Surfactants foam stabilising properties

Foam stabilising properties of surfactants determined by Foam Pressure... 

These two examples with the homologous series of alkylsulphonates and alkylsulphates indicate the undoubted advantages of Foam Pressure Drop Technique for determining the foam stabilising properties of surfactants. This technique allows to distinguish small differences in the foam stabilising ability of surfactants. 

Certain antifoams, for example, methyl or ethyl alcohols, when introduced in the foaming solution, affect indirectly the foam stabilising properties of the adsorption layers because they change either the surfactant solubility or its CMC. It has been established [39] that addition of antifoams (2-ethylhexanoI and tributyl phosphate) increases CMC. Schick and Fowkes [40] have observed a certain change in CMC of NaDoS when tetradecanol is added. If the compounds added improve the foaming ability (such as dodecylglycol ether and (3-hydroxyethyl laurylamide), CMC decreases. 

Industrially, silicone surfactants are used in a variety of processes including foam, textile, concrete and thermoplastic production, and applications include use as foam stabilisers, defoamers, emulsifiers, dispersants, wetters, adhesives, lubricants and release agents [1]. The ability of silicone surfactants to also function in organic media creates a unique niche for their use, such as in polyurethane foam manufacture and as additives to paints and oil-based formulations, whilst the ability to lower surface tension in aqueous solutions provides useful superwetting properties. The low biological risk associated with these compounds has also led to their use in cosmetics and personal care products [2]. 

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],... 

An actual overview on interfacial rheological properties of adsorbed surfactant layers stabilising foams and emulsions has been given by Malhotra Wasan (1988). The results of... 

Present in the papermaking process are air, water, and detrimental substances or surfactants that stabilise foam and entrained air. A fourth component that further enhances foam stabilisation is the presence of fines in the white-water system and papermaking process. Fines are finely divided particles that are often the result of the pulping or papermaking process, or they may be filler or pigment particles added to provide key paper properties. These particles tend to insert themselves between bubbles to interrupt the processes of foam or bubble destruction. 

The authors of this monograph consider reasonable to express foaming ability as the foam volume obtained from a known solution volume under defined conditions (temperature, surfactant concentration, mode of foam formation). As a more general characteristic of the ability of the surfactant solutions to form foams with a definite stability it is suitable to use the terms stabilising ability or foaming property. The volume of the foam obtained and its lifetime can serve as a qualitative measure for the latter. A more detailed estimation requires the use of a number of characteristics including drainage, internal foam collapse, etc. 

Before discussing the various forms of polymers which may be encountered it is pertinent to describe briefly the basic structure of water-based polymer dispersions(ll). The starting point is a monomer which forms droplets in water. Aqueous surfactants are adsorbed at the droplet surface to stabilise the emulsion before an initiator is added to cause polymerisation under controlled conditions of pressure, temperature and stirring rate. The latex is thus an aqueous dispersion of small discrete polymer particles to which is added a range of additives, such as coalescents, anti-foaming agents, bacteriocide and anti-oxidants, to improve shelf life and properties related to its end use. 

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