Surfactants alkyl chains

FIG. 4 Onion model of spherical water-containing reversed micelles. Solvent molecules are not represented. A, surfactant alkyl chain domain B, head group plus hydration water domain C, hulk water domain. (For water-containing AOT-reversed micelles, the approximate thickness of layer A is 1.5 nm, of layer B is 0.4 nm, whereas the radius of C is given hy the equation r = 0.17R nm.)... 

Also, the segmental mobility and preferential conformation of surfactant alkyl chains is perturbed by water addition [92,99]. 

By and NMR, the occurrence of conformational changes of the AOT molecules with R has been emphasized [13]. An increase of the lateral packing order of the surfactant alkyl chains located in the micellar palisade layer due to water addition has also been pointed out by FT-IR [58,92]. 

Fig. 4.6 Correlation of relative dynamic surface pressures with foam kinetics data dh/dt as a function of the type of surfactant, alkyl chain length and salt concentration [47],...

The intermicellar potential, deduced from Baxter model, decreases with the number of carbon atoms (25). This has been explained in term of solvent penetration bulk solvent molecules having a small number of carbon atoms penetrate easily in the surfactant alkyl chains, which are then well solvated. This induces a decrease in the intermicellar interactions. The increase in the number of carbon atoms of the bulk solvent induces a decrease in the solvation of the surfactant and then an increase in the intermicellar attractive potential. 

Measurement of K for NBF from solution of four homologues of the cationic surfactants alkyltrimethylammonium chlorides [488] indicated that K decreased with increasing surfactant alkyl chain length. 

Shin, M., Barrington, S. F., Marshall, W. D., and Kim, J. W. (2005). Effect of surfactant alkyl chain length on soil cadmium desorption using surfactant/ligand systems. Chemosphere 58(6), 735-742. 

In an analogous approach to those discussed above, Klok, Mezzenga, and co workers prepared bioinspired complexes by ionic complexation of hyperbranched polypeptides and surfactants [113] that lead to columnar hexagonal or lamellar mesophases, as a function of surfactant alkyl chain length [113]. 

Since cannot exceed the extended length of a surfactant alkyl chain,... 

Fig. 5 Residence time 7r of surfactants in micelles. Variation with the carbon number m of the surfactant alkyl chain for sodium alkylsulfates (A), potassium alkylcarboxylates (O).and alkylpyridinium chlorides ( ). Reproduced from Ref. [26].

Lindell, K. and Engstrom, S., Investigation of surfactant alkyl chain length and counterion effects on the thermogelling EHEC system, Int. J. Pharm., 124, 107-118 (1995). 

Since Rmic cannot exceed the extended length of the surfactant alkyl chain, /max = 1.5+ 1.265 c we find that is less than or equal to 1/3 for a spherical... 

In the presence of a polymer, the surfactant chemical potential is lowered with respect to the situation without polymer (Figure 20.6). There are several interactions which can be responsible for surfactant binding or a polymer-induced micellization. We note that in many respects (variation with surfactant alkyl chain length, solubilization, micelle structure and dynamics) there is a close similarity to the micellization of the surfactant alone. The normal hydrophobic interaction between the alkyl chains must therefore still be a dominating contribution to the free energy of association. However, it is modified by mainly one of the following two factors. 

The extent of phase separation in the system shown in Figure 20.21 increases strongly with the surfactant alkyl chain length and polymer molecular weight. On addition of electrolyte, the phase separation is eliminated, but at higher electrolyte content there is a phase separation again. However, as we can see in Figure 20.22, it is of a different nature. This behaviour, which is... 

DEL DeLisi, R., Lazzara, G., Milioto, S., and Muratore, N., Thermodynamics of aqueous poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)/surfactant mixtures. Effect of the copolymer molecular weight and the surfactant alkyl chain length, J. Phys. Chem. B, 108, 18214, 2004. 

The recommendation to use the same column with the same surfactant was done because, in some instances, it may be impossible to fully remove the surfactant-adsorbed layer. It was not possible to eliminate a small part of SDS adsorbed on a 1980 Hypersil ODS phase even when using a pure methanol mobile phase [8]. However, a complete SDS desorption from a 1988 Hypersil ODS phase was possible with a pure methanol mobile phase [24]. Part of the nonionic Brij 35 surfactant could not be removed from a Resolve C18 phase after a 24-hour elution of water-acetonitrile 70-30% v-v [16]. Conversely, there are many examples where the surfactant layer can be completely stripped off the stationary phase [11, 19, 21, 24]. It was suggested that partial irreversible surfactant adsorption was due to a tight insertion of the surfactant alkyl chains in the alkyl moieties of the bonded layer of densely grafted phases [35]. A column could be used with different... 

The striking difference of behavior between SDS and TTAB as far as changes of CMC and 3 are concerned suggest that the polymer-surfactant interaction occurs at the level of the surfactant ionic head group and does not involve the surfactant alkyl chain. This is turn means that the penetration of the polymer in the micelle will be restricted to the head group region, with little if any at all, penetration of the polymer in the micelle hydrophobic interior. Thus, the polymer surfactant interaction can be looked at as an adsorption of the polymer chain on the micelle surface. ... 

Fig.4a XRD pattern of Mo-oxide surfactant Fig.4b Dependence of the (001) d-spacing synthesised with hexadecyltrimethyl- on the surfactant alkyl chain length...

Fig. 3 Aggregates obtained in F127/SDS mixtures (redrawn after [68]). The hydrophobic PPO part interacts with the surfactant alkyl chains...

The aforementioned group has also studied the interaction of amphiphilic diblock copolymers with surfactants carrying the same charge as the polyelectrolyte block [123]. The ionic block in this study was poly(A/-alkyl-4-vinylpyridinium bromide) and the cationic surfactants added were CTAB, DTAB, CPB, and DPB. It was shown that the surfactants form different structures with the charged amphiphilic diblock copolymers. The type of structure formed depends on the surfactant concentration. At low surfactant concentration (hydrophobic clusters are formed that consist of the surfactant alkyl chains and the hydrophobic block of the copolymer. At high surfactant concentration, a change in complexation character is reported [123]. 

Fig. 3.7.1 Variation of (a) surface tension % and (b) critical surface tension 7c of surfactant treated glass surfaces with increasing carbon content of the surfactant alkyl chain, (a) Surface tension Jb for substrates with n-alkyl monoamine layers [6]. (b) Critical surface tension for substrates with n-alkyltrimethylammonium bromide layers [7].

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