Surfactant solutions size distribution

Some of the reports are as follows. Mizukoshi et al. [31] reported ultrasound assisted reduction processes of Pt(IV) ions in the presence of anionic, cationic and non-ionic surfactant. They found that radicals formed from the reaction of the surfactants with primary radicals sonolysis of water and direct thermal decomposition of surfactants during collapsing of cavities contribute to reduction of metal ions. Fujimoto et al. [32] reported metal and alloy nanoparticles of Au, Pd and ft, and Mn02 prepared by reduction method in presence of surfactant and sonication environment. They found that surfactant shows stabilization of metal particles and has impact on narrow particle size distribution during sonication process. Abbas et al. [33] carried out the effects of different operational parameters in sodium chloride sonocrystallisation, namely temperature, ultrasonic power and concentration sodium. They found that the sonocrystallization is effective method for preparation of small NaCl crystals for pharmaceutical aerosol preparation. The crystal growth then occurs in supersaturated solution. Mersmann et al. (2001) [21] and Guo et al. [34] reported that the relative supersaturation in reactive crystallization is decisive for the crystal size and depends on the following factors. 

The Microtrac-XlOO (a laser particle size analyzer) was used to determine the size distribution of the powder. The method is based on a liquid mode of operation, that is before laser scanning, the powder is added to a solution of deionized water, containing a surfactant. 

Microemulsions are a convenient medium for preparing microgels in high yields and rather uniform size distribution. The name for these special emulsions was introduced by Schulman et al. [48] for transparent systems containing oil, water and surfactants, although no precise and commonly accepted definitions exist. In general a microemulsion may be considered as a thermodynamically stable colloidal solution in which the disperse phase has diameters between about 5 to lOOnm. 

An aqueous dispersion of a disperse dye contains an equilibrium distribution of solid dye particles of various sizes. Dyeing takes place from a saturated solution, which is maintained in this state by the presence of undissolved particles of dye. As dyeing proceeds, the smallest insoluble particles dissolve at a rate appropriate to maintain this saturated solution. Only the smallest moieties present, single molecules and dimers, are capable of becoming absorbed by cellulose acetate or polyester fibres. A recent study of three representative Cl Disperse dyes, namely the nitrodiphenylamine Yellow 42 (3.49), the monoazo Red 118 (3.50) and the anthraquinone Violet 26 (3.51), demonstrated that aggregation of dye molecules dissolved in aqueous surfactant solutions does not proceed beyond dimerisation. The proportion present as dimers reached a maximum at a surfactant dye molar ratio of 2 5 for all three dyes, implying the formation of mixed dye-surfactant micelles [52]. 

An interesting method to produce water-soluble iridium nanoparticles was proposed by Chaudret and coworkers [13]. Here, aqueous soluble iridium nanoparticles were synthesized by the chemical reduction of iridium trichloride with sodium borohydride in an aqueous solution of the surfactant N,N-dimethyl-N-cetyl-N-(2-hydroxyethyl)ammonium chloride (Scheme 15.2). The precursor reduction was assisted by sonication, while the gradual conversion of Ir(lll) ions to lr(0) nanoparticles was followed using UV spectroscopy. The use of a molar surfactant Ir ratio of 10 proved sufficient to obtain stable aqueous soluble iridium nanoparticles however, if the molar surfactant Ir ratio used was <10 then agglomeration was observed in solution after several days. TEM analysis of the iridium nanoparticles revealed a monodispersed size distribution and a mean diameter of 1.9 0.7nm (Figure 15.2). 

In another communication using w/o microemulsions containing a nonionic surfactant, it is shown that TEOS hydrolysis and siUca-particle growth occur at the same rate, indicating the growth of siUca particles is rate-controlled by the hydrolysis of TEOS [54], The rate of TEOS hydrolysis also depends on the surfactant concentration, which controls the molecular contact between hydroxyl ions and TEOS in solution. Because of the reaction-controlled growth mechanism, the silica-particle size distribution remains virtually same over the growth period. 

The procedure to fabricate colloidal silver, (Ag°) , spherical nanoparticles is similar to that already described (see Section 9.3.3) The Cu( AOT)2 is replaced by the silver derivative. The relative concentration of Na(AOT), Ag(AOT)2, and the reducing agent remain the same. Control of the particle size is obtained from 2 nm to 6 nm (67). To stabilize the particles and to prevent their growth, 1 p.l/mL of pure dodecanethiol is added to the reverse micellar system containing the particles. This induces a selective reaction at the interface, with covalent attachment, between thio derivatives and silver atoms (68). The micellar solution is evaporated at 60°C, and a solid mixture of dodecanethiol-coated nanoparticles and surfactant is obtained. To remove the AOT and excess dodecanethiol surfactant, a large amount of ethanol is added and the particles are dried and dispersed in heptane. A slight size selection occurs, and the size distribution drops from 43% to 37%. The size distribution is reduced through the size selected precipitation (SSP) technique (38). 

Emulsions made by agitation of pure immiscible liquids are usually very unstable and break within a short time. Therefore, a surfactant, mostly termed emulsifier, is necessary for stabilisation. Emulsifiers reduce the interfacial tension and, hence, the total free energy of the interface between two immiscible phases. Furthermore, they initiate a steric or an electrostatic repulsion between the droplets and, thus, prevent coalescence. So-called macroemulsions are in general opaque and have a drop size > 400 nm. In specific cases, two immiscible liquids form transparent systems with submicroscopic droplets, and these are termed microemulsions. Generally speaking a microemulsion is formed when a micellar solution is in contact with hydrocarbon or another oil which is spontaneously solubilised. Then the micelles transform into microemulsion droplets which are thermodynamically stable and their typical size lies in the range of 5-50 nm. Furthermore bicontinuous microemulsions are also known and, sometimes, blue-white emulsions with an intermediate drop size are named miniemulsions. In certain cases they can have a quite uniform drop size distribution and only a small content of surfactant. An interesting application of this emulsion type is the encapsulation of active substances after a polymerisation step [25, 26]. 

From this description a well-defined critical concentration emerges as that total amphiphile concentration corresponding to a transition from the monotonic decreasing size distribution function to a size distribution function exhibiting two extrema. This critical concentration corresponds to a surfactant solution with no appreciable amount... 

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