Silicone surfactants Microemulsions

Kumar, A., Uddin, H., Kunieda, H., Furukawa, H. and Harashima, A. (2001) Solubilization enhancing effect of A-B-type silicone surfactants in microemulsions. /. Dispersion Sci. Technol, 22(2-3), 245-53. 

Silicone oils with amino groups have also been solubilized in ionic surfactant microemulsions [58]. Organic bases such as pyridine, picoline, isoquinoline, and piperidine have been solubilized in anionic and cationic microemulsions [59], as well as dialkyl phthalate ester oil [60] or diesel oil [61], but no EACN value was reported. 

Solubilization enhandng effect of A-B-type silicone surfactants in microemulsions. /. Dispersion Sci. Technol, 22, 245-253. 

As for direct emulsions, the presence of excess surfactant induces depletion interaction followed by phase separation. Such a mechanism was proposed by Binks et al. [ 12] to explain the flocculation of inverse emulsion droplets in the presence of microemulsion-swollen micelles. The microscopic origin of the interaction driven by the presence of the bad solvent is more speculative. From empirical considerations, it can be deduced that surfactant chains mix more easily with alkanes than with vegetable, silicone, and some functionalized oils. The size dependence of such a mechanism, reflected by the shifts in the phase transition thresholds, is... 

Silica Nanoparticles. The base-catalyzed hydrolysis of silicon aikoxides in microemulsions produces nanoparticles (20-39). Aqueous ammonia has been used primarily as the base, with AOT and nonionic polyoxyethylene ethers as the main surfactants. Figure 2.2.6 presents a flow diagram for the synthesis of pure silica (23-32) the microemulsion is first prepared and then the alkoxide is added. As can be seen from Table 2.2.1, the microemulsions include the systems AOT/ isooctane/water/ammonia, AOT/toluene/water/ammonia, NP-5/cyclohexane/water/ ammonia, and NP-4/heptane/water/ammonia. Typical reaction times are l -5 days. Various modified silica nanoparticles have also been prepared, including hydropho-... 

Our synthesis is based on the hydrolysis of a silicon alkoxide (TEOS Si(OCH2CH3)4) in a diluted solution of nonionic polyethylene oxide-based surfactants. The hydrolysis is then induced by the addition of a small amount of sodium fluoride [5], Depending on the initial mixing conditions, the size of the solubilized objects leads to either a colorless or milky emulsion. Small particles ( 300 nm) with a 3D worm-hole porous structure or small hollow spheres with mesoporous walls, are usually obtained [6]. The synthesis we report herein after exhibits an apparently slight but actually drastic change in the preparation conditions. The main feature of this approach is an intermediate step that utilizes a mild acidity (pH 2 - 4), in which, prior to the reaction, a stable colorless microemulsion containing all reactants is... 

All these techniques can be combined to obtain more precise control over several scales, as done by Stucky et al. to create hollow microcavities in mesoporous silica. In order to do that, the inorganic precursor (silicon alkoxide) was dissolved in the oil droplets of a regular (not inverse) microemulsion, while the surfactants were in the aqueous phase. Both the mesopore (produced by the surfactant) and microcavity (formed by the oil droplets) sizes could be controlled by varying the... 

Mixtures of low molecular weight silicon-based surfactants and cosurfactants have been used to prepare a self-dispersing microemulsion of silicone agents applied to building materials to impart water repellency [54, 55]. The structure of the surfactants used was not disclosed but they are described as being themselves reactive so that they bind to the surfaces of the building materials and become part of the water-repellancy treatment. 

Like the alkane solvents discussed previously, CO2 is a poor solvent for nonvolatile hydrophilic molecules. Some enhancement in hydrophile solvation was achieved by addition of cosolvents such as methanol and of complexing agents such as tri- -butyl phosphate [8,54]. Chelating agents have been designed with tails that have highly favorable interactions with CO2, such as fluoroethers and silicones [55]. A much wider range of hydrophilic compounds could be solubilized with surfactants that form reverse micelles and microemulsions in CO2 with polar or aqueous cores. However, extremely few commercial surfactants have tails compatible with the weak van der Waals forces of CO2. This limitation has made the formation of reverse micelles and microemulsions in CO2 more difficult than was the case for the alkane solvents discussed in the previous sections. 

As a solution-based materials synthesis technique, the microemulsion-mediated method [10-18] offers the unique ability to effect particle synthesis and particle stabilization in one step. The solubilized water droplets serve as nanosize test tubes, thus limiting particle growth, while the associated surfactant films adsorb on the growing particles, thereby minimizing particle aggregation. The purpose of this chapter is to review the literature on the microemulsion-mediated synthesis of metal hydroxides and oxides the definition of a metal is extended here to include the semimetal silicon. Since metal oxides are frequently produced by decomposing metal salts, aspects of the literature on microemulsion-derived metal salts are also considered. In principle, any previously established aqueous precipitation chemistry can be adapted to the microemulsion synthesis technique. Accordingly,... 

Silicone emollients are often used in skin products such as moisturizers and antiperspirants because of their ease of spreading and nonoily feel. In addition, the volatile cyclomethicones can provide a cooling sensation as they evaporate after application. Microemulsions can be formed by using nonionic alkoxylated surfactants or dimethicone copolyol surfactants as shown in Table 15. 

PDMS oil/water emulsions have been stabilized by adsorbing hybrid silox-ane polymers at the droplet surface. Examples of such additives are PDMS backbones with side chains consisting of trimethylene spacers ending with amino groups, methylated amino groups, acid groups, or an ethylene oxide decamer. Microemulsions have also been prepared directly from silicone oil with an anionic/nonionic surfactant mixture. ... 

Wolf, L. Hoffmann, H. Watanabe, K. Okamoto, T., Microemulsions from Silicone Oil with an Anionic/Nonionic Surfactant Mixture. Phys. Chem. Chem. Phys. 2011,13, 3248-3256. 

Nonionic surfactants with sugar hydrophilic groups -alkylpolyglucoside surfactants - are highly hydro-philic, and form temperature-insensitive microemulsions upon addition of alcohol (47, 48), as do sucrose ester surfactants (49). Zwitterionic surfactants such as lecithins also form microemulsions upon the addition of cosurfactant (50-52). In addition, trisiloxane surfactants microemulsify silicon oils (53), and fluorocarbon-tailed surfactants microemulsify fluorinated oils (54, 55). 

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