Surfactants CTAB

Figure 2.7. Force-distance profiles at different CTAB surfactant concentrations. Droplet radius = 98 nm. The continuous fines are the best fits obtained with Eqs. (2.14), (2.15) (for double-layer repulsion), and (2.17) (for depletion attraction). (Adapted from [22].)...

The latter indicates that some ions (in the present case, cations, Na+) are partially bound to the SDS-micelles, which results in a change in the slope of the conductivity of the solution. Similar behavior is observed for other ionic detergents such as cationic (CTAB) surfactants. 

It is noteworthy that the indenyl complex RuCl(ri -C9H7)(PPh3)2l4 provides an efficient catalyst precursor for the anti-Markovnikov hydration of terminal alkynes in aqueous media, especially in micellar solutions with either anionic (sodium dode-cylsulfate (SDS)) or cationic (hexadecyltrimethylammonium bromide (CTAB)) surfactants [38]. This system can be applied to the hydration of propargylic alcohols to selectively produce P-hydroxyaldehydes, whereas RuCl(Cp)(PMe3)2 gives a,P-unsat-urated aldehydes (the Meyer Schuster rearrangement products)(Scheme 10.8) [39]. 

The main properties of these materials were characterized by means of x-ray diffraction (Siemens D-500 with A.Cu radiation of 1.54 A), Transmission Electron Microscopy (Phillips-CM200) and N2 adsorption (Micromeritics ASAP-2000), 29Si-NMR(MAS). As the textural properties of the catalytic materials, for example the inner pore structure, is a key parameter for their performance, in the present work the N2 adsorption isotherms of the calcined mesoporous Si02-based solids were determined. The solids were prepared using different CTAB surfactant and some co-surfactants based in the light alcohols, i.e. MeOH, EtOH and PrOH. Thus, Figure 15.5 shows the isotherms of the mesoporous solids prepared with MeOH (co-surfactant). In all... 

Smith, D. K. and Korgel, B. A. (2008). The importance of the CTAB surfactant on the colloidal seed-mediated synthesis of gold nanorods. Langmuir 24 644-649. 

Table I shows the effect of various systems such as micelles, swollen micelles (achieved by adding hexanol to CTAB), microemulsion systems, vesicles formed from a double-chain CTAB surfactant, and reversed micelles with water cores formed with benzyl dimethylcetylammonium bromide in benzene. Hie active chromophore exists either as pyrene, pyrene sulfonic acid or pyrene tetrasulfonlc acid. Essentially the concept here is that the polar derivatives of pyrene will always locate pyrene at the surface of the micelle as these anionic species of pyrene complex with the positively charged surface. Dimethylaniline is used as an electron donor in each case, it can be seen that for pyrene, a continual decrease in the yield of the pyrene anion (ion yield of unity in the micelle) is observed on going from micelle to swollen micelle, to microemulsion, and no yield of ions is observed in a reversed micelle system. With pyrene tetrasulfonic acid the yield of ions over the different systems is fairly constant, even across to the reverse micellar system. However, the lifetime of the ions is extremely short in the reversed micellar system. An explanation for such behavior can be given as follows as we transverse across the...

Xiao[207] reported the preparation of ordered hexagonal mesoporous aluminosilicates (MAS-5) with uniform pore sizes from self-assembly of preformed aluminosilicate precursors with CTAB surfactant. The XRD pattern for a typical as-made MAS-5 sample shows four well resolved peaks that can be indexed as (100), (110), (200), and (210) reflections associated with the hexagonal symmetry. No diffraction peak was observed in the region of higher angles 10-40°, which indicates the absence of large... 

Because of a preferential binding to a single face of clusters, some surfactants are known (CTAB, cetylmethyl ammonium bromide, for example) to drive the growth of metal nanocrystals unidirectionally.Single monocrystalline Pt nanorods, monodisperse in diameter (3-4 nm) and 20-40 nm long, were recently obtained by orientated coalescence of spherical seeds of 3-4 nm radiolytically produced in the presence of CTAB surfactant [10] (Fig. 3g). 

Strong acidic and high temperature hydrothermally stable mesoporous aluminosilicates with well-ordered hexagonal structure (MAS-5) have been successfully synthesized from assembly of pre-formed aluminosilicate precursors with cetyltrimethylammonium bromide (CTAB) surfactant. The MAS-5 shows extraordinary stability both in boiling water (over 300 h) and in steam (800°C for 2 h). Temperature programmed desorption of NH3 shows that acidic strength of MAS-5 is much higher than that of MCM-41. 

MPc complexes have been employed as catalytic components in microemulsions and as composite films for the analysis of phenols and organohalides. Rusling and coworkers reported on FePc/DDAB, CuPc/DDAB, CuTSPc/DDAB, NiPc/DDAB, NiTSPc-DDAB, ZnPc/DDAB or ZnPc/CTAB surfactant films , and Jiang et al. on CoTSPc/DDAB for use in catalyzed reduction of trichloroacetic acid (TCA) and other organohalides. The catalytic reduction of TCA was more efficient in the acetonitrile/water solvent mixture than in the microemul-sions . Table 7.1 shows that lower potentials were observed for catalysis of TCA on surfactant films containing NiPc complexes than for the corresponding CuPc species. 

The structure of SDS and CTAB surfactant layer adsorbed on porous silica was studied by NMR. The C18 (Microsorb ODS, 5 pm, 6 nm pore diameter) and C8 (Microsorb) bonded phases were studied first [17]. The cyanopropyl bonded phase (Microsorb), was also studied [18]. Cross polarization (CP), magic angle spinning (MAS) with high power proton... 

As in the case of FAB-MS, the use of surfactants such as cetyltrimethylammonium bromide (CTAB) can be used to substantially or even completely suppress the matrix-related ion background [81]. Use of the CTAB surfactant also resulted in an improved mass resolution for low-molecular-weight molecules including amino acids, peptides, drugs, and cyclodextrins. This technique has been used successfully for the analysis of caffeine, and the vitamins riboflavin, nicotinamide and pyridoxine in various energy drinks [82]. 

Scheme 6.11 Electrodeposition of MWCNTs using CTAB surfactant, (a), (b) and (c) show the possible arrangements of CTAB on MWCNTs. (Reprinted from Ref. [149]. Copyright 2013 Elsevier Ltd.)...

Recently, MCM-48, with Ia3d symmetry and a three-dimensional pore structure, was also synthesized using silatrane as a silica precursor (Longloilert et al. 2011). This research focused on the effects of synthesis parameters, namely crystallization temperature and time, cetyl trimethylammonium bromide (CTAB) surfactant concentration, amount of NaOH, and silica source. The results revealed that all synthesis parameters affected the synthesis of MCM-48. Various techniques used for characterizing MCM-48 showed a long-range ordered structure with a truncated octahedral shape and a surface area as high as 1300 mVg with a pore size of 2.86 nm. 

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