In multiphase systems, decreasing the phase size induces an increase of interfacial phenomena. In those regions, changes in macromolecular mobility (intercrystalline phase, rigid amorphous phase, confining) and creation of distorted structures or phases (interphase between immiscible polymers, transcristallinity…) are witnessed.

In this domain, we focus on systems manufactured by the multinanolayer coextrusion technique. This process consists in coextruding two immiscible polymers (A and B) to obtain a trilayer A-B-A, which is later stacked using N multiplying elements so as to get 2^N+1 +1 layers. It is noteworthy that our group has a leading activty in this research activity with strong industrial applications.

                                                                                         

                                                                                                           Scheme of multinanolayer process.

 

Those investigations lead us to use advanced experimental methods to characterize the microstructure and the interphases (AFM microscopy, X ray scattering, Synchrotron, Modulated Differential Scanning Calorimetry and later their influence on macroscopic (barrier and mechanical properties) of materials.  

                                                                                  

Self-assembled triblock copolymer poly(methyl methacrylate-b-butyl acrylate-b-methyl methacrylate) (MAM) confined by poly(methyl methacrylate) (PMMA) obtained with multilayer coextrusion. Here, A double level of organization is achieved: the obtained films are made of thousands of alternating continuous nanolayers of each component, while within the nanolayers, MAM is self-assembled with a cylindrical morphology.

 

We also investigate the mechanisms of confined crystallization and the possible effect of resulting orientation which is a promising way to improve the barrier properties of polymers.

                                                                           

                                                      Confinement effect in PC/MXD6 multilayer films: Impact of the microlayered structure on water and gas barrier properties.

 

At the nanoscale interfacial instabilities may lead to layer break-ups. The complete understanding of the physical origin of these instabilities is an open question. We hypothesized the mechanisms leading to ruptures in multilayer films are similar to those responsible for dewetting in thin films and developed model experiments to study this problem. The dewetting dynamics of an ultrathin film embedded in an immiscible matrix can be described with a simple model balancing interfacial tension and viscous dissipation. For the viscous dissipation, finite size effects and a no-slip conditions should be taken into account.

                                                                                                      

                                                                                                      

                                                                                                                                                                           

                                                                                                                                   Dewetting phenomena.

 

Macromolecular synthesis and chemical modifications of polymers aimed at improving the compatibility of phases, together with strategy for better blending or dispersing are also explored in the research topic.