Surfactant length

Figure 1.22 This surfactant orientation is supported by the 4-spacing values that were obtained from transmission electron microscopy measurements. In (A) the first suggested orientation the surfactant length is 2.4 nm and in (B) another orientation the surfactant length is 1.85 nm. (Reproduced from ref. 49, with permission.)... 

Here, is the surfactant volume fraction and l = vja is the surfactant length, which is defined as the surfactant molecular volume divided by the average area a that the surfactant molecule occupies at the water-oil interface. 

Here, l — v /a is the surfactant length, where Vs is the molecular volume and a is the area which the surfactant occupies at the polar-apolar interface. For reverse structures, 0 in equations (17.3)-(17.5), should be replaced by —0w... 

The interparticle spacing in these arrays is known to be a function of the stabilizer, surfactant length, or polymer molecular weight [256,257]. 

This form is obeyed fairly well above x values of 5-10 dyn/cm in Fig. Ill-15c. Limiting areas or a values of about 22 per molecule result, nearly independent of chain length, as would be expected if the molecules assume a final orientation that is perpendicular to the surface. Larger A values are found for longer-chain surfactants, such as sodium dodecyl sulfate, and this has been attributed to the hydrocarbon tails having a variety of conformations [127]. 

After reviewing various earlier explanations for an adsorption maximum, Trogus, Schechter, and Wade [244] proposed perhaps the most satisfactory one so far (see also Ref. 243). Qualitatively, an adsorption maximum can occur if the surfactant consists of at least two species (which can be closely related) what is necessary is that species 2 (say) preferentially forms micelles (has a lower CMC) relative to species 1 and also adsorbs more strongly. The adsorbed state may also consist of aggregates or hemi-micelles, and even for a pure component the situation can be complex (see Section XI-6 for recent AFM evidence of surface micelle formation and [246] for polymeric surface micelles). Similar adsorption maxima found in adsorption of nonionic surfactants can be attributed to polydispersity in the surfactant chain lengths [247], Surface-active impuri-... 

An important application of foams arises in foam displacement, another means to aid enhanced oil recovery. The effectiveness of various foams in displacing oil from porous media has been studied by Shah and co-workers [237, 238]. The displacement efficiency depends on numerous physicochemical variables such as surfactant chain length and temperature with the surface properties of the foaming solution being an important determinant of performance. 

Molecular packing of surfactants in crystals has been reviewed at some length [1 ]. An almost universal factor... 

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