Critical film properties

Critical Film Properties that Affect Degradation Rate... 

The chemical literature reveals relatively new and varied interests for nitrile elastomer-modification of epoxy resins in diverse areas of coatings and primers. Desirable properties such as impact resistance, mandrel bend and adhesion improvement are attainable with little or no sacrifice in critical film properties. In some instances, it is documented that proper elastomer modification of select epoxy coatings will enhance corrosion and moisture resistance. This may relate to better film/substrate adhesion durability. The combined literature, journal and patent, has led to continuing study of nitrile elastomer modified epoxy coatings. 

Table 1 contains the metal-to-metal engineering property requirements for Boeing Material Specification (BMS) 5-101, a structural film adhesive for metal to metal and honeycomb sandwich use in areas with normal temperature exposure. The requirements are dominated by shear strength tests. Shear strength is the most critical engineering property for structural adhesives, at least for the simplistic joint analysis that is commonly used for metal-to-metal secondary structure on commercial aircraft. Adhesive Joints are purposefully loaded primarily in shear as opposed to tension or peel modes as adhesives are typically stronger in shear than in Mode I (load normal to the plane of the bond) loading. 

The capacity of the ordered film for supporting loads is between that of the static film and that of the dynamic fluid film. The orientation property of the ordered layer gradually becomes weak with the distance apart from the metal surface. The transition occurs as the ordered film appears more important between the two solid surfaces. The thickness of the ordered film is related to the initial viscosity or molecular size of the lubricant, as shown in Fig. 13, so that we can generally write the critical film thickness as follows ... 

The measurement of the parameters reflecting film properties which sharply change at the CBF/NBF transition lays at the basis of all experimental techniques for determination of the black film type. Microscopic black films render vast opportunities in the study of this transition by the dependences of film thickness, lifetime and contact angle on electrolyte concentration in the initial solutions. These dependences allow to estimate the critical electrolyte concentration Cei cr at which the CBF/NBF transition occurs. 

The coalescence process can be described by two steps. At first, there is a mutual approach of the drops which is controlled by the rheological properties of the continuous (organic) phase (see Figure 4a). Secondly, a flattening of the droplets appears by the formation of a so called "dimple" (see Figure 4b). The decrease in distance d is determined by the rate of flow out of the continuous phase between the droplets (14,15). A thin film is formed which decreases to a certain critical film thickness, dcrit at which point approach stops (16). 

It is evident from these results, as well as from results cited later in this discussion, that the choice of solvent is of critical importance in achieving the best film properties from a resin system. The cheapest solvent combination may not and probably will not give best film properties. It is also evident that in the process of evaluating the merits of resins, conclusions could be erroneous unless the optimum solvent blend is chosen for each resin. Extrapolating these considerations further, it can be expected that the same resin could yield entirely different properties if it is applied to a surface in different forms, for example, as a solution, a dispersion in solvents, a dispersion in water, or as a powder. 

X-ray and electron diffraction methods are applied in order to measure atomic distances in the crystal lattice and their changes. Hence, the diffraction methods are also basically suitable for measuring the strain/stress behaviour in thin films. However, since the film thickness and the crystallite size in thin films are small, some line broadening already arises from this. In order to determine what contribution the mechanical stresses have on the diffuse lines, careful analysis of the line profiles must be undertaken [148, 151]. This method is less suitable for routine determination of stresses in thin films. In some cases, it is possible though rarely applied to determine the stresses in the films through their influence on other, known film properties, at least approximately. Such properties are, for example, the position of an absorption edge [152], the Hall effect [153], electron spin resonance spectra [155] and in the case of superconducting films, variations in the critical transition temperature [156]. However, these effects can, unfortunately, also arise for other reasons, and thus these techniques can usually only be used as supplemental experiments. 

Low Shear Rates. Small-particle latices provide higher critical pigment volume concentrations and thereby greater coating formulation latitude. Their viscosities are, however, too high at low shear rates and too low at high shear rates to provide acceptable applied film properties. This phenomenon is illustrated in part in Figure 14. The latices used in this study (26) included three commercial binders (half symbols) the others were ex-... 

The lowest interfacial tensions in Winsor systems have a different origin than that of the largest ones they do not depend on the surfactant film properties and are due to the nearness of a critical point. Close to the boundaries Winsor I Winsor III, S = S and Winsor III -> Winsor II, S = Si, the corresponding excess phase becomes slightly turbid. This is reminiscent of the vicinity of a critical point. This particular type of critical point, where... 

Critical pigment volume concentration (CPVC) n. That level of pigmentation, PVC, value in the dry paint, where just sufficient binder is present to fill the voids between the pigment particles. At this level, a sharp break occurs in film properties such as scrub resistance, hiding, corrosion resistance, ease of stain removal, etc. Different requirements for each product would dictate different PVC or CPVC... 

Catalyst systems used for polymerization have a large impact on the molecular weight distribution and have undergone tremendous changes in the last decade (1). As older catalysts systems are replaced by new catalysts, film manufacturing processes and material selection have become more critical to ensure maintenance or improvement in film properties without adversely impacting the manufacturing process. 

The basic features of inks or pastes printed and fired on the substrate are particles of metals and/or metal oxides, glass (metal oxides mixture), a binder, and a solvent to make the paste fluid in nature [24-26]. A metallic conductive component comprising one or more precious metals in finely divided powder form with powder sizes ranging from 1 to 10 pm in size. Structural shape and particle morphology are critical parameters that affect the desired electrical characteristics, and controlling these parameters ensures uniformity of the fired film properties. 

Referring to PVC values (zinc content in dry film), previous results of laboratory tests demonstrated that a higher amount of microzinc leads to a longer useful life of primers. Nevertheless, it is important to mention that the choice of zinc content must be made by considering the physical characteristic of the primer film required for each particular case. When pigment volume concentration exceeds largely the CPVC, film properties such as adhesion, flexibility, abrasion resistance, etc. are drastically reduced while when the percentual level is slight under the critical value the efficiency is also considerably diminished. 

Callaghan and Neustadter [31] have made a study of the foam stabilities of air-crude oil and natural gas-crude oil systems using a variety of light crude oils of viscosities 14 mPa s. This study, at ambient temperature using a sparging method, concerned so-called dead oils from which natural gas had been separated. It also involved a comparison of the foam behavior with critical film rupture thicknesses, bulk phase, and surface shear viscosities together with dilatational surface properties. 

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