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The influence of surfaces on structure formation: I. Artificial epitaxy of metals on polymers. II. Phase separation of block copolymers and polymer blends under nonplanar surface constraints
Abstract
In order to understand the fundamental cause of preferential lattice orientations when certain metals are vapor deposited onto oriented semicrystalline polymers, Sn deposited onto various polyolefins was investigated as a function of polymer crystallinity, crystallography, morphology and Sn deposition conditions. Crystallinity is necessary, however, the invariance of the orientations to changes in the polymer crystallography indicates that the orientation of the metal is not due to lattice matching, but the result of artificial epitaxy on anisotropic surface features related to the direction of the chain axis (possibly atomic scale surface steps parallel to the chain axis) and the shape anisotropy of the polymer crystals. Features common to many semicrystalline polymers can thus induce orientations in metal overgrowths. The influence of a spherical external surface constraint on the microphase separation of block copolymers (poly(styrene-co-butadiene) and poly(styrene-co-isoprene)) and block copolymer-polystyrene homopolymer blends was investigated by producing very small droplets of the polymers via an aerosol technique. In microdroplets, compositions which exhibit bulk lamellar, OBDD, cylindrical and spherical morphologies result in concentric packing of lamellae, concentric disordered 'honeycomb-like' layers, layers of curved cylinders and irregularly packed spheres respectively. This constraint changes the magnitude of various contributions to the free energy, the respective roles of which can be better understood by observing which structures are produced. External surface energy is the strongest influence, resulting in the spherical microdroplets with uniform surface coatings of the lower surface free energy diene component. Maintaining preferred separations between adjacent intermaterial dividing surfaces (IMDS), which were approximately equivalent to those in the corresponding bulk structures, was also a dominant factor. Except for spherical microdomains, the observed IMDS exhibit radially dependent shapes and curvatures. Locally this results in additional interfacial area relative to the bulk, but likely provides a minimum in interfacial area given the microdroplet spherical geometry and required separations of adjacent IMDS. The most accommodating factor is the IMDS curvature. Rather than create interfacial area by truncation of the continuous microdomain morphology at the surface of the droplet, the structures curve to fit within the spherical external constraint by adopting radially periodic, concentrically ordered morphologies.
Subject Area
Polymers|Materials science
Recommended Citation
Reffner, John Richard, "The influence of surfaces on structure formation: I. Artificial epitaxy of metals on polymers. II. Phase separation of block copolymers and polymer blends under nonplanar surface constraints" (1992). Doctoral Dissertations Available from Proquest. AAI9219485.
https://scholarworks.umass.edu/dissertations/AAI9219485