Séchage de nanocomposites à base de poly(acide méthacrylique) et de nanoparticules de silice, de la solution au solide
Nanocomposites drying based on poly methacrylic acid and silica nanoparticles, from solution to solid
ERMAN
Type de document
THESE
Langue
français
Auteur
ERMAN
Résumé / Abstract
The dispersion of nanoscale inorganic fillers within a polymer allows to modulate the mechanical properties of a material. One of the ways used to prepare these nanocomposite materials relies on solvent evaporation. The purpose is to monitor the drying of these materials and to study their evolution from the semi-dilute solution towards the solid state. The results obtained should help understanding the mechanisms involved during drying, their impact on the charge organization and on the mechanical behavior of the final nanocomposites. For this aim, a stimulable system composed of a polymer matrix and a filler is used to modulate the interactions at the matrix-filler interface. A polyelectrolyte, poly (methacrylic acid), is used: its charge rate and conformation vary, neutral and globular at pH3, fully negatively charged and conformation expanded at pH9. Silica nanoparticles with three different surface condition are chosen. A first work is carried out in aqueous solutions to obtain information on the structuring of these systems in the semi-diluted regime and under conditions close to thermodynamic equilibrium. State diagrams of each system are analyzed by small angle X-ray scattering (SAXS): information on the distribution of the two components is obtained when a phase separation occurs but also on the structures formed by silica nanoparticles. In order to understand structuring processes during drying, two drying experiments in confined geometry are performed. The first is at the macroscopic length scale and concerns the drying of a drop that allows the follow of the morphology but also of the polymer concentration at different stages of drying. The second is at the nanoscale where in-situ structural characterizations are carried out by SAXS during the drying process which follows the formation and evolution of structures formed by silica nanoparticles: drying on three types of silica and at three pH values is carried out and various structures are obtained. Larger bulk materials are developed and then structurally and mechanically characterized by combining SAXS, Atomic Force Microscopy (AFM) and microindentation techniques. The mechanical properties on several size scales (nanometric and micrometric) are compared for two materials prepared at pH3 and pH9. The degree of reinforcement of the elastic modulus is correlated with the structure formed by silica nanoparticles: compact aggregates at pH3 for a weak reinforcement and fractal aggregates at pH9 for a larger reinforcement.
