Characterization, film chemical stability

In one of the earliest reports of the use of clean evaporated alloy films in surface studies, Stephens described the preparation and characterization of Pd-Au films and presented some results for the adsorption of oxygen on them 46). Films of pure Pd and 60% Au were evaporated directly from wires, while films of 80% Au and pure Au were evaporated from a pre-outgassed tungsten support wire. The films were evaporated in a UHV system and the pressure was kept below PC8 Torr during evaporation. After evaporation, the films were stabilized by cycling between —195° and 30°C four times. They w ere characterized by X-ray diffraction and chemical analysis surface areas were measured by the BET method using krypton adsorption. 

Metal ion modified polyimide films have been prepared to obtain materials having mechanical, electrical, optical, adhesive, and surface chemical properties different from nonmodified polyimide films. For example, the tensile modulus of metal ion modified polyimide films was increased (both at room temperature and 200 0 whereas elongation was reduced compared with the nonmodif ied polyimide (i). Although certain polyimides are )cnown to be excellent adhesives 2) lap shear strength (between titanium adherends) at elevated temperature (275 0 was increased by incorporation of tris(acetylacetonato)aluminum(III) (2). Highly conductive, reflective polyimide films containing a palladium metal surface were prepared and characterized ( ). The thermal stability of these films was reduced about 200 C, but they were useful as novel metal-filled electrodes ( ). 

The term moisture, usually defined as wetness conferred by an unidentified liquid, is assumed here to be due to water. Thus, the scope of this article is the characterization of and consequences due to relatively small amounts of water associated with solids of pharmaceutical interest. Chemical stability, crystal structure, powder flow, compaction, lubricity, dissolution rate, and polymer film permeability are some properties of pharmaceutical interest that have been demonstrated to be influenced by the presence of moisture. Wet granulation, extrusion, spheronization, tray drying, freeze drying, spray drying, fluid-bed drying, tableting, and aqueous film coating are some unit operations that obviously depend on the amount and state of water present. 

Polyolefins. Low density polyethylene and polypropylene have been developed as sheet and hollow fiber mlcroporous membranes, respectively, for use In plasmapheresis. Polyethylene Is made porous by stretching the annealed film ( ), while polypropylene la made porous by coextruding hollow fibers with a leachable plasticizer. Neither membrane has been prepared with small pore dimensions suitable for protein rejection. These polyolefin membranes are characterized by good chemical stability, but require special surfactant treatments to make them wettable. Their low deformation temperature precludes the use of steam sterilization. Because they are extruded without the usual antl-oxldants and stabilizers, their stability la lower than Injection molding formulations of the same polymer. 

The processing sequence for silicon dioxide (SiOi) depends on its specific use. For example, silica for use as inter-metallization insulation the order is deposition, densi-fication by annealing, and etching to the correct configuration. CVD processes for Si02 films can be characterized by chemical reaction type, the growth pressure, or deposition temperature. The choice of route is often dictated by requirements of the thermal stability of the substrate or the conformality. Table 5-4 summarizes selected... 

The company BASF (Germany) has launched the production of poly-ethersulfone labeled Ultrason E [169] representing amorphous thermoplastic product of polycondensation it can be characterized by improved chemical stability and fire-resistance. The pressed articles made of it differ in solidity and rigidity at temperature 200 °C. It is assumed to be expedient to use this material when producing articles intended for exposure to increased loadings when the sizes of the article must not alter at temperatures from -100 °C till 150 °C. These items are, for instance in electrotechnique, coils formers, printing and integrated circuits, midspan joints and films for condensers. 

Among various strategies that have been used to synthesize polyimides with lower dielectric constants, the most common approach is to incorporate fluorene, in the form of trifluoromethyl groups, into diamine and dianhydride units that minimize polarizability and increase the free volume [46]. It is well-known that fluorene atom has unique characteristics such as high electronegativity and low electric polarity. These properties give fluorinated polymers (e.g., poly[tetrafluoroethylene]) attractive features such as low water uptake, water and oil repellency, low permittivity, low refractive indices, resistance to wear and abrasion, and thermal and chemical stability. Fluorination is also known to enhance solubility and optical transparency and to lower the moisture absorption of polyimides. Therefore, it is expected that fluorinated polyimides will be widely applied in the electro-optical and semiconductor industries. The polymer series studied was essentially limited mainly to 6F dianhydride because it proved to be the only dianhydride with which many of the fluorinated diamines would form polymer films suitable for physical characterization. 

The first step in systematic emulsion breaking is to characterize the emulsion in terms of its nature (O/W, W/O, or multiple), the number and nature of immiscible phases, the presence of a protective interfacial film around the droplets, and the sensitivity of the emulsifiers. In oilfield W/O emulsions, a stabUizing interfacial film can be formed from the asphaltene and resin fractions of the crude oil. This causes special problems because if the films are viscoelastic then a mechanical barrier to coalescence exists, which may be quite intractable and yield a high degree of emulsion stability. More detaUed descriptions are given in references [J33-J35]. Based on an emulsion characterization, a chemical addition could be made to neutralize the effect of the emulsifier, followed by mechanical means to complete the phase separation. 

ETEROAROMATics FURAN AND THIOPHENE. The chemical transformation of thiophene at high pressure has not been studied in detail. However, an infrared [441,445] study has placed the onset of the reaction at 16 GPa when the sample becomes yellow-orange and the C—H stretching modes involving sp carbon atoms are observed. This reaction threshold is lower than in benzene, as expected for the lower stability of thiophene. The infrared spectrum of the recovered sample differs from that of polythiophene, and the spectral characteristics indicate that it is probably amorphous. Also, the thiophene reaction is extremely sensitive to photochemical effects as reported by Shimizu and Matsunami [446]. Thiophene was observed to transform into a dark red material above 8 GPa when irradiated with 50 mW of the 514.5-nm Ar+ laser line. The reaction was not observed without irradiation. This material was hypothesized to be polythiophene because the same coloration is reported for polymeric films prepared by electrochemical methods, but no further characterization was carried out. 

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