Dimethyl dodecylamine oxide micelles

To provide a specific example, Imae and Ikeda (ref. 479) state that amine oxide is very hydrophilic and can constitute a good polar head group for nonionic surfactants at neutral pH. Dimethyl-dodecylamine oxide was first prepared by Hoh et al. (ref. 494), and its surface-active properties in aqueous solutions were investigated by measurements of surface tension (ref. 495), light scattering (ref. 496-498), and hydrodynamic properties (ref. 499). It was found that dimethyldodecylamine oxide can form only spherical micelles in water and aqueous NaCl solutions, when the micelle concentration is dilute (ref. 496,498). Similarly, the homolog dimethyltetradecylamine oxide forms only spherical micelles in water (ref. 496). 

The exponent b depends also on the polyelectrolyte linear charge density p and on the polyelectrolyte stiffness [130], which make it a nonuniversal characteristic for the used polyelectrolytes. Typically, polyelectrolytes with smaller p reveal a stronger dependence of <7 on The polyelectrolyte-sphere binding affinity was shown to decrease with the polymer persistence length and to increase with the polyelectrolyte linear charge density. Note that for complexation of polyelectrolytes of different p with the spherical dimethyl dodecylamine oxide (DMDAO) micelles, a modified dependence on the critical micelle charge density has been suggested, namely cT(. [128]. 

The solubilizing capacity of micelles and microemulsions prepared using the surfactant N,N-dimethyl-dodecylamine-N-oxide (C12AO), and containing either one of two semipolar ethyl ester oils (i.e., EH or EO) for the poorly water soluble, lipophilic steroidal drug, testosterone enanthate, has been determined recently (Barlow, D.J. Lawrence, M.J. Zuberi, T. Zuberi, S. Heenan, R.K. Personal communication, 2005). 

The coalescence of hydrocarbon chains allows the ordered hydration layers to be expelled into the bulk phase, resulting in a considerable net gain in entropy. Indeed, micelle formation is primarily an entropy-driven process the enthalpy of hydrocarbon association is comparatively weak and can even be endothermic (opposing association). As an example, dimethyl-n-dodecylamine oxide (illustrated in Fig. 2) undergoes or free energy change of micellization of AG = —6.2 kcal/mol (a fairly typical value), of which the enthalpic contribution AH = 4-1.1 kcal/mol and the entropic contribution — T A S = -7.9 kcal/mol. 

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