Foam properties physicochemical

Since it is the properties of foams that determine their application in technological processes, it is reasonable to group foams and to establish the general principles of optimisation of foam properties, such as the conditions of foam formation, composition of the initial foaming solution, physicochemical parameters of the foam produced, etc. 

Foam films are usually used as a model in the study of various physicochemical processes, such as thinning, expansion and contraction of films, formation of black spots, film rupture, molecular interactions in films. Thus, it is possible to model not only the properties of a foam but also the processes undergoing in it. These studies allow to clarify the mechanism of these processes and to derive quantitative dependences for foams, O/W type emulsions and foamed emulsions, which in fact are closely related by properties to foams. Furthermore, a number of theoretical and practical problems of colloid chemistry, molecular physics, biophysics and biochemistry can also be solved. Several physico-technical parameters, such as pressure drop, volumetric flow rate (foam rotameter) and rate of gas diffusion through the film, are based on the measurement of some of the foam film parameters. For instance, Dewar [1] has used foam films in acoustic measurements. The study of the shape and tension of foam bubble films, in particular of bubbles floating at a liquid surface, provides information that is used in designing pneumatic constructions [2], Given bellow are the most important foam properties that determine their practical application. The processes of foam flotation of suspensions, ion flotation, foam accumulation and foam separation of soluble surfactants as well as the treatment of waste waters polluted by various substances (soluble and insoluble), are based on the difference in the compositions of the initial foaming solution and the liquid phase in the foam. Due ro this difference it is possible to accelerate some reactions (foam catalysis) and to shift the chemical equilibrium of some reactions in the foam. The low heat... 

In the present monograph, we have attempted to both explain and describe the processes running in the foams and their equilibrium properties on the basis of quantitative regularities of electrostatic, molecular, etc. interactions, physicochemical, hydrodynamic and other surface phenomena. However, considering the complex nature of foam properties, it has, understandably, proved impossible for a number of properties and processes, still awaiting quantitative explanation. 

The physicochemical characteristics of surfactants, such as adsorption, micelle formation, foam properties, and in vitro skin mildness, as well as the PBS in personal care products will be discussed. 

Alahverdjieva, V. S., Khr. Khristov, D. Exerowa, and R. MiUer. 2008. Correlation between adsorption isotherms, thin liquid films and foam properties of protein/surfactant mixtures Lysozyme/CIODMPO and lysozyme/SDS. Colloids Surf. A Physicochem. Eng. Aspects 323 (1-3) 132-138. 

An important application of foams arises in foam displacement, another means to aid enhanced oil recovery. The effectiveness of various foams in displacing oil from porous media has been studied by Shah and co-workers [237, 238]. The displacement efficiency depends on numerous physicochemical variables such as surfactant chain length and temperature with the surface properties of the foaming solution being an important determinant of performance. 

Because of their preferential use as detergents, the main interest in the physicochemical properties of the salts of a-sulfo fatty acid esters is related to their behavior in aqueous solution and at interfaces. In principle these are surface-active properties of general interest like micelle formation, solubility, and adsorption, and those of interest for special applications like detergency, foaming, and stability in hard water. 

The binding of fluorescent probes of different hydrophobicities can be used to compare the surface properties of proteins in relation to their physicochemical properties, such as foaming and emulsifying. CPA (cfr-parinaric acid) has been used to study eleven food-related proteins, and the results have been compared with theoretical models for predicting foam capacity (Arteaga and Nakai, 1993 also see... 

The properties of syntactic materials are influenced by several factors including the binder/filler ratio, the process and hardening conditions, and the physicochemical processes at the binder/filler interface 12,76,99). The best syntactic foams, at given apparent densities of 680-700 kg/m3, have a compression strength of 10 MPa, shear and tension elastic moduli of 2500—3000 MPa ultimate bending strengths of 40 to... 

Sucrose reacts with diisocyanates leading to polyurethanes, which are used as thermal insulating foams, notably in cars. Partially protected sucrose esters can be used for the synthesis of better-defined polymers (Scheme 46).265 A first step of hydroxypropylation is sometimes necessary to obtain sufficient miscibility with the diisocyanate derivative, as well as for tuning the physicochemical properties of the polyurethane foams.78,305,420... 

Some physicochemical properties and applications of oligomethylsiloxanes are given in Table 15. As seen from the table, PMS-300, PMS-400 and PMS-500 oligomethylsiloxane brands can be used as a basis in the production of mineral butters, anti-foaming and anti-adhesion emulsions. 

A simple and largely applied method for foam formation is dispersion of gas through porous plates (filters) placed at the lower parts of foam generation apparatus [5-10], This method is employed in flotation, in gas adsorption and dust collection in set-up with turbulent gas emulsion, and in the equipment for foam separation. The dispersity of a foam thus obtained depends on filter pore size or capillary diameter, hydrophility of the material used in the dispersion device construction, physicochemical properties of the foaming solution (surface tension, viscosity, surfactant concentration, etc.) and conditions of the dispersion process. 

A semi-quantitative estimation of the influence of the structural parameters and physicochemical properties of the foaming solution on the initial drainage rate can be obtained from the equation describing the drainage in a homogenous polyhedral foam, the liquid of which flows out only through the borders [7]... 

In order to develop efficient techniques for the preparation and application of foams in industry, agriculture, firefighting, etc., it is necessary to know the physicochemical parameters of surfactants and their relationship with the foam stabilising ability of the surfactant solutions. Usually the criterion of the surfactant foaming ability is the adsorption of these compounds at the solution/air interface and the related to it properties, such as decrease in surface tension, adsorption work, maximum adsorption T. [13,39,43]. CMC is often used as a characteristic of a foaming agent (if micellisation is possible in the surfactant solution). Parameters related to foam stability, such as foam lifetime and foam column height, are also employed [12,13,39],... 

A number of physicochemical constants are derived and used to characterise the foaming agents on the basis of the properties of microscopic foam films being the most appropriate foam model. The first place belongs to the surfactant concentration Cm at which black spots are formed in the film [43,67]. As already shown, this concentration is related to the sharp increase in foam stability. Each foaming agent is characterised by its Cu value which... 

These physicochemical constants deal with the properties of the foam films. The foaming agents can be described more fully by the parameters related to the foam itself, e.g. foam lifetime xp at constant pressure and the time of foam column destruction by a-particle irradiation Xm [17,75], Table 7.4 presents xp and Xr of various surfactants. 

The efficiency of antifoams depends not only on their physicochemical nature but also on their concentration, the way of introduction into the foam, the properties of the foaming solutions as well as many other factors. That is why the clarification of the mechanism of defoaming ability appears to be a complicate matter. Additional difficulties arise also from the fact that the reasons for foam stability still remain unclear even for simple systems (in the absence of antifoams). 

There lacks a unified concept about the defoaming mechanism. The major physicochemical properties of an antifoam determining its efficiency comprise its low solubility, high surface activity, ability to spread on the surface of the foaming solution and form a polymolecular film, etc. The influence of these properties on antifoam efficiency implies the existence of a number of mechanisms of defoaming. 

The physicochemical properties of foam and foam films have attracted scientific interest as far back as a hundred years ago though some investigations of soap foams were carried out in the seventeen century. Some foam forming recipes must have been known even earlier. The foundations of the research on foam films and foams have been laid by such prominent scientists as Hook, Newton, Kelvin and Gibbs. Hook s and Newton s works contain original observations on black spots in soap films. 

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