Rheological Rouse model for a polymer in a nematic matrix

We present and develop a model of coupling between a Rouse chain and a nematic order parameter. The geometry of the chain, for each mode, in simple shear flow is calculated. We discuss local torque and normal stress sign. This implies non trivial ways to introduce the opposite coupling (from chain to parameter order) in order to get a model for Rouse nematic polymers

The long-time tail of the angular-velocity auto-correlation function for a rigid brownian particle of arbitrary centrally symmetric shape

The long-time t-f behaviour of the angular-velocity autocorrelation function is determined by the diffusion of fluid motion to large distances, from where the particle appears a point singularity. From an examination of this flow, the coefficient of tf can be related to some effective aspect ratios which describe how the particle rotates in a simple shear flow

Effect of Interfacial Rheology on Foams Viscoelasticity, an Effective Medium Approach

We have computed in 3-dimensional foams the influence of interfacial rheology on the macroscopic foam viscoelasticity. We show that the two interfacial moduli play different roles. The dilational viscosity is not at all additive to the macroscopic modulus, while both the interfacial shear viscosity and the internal phase modulus are nearly additive. The dilational viscosity is shunted by a grid mode at high frequency. The calculations are done in a selfconsistent effective medium approximation

Frequency-dependent compressibility in emulsions: Probing interfaces using Isakovich's sound absorption

The average compressibility of an emulsion acquires a frequency-dependent, relaxing behavior due to the thermoconduction between adjacent phases heated through thermo-mechanical coupling. Introducing the relaxing compressibility into the sound propagation equations, we extend Isakovitch's theory of sound absorption to emulsions of an arbitrary number of liquids with the same density. The sound propagation speed and attenuation are found to be isotropic, even if the emulsion morphology is anisotropic. In the limit of frequencies greater than the inverse heat diffusion time, both the relaxing part of the compressibility and the sound attenuation are proportional to a single parameter depending linearly on the emulsion interfacial area per unit volume, thus giving easy access to this quantity in non-transparent systems

Flow birefringence study at the transition from laminar to Taylor vortex flow

We have studied the birefringence induced by the flow in a liquid containing very fine particles in the vicinity of the transition between the Couette flow and the Taylor vortex flow. We derive at first an analytical expression of the axisymmetrical hydrodynamical field and then the angular velocity of a particle in the flow. The resolution of the diffusion equation leads to the orientation distribution function F. On condition of some simplifying but realistic hypotheses, we show that the extinction angle χ and the birefringence Δn of the solution are the same as the properties of an equivalent stratified medium composed of very thin layers the orientation of which varies continuously. The results concerning the velocity profile and the critical Taylor number are in good agreement with other sources ; the theoretical computation of χ and Δn are then compared to experimental curves realized with solutions of bentonite and T.M.V. ; interesting conclusions can be drawn on the influence of the shape of the particles on the behavior of the angle of extinction and of the birefringence intensity in the region of the Taylor vortex flow.La biréfringence induite par l'écoulement dans un liquide contenant de fines particules et confiné entre deux cylindres coaxiaux est étudiée au voisinage de la transition entre écoulement de Couette et tourbillons de Taylor. Après avoir établi l'expression analytique du champ hydrodynamique dans le domaine d'écoulement axisymétrique, nous en déduisons la vitesse angulaire d'une particule entraînée par ce champ puis la fonction de distribution des orientations de la particule. Moyennant certaines hypothèses simplificatrices mais néanmoins réalistes, on montre que les expressions théoriques de l'angle d'extinction χ et de l'intensité de la biréfringence induite Δ n s'obtiennent en considérant la suspension comme une superposition de couches infiniment minces d'orientation continuement variable. Les résultats théoriques sont ensuite comparés aux courbes expérimentales tracées à l'aide de mesures effectuées sur des suspensions de deux types de particules : la bentonite et le virus de la mosaïque du tabac. En écoulement de Couette, la forme des particules en solution n'influe pas sur l'allure générale des courbes χ (G ) et Δn(G), G étant le gradient de cisaillement dans l'espace annulaire. Il n'en est plus de même en écoulement axisymétrique de Taylor pour lequel ces mêmes courbes présentent un aspect différent pour les solutions contenant des particules allongées (V.M.T.) ou aplaties (bentonite). Ces résultats sont confirmés par le calcul théorique

Effective Medium Model for Ultrasonic Attenuation Due to the Thermo-Elastic Effect in Concentrated Emulsions

In this article, we deal with the propagation of ultrasonic waves in monodisperse concentrated oil–in–water emulsions. Using the approximation of Isakovich, we propose two different models, a mirror model and a core–shell model, aiming to describe the temperature field in the dense medium and to supply a correct expression of the ultrasonic wave vector. The comparison between experimental data and theoretical models shows that the core–shell model leads to a very accurate description of the ultrasonic attenuation, in a wide range of frequencies and concentrations, in the case where the thermo–elastic effect, due to the scattering of thermal waves by the particles, is the dominant loss mechanism