Surfactant interaction with abundant

This equation contains a single activity coefficient. However, as the activity of the surfactant anion is dominated by its interaction with the abundantly present Na ions and hence virtually constant, dlny. = 0. Hence,... 

Initially the surfactant monomers interact with the hydrophobic groups of the HM polymer, and at some surfactant concentration (CAC) the micelles can crosslink the polymer chains. At higher surfactant concentrations, the micelles, which are now abundant, will no longer be shared between the polymer chains, i.e. the cross-links are broken. These effects are reflected in the variation of viscosity with surfactant concentration for HM polymer (Figure 2.17). The viscosity of the polymer rises with increasing surfactant concentration, reaching a maximum at an optimum concentration (maximum cross-links) and then decreases with further increase of surfactant concentration. For the unmodified polymer, the changes in viscosity are relatively small. 

With mixed surfactants, the CMC of the mixed micelle varies according to the CMCs of the individual surfactants, and their proportions. Clearly, micelle composition varies with concentration since the micelles that form at lowest concentration are rich in the lowest-CMC surfactant, while the higher-CMC materials become more abundant in micelles as the overall concentration is increased. The detailed dependence of CMC values on mixed surfactant composition varies according to whether there are specific interactions between head-groups which lead to non-ideal mixing in the micelle. This applies particularly with mixtures of nonionic and ionic surfactants, and ionic surfactants of opposite charge. Various treatments are available to describe the behaviour (see Chapter 19), for example, as outlined in the text by Clint (3) (Chapters 5 and 6). 

Andrews and Larson coated black carbon particles with organic surfactants like Tween 80 or azelaic acid and observed an enhancement in the hygroscopicity of these ordinarily hydrophobic compounds [283], Knowing that these elemental carbon particles are quite abundant in the atmosphere, typically formed in combustion processes, this study is key in hying to understand how organic compounds on their surface can change their chemical and physical interactions in the atmosphere. 

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