Higher surfactants

In comparison to U.S. wash conditions, European wash conditions are characterized by higher temperatures, higher surfactant concentrations, and longer agitation times. These differences as well as differences in washing machine design require more control of foam in European formulations than in U.S. formulations. 

Thus, the enhancement of heat transfer may be connected to the decrease in the surface tension value at low surfactant concentration. In such a system of coordinates, the effect of the surface tension on excess heat transfer (/z — /zw)/ (/ max — w) may be presented as the linear fit of the value C/Cq. On the other hand, the decrease in heat transfer at higher surfactant concentration may be related to the increased viscosity. Unfortunately, we did not find surfactant viscosity data in the other studies. However, we can assume that the effect of viscosity on heat transfer at surfactant boiling becomes negligible at low concentration of surfactant only. The surface tension of a rapidly extending interface in surfactant solution may be different from the static value, because the surfactant component cannot diffuse to the absorber layer promptly. This may result in an interfacial flow driven by the surface tension gradi-... 

Because the inverse Debye length is calculated from the ionic surfactant concentration of the continuous phase, the only unknown parameter is the surface potential i/io this can be obtained from a fit of these expressions to the experimental data. The theoretical values of FeQx) are shown by the continuous curves in Eig. 2.5, for the three surfactant concentrations. The agreement between theory and experiment is spectacular, and as expected, the surface potential increases with the bulk surfactant concentration as a result of the adsorption equilibrium. Consequently, a higher surfactant concentration induces a larger repulsion, but is also characterized by a shorter range due to the decrease of the Debye screening length. 

In the Will case, provided that there is enough surfactant but not too much, e.g., 1 wt. %, the system splits into three phases, i.e., a microemulsion in equilibrium with excess water and excess oil. At a higher surfactant concentration than the top vertex of the 3

single phase microemulsion often called WW behavior is attained. However, this occurrence generally requires a large amount of surfactant, e.g., 20 wt. %, which is in most practical cases too much for cost reasons. At a very low surfactant concentration, around the CMC, only two phases are in equilibrium, and the tension is not necessarily very low. Hence, the convenient surfactant concentration to carry out a phase behavior study is in the range 0.5-3 wt. % for which three-phase behavior and a very low inter facial tension is exhibited in most Will cases. 

Micelles are spontaneously formed by most surfactants (especially single-chained ones) even at fairly low concentrations in water, whereas at higher surfactant concentrations, with or without the addition of an oil (e.g. octane) or co-surfactant (e.g. pentanol), a diverse range of structures can be formed. These various structures include micelles, multibilayers (liquid crystals), inverted micelles, emulsions (swollen micelles) and a range of microemulsions. In each case, the self-assembled structures are determined by the relative amounts of surfactant, hydrocarbon oil, co-surfactant (e.g. pentanol) and water, and the fundamental requirement that there be no molecular contact between hydrocarbon and water. 

I % Tolutein added (6) 2% Tolutein added. Note that all surfactants could decrease the fibrousness of the protein matrix. This effect became more significant at higher surfactant concentrations. P, protein C, insoluble carbohydrate. 

Thus it appears justified to expect that this technique will prove invaluable for investigations of nonpolar detergent solutions and even more for the study of phase transitions (at higher surfactant concentrations). 

Regioselectivity of aromatic bromination of co-phenylpolyoxaalkanols in aqueous solutions of SDS or CTAB are related to the concentration of the surfactant. At equal detergent/substrate ratio para bromination is preferred, and at higher surfactant concentration ortho bromination is promoted. These results are attributed to the orientation of the substrates in the micellar microenvironment which is also supported by -NMR studies1018. 

The pzc is marked in Fig. 8 for photoresist layers processed with < 80% and > 100% of the threshold dose. For the latter, the pzc is about one order of magnitude higher than for unexposed photoresist, i.e. a higher surfactant concentration is necessary to neutralize the acid groups... 

