XPS study of the effect of hydrocarbon contamination on polytetrafluoroethylene (teflon) exposed to atomic oxygen

The presence of hydrocarbon contamination on the surface of polytetrafluoroethylene (PTFE) markedly affects the oxygen uptake, and hence the wettability, of this polymer when exposed to an oxygen plasma. As revealed by X-ray photoelectron spectroscopy (XPS) analysis, the oxygen-to-carbon ratio (O/C) for such a polymer can increase sharply, and correspondingly the fluorine-to-carbon ratio (F/C) can decrease sharply, at very short exposure times; at longer times, however, such changes in the O/C and F/C ratios reverse direction, and these ratios then assume values similar to those of the unexposed PTFE. The greater the extent of hydrocarbon contamination in the PTFE, the larger are the amplitudes of the 'spikes' in the O/C- and F/C-exposure time plots. In contrast, a pristine PTFE experiences a very small, monotonic increase of surface oxidation or O/C ratio with time of exposure to oxygen atoms, while the F/C ratio is virtually unchanged from that of the unexposed polymer (2.0). Unless the presence of adventitious hydrocarbon is taken into account, anomalous surface properties relating to polymer adhesion may be improperly ascribed to PTFE exposed to an oxygen plasma

Using Electron Spectroscopy for Chemical Analysis (ESCA) in Failure Analysis: Some Recent Developments

Electron spectroscopy for chemical analysis (ESCA) is receiving increased attention as a surface-sensitive failure analysis technique because of several recent developments. These are: first - substantially improved spatial resolution, allowing a much broader range of problems to be studied; second - new ways to apply analytical results to practical problems, resulting from better technical understanding of ESCA and better data reduction techniques; and third - the development of sample handling systems which can handle large, outgassing samples, making ESCA a relatively non-destructive technique. In this paper we consider ESCA\u27s niche as a surface analysis tool, and discuss the impact of the new features mentioned above on the types of analytical problems we have routinely encountered in failure analysis and problem solving for industry. It should be noted that this technique is also known as X-ray photoelectron spectroscopy (XPS). The terms ESCA and XPS describe the same technique

Magnetocaloric Studies of the Peak Effect in Nb

We report a magnetocaloric study of the peak effect and Bragg glass transition in a Nb single crystal. The thermomagnetic effects due to vortex flow into and out of the sample are measured. The magnetocaloric signature of the peak effect anomaly is identified. It is found that the peak effect disappears in magnetocaloric measurements at fields significantly higher than those reported in previous ac-susceptometry measurements. Investigation of the superconducting to normal transition reveals that the disappearance of the bulk peak effect is related to inhomogeneity broadening of the superconducting transition. The emerging picture also explains the concurrent disappearance of the peak effect and surface superconductivity, which was reported previously in the sample under investigation. Based on our findings we discuss the possibilities of multicriticality associated with the disappearance of the peak effect.Comment: 30 pages, 10 figure

Neurotic excoriations: A review and some new perspectives

Neurotic excoriation is a commonly encountered dermatologic syndrome, which is usually associated with psychiatric pathology, most commonly obsessive-compulsive traits and depression. This disorder typically runs a chronic course. In addition to symptomatic dermatologic treatments for the self-inflicted excoriations and secondary pruritus, the treatment for this disorder is primarily psychiatric. In spite of this, neurotic excoriation has received little attention in the psychiatric literature, probably reflecting a lack of adequate collaboration between the dermatologist and the psychiatrist. This article critically reviews the literature on this disorder, and presents the salient features of five consecutive cases seen at the psychiatry-dermatology liaison clinic at our hospital. Possible etiology and treatment strategies in a previously unreported subgroup of patients with seemingly intractable symptoms are discussed. Further, the review highlights the fact that knowledge of this symptom complex is important for all psychiatrists, since it is frequently a "cutaneous sign" of psychopathology.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26126/1/0000202.pd

Microphase separation induced by competitive hydrogen bonding interactions in semicrystalline triblock copolymer/homopolymer complexes

Microphase separation through competitive hydrogen bonding interactions in ABC/D triblock copolymer/ homopolymer complexes is studied for the first time. This study investigated self-assembled nanostructures that are obtained in the bulk, by the complexation of a semicrystalline polystyrene-block-poly(4-vinylpyridine)-block-poly(ethylene oxide) (SVPEO) triblock copolymer with a poly(4-vinyl phenol) (PVPh) homopolymer in tetrahydrofuran (THF). In these complexes, microphase separation takes place due to the disparity in intermolecular interactions among PVPh/P4VP and PVPh/PEO pairs. At low PVPh concentrations, PEO interacts relatively weakly with PVPh, whereas in the complexes containing more than 30 wt% PVPh, the PEO block interacts considerably with PVPh, leading to the formation of composition-dependent nanostructures. SAXS and TEM results indicate that the cylindrical morphology of a neat SVPEO triblock copolymer changes into lamellae structures at 20 wt% of PVPh then to disordered lamellae with 40 wt% PVPh. Wormlike structures are obtained in the complex with 50 wt%PVPh, followed by disordered spherical microdomains with size in the order of 40–50 nm in the complexes with 60–80 wt% PVPh. Moreover, when the content of PVPh increases to 80 wt%, the complexes show a completely homogenous phase of PVPh/P4VP and PVPh/PEO with phase separated spherical PS domains. The fractional crystallization behavior in SVPEO and complexes at lower PVPh content was also examined. A structural model was proposed to explain the microphase separation and self-assembled morphologies of these complexes based on the experimental results obtained. The formation of nanostructures and changes in morphologies depend on the relative strength of hydrogen bonding interactions between each component block of the copolymer and the homopolymer

Polymer Crystallization in 25 nm Spheres

Crystallization within the discrete spheres of a block copolymer mesophase was studied by time-resolved x-ray scattering. The cubic packing of microdomains, established by self-assembly in the melt, is preserved throughout crystallization by strong interblock segregation even though the amorphous matrix block is well above its glass transition temperature. Homogeneous nucleation within each sphere yields isothermal crystallizations which follow first-order kinetics, contrasting with the sigmoidal kinetics normally exhibited in the quiescent crystallization of bulk polymers.Comment: accepted for publication in Physical Review Letters, 2/28/2000; scheduled for 5/1/2000 issu

Differential Expression between Human Dermal Papilla Cells from Balding and Non-Balding Scalps Reveals New Candidate Genes for Androgenetic Alopecia

Agency for Science, Technology and Research (A*STAR). EC is supported by the A*STAR Graduate Scholarship program