Alkyl surfactant film

The i and j snbscripts correspond to the various system components (layered silicate s, alkyl surfactant film a, and polymer p) and the LW and AB superscripts to the nature of interactions (apolar LW and polar AB). These relations can be... 

Different surfactants are usually characterised by the solubility behaviour of their hydrophilic and hydrophobic molecule fraction in polar solvents, expressed by the HLB-value (hydrophilic-lipophilic-balance) of the surfactant. The HLB-value of a specific surfactant is often listed by the producer or can be easily calculated from listed increments [67]. If the water in a microemulsion contains electrolytes, the solubility of the surfactant in the water changes. It can be increased or decreased, depending on the kind of electrolyte [68,69]. The effect of electrolytes is explained by the HSAB principle (hard-soft-acid-base). For example, salts of hard acids and hard bases reduce the solubility of the surfactant in water. The solubility is increased by salts of soft acids and hard bases or by salts of hard acids and soft bases. Correspondingly, the solubility of the surfactant in water is increased by sodium alkyl sulfonates and decreased by sodium chloride or sodium sulfate. In the meantime, the physical interactions of the surfactant molecules and other components in microemulsions is well understood and the HSAB-principle was verified. The salts in water mainly influence the curvature of the surfactant film in a microemulsion. The curvature of the surfactant film can be expressed, analogous to the HLB-value, by the packing parameter Sp. The packing parameter is the ratio between the hydrophilic and lipophilic surfactant molecule part [70] ... 

What are typical values for the parameters k and kl The bending rigidity of surfactant films is typically of the order of 1-20 kBT at room temperature. Factors that reduce k are short alkyl chains, cosurfactants, double-chain surfactants with unequal chains, and cis-unsaturated bonds. For the saddle-splay modulus only few measurements have been done. It tends to be negative with an amount much smaller than the bending rigidity for the same system. 

A further complication arises when the surfactant is not confined to the surfactant films but has significant solubility in one of the solvents. This retards solvent diffusion due to solvation. The effect occurs in general for weakly amphiphilic, mainly short alkyl chain, surfactants. Another example is that of nonionic ethylene oxide (EO) surfactants, which have a relatively high monomer solubility in oil, especially at higher temperatures. 

The procedure of evaluating self-diffusion data in terms of microstructure is to calculate the reduced or normalized diffusion coefficient, D/Dq, for the two solvents. Do being the neat solvent value under the appropriate conditions. Here we also have to account for reductions in D resulting from factors other than microstructure, mainly solvation effects. As discussed above, solvation will lead to a reduction of solvent diffusion that is proportional to the surfactant concentration. Normally the correction has been empirical and based on diffusion studies for cases of established structure, notably micellar solutions. We need to distinguish between corrections due to polar head-water and alkyl chain-oil interactions. The latter have often been considered insignificant, but a closer analysis (either experimental or theoretical) is lacking. However, it is probably reasonable to assume, for example, that the resistance to translation is not very different in the lipophilic part of the surfactant film and in an alkane solution. (This is supported by observations of molecular mobilities of surfactant allQ l chains on the same order of magnitude as for a neat hydrocarbon.)... 

In we want to make a quantitative comparison with theory we have to specify in more detail where in the surfactant film, which has a finite thickness, we evaluate the curvature. For the nonionic surfactant of C12E5, it turns out that the interface separating oil and the alkyl chain of C12E5 from the ethylene oxide chain and water has an essentially invariant area, per molecule, independent of the curvature. It is therefore useful to define the curvature at this particular interface. 

A wide class of aiyl-based quaternary surfactants derives from heterocycles such as pyridine and quinoline. The Aralkyl pyridinium halides are easily synthesized from alkyl halides, and the paraquat family, based upon the 4, 4 -bipyridine species, provides many interesting surface active species widely studied in electron donor-acceptor processes. Cationic surfactants are not particularly useful as cleansing agents, but they play a widespread role as charge control (antistatic) agents in detergency and in many coating and thin film related products. 

Fuming sulfuric acid containing 10-60% sulfur trioxide hydrolyzes perfluoro-Af-alkylcyelic amines to perfluoro-Al-alkyl lactams. Mercuric sulfate acts as a Catalyst [JO, 31] (equation 33). The lactams ate highly reactive and can be used to prepare polymenc films and surfactants... 

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