Jean-François Palierne

Quantitative relationship between rheology and morphology in emulsions

Calculations based on the Grmela et al. model [M. Grmela, M. Bousmina, and J. F. Palierne, Rheol. Acta 40, 560 (2001)] for the simple case of ellipsoidal droplet-type morphology express a direct quantitative relationship between flow and microstructure both in the steady and transient regimes. The results of calculations show that in shear, elongational, and planar hyperbolic flow it is possible to extract the morphology (the deformation and the orientation of the droplet) from rheological material functions and, conversely, rheological material functions can be obtained from in situ morphological observation.

Counterclockwise Circular Motion of Bacteria Swimming at the Air-Liquid Interface

Flagellar propulsion of swimming Escherichia coli produces circling clockwise motions near planar solid surfaces. Counterclockwise motion was first reported near air-TN medium interfaces, showing that slip at the interface is a key parameter of bacterial swimming.

Curvature reversal of the circular motion of swimming bacteria probes for slip at solid/liquid interfaces

The orientation of the circular motion of most swimming E. coli at a solid surface is shown to be (i) reversed by supplementing the medium with alginate and (ii) restored by rendering the glass surface positively charged. Given slip promotion by the polymer and suppression by its anchoring on the surface, observations are interpreted by slip at the boundary. This points out bacterial swimming as a probe of the solid/fluid boundary condition.

High-frequency rheological behaviour of a multiconnected lyotropic phase

High-frequency (up to ω = 6 104 rad/s) rheological measurements combined with light-scattering investigations show that an isotropic and multiconnected phase of surfactant micelles exhibits a terminal relaxation time of a few μs, much smaller than in solutions of entangled wormlike micelles. This result is explained in terms of the local hexagonal order of the microscopic structure and we discuss its relevance for the understanding of dynamic behaviour in related systems, such as wormlike micelles and sponge phases.

High frequency linear rheology of complex fluids measured from their surface thermal fluctuations

We characterize the linear viscoelastic properties of complex fluids using a new technique, based on the measurement of surface fluctuations: surface fluctuation specular reflection (SFSR) spectroscopy. The thermally excited waves propagating on a free surface are measured through the deflection of a laser beam specularly reflected from that surface. Elastic and loss moduli of the complex fluids are inferred from the measured power spectrum density of thermal noise, with the implicit use of Kramers–Kronig relations. The technique, besides being noninvasive, provides rheological data in a large frequency range and at vanishing strains. It is therefore especially well suited for the rheological characterization of complex fluids. We present measurements of the viscoelastic modulus of supramolecular polymer solutions in a frequency range extending up to six decades. We compare the SFSR measurements with rheometric data at low and high frequencies, and show that they are in good agreement. Using supramolecular polymer solutions of different natures, exhibiting or not surface viscoelasticity, we furthermore show that SFSR provides a characterization of the bulk properties of the fluids. In addition, we discuss the accuracy of the measurements.

Sticky dumbbells: from Hookean dumbbells to transient network

The Green-Tobolsky theory of transient networks is merged to the Hookean dumbbell model by considering Hookean sticky dumbbells, whose beads can randomly be stuck to a network submitted to affine deformation, or be set free from the network and undergo a free diffusive Brownian motion in the solvent. Sticking to and releasing from the network is treated as an instantaneous chemical reaction. This model has a closed-form solution, in which the stress is the sum of two (resp. three) Maxwellian codeformational relaxations for dumbbells with one (resp. two) sticking beads. When Brownian diffusion is faster than the chemical kinetics, one of the modes of two-sticking beads dumbbells is the Green-Tobolsky network relaxation, whereas the other modes correspond to fast configurational relaxations. In the opposite limit of fast chemical kinetics compared to Brownian relaxation, the effect of the network is to slow down the configurational response of Hookean dumbbells. Sticky dumbbells thus realise a continuous transition from Hookean dumbbells to transient networks.

Structural transition in the isotropic phase of the C12EO6/H2O lyotropic mixture: A rheological investigation

We study the structural changes occurring in the isotropic phase of the C12EO6/H2O lyotropic mixture (up to 35% surfactant weight concentration) upon increasing the concentration and temperature, from small individual micelles to an entangled network which subsequently becomes connected. High-frequency (up to ω = 6 × 104 rad/s) rheological measurements give us access to the viscoelastic relaxation spectrum, which can be well described by the sum of two Maxwell models with very different temperature behaviors:  the slower one (τ1 ≈ 10-4 s) is probably due to reptation, and its associated viscosity first increases with temperature (micellar growth) and then decreases after reaching a maximum (appearance of connections). The fast mechanism (τ2 ≈ 10-6 s) remains practically unchanged in temperature and can be related to the relaxation of local micellar order, as observed at higher concentration in a previous investigation. This interpretation is confirmed by additional measurements in aqueous mixtures of the ...

Host cell surfaces induce a Type IV pili-dependent alteration of bacterial swimming

For most pathogenic bacteria, flagellar motility is recognized as a virulence factor. Here, we analysed the swimming behaviour of bacteria close to eukaryotic cellular surfaces, using the major opportunistic pathogen Pseudomonas aeruginosa as a model. We delineated three classes of swimming trajectories on both cellular surfaces and glass that could be differentiated by their speeds and local curvatures, resulting from different levels of hydrodynamic interactions with the surface. Segmentation of the trajectories into linear and curved sections or pause allowed us to precisely describe the corresponding swimming patterns near the two surfaces. We concluded that (i) the trajectory classes were of same nature on cells and glass, however the trajectory distribution was strikingly different between surface types, (ii) on cell monolayers, a larger fraction of bacteria adopted a swimming mode with stronger bacteria-surface interaction mostly dependent upon Type IV pili. Thus, bacteria swim near boundaries with diverse patterns and importantly, Type IV pili differentially influence swimming near cellular and abiotic surfaces.

A search for primes from lesser primes

Abstract The purpose of this paper is to show that there is an algorithm which permits to define new primes from lesser already known primes. The method is based on the definition of “compact” sets of primes, and on the fundamental property, i.e., the fact that the sum or difference of two mutually prime integers have no common decomposition factors with these two mutually prime integers.

Complementary results on the search of primes from lesser primes

Abstract In this short note we complete recently published results on the search of primes from lesser primes. The method is based on the concept of “compact” sets of primes and on the “fundamental property”, i.e., the fact that the decomposition in primes of the sum or the difference of two coprime integers never has common decomposition factors with these two coprime integers. The earlier finding is here enhanced, according to which a proportion of primes of about two thirds is to be found in the specified intervals where the result of the algorithm leads either to primes or the product of two primes.