Hydrogenous surfactant, dispersion

Fig. 2 shows a schematic of a set of contrast variation SANS experiments that could be performed to determine the detailed molecular architecture of a micelle, assuming that the various deuterated forms are available. Fig. 2A shows micelles formed from fully hydrogenous surfactant dispersed in D2O In this case, the information obtained from the SANS experiment is primarily about the whole micelle, i.e., its shape and size. Fig. 2B shows the micelles formed by the chain-deuterated version of the surfactant in D2O In this experiment, information is mainly obtained about the head group region (shell) of the micelle. Finally Fig. 2C shows the micelles formed from the chain-deuterated version of the surfactant in H2O In this case, information is obtained about the chain region of the surfactant. It is possible to simultaneously fit the SANS data obtained for these three systems to obtain a self-consistent, detailed picture of the size. 

Whatever the specific type, a valid question for all ordinary emulsions with or without surfactants is what is the maximum amount of the dispersed phase in the continuous phase when the former will still remain dispersed In other words, at what volume ratio does an inversion (i.e. OAV to W/O and the reverse) take place Emulsions for particle preparation are known to have been prepared where the volume ratio of the two phases can go up to near 1 1 [18]. In addition and contrast to this general idea about the relative contents of the two phases, one must also refer to the highly concentrated water-in-oil emulsions which can be prepared with a fluorinated surfactant and a fluorocarbon/hydrogenated surfactant (pronouncedly hydrophobic) and a hydrocarbon [19]. In these W/O emulsions, up to 98% w/w water is added, but inversion is never achieved. Highly concentrated W/O emulsions have also been described recently by Hakansson etal. [20] where the surfactant is of the alcohol ethoxylated type, the dispersed phase is aqueous in nature and the continuous phase, an aliphatic hydrocarbon. It has been indicated that such emulsions may contain more than 99% of the dispersed phase. These are, however, very special cases and do not demand further discussion here. Without going into specificities, let us look at the general factors that may influence inversion [3, 21, 22] ... 

Moreover, stable liquid systems made up of nanoparticles coated with a surfactant monolayer and dispersed in an apolar medium could be employed to catalyze reactions involving both apolar substrates (solubilized in the bulk solvent) and polar and amphiphilic substrates (preferentially encapsulated within the reversed micelles or located at the surfactant palisade layer) or could be used as antiwear additives for lubricants. For example, monodisperse nickel boride catalysts were prepared in water/CTAB/hexanol microemulsions and used directly as the catalysts of styrene hydrogenation [215]. 

AOT is an anionic surfactant complexed to the counterion, usually sodium. The water molecules in the intramicellar water pool are either free or bound to the interface. The bound water can interact with various parts of the surfactant. These interactions include hydrogen-bonding interactions with oxygen molecules on the sulfonate and succinate groups, ion-dipole interactions with the anionic surfactant headgroup and counterion, dipole-dipole interactions with the succinate group, and dispersive forces with the hydrocarbon tails. 

The formation of peroxides and formaldehyde in the high-purity polyoxyethylene surfactants in toiletries has been shown to lead to contact dermatitis [31], Peroxides in hydrogenated castor oil can cause autoxidation of miconazole [32], Oxidative decomposition of the polyoxyethylene chains occurs at elevated temperature, leading to the formation of ethylene glycol, which may then be oxidized to formaldehyde. When polyethylene glycol and poloxamer were used to prepare solid dispersions of bendroflumethiazide, a potent, lipophilic diuretic drug, the drug reacted with the formaldehyde to produce hydroflumethiazide [33],... 

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 the stability of CLAs displays a strong dependence on ionic strength, due to electrostatic interactions associated with the surfactant head groups, pH should also have an influence on CLA half-lives. The effect of continuous phase pH on the stability of CLAs dispersed in deionized water at 25°C was investigated by Lye and Stuckey [65]. Above a pH of 6-7, ti/2 values were essentially constant, but began to decline as the continuous phase became more acidic. At low pH values, the excess hydrogen ion concentration led to protonation of the sulfonate head groups of the SDS molecules located at the outer soapy-shell interface. This would have two... 

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