arXiv subjects

Jean-Francois Joanny

Publications and source records attributed to Jean-Francois Joanny.

24 records · Page 2Linked to original sources

arXiv2003

Motion of an Adhesive Gel in a Swelling Gradient: a Mechanism for Cell Locomotion

Motivated by the motion of nematode sperm cells, we present a model for the motion of an adhesive gel on a solid substrate. The gel polymerizes at the leading edge and depolymerizes at the rear. The motion results from a competition between a self-generated swelling gradient and the adhesion on the substrate. The resulting stress provokes the rupture of the adhesion points and allows for the motion. The model predicts an unusual force-velocity relation which depends in significant ways on the point of application of the force.

physics.bio-ph↗

arXiv2001

Complexation between oppositely charged polyelectrolytes: beyond the Random Phase Approximation

We consider the phase behavior of polymeric systems by calculating the structure factors beyond the Random Phase Approximation. The effect of this correction to the mean-field RPA structure factor is shown to be important in the case of coulombic systems. Two examples are given: simple electrolytes and mixtures of incompatible oppositely charged polyelectrolytes. In this last case, all former studies predicted an enhancement of compatibility for increasing charge densities; we also describe the complexation transition between the polyelectrolytes. We determine a phase diagram of the polyelectrolyte mixture that includes both complexation and incompatibility.

cond-mat.soft↗

arXiv2000

Polyelectrolyte Adsorption

The problem of charged polymer chains (polyelectrolytes) as they adsorb on a planar surface is addressed theoretically. We review the basic mechanisms and theory underlying polyelectrolyte adsorption on a single surface in two situations: adsorption of a single charged chain, and adsorption from a bulk solution in $θ$ solvent conditions. The behavior of flexible and semi-rigid chains is discussed separately and is expressed as function of the polymer and surface charges, ionic strength of the solution and polymer bulk concentration. We mainly review mean-field results and briefly comment about fluctuation effects. The phenomenon of polyelectrolyte adsorption on a planar surface as presented here is of relevance to the stabilization of colloidal suspensions. In this respect we also mention calculations of the inter-plate force between two planar surfaces in presence of polyelectrolyte. Finally, we comment on the problem of charge overcompensation and its implication to multi-layers formation of alternating positive and negative polyelectrolytes on planar surfaces and colloidal particles.

cond-mat.soft↗

arXiv2000

Counter-ion release and electrostatic adsorption

The effective charge of a rigid polyelectrolyte (PE) approaching an oppositely charged surface is studied. The cases of a weak (annealed) and strongly charged PE with condensed counterions (such as DNA) are discussed. In the most interesting case of the adsorption onto a substrate of low dielectric constant (such as a lipid membrane or a mica sheet) the condensed counterions are not always released as the PE approaches the substrate, because of the major importance of the image charge effect. For the adsorption onto a surface with freely moving charges, the image charge effect becomes less important and full release is often expected.

cond-mat.soft↗

arXiv1999

Charge Distribution on Annealed Polyelectrolytes

We investigate the equilibrium charge distribution along a single annealed polyelectrolyte chain under different conditions. The coupling between the conformation of the chain and the local charge distribution is described for various solvent qualities and salt concentration. In salt free solution, we find a slight charge depletion in the central part of the chain: the charges accumulate at the ends. The effect is less important if salt is added to the solution since the charge inhomogeneity is localized close to the chain ends over a distance of order of the Debye length. In the case of poor solvent conditions we find a different charging of beads and strings in the framework of the necklace model. This inhomogeneity leads to a charge instability and a first order transition between spherical globules and elongated chains.

cond-mat.soft↗

arXiv1996

Theory of Polyelectrolyte Solutions

1. Introduction 2. Charged chains at infinite dilution - asymptotic properties 2.1 Definition of the model and Flory-like calculation 2.2 Variational approaches 2.3 Renormalization group calculations 2.4 Screening of electrostatic interactions 2.5 Annealed and quenched polyelectrolytes 3. Local aspects of screening 3.1 Counterion condensation 3.2 Poisson Boltzmann approach 3.3 Attractive electrostatic interactions 4. Electrostatic rigidity 4.1 The Odijk-Skolnick-Fixman theory 4.2 Alternative calculations for flexible chains 4.3 The case of poor solvents 5. Charged gels and brushes 5.1 Grafted polyelectrolyte layers 5.2 Polyelectrolyte gels 6. Semidilute solutions 6.1 Ordering transitions in polyelectrolyte solutions 6.2 Correlation length and osmotic pressure of semi-dilute polyelectrolyte solutions 6.3 Electrostatic rigidity in semidilute solutions 6.4 Concentrated solutions of flexible polyelectrolytes 6.5 Mesophase formation in poor solvents 7. Dynamical properties 7.1 Mobility and electrophoretic mobility of a single charged chain 7.2 Viscosity of polyelectrolyte solutions 8. Conclusions

cond-mat↗