Dodecyl dimethyl amine oxide, surfactants

When the concentration of the added electrolytes is very high, the cmc values are decreased to values close to those of surfactants which are either zwitteripnic or nonionic. For example, at 25 °C, the cmc is 1.5 mM for n-dodecyl trimethylammonium ion in 0.5 M NaBr, 2.4 mM for n-dodecyl betaine, and 2.0 raM for n-dodecyl dimethyl amine oxide. 

Surfactants Ionic, anionic (e.g., sodium dodecyl sulphate, Cj2H250S03 Na ), cationic (e.g., cetyl trimethyl ammonium chloride, Ci,H33-N+(CH3)3C1-), zwitterionic [e.g., 3-dimethyldodecylamine propane sulphonate (betaine CJ2H25-N" (CH3)2-CH2-CH2-CH2-S03)], nonionic, alcohol ethoxylates C H2 +i-0-(CH2-CH2-0) -H, alkyl phenol ethoxylates C H2 +i-CgH4-0-(CH2-CH2-0) -H, amine oxides (e.g., decyl dimethyl amine oxide, C10H21-N ( 113)2 0), and amine ethoxylates. 

Amine oxides constitute another important class of nonionic surfactants. Examples of these surfactants include dimethyl dodecyl amine oxide (DMDAO) and cocoamidopropyl dimethyl amine oxide (CAPAO). This type of surfactant is nonionic at pHs above its pK and cationic below that point. When functioning as a nonionic, amine oxides have many useful properties. They interact strongly with anionics, which can result in performance benefits. Amine oxides help to mitigate anionic surfactant irritation, act as foam stabilizers, and can also function to improve grease removal. 

Ahphatic amine oxides behave as typical surfactants in aqueous solutions. Below the critical micelle concentration (CMC), dimethyl dodecyl amine oxide exists as single molecules. Above this concentration micellar (spherical) aggregates predorninate in solution. Ahphatic amine oxides are similar to other typical nonionic surfactants in that their CMC decreases with increasing temperature. 

A fascinating area is micellar autocatalysis reactions in which surfactant micelles catalyse the reaction by which the surfactant itself is synthesized. Thus synthesis of dimethyldoceylamino oxide (reaction between dimethyl dodecyl amine and H2O2) benefits from this strategy. Here an aqueous phase can be used and an organic solvent can be avoided. Synthesis of mesoporous molecular sieves benefit through micellar catalysis and silicate polymerization rates have been increased by a factor 2000 in the presence of cetyltrimethyl ammonium chloride (Rathman, 1996). 

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