Transmission electron microscopy copolymer surface morphology

Siebert and Riew (4) described the chemistry of the in situ particle formation. They proposed that the composition of the particle is a mixture of linear CTBN-epoxy copolymers and crosslinked epoxy resin. The polymer morphology of the CTBN toughened epoxy systems was investigated by Rowe (5) using transmission electron microscopy by carbon replication of fracture surfaces. Riew and Smith (6) supported the... 

The synthesis of these materials is outlined in Scheme I. Transmission electron microscopy shows that the morphology of nearly equimolar compositions of the siloxane-chloromethylstyrene block copolymers is lamellar, and that the domain structure is in the order of 50-300 A. Microphase separation is confined to domains composed of similar segments and occurs on a scale comparable with the radius of gyration of the polymer chain. Auger electron spectroscopy indicates that the surface of these films is rich in silicon and is followed by a styrene-rich layer. This phenomenon arises from the difference in surface energy of the two phases. The siloxane moiety exhibits a lower surface energy and thus forms the silicon-rich surface layer. 

Figure 4.25. High magnification image.s obtained by transmission electron microscopy of stained thin sections of a hyperbolic mesopha.se of a linear diblock copolymer, polystyrene-polyisoprene, whose morphology follows the D-surface (single node circled in middle picture) and possibly the gyroid. Staining produces high contrast between the two block domains. Note the very different magnifications.

The surface morphology of block copolymer films can be investigated by atomic force microscopy. The ordering perpendicular to the substrate can be probed by secondary ion mass spectroscopy or specular neutron or x-ray reflectivity. Suitably etched or sectioned samples can be examined by transmission electron microscopy. Islands or holes can have dimensions of micrometers, and consequently may be observed using optical microscopy. 

The removal of direct carbon replicas is dependent upon the polymer. Boiling xylene vapor was used to remove drawn PE from replicas [436] in work on drawn polymer morphology. A direct carbon replica method for a PBT impact fracture surface was described by evaporation of platinum at 20° and PBT removal in hexafluoroisopropanol (HFIP) [437], Latex film coalescence in poly(vinyl acrylate) homopolymer and vinyl acrylic copolymer latexes was studied using direct replicas [438]. As the latex films have a low glass transition temperature, they were cooled by liquid nitrogen to about -150°C in the vacuum evaporator and shadowed with Pt/Pd at 45° followed by deposition of a carbon support film at 90° to the specimen surface. The latex films were dissolved in methyl acetate/methanol. Transmission electron microscopy micrographs of the latex films show the difference between films aged for various times (see Section 5.5.2). 

The knowledge of the morphology of the block copolymers makes a great progress. Numerous studies are theoretical, but they are often coupled with one or several experimental techniques. Hashimoto et al. [114] used SAXS to investigate the hexagonally packed cylindrical particles with paracrystalline distortion by comparing experimental and theoretical values. Stocker et al. [115] associated transmission electron microscopy to atomic force microscopy or SAXS and theoretical calculations or electron microscopy to treat surface problems [116] (see also Chapters 6 and 7). 

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