Inorganic colloidal nanoparticles

A wide range of inorganics has been used as components in polymer composites. However, silica offers a broad and interesting variety of structural modifications such as layered silicates like montmorillo-nite, colloidal nanoparticles like Stoeber synthesis products or highly ordered archi-... 

Figure 13.7 shows schematically both ways of stabilizing colloidal nanoparticles. The stabilization using inorganic colloid method is limited to aqueous solutions and some polar protonic solvents. Due to the d3uiamic nature of the electrical double layer (EDL), these systems are extremely susceptible to environmental conditions (temperature, concentration, pH), reducing considerably its stability compared to other forms of stabilization. 

Use of the LbL technique is not restricted to the preparation of planar thin films. One of the most outstanding strategy modifications of the LbL technique involves assembly on colloidal particles followed by hollow capsule formation. For example, Caruso and co-workers reported the formation of hollow silica vesicles through LbL assembly on colloidal nanoparticle templates (Fig. 14). Polyelectrolytes and smaller silica particles were initially formed on a larger colloidal core, which was subsequently selectively destroyed. Calcination of the hybrid vesicles resulted in a hollow vesicle composed of silica. Formation of controlled organic-inorganic layer structures on colloidal particles by LbL assembly also provides media appropriate for investigation of fundamental phenomena. 

Hannisdal et al. [16] have studied the effects on the emulsion stability of the addition of silica particles, because their properties resemble those of natural inorganic colloids like clays. They coated some commercially available dry silica nanoparticles with heavy cmde oil components (asphaltenes and resins) to investigate the performance of these solids as stabilizers in water-in-model oil emulsions. 

The approaches used for preparation of inorganic nanomaterials can be divided into two broad categories solution-phase colloidal synthesis and gas-phase synthesis. Metal and semiconductor nanoparticles are usually synthesized via solution-phase colloidal techniques,4,913 whereas high-temperature gas-phase processes like chemical vapor deposition (CVD), pulsed laser deposition (PLD), and vapor transfer are widely used for synthesis of high-quality semiconductor nanowires and carbon nanotubes.6,7 Such division reflects only the current research bias, as promising routes to metallic nanoparticles are also available based on vapor condensation14 and colloidal syntheses of high-quality semiconductor nanowires.15... 

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