Nanocomposites Drying: Correlation Structure – Rheological Behavior
Supervisors : Catherine Amiel, Clémence Le Cœur, Abdoulaye Fall, Cédric Lorthioir, Guillaume Ovarlez
Keywords : Nanocomposite, Polymer, Drying, Rheology, Structure.
The dispersion of nanoscale inorganic fillers within a polymer matrix may potentially lead to a significant improvement of some of his mechanical properties. One of the ways used to prepare these nanocomposite materials relies on solvent evaporation. The formation of the microstructure over the drying process remains poorly understood. For this aim, we chose a system based on a water-soluble polymer, poly(methacrylic acid), the conformation of which is pH dependent, and silica nanoparticles with well-controlled size, well-known geometry and surface functionalization. The solvent used (water) was selected to take into account the environmental issues and to limit the contribution of organic solvents in the preparation of such materials.
The purpose of this project is to investigate the drying of these materials and their evolution towards the solid state. This should help to improve our understanding of the mechanisms involved by drying, their impact on the structuration of the filler particles and, correspondingly, on the mechanical behavior of the resulting nanocomposite. Upon evaporation of polymer/particles mixtures in solution, the organization in the solid phase should result from the evolution of the local order induced by the particles and the chain organization. One of the key steps in this drying process is the evolution towards a gel phase in which the material corresponds to a “soft solid”, the structure of particles is fixed but can be further modified by shearing. In order to achieve this purpose, we will use some methods aimed at structural characterization at the nanoscale (SAXS, SANS, Transmission Electron Microscopy), describe the local dynamics of polymer chains by means of NMR, and characterize the rheological behavior of these hybrid materials. This should help to get a correlation between the local organization (nano and micrometer scale) to the macroscopic properties. Some of these experimental approaches will be coupled to monitor, for example, the influence of shear on the structure and dispersion of particles (Rheo-SANS or Rheo-SAXS). For such materials, the structure should also depend on the rheological behavior. It will therefore be particularly informative to characterize structurally and mechanically (DMA, tensile tests) solid material obtained by drying according to two distinct situations: starting from a solution at rest or starting from a solution that has experienced a previous shear.
We also plan to carry out the drying of the polymer/particles water mixtures using an approach named microfluidic pervaporation. This technique should allow us to get a precise control of the drying kinetics, to limit the occurrence of concentration inhomogeneities, and to monitor in-situ the transition solution – gel – solid.