Most surfactant mixtures display synergistic physicochemical properties, which have led to their extensive application in various technologies. Aqueous mixtures of two oppositely charged surfactants, so-called catanionic surfactant mixtures, exhibit the strongest synergistic effect, which is manifested as high surface activity, enhanced adsorption and a low critical aggregation concentration. In addition, catanionic systems display rich phase behavior and a range of nano and microstructures, including small spherical micelles, rod-like micelles as well as open and closed bilayers (vesicles). The spontaneous formation of catanionic vesicles is of special interest due to their various applications in nanotechnology and pharmaceutical formulations. In this chapter, the properties of catanionic mixtures of amphiphilic molecules with advantageous properties are discussed. Since numerous papers dealing with catanionic mixtures of monomeric surfactants already exist, the aim of this chapter is to summarize recent progress in mixtures of structurally different surfactants. At the end of the chapter, special emphasis is placed on applications of catanionic mixtures.

Following the assumption that the crucial processes governing the formation, properties and evolution of the core(amorphous silica)@shell(organocations) nanoparticles take place during short-time, room-temperature (rt) stirring/aging of the homogeneous reaction mixtures (HmRMs) formed by hydrolysis of TEOS (tetraethyl orthosilicate) in solutions of Org(OH)n, we investigated these processes by various experimental methods (pH, ionic conductivity, 29 Si-NMR, dynamic light scattering and atomic force microscopy). The analysis of the data obtained by detail and careful investigation of the "model" HmRMs having the starting chemical composition: xTEOS:0.25TPAOH:20H2O (TPAOH = tetrapropylammonium hydroxide; x = 0.05 -1), offer some new elements for the understanding of the mechanisms of formation and rt evolution of the core@shell silica nanoparticles: (1) There is a resolute evidence of the formation of the stable, about 1.2 nm sized core(amorphous SiO2)@shell(TPA + ions) nanoparticles below the critical aggregation concentration (CAC). (2) Due to the intensive particulate processes (growth, aggregation, disaggregation, dissolution) which take place during the rt aging of the investigated HmRMs, the equilibrated core@shell silica nanoparticles do not exist as individual primary ones, but as the aggregates (about 2 nm to about 20 nm), composed of 1 -2 nm sized "primary" nanoparticles. (3) In spite of the most frequent meaning that the nanoparticle shell is composed of the "free" TPA + ions adsorbed on the surface of the nanoparticle core, the results of this study show that the nanoparticle shell can be formed mainly by attachment of the polysilicate anions (silicate oligomers), associated with TPA + ions, on the surfaces of the nanoparticles cores.

Self-assembly of organic molecules onto metallic surfaces is an efficient way to modify surface properties of metallic materials. The aim of this paper was to examine the possibility of improving the corrosion stability of copper nickel alloy in chloride environment by self-assembled films of palmitic and stearic acid. Electrochemical techniques such as potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used to determine the protective properties of the fatty acids films. Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and contact angle (CA) measurements were used to evaluate structural properties of the surface layers. It was found that even a small difference in a fatty acid chain length might have a strong effect on layer stability in aqueous medium.

Amorphous calcium phosphate (ACP) attracts attention as a precursor of crystalline calcium phosphates (CaPs) formation in vitro and in vivo as well as due to its excellent biological properties. Its formation can be considered to be an aggregation process. Although aggregation of ACP is of interest for both gaining a fundamental understanding of biominerals formation and in the synthesis of novel materials, it has still not been investigated in detail. In this work, the ACP aggregation was followed by two widely applied techniques suitable for following nanoparticles aggregation in general: dynamic light scattering (DLS) and laser diffraction (LD). In addition, the ACP formation was followed by potentiometric measurements and formed precipitates were characterized by Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The results showed that aggregation of ACP particles is a process which from the earliest stages simultaneously takes place at wide length scales, from nanometers to micrometers, leading to a highly polydisperse precipitation system, with polydispersity and vol. % of larger aggregates increasing with concentration. Obtained results provide insight into developing a way of regulating ACP and consequently CaP formation by controlling aggregation on the scale of interest.

Self-assembled mono-and multilayers of stearic acid have been examined as corrosion protection systems for copper-nickel alloy in 3% sodium chloride solution. We found that self-assembled multilayers of stearic acid provide more efficient and durable corrosion protection to copper-nickel alloy than just a single monolayer. Electrochemical techniques, such as potentiodynamic polarization and electrochemical impedance spectroscopy, were used to determine the protective properties of the stearic acids films. Sum frequency generation spectroscopy, atomic force microscopy, contact angle measurements and ellipsometry were used to evaluate structural properties and thickness of the surface layers. It was found that the increase of corrosion protection from mono-to multilayer films depends on the number of layers that are formed but also on their homogeneity.