DTAC

A surfactant solution is a mixture of DTAC (dodecyltrimethylammonium chloride) and CPC (cetyl pyridinium chloride) the respective CMCs of the pure surfactants are 2 X lO M and 9 x IO M (Ref. 140). Make a plot of the CMC for mixtures of these surfactants versus the mole fraction of DTAC. 

Toshima et al. obtained colloidal dispersions of platinum by hydrogen- and photo-reduction of chloroplatinic acid in an aqueous solution in the presence of various types of surfactants such as dodecyltrimethylammonium (DTAC) and sodium dodecylsulfate (SDS) [60]. The nanoparticles produced by hydrogen reduction are bigger and more widely distributed in size than those resulting from the photo-irradiation method. Hydrogenation of vinylacetate was chosen as a catalytic reaction to test the activity of these surfactant-stabilized colloids. The reaction was performed in water under atmospheric pressure of hydrogen at 30 °C. The photo-reduced colloidal platinum catalysts proved to be best in terms of activity, a fact explained by their higher surface area as a consequence of their smaller size. 

Since triplet N-methyl-phenothiazine reduces NOj, the redox potential of JmPT must be <-l V and has been estimated to be -1.8 V (20). The electron transfer rate observed for reaction 22 in aqueous DTAC micellar systems is 3.5xl03 M- s- and, thus, under the experimental conditions reported, about a factor of 10 slower than reaction 18. 

Materials. Sodium dodecylsulfate (SDS) and fully deuterated sodium dodecylsulfate (SDS-d ) were obtained from Sigma and Cambridge Isotope Laboratories respectively, and used as received. The cationic surfactants, dodecyltrimethylammonium chloride (DTAC), dodecyltrimethylammonium bromide (DTAB), and didodecyldimethylammonium bromide (DDAB) were purchased from Eastman Kodak, and purified by repeated recrystallization from an ethanol/acetone solvent pair. Even so, a small amount of surface active impurity was observed in surface tension plots for DTAC. The tetradecyldimethylamine oxide (C14AO) was a commercial sample (Ammonyx MO) obtained from Stepan (Control No. 533-30027). This sample is primarily C14AO, but also contains other chain length components. Sodium chloride (NaCl) was obtained from EM Science and used as received. Water was purified by a three stage Bamstead water purification system. 

The transition moment vector of va, S-O points between surfactant molecules, and is therefore extremely sensitive to surfactant-surfactant interactions. The enhanced perturbation of vas S-O indicates that the electrostatic interactions between the dissimilar headgroups reduces a0 sufficiently to "drive" rod micelle formation in mixtures of DTAC and SDS. 

Figure 9 Plot of the frequency dependence of the composite symmetric CH2 stretching band and micelle aggregation numbers (19) vs. mixed micelle composition in 0.3 M DTAC/SDS mixed micelles (T = 23°C). Reprinted from ref. 47. Copyright 1990 American Chemical Society.

Figure 13 Difference spectra in the S-0 stretching region for 10 wt.% C14AO/SDS mixtures (T = 20°C). Also pictured are difference spectra from DTAC/SDS mixed micelles, and SDS/NaCl mixtures, and the spectrum of SDS micelles in water (Reproduced with permission from ref. 49. Copyright 1990 Steinkopff Verlag).

FIGURE 2.7. VSFS spectra of four surfactants, each with an alkyl chain of 12 carbons, but with different headgroups. Each spectrum was obtained for a bulk concentration of 5.0 mM. Spectra acquired unda ssp polarization (a) SDS, (c) DDS, (e) DTAC and (g) DAC. Spectra acquired under sps polarization (b) SDS, (d) DDS, (f) DTAC and (h) DAC. From Ref. [37]. 

FIGURE 2.16. (a) VSF spectra of the CCI4/H2O interface at 292 nM aqueous phase concentration SDS. (b) VSF spectra of the CCI4/H2O interface with 399 nM aqueous phase concentration DTAC. 

SDS sodium dodecyl sulfate HDTC1 hexadecyltrimethylammonium chloride HDTBr hexadecyltrimethylammonium bromide Brij 35 polyoxyethylene (23) lauryl ether DTAC dodecyltrimethylammonium chloride TTAC1 tetradecyltrimethylammonium chloride HDPB hexadecylpyridinium bromide KDC potassium decanoate SPFO sodium perfluorooctanoate KTC potassium tetradecanoate... 

Pyrene can sensitize the photooxidation of 1,3-diphenylisobenzofuran (72) in DTAC micellar solutions 61>. The reaction involves sensitization of singlet oxygen by pyrene which diffuses into another micelle and reacts with (72). Indole and tryptophan, which also react with singlet oxygen, quench the above reaction in ethanol solutions. However, in micellar systems they enhance the rate of reaction. Because of the high local concentrations of the quencher, the pyrene excited state is quenched by indole and tryptophan which leads to the photooxidation of (72) by a Type I process. 

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