Interaction with Other Surfactant

This much stronger interaction of geminis with other surfactants in mixed monolayers than in mixed micelles means that there is a strong possibility of 

TABLE 12-2 Interaction Parameters of Gemini Surfactants with Conventional Surfactants at 25° C 

C10H21C6H3(SO Na+)OC6H4SO Na+-C12H25(OC2H4)7OH 0.1 MNaCl -1.8 -0.9 Rosen, 1993b 

C10H2iC6H3(SO3-Na+)OC6H5A 14H29N(CH3)2O, pH = 5.8 0.1 MNaCl -4.7 -3.2 Rosen, 1993b 

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This greater interaction of the betaine with anions than with cations is seen also in its interaction with other surfactants (17)... 

Betaines are zwitterionic at neutral and alkaline pHs. At acidic pHs, below the isoelectric point, they are strictly cationic. They are generally compatible with both anionic and cationic surfactants except at low pHs, where they are incompatible with anionic surfactants. The most interesting properties of betaines are derived from their strong interactions with other surfactants, in particular anionics. Studies on reported synergistic properties of betaines and anionics have been published by Rosen and coworkers. When betaines are used as a secondary surfactant with anionic surfactants, the mildness, foaming, and viscosity properties of the formulation are all improved. 

Like a conventional surfactant such as SDS, amino acid-based surfactants can interact with other surfactants, solvents, electrolytes, polymers, proteins, and membrane of cells to show specific behavior. In view of the unique structure of amino acids, where an amino group and a carboxyl group are combined in one molecule, the interaction of amino acid-based surfactants with other ingredients is of great interest to fundamental study and practical applications. 

Based on the surface property data discussed earlier, methyl ester ethoxylates would be expected to perform similarly to alcohol ethoxylates, which is indeed the case. As shown in Fig. 13, methyl ester ethoxylates are comparable to alcohol ethoxylates, as well as other commonly used surfactants (see Table 1), in their ability to remove soil from fabric. Compositional variables affect the performance of methyl ester ethoxylates and alcohol ethoxylates. Lauryl range and tallow range methyl ester ethoxylates provide the best detergency, while optimal ethylene oxide content appears to depend on soil/ cloth-type (Fig. 14). Interaction with other surfactants also affects detergency performance. As shown in Fig. 15, methyl ester ethoxylates act synergistically with alcohol ethoxylates, while the opposite can be observed with alcohol sulfate and alcohol ether sulfate. 

An interesting by-product of this study was some insights into the effect of multiple ether linkages in the molecule on interfacial properties and interactions with other surfactants [13]. The molecules under investigation have the structures shown in Fig. 3. Those with multiple ether linkages in the molecule showed a smaller increase in their interaction with an amine oxide with a decrease in the pH of the system than molecules without multiple ether linkages. Data are shown in Table 8. 

Although these examples demonstrate the feasibility of using calculated values as estimates, several constraints and assumptions must be kept in mind. First, the diffusant molecules are assumed to be in the dilute range where Henry s law applies. Thus, the diffusant molecules are presumed to be in the unassociated form. Furthermore, it is assumed that other materials, such as surfactants, are not present. Self-association or interaction with other molecules will tend to lower the diffusion coefficient. There may be differences in the diffusion coefficient for molecules in the neutral or charged state, which these equations do not account for. Finally, these equations only relate diffusion to the bulk viscosity. Therefore, they do not apply to polymer solutions where microenvironmental viscosity plays a role in diffusion. 

Both the N- (a-methylbenzy 1) stearamide and phospholipid systems as detailed above proved to be difficult systems with which to work. The inability of N- a-methylbenzy 1)stearamide to form stable monolayers or even to spread from the crystal on anything but very acidic subphases presents a significant technical challenge despite the presence of a chiral headgroup that is unobstructed by other molecular features. On the other hand, the phospholipid surfactants that spread to form stable films both from solution and from their bulk crystals on pure water subphases at ambient temperatures displayed no discernible enantiomeric discrimination in any film property. The chiral functionality on these biomolecules is apparently shielded from intermolecular interactions with other chiral centers to the extent... 

