Emulsion film

The diversity of release products and the wide range of release problems make classification difficult. One approach is by product form, with subdivisions such as emulsions, films, powders, reactive or iaert sprays, reactive coatings, and so on. Another approach is by appHcation, eg, metal casting, mbber processiag, thermoplastic iajection mol ding, and food preparation and packagiag. 

Film-bildschicht, /. Photog.) film emulsion, film layer, film coat, -schicht, /. film layer. 

Initially devised to measure interactions in single soap films (air/water/air) [8], the TFB technique has been progressively improved and its application has been broadened to emulsion films (oil/water/oil) [ 12] and asymmetric films (air/water/oil or air/water/solid) [13,14]. In a classical setup, a thin porous glass disk is fused on the side to a capillary tube and a small hole is drilled in the center of the disk. The liquid solution fills the disk, part of the capillary, and a thin horizontal film is formed across the hole. The disk is enclosed in a hermetically sealed box, with the capillary tube exposed to a constant reference pressure Pr. Under the effect of the pressure difference AP between the box and the reference, the... 

This technique allows measuring interparticle forces as small as 10 N, corresponding to the minimum force required for forming chains. One advantage of this particular experiment is the built-in averaging over extremely large number of emulsion films. 

Figure 2.22. (a) Disjoining pressure vs. thickness isotherm for an emulsion film stabilized by 0.1% BSA, ionic strength of 10 mol/1 NaCl, oil phase = hexadecane. The dots are the experimental data, dashed line is the double-layer contribution to the total disjoining pressure, and the solid line is the best fit done supposing additivity of the double-layer and steric forces, (b) Force vs. distance profiles for ferrofluid emulsions stabilized with mixed BSA-Tween-20 adsorption layers. The total concentration of the Tween-20 is kept constant = 5CMC, pH = 5.8. (Adopted from [78].)... 

Rgure 2.26. Six consecutive steps in shrinking of an emulsion film stabilized with 0.1 wt% BSA. Oil phase is hexadecane the ionic strength is 10 mol/1. The bar corresponds to 100 j,m. The local adhesion on aggregates is evident. Arrows indicate some of the points of adherence at the interfaces. (Adapted from [87].)... 

V. Bergeron Stability of Emulsion Films. In Proceedings of the Second World Congress of Emulsions 4, 247, Bordeaux, France (1997). 

T.D. Dimitrova, F. Leal-Calderon, T.D. Gurkov, and B. Campbell Disjoining Pressure vs. Thickness Isotherms of Thin Emulsion Films Stabilized by Proteins. Langmuir 17, 8069 (2001). 

As another example of utilizing platy forms of twinned crystals, we should mention a recent remarkable increase in the photosensitivity of photographic film. Photographic emulsion film consists of minute AgBr crystallites, with octahedral or cubo-octahedral Habitus. The photosensitivity is determined by the area... 

Marinova, K., Gurkov, T., Velev, O., Ivanov, I., Campbell, B., Borwankar, R. (1997). The role of additives for the behaviour of thin emulsion films stabilized by proteins. Colloids and Surfaces A Physicochemical and Engineering Aspects, 123-124, 155-167. 

A similar technique can be used to study the rheological properties of liquid films. Figure 4 shows the formation of a W/O/W emulsion film with two, identical aqueous phases (such as in water-in-oil emulsions) at the tip of the capillary. A pre-requisite of the experiment is that the surface of the capillary must be well wetted by the film phase, i.e., it should be hydrophobic in this case. First, an aqueous drop is formed inside the oil (film liquid) and the aqueous phase is in the bottom of the cuvette. Then, the level of the aqueous phase is slowly increased. As the oil/water interface passes the drop, a cap shaped oil film, bordered by a circular meniscus, covers the drop. This film can be studied in equilibrium and in dynamic conditions, similar to the single interfaces (See above). The technique can be used to study films from oil or aqueous phase which can be sandwiched between identical or different liquid or gas phases. 

The film is observed by a microscope using reflected light The film holder and the objective are immersed in air in the case of foam (i.e., air/liquid/air) film and in the oil phase, in the case of an O/W/O emulsion film, respectively. The film thickness can be determined by measuring the intensity of the light reflected from the film surfaces [9]. Further details of the technique will be discussed in Chapter 2. 

