Microemulsions large-scale applications

Meanwhile, there are a variety of large-scale applications of microemulsion systems. Many products used in daily life contain micro emulsions or formulations which are able to form microemulsions (some prominent examples are discussed in Chapters 8 and 9 of this book). Concentrates, surfactants or surfactant mixtures which can be used for microemulsification are frequently applied. All these materials are produced and handled in large quantities. In particular, oil-in-water (o/w) droplet and water-in-oil (w/o) droplet microemulsions are found in many products or technical processes today. Whereas their usage is not very different from ordinary solvents in most cases, the use of bicontinuous microemulsions poses specific problems which will be discussed later on. 

For large-scale applications, microemulsions have often to fulfil further requirements which are not directly connected to the desired phase behaviour or the structure. Harmlessness, biocompatibility, biodegradability or long-term stability of all components maybe needed depending on the application. Inertness and tolerance to the contacted target materials is necessary. Last but not least, cost-effectiveness of the components also plays a very important role. 

The susceptibility of microemulsions to destabilization by electrolytes severely limits the highest metal concentrations that can be used for precipitation reactions. This, in turn, discourages the large-scale application of microemulsion-mediated materials synthesis. A possible approach to tackling this problem appears to lie in the judicious selection of cosurfactants for microemulsion formulations. Darab et al. [125] reported that addition of SDS to the AOT/isooctane/water microemulsion increased dramatically the tolerable concentration of metal salts in the water pools. According to Chhabra et al. [50], addition of -hexanol to the Triton X-lOO/cyclohexane/water microemulsion led to a significant improvement in the water-solubilizing capacity. 

The use of microemulsions in the context of washing and cleaning was recently reviewed [1]. There seem to be no reasons to believe that any fundamental new impact is needed in this area from a physicochemical point of view. Large-scale applications in the area of soil remediation can be expected in the near future. In this context it will be essential to estimate microemulsion formation, price, chemical performance, and mechanisms of retention (adsorption) on the solid material when designing these kinds of washing systems. Microemulsions for use in soil remediation have been summarized by Miller and coworkers [12,13] and Schwuger and coworkers [14,15]. 

Emulsifiers are used in many technical applications. Emulsions of the oil-in-water and the water-in-oil type are produced on a large scale in the cosmetic industry. Other fields of employment are polymerization of monomers in emulsions and emulsification of oily and aqueous solutions in lubricants and cutting oils. In enhanced oil recovery dispersing of crude oil to emulsions or even microemulsions is the decisive step. 

Chapter 11). I hope that these challenges will be dealt with and solved in the future so that microemulsions will be considered a versatile tool for all kinds of applications including sensitive cosmetic and pharmaceutical products, large-scale processes and the design of new composite materials. 

The synthesis approaches for fabrication of hollow spheres of different semiconductor materials through irradiation route in large scale and under mild conditions could be of interest for both applications and fundamental studies. Indeed, it has been found that the combination of ionizing radiation and microemulsion can afford more unique conditions to control the composition, morphology, and size of NPs. Compared with other routes of building hollow spheres, radiation chemical approach is a one-step facile and effective method and has potential to produce various inorganic/polymer nanocomposite hollow spheres with potential applications in the fields of materials science and biotechnology. 

Let us start the description of the principles with a simple case. Assume a dispersion of one solvent in another. If the (discrete) drops of the dispersed phase are large, i.e., considerably larger than the distance over which diffusion is monitored, then the self-diffusion of both components will be unrestricted on the relevant time scale and we will observe high D values for both solvents. In fact, except for an obstruction correction, which may amount to at most about 30%, the D values will be the same as for the neat solvents. If the diffusion distance and the drop sizes match each other, the observed diffusion will be critically dependent on the (variable) diffusion time chosen. These cases are not applicable to microemulsions but give the basis for a very important general and noninvasive technique of monitoring drop sizes (and fusion processes) in (macro)emulsions [13,20-27]. 

Modem scaling theory is also a powerful theoretical tool (applicable to liquid crystals, magnets, etc.) that has been well established for several decades and has proven to be particularly useful for multiphase microemulsion systems (46). Scaling theory relies on the hypothesis that diverse physical systems exhibit large compositional and density fluctuations and essentially behave the same near their critical points. Hence, the only factors that determine their critical properties are the dimensionality of the space and dimensionality of the order parameter. For example, the shape of the critical scaling theory. The temperature dependence is given by... 

---