Sujets de mémoire et stage

Polymer coatings of nanometric thickness are about to enter in our everyday life in the form of protective layers, stimuli-responsive membranes, components of revolutionary flexible electronics devices, etc. With respect to thin films of inorganic materials, the these “soft” systems are preferred because of easier and more versatile fabrication methods and the lack of degradation within long shelf time.

Experimental investigation of Slow Arrhenius Processes

Recent and growing literature has shown that the properties of thin organic layers prepared via spincoating (a fast and inexpensive method to coat large surfaces) evolve over time. Current models cannot explain the occurrence of such transient phenomena (equilibration kinetics), as their timescales exceed by far the longest relaxation times predicted by the current theories of polymer dynamics.

In this project we will investigate a new molecular mechanism (SAP) recently observed by our lab (Song et al. Science Advances, 8 eabm7154), responsible for the equilibration of liquids and glasses. The SAP, which we show is intimately connected to high temperature flow, can efficiently drive soft matter and other materials towards  more stable, less energetic states. In this project we will perform measurements of molecular dynamics and monitor equilibration kinetics. Our aim is to develop models to predict the timescale of equilibration of polymer coatings. 

Competition between crystallization and adsorption

We will focus on the crystallization of polymer coatings, a benchmark system to study how mass transport can be controlled by imposing non-equilibrium constraints at fixed walls. Polymers do not crystallize easily. Similar to smaller molecules, crystallization of macromolecules gets even more sluggish upon confinement at the nanoscale level where the conversion rate significantly drops. Below a system-dependent critical size, the formation of ordered structures is not observed within experimental time scales exceeding several months. This intriguing phenomenon has been imputed to a series of concomitant mechanisms involving a reduction of nuclei density and slower interfacial dynamics. Our laboratory has experimentally disproved the latter hypothesis,  verifying that slower crystallization kinetics do not require a perturbation in molecular dynamics. We have also demonstrated that interfacial interactions affect crystallization because they induce the adsorption of polymer molecules onto attractive walls, which in turns limits the amount of crystallizable material. In this project, we will study methods to control the mass transport towards the crystal growth front based on kinetic competition with irreversible adsorption on the walls.