Abstract : We study the interface, formed by the welding of:
- a polymer melt, composed of free chains
- a network of interconnected chains, designated by "mesues"
The profile of this network/melt interface is studied by neutron reflectometry. We find that the chains permeate the bulk network only if their weight is below that of the mesh. Above that, the swelling of the network at equilibrium remains very weak. The width of the interface is restricted to the size of a mesh.
The existence of heterogeneities in the reticulation (established in previous studies of neutron scattering) is not clear in the present study. The kinetic of establishment of the interface is slower than in the case of interdiffusion between two melts.
The adhesion of this network/melt interface is studied by cleavage of two thin layers of network and melt, previously welded in a sandwich between two polymer sheets. Here, the problems of contamination of the interface by diffusion of polymer from the sheets have been resolved. In the context of adhésion, the original aspects here are: a controlled interface (possibly wide because of heterogeneities, hence a strong interface) and the cohésion of the chains in a network (hence a coopérative dissipation of energy). We have also compared the static and dynamic measurements of cleavage. The probing of the surface after the crack by ion beam spectroscopy (détection of deutérium) allows an accurate characterization of the crack path, after solving problems of roughness.
These measurements of adhésion show a strengthening of the interface when the weight of the melt is higher than that of the mesh, in spite of a narrower interface. We interpret this paradox by an increase in the number of loops at the interface.
We also report also preliminary but promising studies of the interface between two networks.