Emulsion Film Emulsion Flotation Emulsion Test... 

Bergeron, V., An Introduction to Forces and Structure in Individual Foam and Emulsion Films in Foams and Emulsions, Sadoc, J.F. Rivier, N. (Eds.), NATO ASI Ser., Ser. E, Kluwer Academic Publishers Boston, 1999, pp.45-72. 

Slow, thin emulsion films, such as Kodak Technical Pan or Ilford Pan-F, developed in high-definition developers such as Windisch Extreme Compensating Developer or POTA, will produce negatives, even from 35 mm, of extremely high acutance with the ability to enlarge to mural size. The trade-off is an extremely low EL... 

The fixing process involves a series of chemical reactions in which the silver bromide is converted into complex argentothiosulfates, which are then dissolved by contact with fresh fixer and finally washed out of the film or paper. Upon immersing an emulsion (film or paper unless otherwise noted) into fixer, the first reaction is the conversion of unused silver bromide into an insoluble but not very stable compound. This compound can be seen by looking at negatives (not prints) after only a few seconds in the fix. They will appear milky in appearance. If fixation is not continued and the compound not completely dissolved, the negatives will rapidly degenerate. 

Develop conventional emulsion films for 3 minutes in each solution do not rinse in-between. Develop T-grain films for 4 minutes in each bath. Use continuous agitation in both baths. 

NOTE This formula may cause dichroic fog on some modern emulsion films. Testing is advised. 

P. Kruglyakov and A. Nushtayeva, Emulsions stabilized by solid particles the role of capillary pressure in the emulsion films, in Emulsions Structure Stability and Interactions, edited by D. N. Petsev (Elsevier, Amsterdam, 2004), pp. 641-676. 

The techniques involving microscopic foam films can be applied to the study of other types of thin films, such as emulsion films [e.g. 4-9], thin films on a substrate [e.g. 10-12], as long as a suitable measuring cell is utilised. 

Early studies of rupture of unstable thin films have been performed with macroscopic emulsion films [94] and foam films [53]. Very high values for hcr were obtained (of the order of 10 pm). Systematic investigations with microscopic films [e.g. 29,64,73] have shown that their critical thickness is considerably smaller. The probability character of rupture is illustrated by the curves in Fig. 3.12. As it is seen the most probable critical thickness increases with the increase in film radius. The most probable critical thickness of rupture is 30 nm (r = 0.1 mm). Usually such a thickness is reached by films from aqueous solutions of low molecular fatty alcohols at which the surfactant concentration is chosen so that the surface tension is equal in all cases [29,73]. Aniline films exhibit a higher hcr 42 nm. 

A stratification phenomenon in foam films from sodium oleate aqueous solutions has been described by Johonnott [314] and Perrin [318] in the beginning of the century. The stepwise thinning has been studied by many authors [e.g. 235,345], It became evident that this phenomenon is universal and has been observed also in emulsion films [346,347], asymmetric films of the air-water/oil type [348], films from latex suspensions [349] and liquid crystalline films [350],... 

Data on emulsion film formation from insoluble surfactant monolayer are rather poor. It is known, however, that such films can be obtained when a bubble is blown at the surface of insoluble monolayers on an aqueous substrate [391,392]. Richter, Platikanov and Kretzschmar [393] have developed a technique for formation of black foam films which involves blowing a bubble at the interface of controlled monolayer (see Chapter 2). Experiments performed with monolayers from DL-Py-dipalmitoyl-lecithin on 510 3 mol dm 3 NaCl aqueous solution at 22°C gave two important results. Firstly, it was established that foam films, including black films, with a sufficiently long lifetime, formed only when the monolayer of lecithin molecules had penetrated into the bubble surface as well, i.e. there are monolayers at both film surfaces on the contrary a monolayer, however dense, formed only at one of the film surfaces could not stabilize it alone and the film ruptured at the instant of its formation. Secondly, relatively stable black films formed at rather high surface pressures of the monolayer at area less than 53A2 per molecule, i.e. the monolayer should be close-packed, which corresponds to the situation in black films stabilized with soluble surfactants. 

As already noted, the NB foam films, the bilayer emulsion films and the BLMs, are amphiphile bilayers, and their stability in respect to rupture and their permeability can be considered from a unified point of view. 

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