ABSTRACT
Nanoparticles meet the need for materials with specifi c physical, chemical, and electronic properties by virtue of their size-dependent properties [1-5]. Consequently, ability to control particle size is considered an essential aspect of a nanoparticle preparation technique. (w/o) Microemulsions have been extensively used to prepare different types of nanoparticles [4-13]. These systems
17.1 Introduction ............................................................................................ 465 17.2 Nanoparticle Uptake in Reactive Surfactant Systems ............................ 467 17.2.1 Particle Formation Mechanism.................................................. 467 17.2.2 Effect of Mixing ........................................................................ 468 17.2.3 Effect of Temperature ................................................................ 468 17.2.4 Effect of Surfactant Concentration ............................................ 470 17.2.5 Effect of Water to Surfactant Mole Ratio, R ............................. 471 17.2.6 Effect of Cosurfactant ............................................................... 471 17.3 Nanoparticle Uptake in Nonreactive Surfactant Systems ...................... 472 17.3.1 Particle Formation Mechanism .................................................. 473 17.3.2 Effect of Reactant Addition Sequence ....................................... 474 17.3.3 Effect of Mixing Time ............................................................... 474 17.3.4 Effect of Surfactant Concentration ............................................ 474 17.3.5 Effect of Water to Surfactant Mole Ratio, R.............................. 476 17.3.6 Effect of Initial Precursor Salt Concentration ........................... 477 17.4 Conclusions ............................................................................................. 478 Symbols and Terminologies .............................................................................. 479 References ......................................................................................................... 479
provide good control over particle size and produce highly homogeneous particles, due to their effi cient mixing at the molecular level [14-18]. Moreover, (w/o) microemulsions were employed to form core-shell and onion-structured nanoparticles [19], which fi nd applications in catalysis. Particle size manipulation in these systems is achieved by controlling some microemulsion and operating variables [4,8,20-28]. The effect of a given variable is, however, dependent on the reactant addition scheme [20,21,26-28]. Two reactant addition schemes have been identifi ed in the literature: the mixing of two microemulsions and the single microemulsion schemes. The fi rst scheme involves adding the precursors to two identical (w/o) microemulsions followed by mixing the microemulsions. This mode of preparation typically limits rapid reactions of nanoparticle formation to the rate of opening of the surfactant surface layer [7,8,29,30]. Slow rate of successful collisions leads to simultaneous nucleation and growth and produces large and polydispersed particles [29]. This, in turn, limits the ability to control particle size. The review by Eastoe et al. [20] reported on the sometimes confl icting trends found in the literature on the effect of a given microemulsion or operating variable on the fi nal particle size. The single microemulsion scheme, on the other hand, involves sequential addition of precursors to the same microemulsion. This mode of reactant addition allows for intramicellar nucleation and growth, thus reduces the impact of intermicellar nucleation and growth on the fi nal particle size. A review of trends in nanoparticle size in response to changes in microemulsion and operating variables has been recently communicated by Husein and Nassar [26]. It is worth noting that the use of microemulsions with reactive surfactants, functionalized surfactants, is more common in the single microemulsion scheme. The single microemulsion scheme requires the use of lesser microemulsion volumes and is more suited for in situ preparation of nanoparticles [21,22,31-33].