Another feature of the study by Penfold et al. [74] was that the polyDMDAAC layer is robust, and not removed by surfactant. However, in contrast, in other cases [76, 78, 80], desorption of the polymer is observed at higher surfactant concentrations. 

The high homogeneity and rather well-defined character of those latexes is clearly observed. Again, already surfactant loads as low as 1.8% relative to the dispersed phase result in stable latexes. The particle size is getting smaller with increasing amounts of the surfactant, and the surface area per surfactant molecule Asurf is between 18 nm2 at low surfactant amounts (1.8 rel.%) and 7 nm2 for higher surfactant amounts (7.1 rel.%), depending on the particle size. 

The surfactants only slightly affect polystyrene incorporation up to the surfactant concentration where surfactant adsorption on the particles is maximal,54,76 that is 0.02 mol kg 1. At higher surfactant concentrations the amount of free surfactant that is surfactants not adsorbed on the particles... 

At higher electrolyte concentrations in the NaDoS solution, e.g. 0.35 mol dm-3 (curve 2, Fig. 3.77), formation of black spots is observed at higher surfactant concentrations which correspond to closer packing of the adsorption layer. Probably with the increase in electrolyte concentration the stabilizing ability of the electrostatic component of disjoining pressure decreases. 

A correlation between the formation of a liquid-crystalline phase in the foam (in borders and films) and its stability has been discussed in [60]. In this case the stabilising effect is observed at considerably higher surfactant concentrations and quite often, when there are two or more surfactants present in the foaming solution. 

It has been established [55] that hydrocarbon (decane, benzene) promoted foam breakdown, occurring with formation of unstable films (barrierless rupture), is only possible at very low surfactant concentrations (less than 0.003-0.004% saponin and OP-10). At higher surfactant concentrations the defoaming ability of the antifoam results from the lowering of the energy barrier of film rupture. The latter is determined by the properties of the adsorption layers and other film parameters. 

The results showed distinct and regular changes for the aqueous solubility region in pentanol surfactant mixtures. With increased electrolyte content, the "minimum amount of water for solubility was enhanced, the solubility limit towards the pentanol water axis was shifted to higher soap concentrations, and the "maximum solubility of the aqueous sodium chloride solution was obtained for higher surfactant alcohol ratios (Figure 2). 

Equation 4 predicts a square dependence of the energy on the electric potential of the interface of the inverse micelle. Addition of electrolyte will not change the surface potential much a slightly reduced stability may be expected. The higher surfactant alcohol ratio that was observed (Figure 2) will increase the surface potential. 

For the 1 M NaCl system the solubility region was further reduced. Fig. 13, and the water solubilization maximum found at even higher surfactant/cosurfactant ratio. The series with the lower ratios of surfactant to cosurfactant showed an uptake of the aqueous solution somewhat similar to the series in the system with 0.5 M NaCl. The series with the surfactant/(cosurfactant + surfactant) ratio equal to 0.4 gave an initial liquid crystal formation lasting for 2-3 days folllowed by a middle phase lasting a longer time. The liquid crystalline and the middle phase layer were both more pronounced for the sample with initial salt concentration equal in the water and in the microemulsion. Fig. 14A, than for the sample with all the salt in the water. Fig. 14B. 

A more rapid transport of the surfactant than the cosurfactant to the lower layers gives a higher surfactant/cosurfactant ratio in the aqueous part and vice versa in the upper layers. The result is compositions to the right of the straight line between water and the original microemulsion composition for the lower layers and a corresponding deviation to the left of the line for the upper layers. 

A position to the right of the microemulsion area means the presence of a lamellar liquid crystal as has been repeatedly demonstrated by Ekwall (19). The temporary appearance of liquid crystals when W/0 microemulsions are brought into contact with water have, with this result, been given a satisfactory explanation. The faster transport of the surfactant into the aqueous layers gives rise to temporarily higher surfactant concentrations and the stability limits for the water rich W/0 microemulsions phase are exceeded towards the liquid crystalline phase in water. 

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