Synergistic interactions, surfactant

LDLDs are mixtures of surfactants. Surfactant mixtures often perform better than the sum of the individual surfactant contributions, or perform synergisti-cally. The origin of this synergistic interaction is head group interactions and is dipolar in nature. The surfactant pairs having the greatest dipolar forces have the... 

Mixtures of two or more different types of surfactants often show a synergistic interaction, i.e., the interfacial properties of the mixture are more pronounced than those of the individual components by themselves. As a result, in many industrial products and processes, mixtures of different types of surfactants, rather than individual materials, are used. A study of the adsorption of the individual surface-active components in the mixture and of the interaction between them affords an understanding of the role of each and makes possible the selection in a rational, systematic manner of components for optimal properties. 

The conditions for synergistic interaction between the two surfactants are discussed in Chapter 11. 

Binks BP, Rodrigues JA, Frith WJ (2007) Synergistic interaction in emulsions stabilized by a mixture of sflica nanoparticles and cationic surfactant. Langmuir 23(7) 3626-3636... 

Jenkins RD, Bassett DR. Synergistic interactions among associative polymers and surfactants. In Asua JM ed. Polymeric Dispersions Principles and Applications. Netherlands Kluwer Academic Publishers, 1997 477-495. 

The synergistic interactions of alkyl polyglycosides with the various primary surfactant systems enables the product developer to formulate even more effective products for the same active substance content or to reduce the active substance content without affecting the performance level (Fig. 23). 

The interest in mixed surfactant systems has theoretical as well as practical reasons. The realization that surfactants are used most often as mixtures has shifted research from pure surfactants to mixed systems. Industrial fluorinated surfactants are usually mixtures [62,63] because (1) they are synthesized as a mixture of isomers or telomers which are difficult to separate or (2) different surfactants are mixed to enhance the performance of the individual components by synergistic interactions. Some commercial fluorinated surfactants contain hydrocarbon-type surfactants which have been blended with the fluorinated surfactant to improve its performance. 

Xanthan exhibits an interaction with anionic surfactants (petroleum sulfate), which is a beneficial synergistic effect for mobility control in chemical-enhanced oil-recovery processes [1115]. 

LDAO/SDS Interaction. Mixing of cationic and anionic surfactant solutions results In the formation of a mixed species that Is more surface active than the Individual species. The enhanced synergistic effect has been explained (2,3) by showing that a close-packed adsorption of electroneutral R R takes place (R" " and R represent the long chain cation and anion respectively). In the case of Ci2 and C14-DAO, a 1 1 LDAO/SDS molar ratio produces a minimum In surface tension and Is accompanied by an Increase In pH In the bulk solution the association seems to be of the type R R", and the absence of visible precipitate may be attributed to the solubilization of the R R" complex In the solution. In the region where LDAO Is In excess, the structure Is probably [cationic (LDAOH ) anionic (SDS)] nonlonlc (LDAO), while [cationic (LDAOH anionic (SDS)] anionic (SDS) Is formed when SDS Is In excess. Equal molar concentration results In cationic (LDAOH ) anionic (SDS) complex which should favor precipitation. However, at pH >9, there Is no Indication of precipitation (even when the total solute concentration Is 0.35 M). When the pH Is below 9, then precipitation will take place. 

Surfactants used in practical applications essentially always consist of a mixture of surface-active compounds. Isomerically pure surfactants are often expensive to produce and generally have only a small potential advantage in performance over the less expensive surfactant mixtures. In many applications, mixtures of dissimilar surfactants can have superior properties to those of the individual surfactant components involved. These synergistic properties of surfactant mixtures have provided impetus for much of the research on interactions between surfactants. 

The second factor, namely the head group interaction, can also influence the surface properties of mixed surfactant markedly. In particular, anionic/catlonic surfactant mixtures exhibit the largest effect (17,18). In nonionic/anionic surfactant mixtures, synergistic effects can still take place to a significant extent, as revealed in Figure 3 (pH 10.9, nonionic amine oxide with anionic long chain sulfate), since insertion of nonionic surfactant molecules into an ionic surfactant molecular assembly minimises electrostatic repulsion (19). 

An improvement in foam stability was observed as R was increased to >0.15 (Figure 17). This was accompanied by the onset of surface diffusion of a-la in the adsorbed protein layer. This is significantly different compared to our observations with /8-lg, where the onset and increase in surface diffusion was accompanied with a decrease in foam stability. Fluorescence and surface tension measurements confirmed that a-la was still present in the adsorbed layer of the film up to R = 2.5. Thus, the enhancement of foam stability to levels in excess of that observed with a-la alone supports the presence of a synergistic effect between the protein and surfactant in this mixed system (i.e., the combined effect of the two components exceeds the sum of their individual effects). It is important to note that Tween 20 alone does not form a stable foam at concentrations <40 jtM [22], It is possible that a-la, which is a small protein (Mr = 14,800), is capable of stabilizing thin films by a Marangoni type mechanism [2] once a-la/a-la interactions have been broken down by competitive adsorption of Tween 20. 

Assemblies formed by the coadsorption of surfactants at the solid-liquid interface represent attractive model systems for probing the nature and strength of lateral interactions among surfactants. These studies reveal strong synergistic effects in... 

Recently, it has been found that aqueous solutions of two different hydrocarbon chain surfactants can also show superspreading on highly hydrophobic substrates (Rosen, 2002 Zhou, 2003). In these mixtures, the two different hydrocarbon-chain surfactants also interact to produce synergistic enhancement of the total surfactant adsorption at the hydrophobic solid-aqueous solution interface relative to that at the air-aqueous solution interface, and this is accompanied by an enhanced rate of reduction of the contact angle (Zhou, 2003). SF values for these mixtures are also listed in Table 6-3. 

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