Showing papers by "Klaus D. Jandt published in 1996"

Microstructural Evolution of Melt Intercalated Polymer−Organically Modified Layered Silicates Nanocomposites

Abstract: The microstructure of various (ordered and disordered) polymer−organically modified layered silicate hybrids, synthesized via static polymer melt intercalation, is examined with X-ray diffraction and transmission electron microscopy. The ordered intercalates exhibit microstructures very similar to the unintercalated organically modified layered silicate (OLS). Polymer intercalation occurs as a front which penetrates the primary OLS particle from the external edge. The disordered hybrids, on the other hand, exhibit heterogeneous microstructures with increased layer disorder and spacing toward the polymer−primary particle boundary. In these hybrids, individual silicate layers are observed near the edge, whereas small coherent layer packets separated by polymer-filled gaps are prevalent toward the interior of the primary particle. The heterogeneous microstructure indicates that the formation of these disordered hybrids occur by a more complex process than simple sequential separation of individual layers sta...

Transient Surface Roughening of Thin Films of Phase Separating Polymer Mixtures

Abstract: The surface morphology of thin molten films of phase separating mixtures of poly(ethylenepropylene) (PEP) and perdeuterated poly(ethylenepropylene) (dPEP) of the critical composition were investigated using scanning force microscopy. Volume fraction versus depth profiles were also obtained using time-of-flight forward recoil spectrometry (TOF-FRES). The free surface of a film with a nominal thickness of about d = 200 nm is initially smooth but develops a regular roughness pattern, with a wavelength about 500 nm and an amplitude about 2.5 nm, after a certain annealing time, which corresponds to the transition from a four-layer (dPEP/PEP/dPEP/PEP) to a two-layer (dPEP/PEP) phase-separated domain structure in the direction normal to the film thickness. At much longer times the two-layer films become smooth again. We attribute these fine surface patterns to transient pressure differences accompanying mass transport by hydrodynamic flow, where this transport occurs though perforations in the PEP-rich layered d...

Microstructure of block copolymer reinforced interfaces observed with frictional force microscopy

Abstract: We demonstrate that frictional force microscopy may be used to reveal the interfacial morphology of polystyrene (PS)/poly(2-vinylpyridine) (PVP) interfaces reinforced with a PVP6PS-PVP triblock copolymer

Direct Observation of Fracture Mechanisms in Polymer-Layered Silicate Nanocomposites

Abstract: Conventional three point bending and TEM techniques are employed to determine the fracture toughness and identify the failure mechanisms in model layered-silicate polymer nanocomposites.

Microscopic aspects of polymer-metal epitaxy

Abstract: The textured oriented overgrowth (epitaxy) of certain metals evaporated on to substrates consisting of highly oriented ultra-thin thermoplastic polymer films has been known for a few years. However, the origin of the observed epitaxy was not clear: the formation of a chemical interface layer, classic epitaxy or graphoepitaxy (artificial epitaxy) all seemed to be possible explanations for the observed orientations. We have used the complementary methods of transmission electron microscopy (TEM) and scanning force microscopy (SFM) to investigate aspects of the polymer-metal epitaxy. Our investigations show that the bulk morphologies of polymer substrates determine their surface topographic properties. Highly oriented surface steps serve as suitable locations for an oriented growth of the evaporated metals. The results of the investigations suggest artificial epitaxy (graphoepitaxy) as an effective orientation mechanism for the oriented metallic growth on polymer substrates.