Liliane Léger | Paris Sud XI University (original) (raw)

Papers by Liliane Léger

arXiv: Soft Condensed Matter, 2018

We report an investigation of the equilibrium and dynamic properties of polyelectrolyte solutions... more We report an investigation of the equilibrium and dynamic properties of polyelectrolyte solutions confined between platinum surfaces with a dynamic Surface Force Apparatus. The polyelectrolyte adsorbs on the surfaces in a dense compact layer bearing a surface charge in good agreement with the theoretical predictions. The flow of the solution on this charged adsorbed layer is probed over four decades of spatial scales and one decade of frequency by dynamic measurements. At distances larger than the hundredth of nanometers, the flow of the viscoelastic solution is well described by a partial slip boundary condition. We show that the wall slip is quantitatively described by an interfacial friction coefficient, according to the original Navier's formulation, and not by a slip length. At smaller distance the partial slip model overestimates the solution mobility, and we observe the presence of a low viscosity layer coating the surfaces. The viscosity and thickness of this boundary la...

Physical Review Letters, 1988

Physical Review Letters, 1986

We present investigations of the spreading behavior of nonvolatile liquids (high-molecular-weight... more We present investigations of the spreading behavior of nonvolatile liquids (high-molecular-weight polydimethylsiloxane) on smooth horizontal surfaces, and estabhsh the following: (1) the existence of a thin precursor fiha extending progressively ahead of the macroscopic front of the drops, and that we directly visuahze by polarized reflection microscopy; (2) the universality of the spreading kinetics, fol-io~ed by means of simultaneous size and contact-angle measurements, which appears insensitive to the spreading parameter 5. Both points give strong experimental support to recent theoretical developments.

Physical Review Letters, Sep 2, 1985

The tracer-diffusion coefficient D& of polystyrene chains in semidilute, good-solvent solutions h... more The tracer-diffusion coefficient D& of polystyrene chains in semidilute, good-solvent solutions has been measured by forced Rayleigh light scattering for different polymerization indices of both labeled and unlabeled chains (N and P, respectively). For P/N » 5, D, is found to be independent of P, and a pure reptative behavior is observed in the entire semidilute concentration range. For P/N (5, the increase of D, when P is decreased demonstrates the existence of tube-renewal effects whose magnitude, for a given P, only depends on the number of entanglements along the test chains.

Physical Review Letters, 1991

Using small-angle neutron-scattering techniques, the scaling laws between the thickness of a graf... more Using small-angle neutron-scattering techniques, the scaling laws between the thickness of a grafted polymer layer h, its graft density a. , and the molecular weight of the grafted chains M have been determined for polydimethylsiloxane chains end grafted on porous silica. The observed laws h = Mcr in bad solvent and h = Mo' ' in good solvent provide the first experimental evidence of the "brush" regime, where the grafted chains, confined by their neighbors, are stretched normal to the surface.

Macromolecules, 2001

The segment density profile of anchored layers of poly(dimethylsiloxane) in good solvents has bee... more The segment density profile of anchored layers of poly(dimethylsiloxane) in good solvents has been measured using neutron reflectometry. Two types of layers have been studied: end-grafted layers (brushes) and irreversibly adsorbed layers, on silicon/silicon dioxide. The latter can be viewed as a polydisperse brush of loops and was obtained by adsorbing the polymer from the melt or from a concentrated solution. A model-free constrained fitting procedure was developed, which gave the concentration profile with a good precision. We present this numerical method and the concentration profiles obtained for the different layers. The profiles of the two types of layers are significantly different. They are in agreement with self-consistent mean field theory for the brushes and with scaling laws descriptions for the irreversibly adsorbed layers. The reflectivity measurement enabled us to verify precisely that the concentration profile in the brush cannot be described by a step function with a Gaussian roughness but has a parabolic shape.

Macromolecules, 1991

The structures of grafted poly(dimethylsi1oxane) layers at the solid-liquid interface, in the reg... more The structures of grafted poly(dimethylsi1oxane) layers at the solid-liquid interface, in the regime of high graft density, have been investigated in various solvents, using small-angle neutron scattering techniques. In a poor solvent, the grafted polymer layer is dense with two well-defined boundaries, leading to interference phenomena. In a good solvent, the chains are stretched and exhibit the same behavior as in semidilute solution. Although the average interfacial density profile is smoother than a step function, the "brush" model is in good agreement with our observations.

