CTAB films

The partial molecular areas of CTAB correspond to a parallel orientation of these molecules to the surface. This orientation occurs over a range of surface pressures which is larger for mixed films than for the pure CTAB films. 

Horseradish peroxidase myoglobin, hemoglobin SWCNT/ CTAB film on saturated calomel electrode H202 detector [116]... 

Mediator 9-phenylanthracene (9-PA) was used to reduce 4-bromobiphenyl in CTAB solutions on Hg electrodes [4, 30]. Voltammetry showed a large preconcentration of 9-PA in a thick film of CTAB on the Hg surface. Reduction of 9-PA at —2.2 V versus SCE gave the anion radical that was stabilized by the positively charged CTAB film. The observed k for reaction of 9-PA anion radical with 4-bromobiphenyl was 10 in 0.1 M CTAB compared... 

Other catalysts with E° values more positive than —2 V showed smaller rate enhancements because a thick CTAB film apparently does not form on Hg electrodes at these potentials. Negatively charged clays on electrode surfaces have been used to form films of cationic micelles on electrodes for organohalide reductions positive of—2 V. Details of these and other mediated reactions in micellar solutions are found in reviews [4, 30]. 

Nanoparticles of the semicondnctor titanium dioxide have also been spread as mono-layers [164]. Nanoparticles of TiOi were formed by the arrested hydrolysis of titanium iso-propoxide. A very small amount of water was mixed with a chloroform/isopropanol solution of titanium isopropoxide with the surfactant hexadecyltrimethylammonium bromide (CTAB) and a catalyst. The particles produced were 1.8-2.2 nm in diameter. The stabilized particles were spread as monolayers. Successive cycles of II-A isotherms exhibited smaller areas for the initial pressnre rise, attributed to dissolution of excess surfactant into the subphase. And BAM observation showed the solid state of the films at 50 mN m was featureless and bright collapse then appeared as a series of stripes across the image. The area per particle determined from the isotherms decreased when sols were subjected to a heat treatment prior to spreading. This effect was believed to arise from a modification to the particle surface that made surfactant adsorption less favorable. 

Grosso, D. Babonneau, F. Albouy, P. A. Amenitsch, H. Balkenende, A. R. Brunet-Bruneau, A. Rivory, J. 2002. An in situ study of mesostructured CTAB-silica film formation during dip coating using time-resolved SAXS and interferometry measurements. Chem. Mater. 14 931-939. 

Many reports are available where the cationic surfactant CTAB has been used to prepare gold nanoparticles [127-129]. Giustini et al. [130] have characterized the quaternary w/o micro emulsion of CTAB/n-pentanol/ n-hexane/water. Some salient features of CTAB/co-surfactant/alkane/water system are (1) formation of nearly spherical droplets in the L2 region (a liquid isotropic phase formed by disconnected aqueous domains dispersed in a continuous organic bulk) stabilized by a surfactant/co-surfactant interfacial film. (2) With an increase in water content, L2 is followed up to the water solubilization failure, without any transition to bicontinuous structure, and (3) at low Wo, the droplet radius is smaller than R° (spontaneous radius of curvature of the interfacial film) but when the droplet radius tends to become larger than R° (i.e., increasing Wo), the microemulsion phase separates into a Winsor II system. 

Spreading of an insoluble (or temporarily insoluble) surfactant monolayer effectively produces a two-dimensional surface phase. This thin molecular layer exerts a lateral film pressure , which can be simply demonstrated by covering a water surface with a uniform layer of finely divided hydrophobic talc and placing a droplet of surfactant solution (0.003M CTAB solution) in its centre. The effect of the film pressure of the spreading surfactant is dramatic, as seen in Figures 8.8 and 8.9. 

The beneficial effect of CTAB was to increase the deposition (film growth) rate due to the less electrostatic repulsion between N03 ions and the cathode after adsorbing CTA+ cations (anionic or nonionic surfactants did not show this effect). 

Fig. 3.27. Thickness of foam films from aqueous solution of CTAB containing 5-10-4 mol dm-3 NaCI ...

Fig. 3.27 depicts the h(Q dependence for foam films from CTAB in the presence of NaCI. In general, three states of the films were realised and observed with increasing CTAB... 

Fig. 3.28. -potential (DDL) vs. surfactant concentration for films from CTAB. 

Stratification of asymmetric aqueous films from NaDoS, CTAB and a commercial surfactant (alpha-olefin sulphonate) solutions at C > Ccmc on a decane substrate have been studied by Bergeron and Radke [236], They found three transitions by thickness in the metastable multilayer films. They observed also stratified CTAB aqueous films on glass. The n(/i) isotherms of stratified films were analysed considering also the oscillatory structural component of disjoining pressure. 

The value of the modulus of equilibrium elasticity of films from typical surfactants (NaDoS, CTAB) of thicknesses from 1 to 4 pm varies within the range of 10 to 60 mN m1. This correlates well with the theory [25]. 

Similar results were obtained for the influence of the film type in CTAB foams (Fig. 7.13). The comparison of the results derived by both techniques should be done at constant capillary pressure, here it is5.5-7.8103 Pa. 

The first results about foam electrokinetics have been reported by Sharovamikov [62,63]. An electroosmotic liquid transport is observed in foams from solutions of ionic surfactants (NaDoS, CTAB, PO-3A, etc.) and it is larger than in systems with solid capillaries (specific transport from 1.6-1 O 6 to 210 6 m3 C 1). The maximum electroosmotic pressure depends on the initial pressure in borders and reaches 1 Pa. The addition of dedecanol to the NaDoS solution sharply decreases the electroosmotic transport but increases the electroosmotic pressure. To reduce the influence of border and film non-homogeneity that originates in a static foam under gravity, the electrokinetic studies have been performed in an advancing foam [62]. The specific electroosmotic transport depends on the capillary pressure and reaches a maximum value at pg = 0.5 kPa. The streaming potential (up to 10 mV)... 

The most prevalent cationic surfactant used for mesoporous thin film synthesis is cetyltrimethylammonium bromide (CTAB). It is a large head group cationic surfactant and has been shown to produce 3-D cubic (Pm3n), 3-D hexagonal (P6 /mmc), and 2-D hexagonal mesostructures The resulting pore size of the... 

Cagnol, F. Grosso, D. Soler-Illia, G.J.D.A.A. Crepaldi, E.L. Babonneau, F. Amenitsch, H. Sanchez, C. Humidity-controlled mesostructura-tion in CTAB-templated silica thin film processing. The existence of a modulable steady state. J. Mater. Chem. 2003, 13 (1), 61-66. 

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