Film instability

The rupture process of a soap film is of some interest. In the case of a film spanning a frame, as in Fig. XIV-15, it is known that rupture tends to originate at the margin, as shown in the classic studies of Mysels [207, 211]. Rupture away from a border may occur spontaneously but is usually studied by using a spark [212] as a trigger (a-radia-tion will also initiate rupture [213]). An aureole or ridge of accumulated material may be seen on the rim of the growing hole [212, 214] (see also Refs. 215, 216). Theoretical analysis has been in the form of nucleation [217, 218] or thin-film instability [219]. 

Lubricating-film instability is the dominant failure mode for sleeve bearings. This instability is typically caused by eccentric, or off-center, rotation of the machine shaft resulting from imbalance, misalignment, or other machine or process-related problems. Figure 44.48 shows a Babbitt bearing that exhibits instability. 

When oil-film instability or oil whirl occurs, frequency components at fractions (i.e.,, etc.) of the... 

There are two objectives triggering the interest in film instabilities. Since film instabilities must be caused by a force acting at one of the film surfaces, the structure formation process mirrors these forces. The observation of film instabilities can therefore be used as a sensitive measurement device to detect interfacial forces. The knowledge of these forces enables us, on the other hand, to control the morphology that is formed by the film break-up. 

The electric field experiment shown here can be considered as a test case for the quantitative nature of capillary instability experiments. It shows the precision, with which the capillary wave pattern reflects the underlying destabilizing force. In the case of electric fields, this force is well understood. Therefore, the good fit in Fig. 1.10b demonstrates the use of film instability experiments as a quantitative tool to measure interfacial forces. The application of this technique to forces that are much less well understood is described in the following section. 

In this representation all data collapses onto a single master curve. The 1 //q scaling of A., on one hand, and the master curve in Fig. 1.13b, on the other hand, are strong evidence for the model, which assumes the radiation pressure of propagating acoustic phonons as the main cause for the film instability. 

G. Reiter, A. Sharma, A. Casoli, M.-O. David, R. Khanna, and P. Auroy, Thin film instability... 

When pressure is enhanced at constant mass flow and constant temperature, the viscosity of the liquid phase and the interfacial tension decrease. Therefore Reynolds number and Film number increase until first appearance of film instability. This is shown in Figure 6 by means of the system pelargonic acid/carbon dioxide at 333 K. With further increase of pressure at constant mass flow the Film number decreases, whereas the Reynolds number increases. At constant temperature and constant mass flow the Film number and also the Reynols number depend on pressure and vary in a large range. This is a unique feature of near-critical extraction. 

Study of processes leading to rupture of foam films can serve to establish the reasons for their stability. The nature of the unstable state of thin liquid films is a theoretical problem of major importance (it has been under discussion for the past half a century), since film instability causes the instability of some disperse systems. On the other hand, the rupture of unstable films can be used as a model in the study of various flotation processes. The unstable state of thin liquid films is a topic of contemporary interest and is often considered along with the processes of spreading of thin liquid films on a solid substrate (wetting films). Thermodynamic and kinetic mechanisms of instability should be clearly distinguished so that the reasons for instability of thin liquid films could be found. Instability of bilayer films requires a special treatment, presented in Section 3.4.4. 

During thinning thermodynamically unstable films keep their shape in a large range of thicknesses until the critical thickness is approached, at which the film ruptures. This thickness is called critical thickness of rupture hcr. Therefore, the thermodynamic instability is a necessary but not a sufficient condition for film instability. There are other factors determining instability which at thicknesses smaller than the critical cease to act. Two are the possible processes involved in film instability - film thinning with retaining film shape, and film rupture. Which of them is realised when thermodynamic instability is reached, requires analysis of the various mechanisms of film rupture. 

In some patients, especially those over age 50 years, a localized or diffuse desquamation of corneal epithelium becomes evident (figure 6-3). This epithelial reaction usually consists of superficial punctate keratitis and probably results from exposure and tear film instability associated with decreased reflex tearing, infrequent blinking, and increased tear evaporation. The punctate keratopathy is frequently absent immediately after anesthetic instillation but may appear 5 to 30 minutes later (Figure 6-4). 

Data suggest that irritation among office workers does not represent a single distribution, but that susceptible subpopulations exist. Experimental studies, in chambers, show that atopic individuals usually have much lower irritation thresholds for agents commonly found indoors, even when their atopy is not active. In addition, the presence of tear-film instability, from Sicca complex, aging, or other underlying causes, poses an increased risk for irritation. 

Both allergic and irritant mechanisms have been proposed as explanations for eye symptoms. More rapid tear-film break-up time, a measure of tear film instability, is associated with increased levels of symptoms. Fat-foam thickness measurement and photography for documentation of ocular erythema have also been used. Some authors attribute eye symptoms at least in part to increased individual susceptibility based on those factors. In addition, office workers with ocular symptoms have been demonstrated to blink less frequently when working at video display terminals. Conjunctival staining with fluorescent dyes is a common clinical test for conjunctivitis sicca. 

The expression for coalescence probability (sometimes named efficiency) of binary fluid particle collisions in dispersions is normally related to the physical phenomena that are considered to determine the overall coalescence process. The coalescence process in stagnant fluids is generally assumed to occur in three consecutive stages, as sketched in Fig 9.2. First, bubbles collide, trapping a small amount of liquid between them under the action of the continuous phase. Second, this liquid drains over a period of time from an initial thickness until the liquid film separating the bubbles reaches a critical thickness, under the action of the film hydrodynamics. The hydrodynamics of the film depends on whether the film surface is mobile or immobile, and the mobility, in turn, depends on whether the continuous phase is pure or a solution. Third, at this point, film rupture occurs due to film instability resulting in instantaneous coalescence. 

The case of most interest above is clearly a > 0, that is 6 > SL. Roughly speaking, this means that the attraction between adsorbent and adsorbate molecules is greater than the attraction between adsorbate molecules themselves (the liquid wets the solid). The amount of adsorption decreases as a —> 0 (Fig. 6) when a = 0 there is no adsorption at all up to x = 1, at which point there is sudden condensation. When a < 0, questions of supersaturation and film instability arise which are discussed in detail by Frenkel (69) the concept of surface excess must be used and the adsorption is negative for p < pa (see Sec. IV.5.a). 

The comprehensive characterization of uitrathin resist (UTR) (<100 nm) processes in terms of defectivity, manufacturahility, and physical properties (structure, dynamics, stability, thermodynamic behavior, etc.) have been a central point of interest in semiconductor microlithography for quite some time. Despite many years of experimental and theoretical efforts along these lines, a number of basic questions still remain to be answered. One of these issues is the fundamental lower physical limit of the resist thickness, below which lithographic patterning is not viable. For resists based on the polyhydroxy styrene platform, this lower limit has been determined to be around 60 nm, with the onset of film instability occurring at around 55 nm. For a host of other resist platforms, this lower limit is yet to be determined. 

In spite of the above-mentioned advantages of UTR processes, practical considerations often impose a choice of resist and substrate that are not fully compatible, resulting in films that are unstable or metastable with finite relaxation time. While thick films (> 300 nm) may be stable or metastable due to gravityfor thin films (<100 nm) intermolecular and surface forces dominate. UTR films are susceptible to both spontaneous thin-film instabilities due to London-van der... 

Okoroanyanwu, Thin film instabilities and implications for ultra thin resist process J. Vac. Sci. Technol. B 18(6), 3381 3387 (2000) U. Okoroanyanwu, Limits of ultra thin resist process Future Fab. Int 10, 157 163 (2001). 

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