Ostwald ripening effect

2 STABILITY OF MONOMER EMULSIONS 5.2.1 Ostwald Ripening Effect 

According to the Lifshitz-Slezov-Wagner (LSW) theory [15-18], the rate of Ostwald ripening (Ro) can be expressed as 

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This difference is probably associated with the chain expansion and/or contraction relative to the interface between the blocks within the particular morphology. In analogy to solid inorganic materials whose solubility increases under external pressure and to colloid systems where the capillary pressure leads to an increase in the solubility (Ostwald ripening effect), one would intuitively expect larger swelling of... 

The water solubility of the hydrophobe is a function of temperature and the nature of the continuous aqueous phase. The water solubility of the hydrophobe decreases with decreasing temperature. Furthermore, the water solubility of the monomer is also lowered as the temperature is decreased. These factors may greatly suppress the Ostwald ripening effect. As a result, the colloidal stability of the emulsion may be improved significantly by lowering the temperature. A monomeric mini-emulsion is generally prepared at room temperature prior to... 

The high oil-solubility of a non-ionic emulsifier indicates that the non-ionic emulsifier may act as an ideal coemulsifier - it partitions between the aqueous and monomer phases. The Ostwald ripening effect is depressed when NP-40 is incorporated into the stabilization system (SDS/DMA) [ 15]. It is then speculated... 

Figure 6.6 Illustration of the Ostwald ripening effect for SrS04 precipitation (after Enustun and Turkevich, 1960). The initial CSD (1) in contact with a saturated solution changed to (2) after 60 days but transformed to (3) in just 45 minutes upon dilution with water.

Figure 5.2. A schematic representation of the mechanism for the transport of monomer between a small monomer droplet and a large droplet. Monomer molecules tend to diffuse from the small monomer droplet to the large droplet due to the Ostwald ripening effect. This will cause a concentration gradient for costabilizer between these two monomer droplets. However, the very hydrophobic costabilizer in the small monomer droplet cannot be dissolved in water, diffuse across the continuous aqueous phase, and then enter the large droplet. Thus, monomer molecules in the large monomer droplet are forced to migrate back to the small droplet in order to relax the concentration gradient for costabilizer (temned the osmotic pressure effect), and a relatively stable miniemulsion product is obtained.

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