RESUMO
The PDMS lamellar sublayers of a poly(styrene)-poly(dimethylsiloxane) diblock (PS-PDMS) and PS-PDMS-PS triblocks are investigated by NMR and dielectric spectroscopy. Some segments of the confined PDMS chains display anisotropic orientational fluctuations along the interfaces with the PS glassy blocks, whereas the others display fluctuations rather parallel to the lamellae normal. This coexistence results from a competitive ordering effect induced by the glassy interfaces and the chain-end anchoring junctions. The distribution of PDMS relaxation times within the sublayers is also examined: in particular, a slowing down of the segmental motions, together with a broadening of this distribution, are detected.
RESUMO
This paper reports an experimental study of a homogeneous nucleation process in the direct space, using an atomic-force microscope. Nucleated patterns are holes in a thin diblock copolymer film. The formation of nuclei from the metastable majority phase is followed either by the dissolution or by the growth of the hole. It is also preceded by the unexpected presence of a bump at the free surface. From the study of the nucleus surface topography at different stages of the evolution, we infer a description of the nucleation mechanism at a molecular level. It involves the existence of ordered metastable states characterized by the presence of compressed internal layers, the formation of pores in the center of the film, and the existence of interfacial flows across these pores. The presence of compressed internal layers was directly demonstrated using Neutron Reflectivity experiments, Our scheme is also consistent with all existing experimental data. After hole nucleation, we identify two distinct growth regimes: the first one is individual and the second one is interactive.
