaxation times that we obtain have the same scaling with chain length L as in the classical reptation model, but differ greatly in factors that are dependent on the ratio of persistence length to entanglement length. We also discuss the diffusion of a tagged monomer under imposed tension and liquid crystalline order.