Influences des instabilités convectives sur l'état de surface final des films polymères fabriqués par procédé de séchage

Polymer film formation from drying of polymer solution is very important process for many applications: coating, printing, nanotechnology. Some applications (automobile coatings) require films with high surface quality with a roughness in range of visible light wavelength. Often drying polymer solutions yields corrugated surfaces. This corrugation can be due to: 1) mechanical instabilities due to buckling of dried surface resulting from a heterogeneous evaporation; 2) hydrodynamic instabilities. In this work we studied in situ the formation of corrugated surface and we related these mechanisms to hydrodynamic convections

Nanomechanical properties of nanoconfined polystyrene nanoparticles in nanoblends

The role of nanoconfinement on the glass transition temperature (Tg) of polymers has been extensively studied in the thin film geometry. This work looks at the Tg of nanoconfined polystyrene in spherical nanoparticles (27- 200 nm), individually dispersed in crosslinked polybuthylmethacrylate matrices. A reduction of Tg compared to the bulk was observed in PS nanospheres via neutron scattering-mechanical tests and was found to decrease with decreasing diameter for D< 50nm. The general trend of Tg depression in nanospheres was found to be similar to the results on thin film geometry

A Novel Method for Studying the Dynamics of Nanoconfined Polymers in Nanoscopic Domains Using S.A.N.S.

International audienc

Role of Bénard−Marangoni Instabilities during Solvent Evaporation in Polymer Surface Corrugations

International audienceFilm formation through the drying of polymer solutions is a widely used process in laboratories and in many industrial applications such as coatings. One of the main goals of these applications is to control the film surface morphology. In many cases, evaporation has been found to yield corrugated patterns on the free surface of films. This has been interpreted in terms of either mechanical or hydrodynamic instabilities. In this article, we present experimental results where mesoscale 2D well-ordered surface corrugation patterns are formed during solvent evaporation from polystyrene/toluene solutions. The transformation of Bénard−Marangoni instabilities into surface corrugation is studied during the entire drying process using particle tracking, 3D morphology analyses, etc. We show that the corrugation wavelength is controlled by the Bénard−Marangoni instability, whereas the corrugation amplitude is controlled by a mechanism that involves a high evaporation rate

Dynamique d'une particule de polystyrène confinée dans un nanocomposite (polymère dur/polymère mou).

National audienc

Effects of the Nanomechanical Properties of Polymer Nanoparticles on Crack Patterns during Drying of Colloidal Suspensions

International audienceCoalescence during drying of suspensions containing glassy polymer nanoparticles generates fascinating crack patterns, whereas coalescence of soft polymer particles gives crack-free films. This process is widely used in environmental-friendly water-based coatings, which use nanosized polymer nanoparticles in the film formation process. Numerous studies have shown that polymer nanoconfinement could lead to a drastic modification of the polymer properties such as a reduction of the glass transition temperature (Tg). If such a change in the properties of polymers also exists when nanoconfined in nanoparticles in suspension, then one would expect an alteration in the film formation process, particularly a reduction in the minimum film formation temperature. In this paper we look at the effect of nanomechanical properties of polymer nanoparticles on crack patterns generated by particle coalescence. We study crack pattern morphology during drying of aqueous suspensions of PBMA nanoparticles (50 nm diameter) with different nanomechanical properties (different cross-linking ratios). We investigate the effect of temperature and relaxation time on crack morphologies in the transition from crack to crack-free films. These results were analyzed in terms of time−temperature superposition and compared to bulk behavior

Une Nouvelle Méthode pour Etudier la Diffusion et la Nanomécanique des Polymères Nanoconfinés.

National audienc

Glass Transition of Spherical Polystyrene Nanoparticles

International audienc

Effet de la Nanomécanique des particules colloïdales dans le procédé de fabrication de film polymère

Le séchage des suspensions à des températures inférieures à la température de transition vitreuse (Tg) des polymères génère des poudres, alors que ce même procédé engendre des films sans craquelures pour T > Tg. Ce problème a été le sujet de recherche de plusieurs groupes; certains ont centrés leur recherche sur les propriétés de films non-craquelés, d'autres ont étudié les mécanismes de formation des fissures pendant le séchage de suspensions colloïdales dures. En revanche, la transition entre les deux a été relativement peu traitée. Nous avons étudié l'évolution des craquelures lors du séchage des suspensions, au dessous et au dessus de Tg. Nous avons montré que le séchage pour T < Tg génère des craquelures parallèles, régulièrement espacées, similaires aux morphologies observées dans le séchage unidirectionnel de colloïdes dures. Et la distance entre craquelures Dc subit une transition brusque dans la zone de Tg du polymère. Nous avons exploité ces observations pour décrire les propriétés nano-mécaniques des nanoparticules et leur rôle dans le procédé de formation de film

Nanomécanique et Transition Vitreuse des Polymères Confinés dans des Nanoparticules.

National audienc