Short commentary: Theoretical considerations on concentrated polymer interfaces: an attempt to explain dewetting of ultra-thin films.

We discuss the dewetting of ultra-thin molten polymer films within the framework of the Cahn-Hilliard theory for liquid interfaces. We argue that a) we need a pair of descriptors to characterize the bulk liquid of polymer chains (rather than the monomer density alone), b) the so-called loop density S, first introduced to describe polymer layers, may be a good scalar candidate for the configurational descriptor, c) the results found for the variation of S with distance might suggest an explanation for dewetting of ultra-thin polymer films.

Mobile polymer connectors.

We study the junction between two solid objects, formed by polymer connectors which are supposed to freely explore the two grafting surfaces. We focus on the sphere-plane and sphere-sphere geometries. Because the chains are mobile, they are able to adapt both the local grafting density and their conformation to the position of the surfaces. Using a scaling approach, we show that, in chemical equilibrium, local grafting density is non-monotonic, and the junction can be divided into two different regions: the center, where connectors are compressed and exert a repulsive force between the objects (high excluded-volume interactions) and an external corona, where chains are stretched and attract the two objects. The relative importance of these regions varies for different separations and depends on surface geometries. When an external force is applied, this spatially inhomogeneous constraint exerted by the junction leads to specific force-distance profiles, which differ from profiles in the case of fixed connectors. An effective interaction potential and the adhesion energy are computed, showing a strong dependence on the geometry of surfaces.

Interfacial properties of polymeric liquids

We show that the variations of the surface tension of polymeric solutions gamma with the molecular weight of the sample M(n), the temperature T, and the volume fraction of monomers straight phi(b) are explained by the self-organization of the long flexible chains that are present in the immediate vicinity of the interface. Within a scaling functional theory we find a simple law gamma(straight phi(b),M(n),T) which accounts quantitatively for the experimental data available in the literature with a very high accuracy.