Experimental Techniques for Studying Foams

The extinction of the luminous flux passing through a foam layer occurs as a result of light scattering (reflection, refraction, interference and diffraction from the foam elements) and hght absorption by the solution [4]. In a polyhedral foam there are three structural elements which are clearly distinct by optical properties films, plateau border, and vertexes. 

The optical properties of single foam films have been extensively studied, but those of the foam as disperse system are poorly considered. It has been concluded that the extinction of luminous flux where I is the intensity of the light 

The interpretation of electrokinetic results is complicated because of surface mobility and border and film elasticity, which cause large non-homogeneities in density and border radii at hydrostatic equilibrium and liquid motion. 

The optical properties of single foam films have been extensively studied, but those of the foam as disperse system are poorly considered. The extinction of luminous flux 1/ lo, where / is the intensity of the light passing through the foam and lo is the intensity of the incident light) is conduded to be a linear function of the specific foam area. This could be used to determine the specific surface area of a foam. 

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Microscopic are considered to be only those foam films the radius of which is within the range of 10 - 500 p.m. Their application as models in the study of foam films has been proved most successful and that is why the experimental technique for their study is... 

Adamson [15] and Miller et al. [410] illustrate some techniques for measuring surface shear viscosity. Further details on the principles, measurement and applications to foam stability of interfacial viscosity are reviewed by Wasan et al. [301,412], It should be noted that most experimental studies deal with the bulk and surface viscosities of bulk solution rather than the rheology of films themselves. 

A new way to form a microscopic foam film in the middle of a biconcave drop (Fig. 2.2) has marked the further improvement of the microinterferometric technique. The increase in accuracy and reliability of the photometric and registering devices contributed to this improvement. The experimental details and the metrological characteristics of the microinterferometric technique for determination of foam film thickness has been the object of numerous studies [e.g. 16,23,39-43,58],... 

A new experimental technique has been introduced by Kruglyakov et al. [82] and Vilkova and Kruglyakov [83] for the kinetic study of the foam expansion ratio increase and foam column destruction in centrifugal field. It involves increase in the excess pressure in the foam liquid phase and reduction of the time needed to reach high excess pressures. 

In order to study reactions in liquid phase, it is necessary to develop new experimental techniques that will allow operando spectroscopy and transient studies of liquid phase heterogeneous catalytic reactions. Essential for such technique is a reactor module. Chromolith HPLC column (Merck) [1] with sihca foam in a polymer cartridge is suitable as a reactor for transient experiments because the high surface area silica foam can act as support with relatively low pressure drop. However, thermal stability of this HPLC column is limited to low temperatures because of the polymer housing (<150°C). It is... 

The main part of the book then concerns the science of defoaming. The general properties of foams are presented in an introductory chapter, which serves as a background to much that follows. Another chapter describes the experimental techniques involved in measurement of the foam properties relevant for study of antifoam action and the various techniques used in establishing the mode of action of antifoams. Various aspects of antifoam behavior and relevant theory are considered in later ehapters. 

Foam fractionation is a relatively inexpensive technique for protein separation. Most studies in the literature are, however, experimental and very few report on industrial appUcations. Among other appUcations, foam liaclionation has been used to separate wheat flour proteins, ovalbumin, lysozyme, egg albumin, milk proteins (e.g., beta-casein, bovine lactoferrin, bovine serum albumin, alpha-lactalbumin, and beta-lactoglobulin) and potato protein from potato juice waste water after starch extraction (Weijenberg et al., 1978 Keller et al., 1997 Hossain and Fenton, 1998 Brown et al., 1999 Wang and Liu, 2(X)3 Wang etal., 2009). 

This method gained a significant improvement with the introduction of the contemporary infrared technique with a Fourier transformer (FT-IR), permitting to obtain measurable values of adsorption of the infrared light even from single black foam films. The thickness of the aqueous core is derived from the adsorption at 3400 cm 1 which is related to the OH stretching vibration of the water molecules. Umemura et al. [114] have employed the polarised Fourier transformed infrared spectra for the study of the water content of NaDoS black films. The cell used to form films of ca. 2 cm2 area is illustrated in Fig. 2.19. By fitting the calculated curved of polarised FT-IR spectra to the respective experimentally obtained... 

The method of equilibrium foam film allows to study the ( -potential at various aspects by means of the microinterferometric technique (see Chapter 2). For instance, to determine cpo at electrolyte solution/air interface (no surfactant) which is very hard to realise experimentally to find the origin of the surface charge in this case [186,187] to find the isoelectric points at the solution/air interface [173,188] to study the effect of the concentration of various kinds of surfactants [95,100,189,190] ionic effects influence of Na+... 

A systematic experimental study was performed to clarify further the role of the entry barrier in the foam destruction by oil-based antifoams. The critical capillary pressure, P, which leads to rupture of the asymmetric oil-water-air film (formed between a pre-emulsified oil drop and the solution surface) and to subsequent drop entry, was measured by the film trapping technique (Fig. 2)—for brevity, is denoted as the entry bar-... 

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