Thin glassy film

Material transfer across a continuous boundary phase. For instance, in Si3N4 boundary movement can occur only if both silicon and oxygen diffuse through the thin, glassy film that usually exists between grains. In some cases, the redissolution of the boundary-anchoring second phase inclusions into the matrix can be rate limiting. 

Figure 15. Contact forming behavior of a continuously evaporated (10 A/sec) Au contact on (a) MEH-PPV and (b) 40 wt% TPD/polycarbonate thin glassy films. Note that as displayed in Fig. 9 the Au/TPD contact in curve (b) achieves contact ohmicity at a much longer time (ca. 800 hrs).

Baer and coworkers demonstrated that thin glassy films without free interfaces exhibited bulk physical aging behavior. For instance, PSF, when confined between polyolefin layers, showed no dependence of film thickness on the rate of physical aging. Motivated by these studies, Roth and coworkers devised a set of experiments to directly investigate the influence of an adjacent mbbery layer on Tg and physical aging in thin polymeric films [137]. The sample geometry consisted of a thin PS... 

Figure 3.3 Diagram of film structure used by Rowe et al., which enabled the study of gas permeability properties and physical aging behavior of ultra-thin glassy films. Reproduced with permission of Elsevier. ...

The SFA, originally developed by Tabor and Winterton [56], and later modified by Israelachvili and coworkers [57,58], is ideally suited for measuring molecular level adhesion and deformations. The SFA, shown schematically in Fig. 8i,ii, has been used extensively to measure forces between a variety of surfaces. The SFA combines a Hookian mechanism for measuring force with an interferometer to measure the distance between surfaces. The experimental surfaces are in the form of thin transparent films, and are mounted on cylindrical glass lenses in the SFA using an appropriate adhesive. SFA has been traditionally employed to measure forces between modified mica surfaces. (For a summary of these measurements, see refs. [59,60].) In recent years, several researchers have developed techniques to measure forces between glassy and semicrystalline polymer films, [61-63] silica [64], and silver surfaees [65,66]. The details on the SFA experimental procedure, and the summary of the SFA measurements may be obtained elsewhere (see refs. [57,58], for example.). 

Owing to the toxicity of mercury and its disposal problem, solid electrodes are now very popular. In particular, electrodes made of carbon such as glassy carbon, graphite, carbon paste, and carbon fibers have gained popularity. Mercury, gold, bismuth, and other metals can be deposited as thin metal films on carbon and serves as thin metal film electrodes (TMFE) with excellent analytical advantages in trace metal analysis. The choice of working electrode is determined by the redox... 

Stripping voltammetry or stripping analysis has a special place in electrochemistry because of its extensive application in trace metal analysis. Stripping voltammetry (SV) is a two-step process as shown schematically in Fig. 18b. 12. In the first step, the metal ion is reduced to metal on a mercury electrode (thin mercury film on glassy carbon or a HMDE) as amalgam. 

Pioneering contact mode AFM studies by Meiners et ai. (1995) show that chemical sensitivity at the surface of thin polymer films can be achieved by measuring the microscopic friction and stiffness for glassy block copolymers. This provides invaluable information to complement topography on the nature of the block at the surface. 

Bismuth-film electrodes (BiFEs), consisting of a thin bismuth-film deposited on a suitable substrate, have been shown to offer comparable performance to MFEs in ASY heavy metals determination [17]. The remarkable stripping performance of BiFE can be due to the binary and multi-component fusing alloys formation of bismuth with metals like lead and cadmium [18]. Besides the attractive characteristics of BiFE, the low toxicity of bismuth makes it an alternative material to mercury in terms of trace-metal determination. Various substrates for bismuth-film formation are reported. Bismuth film was prepared by electrodeposition onto the micro disc by applying an in situ electroplating procedure [19]. Bismuth deposition onto gold [20], carbon paste [21], or glassy carbon [22-24] electrodes have been reported to display an... 

Braun and Metzger [52] showed that trace amounts of nickel obtained from natural environmental samples could be determined voltammetrically as nickel dimethyl glyoximate following adsorptive enrichment onto a rotating glassy carbon electrode, on which a thin mercury film has been deposited electrolytically. See Sect. 7.34.1. 

The experimental results described above show that the gas-permeability properties of thin glassy polymer films (submicrometer in thickness) are more time- or history-dependent than much thicker films (the bulk state for example, 50 pm or thicker) seem to be. This is manifested in terms of physical aging over a period of 1 year and more. The observed permeability values for the current thin films are all initially greater than the reported bulk values but approach or become less than these values after a few days or weeks, depending on the thickness. After a year, the thin films may be as much as four times less permeable than the reported bulk values. Selectivity increases with aging time, as might be expected from a densification process. 

Perlite is an expanded volcanic glass. It is thin and diaphanous except where interconnections of glassy bubbles give the impression of veins. If the veins are separated from the glassy film, they may loosely resemble chrysotile asbestos. The separation is seldom complete. Close observation will detect the film fragments associated with the vein structure. 

An increase of the craze stability of tensile-induced crazes with rising M has been noted in various glassy polymers. In a study made on thin PS films by Berger and Kramer the craze extension ratio was determined at various temperatures for polymers of varying M. For measurements made at room temperature, X varied little with molecular weight but, as the temperature was raised, and chain disentanglement processes became more probable, the situation changed. For example, at 50 °C,... 

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