We have used neutron reflection and phase contrast microscopy to investigate the morphology and surface topology of thin films of nearly symmetric (f=0.55) and asymmetric (f=0.77), poly (ethylene–propylene)–poly (ethylethylene) (PEP–PEE) diblock copolymers (f being the PEP volume fraction) and have identified three important differences in their ordering properties. First, annealed films of the asymmetric diblocks do not form the lamellar microstructure found in symmetric diblocks; their structure can instead be modeled in terms of the hexagonal packing of PEE cylinders observed in bulk small-angle neutron scattering measurements. However, the cylinders show in-plane distortions, which we interpret in the context of nonintegral layering. These distortions are amplified at the surfaces where the PEE assumes lamellarlike form. Second, as-cast films of the asymmetric diblock are characterized by a microstructure lacking long-range order, pinned between strongly segregated PEE at both surfaces. These films can be equilibrated through annealing, leading to the well-ordered structures described earlier. The changes with annealing are surprising given that both PEP and PEE are well above their glass transitions at room temperature. Finally, the block asymmetry and the associated cylindrical structure in the interior are also manifested in the surface topology. Thin films of asymmetric PEP–PEE are smooth on a macroscopic scale unlike their symmetric counterparts, which form islands on the surface to accommodate films of nonintegral lamellar thicknesses.
A description is given of the prototype polarized neutron reflectometer installed at the intense pulsed neutron source. This instrument is designed for determining the magnetic depth profiles near the surfaces of ferromagnets and superconductors, by measuring the spin-dependent reflectivities of a well-collimated (0.01°) beam of cold neutrons from surfaces of a few cm2. Magnetic profiles can be determined with the spatial resolution of 40 Å, over thicknesses up to 5000 Å. Variations of the magnetic flux of the order of 10−5 G cm2 can be detected.
The segment density profile of end-functionalized deuterated polystyrene (EF-dPS) polymers anchored in a surrounding melt of hydrogenated polystyrene (hPS) to an interface with silicon was determined by neutron reflectometry. Thin films of mixtures with various volume fractions of the EF-dPS and hPS were spun cast from toluene solutions onto the silicon. These films as cast were uniform aa a function of depth. After heating to 184 OC for approximately 1 day to allow equilibrium segregation to be achieved in the films, neutron reflection measurements were performed. The EF-dPS segment density profiles d(z) needed to fit the reflectivity data showed a high I $ at the silicon interface which increased to a maximum approximately 10 nm away from the interface and then fell monotonically to the bulk segment density &. The interface excesa determined by integration of these profiles was in excellent agreement with that directly determined by forward recoil spectrometry on the same samples. The form of the profiles is consistent with the predictions of a self-consistent mean field theory if, in addition to a large attachment free energy of the end group to the silicon, there is a weak preferential attraction of the silicon for the more polarizable hPS segments relative to the less polarizable dPS segments.
The concentration profile at the surface in blends of deuterated and protonated polystyrene (d-PS and PS) is inferred from measurements of neutron reflectivity and secondaryion mass spectrometry, using constraints provided by forward recoil spectrometry and X-ray reflectometry results on the same samples. The surface is enriched in d-PS, the volume fraction and the decay length of which are in good agreement with the predictions of mean-field theory but the form of the profile shows small, but statistically significant, deviations from that predicted by the theory.
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