Journal of Colloid and Interface Science, 1992

Silica particles grafted with long polydimethylsiloxane chains have been prepared. A progressive ... more Silica particles grafted with long polydimethylsiloxane chains have been prepared. A progressive grafting process was used, allowing transfer of the beads from their initial polar medium to various organic solvents. They are revealed to be model colloids whose properties are driven by the structure of the grafted polymer layer. Depending upon the grafting density, two basic kinds of particles may be distinguished, exhibiting either coulombian or steric interactions.

The Journal of Physical Chemistry, Sep 1, 1994

... P. G. de Gennes,*'s L. LCger,' Y. Marciano,' and E. Raphael$ PSI, Institut Cur... more ... P. G. de Gennes,*'s L. LCger,' Y. Marciano,' and E. Raphael$ PSI, Institut Curie, 11 rue Pierre et Marie Curie, 75005 Paris, France, and Physique de la Matiere CondensCe, Collkge de France, I1 place M. Berthelot, 75231 Paris Cedex 05, France Received: April 27, 1994@ ...

Macromolecules, Nov 1, 1986

The words "crystallites", "crystal", "crystallization", and the like are employed with quotation ... more The words "crystallites", "crystal", "crystallization", and the like are employed with quotation marks in order to emphasize that we may not be dealing with crystalline systems in the usual sense of the word.

Steinkopff eBooks, Dec 4, 2007

ABSTRACT Oil-water microemulsions of the five components system water/soldium chloride/toluene/1-... more ABSTRACT Oil-water microemulsions of the five components system water/soldium chloride/toluene/1-butanol/sodium dodecyl sulfate exhibit diffuseness (due to a turbidity gradient) for a very low surfactant content, 0.6 ÷ 0.006% w/w. The main characteristics of such microemulsions are described and the existence of nonuniformity is discussed.

World Scientific Publishing Company eBooks, Jul 1, 2009

Tribology series, 1999

The friction coefficient between a flowing polymer melt and a solid surface bearing attached poly... more The friction coefficient between a flowing polymer melt and a solid surface bearing attached polymer chains has been investigated both experimentally and theoretically. As the shear rate is progressively increased, several friction regimes show up linked to a progressive transition between low and high slip at the wall.

Journal of Non-newtonian Fluid Mechanics, May 1, 1994

... 1. Measurement of the contact angle 0 between a liquid drop and a plane solid surface. N. El ... more ... 1. Measurement of the contact angle 0 between a liquid drop and a plane solid surface. N. El Kissi et al. / J. Non-Newtonian Fluid Mech. 52 (1994) 247-259 255 (a) Untreated silica plate (b) Treated silica plate Fig. 2. Wetting test; spread of silicone drops on untreated and treated ...

Annual Review of Physical Chemistry, Oct 1, 1982

Polymer melts flow like conventional (viscous) liquids if they are subjected to slowly varying pe... more Polymer melts flow like conventional (viscous) liquids if they are subjected to slowly varying perturbations; but, at somewhat higher frequencies w, they behave like an elastic rubber. These mechanical properties depend strongly on the polymer structure (linear/branched, flexible/rigid, etc). In this review, we concentrate on the best understood case: linear, flexible chains, with a large number (N) of monomers per chain. The crucial feature is that these chain.s are entangled. The effects of entanglements on the mechanical properties of polymers have been recognized and analyzed in some detail. More recently, entanglements have been probed at a more microscopic level: (a) self-diffusion, follow ing the motions of one labeled chain; (b) measurements involving spatial effects at distances smaller than the coil size: polymer/polymer welding; spinodal decomposition of blends; neutron measurements on stretched samples; chemical reactions in melts. We discuss all these phenomena within a single model, based on the "reptation" idea (1). This model is not final, and may well require future adjustments, but it gives a comparatively simple framework with which to unify these very different types of experiments. The viscoelastic properties of polymers have been measured with great care, beginning with the pioneering work of 1. Ferry (2). These properties display a certain characteristic time 7", which increases very rapidly with the molecular weight (or equivalently, with the number N of monomers per chain)

De Gruyter eBooks, Dec 31, 1985