NMR study of interphase structure in layered polymer morphologies with mobility contrast: disorder and confinement effects vs. dynamic heterogeneities

Nanostructured multiphase polymers with mobility contrast, such as semicrystalline polymers or block copolymers with two separate glass transitions, are usually characterized by the presence of an interphase material with in-between mobility. This interphase is often assumed to form a contiguous layer between the adjacent main phases, possibly exhibiting a mobility gradient. Here, we present evidence from proton low-field NMR experiments based upon the spin diffusion effect that suggests less trivial possible arrangements. A numerical analysis of the NMR data based upon a 2D lattice model demonstrates that a part of the mobile phase must be in rather direct contact with the rigid phase. Tentatively, we assume an island-like distribution of the interphase, or its location within the rigid phase, with sizes on the scale of a few nanometers. We observe qualitatively the same phenomenon in a semicrystalline polymer, poly(e-caprolactone), and in a lamellar poly(styrene)-poly(butadiene) block copolymer, suggesting that the phenomenon has some degree of universality. We hypothesize that the non-trivial location of the interphase results from either a higher than one-dimensional constraint imposed by the surrounding rigid phase and disorder effects arising from local roughness or thickness distributions or from the intrinsic dynamic heterogeneity length scale of material close to the glass transition.