Thin polymer film instabilities. Counter-ion density around an permeable sphere homogeneously charged. ; Instabilités dans les films minces de polymères. Densité de contre-ions autour d'un globule poreux chargé

The first part of this thesis is focused on instabilities in thin polymer films. When an electric field is applied perpendicular to the film surface, and the temperature is above the glass transition temperature, the film becomes unstable against surface modulations. In particular, we study the influence of residual stresses on the growth rate and on the selected wavenumber of this instability. We start by describing the fabrication process of thin films (typically spin-coating) and we explain why residual stresses may appear and should be considered. Then a model is developed and every hypothesis is discussed in detail. Three rheological constitutive laws are investigated : a non-linear elastic Neo-Hookean solid, a viscoelastic Voigt-Kelvin solid and a viscoelastic Maxwell fluid. In the second part, we study the counterion density around a hydrophobic polyelectrolyte. In a bad solvent, this kind of polyelectrolyte adopts a pearl-necklace structure. The counterion density is determined around one of the 'pearls' in this structure. Applying the quasi-localized charge approximation allows us to get scaling laws between the coupling parameter on the one hand and the decay length and the uptake charge on the other hand. The scaling laws were confirmed by numerical simulations. Finally we applied Density Functional Theory to this system, also being in good agreement with the two other methods. Keywords : thin films, instabilities, non-linear elasticity, viscoelasticity, polyelectrolyte, strong coupling. ; Dans cette thèse, nous nous sommes intéressés dans la première partie aux instabilités dans les films minces de polymères. Sous champ électrique perpendiculaire à la surface, cette dernière devient instable lorsque la température du film mince est supérieure à sa température de transition vitreuse. Nous y étudions plus particulièrement l'influence des contraintes résiduelles à la fois sur le taux de croissance de cette instabilité et sur les longueurs d'ondes sélectionnées. Dans un premier temps, nous décrivons ...