Interaction with other biological surfactants might add to clearance and lipoplex inactivation. Size of the particles plays a major role because extensive microvasculature of the lung leads to pulmonary clearance of larger particles by capillary bed deposition. Vascularization was identified as the main... 

The energetically unfavorable interactions of the hydrophobic tails with the water molecules are then minimized by the surfactants forming aggregates with other surfactant molecules. In those aggregates, the hydrophilic headgroups remain solvated by water molecules while the hydrocarbon moieties are shielded from water and create a hydrophobic microenvironment. Examples of these spontaneously formed aggregates are micelles and lamellae. The intersection of the extrapolations of the linear parts of the surface tension curve (Figure 17.2) is the critical micelle concentration (CMC). 

The basis for separation employing micellar mobile phases stems from their ability to differentially solubilize and bind structurally similar solutes. Skeptics view MLC as a fascinating example of the incorporation of secondary equilibria for control or adjustment of retention (101). However, it is the ultimate of secondary equilibria since the types of interactions possible with micellar aggregates cannot be duplicated by any single other equilibrium system, or for that matter, any one or mixture of traditional normal or reversed phase mobile phase systems. This is due to the fact that solutes can interact with the surfactant aggregates via hydrophobic, electrostatic, hydrogen bonding, and/or a combination of these factors. 

In sections 7.3.1-7.3.4 we have considered only relatively simple dilute emulsions. Many pharmaceutical preparations, lotions or creams are, in fact, complex semisolid or stmc-tured systems which contain excess emulsifier over that required to form a stabilising mono-layer at the oil/water interface. The excess surfactant can interact with other components either at the droplet interface or in the bulk (continuous) phase to produce complex semisolid multiphase systems. Theories derived to explain the stability of dilute colloidal systems cannot be applied directly. In many cases the formation of stable interfacial films at the oil/water interface cannot be considered to play the dominant role in maintaining... 

Use of Nanoparticles, Instead of using reactive precursors that undergo reactions converting them to the final inorganic material, nanometer sized particles of final inorganic materials can themselves be used as the precursors. These particles will be inert, in that they will not interact with each other, but their interaction with the surfactants will allow formation of ordered mesostructure. 

Surfactants may be included in an ophthalmic suspension to disperse the drug effectively during manufacture and in the product during use. Non-ionic surfactants are generally preferred because they tend to be less toxic. The level of surfactant included in the formulation should be carefully evaluated, as excessive amounts can lead to irritation in the eye, foaming during manufacture and upon shaking the product, or interactions with other excipients. The most likely interaction is with the preservative. For example, polysorbate 80 interacts with chlorobutanol, benzyl alcohol, parabens and phenyl ethanol and may result in a reduced preservative effectiveness in the product. 

In works/ the formation of the supramolecular systems based on branched and hydrophobized (alkyl-substituted) PEIs is revealed in both the absence and presence of cationic surfactants including those with hydroxyalkylated head groups. The latter are capable of specific interactions with other components of the systems, in particular, polymer and reagents. Hydrophobization of PEIs is found to result in a sharp increase in their solubilizing and catalytic efficiency. Besides, a marked increase in the catalysis occurs on transfer from conventional cationic surfactants to hydroxyalkylated analogues. By means of the optimization of the catalytic composition and reaction conditions a substantial 7(X)-2(XX)-fold acceleration of the phosphonate 1 is reached at neutral pH. ... 

The presence of surfactants, besides altering the latex particle surface, can also interact with the water-soluble polymer. For instance, poly(ethylene oxide) homopolymer and block copolymers interact with sodium dodecyl sulfate surfactant [109], and hence alter the latex viscosity behaviour [110]. Other water-soluble polymers are also capable of interacting with specifle surfactants [111]. When pigmented latex dispersions are thickened with associative thickeners one must consider the interactions with some of the pigment stabilizers [112] and other additives, like coalescing aids [113]. 

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