Properties surfactant choice

Properties and other criteria influencing surfactant choice... 

Although many factors such as film thickness and adsorption behaviour have to be taken into account, the ability of a surfactant to reduce surface tension and contribute to surface elasticity is among the most important features of foam stabilization (see Section 5.4.3). The relation between Marangoni surface elasticity and foam stability [40-43] partially explains why some surfactants will act to promote foaming while others reduce foam stability (foam breakers or defoamers), and still others prevent foam formation in the first place (foam preventatives, foam inhibitors). Continued research into the dynamic physical properties of thin liquid films and bubble surfaces is necessary to more fully understand foaming behaviour. Schramm et /. [44] discuss some of the factors that must be considered in the selection of practical foam-forming surfactants for industrial processes. Sanders [45] provides a number of surfactant choices and formulation approached for the preparation of non-aqueous foam and non-aqueous aerosol foams. 

Economic considerations can often be almost as important as surface activity in selecting a surfactant for a given appUcation. Unless the cost of the surfactant is insignificant compared to the rest of the system, the least expensive material producing the desired effect will usually be chosen. Economics, however, cannot be the only factor in the choice, since the final performance of the system may well be of crucial importance. To make a rational selection, without resorting to an expensive and time-consuming trial-and-error approach, the formulator should have some knowledge of (1) the surface and interfacial phenomena that must be controlled (2) the characteristic chemical and physical properties of the available surfactant choices (3) the relationships between the structural properties of the available surfactants and their effects on the pertinent interfadal phenomena (4) any restrictions to the use of available materials, as in, for example, foods, cosmetics, or pharmaceuticals and (5) economic constraints on the choice of surfactant. 

Acrylic-Latex Properties. The choice of acrylic latex is critical to obtaining true contact adhesive performance. The first criterion is that the latex and phenolic must yield a stable blend when combined directly, with pH modification, or with the aid of additional surfactants. The properties of the acrylic resin particles then become important A latex resin which is too hard and/or does not properly coalesce may never develop contact tack in the course of drying a latex resin which is too soft may exhibit tack even when fully dry, but may not have adequate cohesive strength for most applications. 

A Dispersion Resins for dear Applications One of tbe problems with the surfactant coatings normally found on dispersion resins is that they ereate issues with clarity. There are dispersion resins available that use low levels of eare-fuUy chosen surfactants to yield clearer products than those made from typieal dispersion resins. Although careful surfactant choice can help minimize the issues associated with reduced surfactant levels on dispersion resins, plastisols based on these resins are mote likely to require other formulation additives to achieve desired rheological properties than typical plastisol resins. 

The characteristic chemical and physical properties of the available surfactant choices... 

Many different combinations of surfactant and protective coUoid are used in emulsion polymerizations of vinyl acetate as stabilizers. The properties of the emulsion and the polymeric film depend to a large extent on the identity and quantity of the stabilizers. The choice of stabilizer affects the mean and distribution of particle size which affects the rheology and film formation. The stabilizer system also impacts the stabiUty of the emulsion to mechanical shear, temperature change, and compounding. Characteristics of the coalesced resin affected by the stabilizer include tack, smoothness, opacity, water resistance, and film strength (41,42). 

Block copolymers possess unique and novel properties for industrial applications. During the past 20 years, they have sparked much interest, and several of them have been commercialized and are available on the market. The most common uses of block copolymers are as thermoplastic elastomers, toughened thermoplastic resins, membranes, polymer blends, and surfactants. From a chemist s point of view, the most important advantage of block copolymers is the wide variability of their chemical structure. By choice of the repeating unit and the length and structure of both polymer blocks, a whole range of properties can be adjusted. 

The composition of choice would therefore contain SAI as the primary surfactant, a binder to ensure sufficient bar cohesiveness, and various other ingredients to modify bar properties as needed [6]. 

Physical properties of the protein structure should be considered in designing strategies to achieve stable formulations because they can often yield clues about which solution environment would be appropriate for stabilization. For example, the insulin molecule is known to self-associate via a nonspecific hydrophobic mechanism66 Stabilizers tested include phenol derivatives, nonionic and ionic surfactants, polypropylene glycol, glycerol, and carbohydrates. The choice of using stabilizers that are amphiphilic in nature to minimize interactions where protein hydrophobic surfaces instigate the instability is founded upon the hydro-phobic effect.19 It has already been mentioned that hydrophobic surfaces prefer... 

The formation of cellular products also requires surfactants to facilitate the formation of small bubbles necessary for a fine cel] structure. The most effective surfactants are polyoxyalkylene-polysiloxane copolymers. The physical properties of polyurethanes are derived from their molecular structure and determined by the choice of building blocks as well as the suprainolecular structures caused by atomic interaction between chains. The ability to crystallize, the flexibility of the chains, and spacing of polar groups are of considerable importance, especially in linear thermoplastic materials. In rigid cross-linked systems, e.g., polyurethane foains, other factors such as density determine the final properties. 

The choice between the static methods (Wilhelmy plate method and the du Noiiy ring method) should primarily be based on the properties of the system being studied, in particular, the surfactant. As mentioned in UNITD3.5, the transport of surfactant molecules from the bulk to the surface requires a finite amount of time. Since static interfacial tension measurements do not yield information about the true age of the interface, it is conceivable that the measured interfacial tension values may not correspond to equilibrium interfacial tension values (i.e., the exchange of molecules between the bulk and the interface has not yet reached full equilibrium and the interfacial tension values are therefore not static). If the surfactant used in the experiment adsorbs within a few seconds, which is the case for small-molecule surfactants, then both the Wilhelmy plate method and the du Noiiy ring method are adequate. If the adsorption of a surfactant requires more time to reach full equilibrium, then the measurement should not be conducted until the interfacial tension values have stabilized. Since interfacial tension values are continuously displayed with... 

Critical micelle concentrations can be determined by measuring any micelle-influenced physical property as a function of surfactant concentration. In practice, surface tension, electrical conductivity and dye solubilisation measurements (see Figure 4.13 and page 90) are the most popular. The choice of physical property will slightly influence the measured c.m.c., as will the procedure adopted to determine the point of discontinuity. 

Sulphosuccinates are prepared using a wide variety of alcohols and the choice of alcohol is a major determinant of the properties of the surfactant. In some instances, the consumers view of what materials are acceptable limits the choice of alcohol source with one example of this being the preference for oleochemical alcohols for personal care applications. 

Composition vs. properties. One of the key properties of a soap, key to determining applications, is solubility. As with other surfactants, the solubility of the soap is dependent upon the carbon chain distribution, which is, in turn, determined by the choice of raw material oils. C12-14 gives a more soluble soap with very high foam generation whereas Ci8+ soaps have much reduced solubility. The use of unsaturated acids, such as oleic, gives improved solubility compared to the saturated equivalents and, where high solubility is required, potassium salt or an amine salt may be used instead of sodium salt. 

There is a vast body of diblock copolymer studies since block choice can be such that they resemble amphiphilic surfactants. For the sake of brevity, we will skip them. Instead, we present an interesting case of triblock copolymers of poly(ethylene oxide), PEO, and poly(propylene oxide), PPO, commonly known by one of its trade names, Pluronics [117]. They have been used as non-ionic surfactants for a variety of applications such as in emulsification and dispersion stabilization. In aqueous solutions, these copolymers form micelles, and there exists a well-defined critical micelle concentration that is experimentally accessible. Several groups have investigated colloidal suspensions of these polymers [118-122], The surface properties of the adsorbed monolayers of the copolymers have been reported with respect to their structures and static properties [123-126]. 

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