ABSTRACT
Experimental Details . . . . . . . . . . . . . . . . . . . . . . . . 82
Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
Preparation and Characterization of Particles . . . 82
Microemulsion Characterization . . . . . . . . . . . . . 82
Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
Particle Characteristics . . . . . . . . . . . . . . . . . . . . . 82
Microemulsion Characterization . . . . . . . . . . . . . 83
Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
TEOS-Microemulsion System . . . . . . . . . . . . . . 85
Amphiphilic Nature of Hydrolyzed TEOS . . . . 85
Locale of Evolving Solid Particles . . . . . . . . . . 85
Distribution of Surfactant Molecules . . . . . . . . 85
Model of Particle Formation . . . . . . . . . . . . . . . . . 85
Particle Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Assessment of Particle Formation Mechanisms . . 87
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
The synthesis of nanometer-sized silica particles by the base-catalyzed, controlled hydrolysis of tetraethoxy-
silane (TEOS) in a nonionic reverse micellar system is described. Spectrofluorometric techniques were used
to characterize the reverse micellar solutions. Particle characterization was conducted by transmission
electron microscopy. The effect of the water-to-surfactant molar ratio (R) on particle size and size distri-
bution was investigated over a wide range of R values (0.50 to 3.54). Stable dispersions of amorphous
silica with mean particle diameters in the range of 46 to 68 nm were produced. Small (46 nm) and extremely
monodisperse particles (polydispersity below 4%) were obtained at intermediate R values (1.4), whereas
both particle size and polydispersity increased at lower and higher R values. The effects of R on particle
size and size distribution are discussed in terms of water “reactivity” (i.e., proportion of bound to free
water), concentration of reverse surfactant aggregates, distribution of hydrolyzed TEOS molecules
among aggregates, and dynamics of intermicellar matter exchange. A mechanistic model for particle
nucleation and growth in these systems is proposed.
