Surfactants, effects increased drag

Amine oxide zwitterionics are not strongly DR effective. At low temperatures oleyl dihydroxyethyl amine oxide (OHAO) shows weak drag reduction from 5 to 15°C. At high temperatures, behenyl dihydroxyethylamine oxide (BMAO) is weakly DR from 60 to 80°C. However, when 2-lauryl carboxymethyl hydroxyethyl imidazolium betaine was added to OHAO at a ratio of 1 to 1.5, at 15°C DR was increased from 55% to 70%. The surfactant also increased drag reduction from 10% to 88% at 80°C when added to BMAO [Nobuchika et al., 2000]. 

Anionic Surfactants Early studies by Savins [1967] showed that sodium oleate soaps with potassium hydroxide and potassium chloride in aqueous solution had good DR effectiveness. Increasing the concentration of KCl from 5% to 10% gave better drag reduction results. Unfortunately, the soaps precipitate and are ineffective as DRAs in the presence of calcium ions, which are present in most aqueous systems. Solutions of anionic surfactants such as SDS and SDBS are not drag reducing. Little research on anionics as DRAs has been carried out. 

Apart from an increased drag force, high gas volume fractions can also lead to occurrence of coalescence and breakup of bubbles. Although the closures derived for these kinds of phenomena are rather mature for droplet-droplet interactions, this is not the case for bubble—bubble interactions. The main reason is probably the role of surfactants, which can have a considerable effect on the rigidness of the bubble surface and hence on the processes occurring on that scale. Given the fact that many closures were derived for water-air systems makes things worse, as the water quahty and in... 

Oral dosage forms may contain various other additives to increase the solubility and hence oral bioavailability of the drag, such as co-solvents, buffers and surfactants. Newer technologies may also incorporate additives such as enzyme inhibitors, to prevent premature degradation of enzymatically labile drags. For example, the inclusion of trypsin inhibitors, such as soyabean trypsin inhibitor and aprotinin, have been shown to be effective in enhancing the effect of insulin in rats. Penetration enhancers may also be included to facilitate the uptake of poorly absorbed moieies. These are discussed below in Section 6.7.4. 

Fig. 8 shows DR vs. of a typical DR cationic surfactant with counterion solution, Ci7H35N(CH3)3Cl/ 3,4-Cl-benzoate (5mM/12.5mM). Drag reduction reaches a maximum of 65%. In the effective temperature range (15-85°C), DR first increases with Arc until a critical Arc (critical wall shear stress) is reached above which it begins to lose its DR ability because of the... 

If the concentration of surfactant is uniform at the interface, the effect is a uniform decrease in surface tension, which may generally change the bubble shape (because of an increase in the capillary number) but otherwise has no influence on the bubble dynamics or on the hydrodynamic drag. The fact is, however, that the surfactant concentration at... 

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