The Ostwald ripening behavior of two-component miniemulsions of monomer methyl methacrylate (MMA) or styrene (ST) stabilized with costabilizers stearyl methacrylate (SMA) or lauryl methacrylate (LMA) was investigated. Kabalnov equation predicted the Ostwald ripening rate data reasonably well at low volume fraction costabilizer, but it failed to describe the experimental data over the whole costabilizer volume fraction range. A semi-empirical equation with two adjustable parameters K1 and K2 was then proposed to adequately predict the Ostwald ripening rate data(1/RO=1/RO,m(1+K1j2c+K2j2c^2). The greater the value of K1 (or K2), the more effective is the costabilizer in stabilizing miniemulsion droplets against the diffusional degradation process. The role of the mixed costabilizers (i.e cetyl alcohol(CA)and hexadecane(HD))in retarding Ostwald ripening occurring in the three-component disperse phase monomer was simply treated as a pseudo-two-component disperse phase miniemulsion system.
The work then continues to study the Ostwald ripening behavior of ST or MMA miniemulsions stabilized by various types of costabilizers. The general validity of the quadratic semi-empirical model with two parameters K1 and K2 was verified and it showed a great potential to describe the general features of the Ostwald ripening process involved in miniemulsions stabilized by a relatively wide range of volume fraction of costabilizers in the disperse phase. The greater the K1/RO,m (or K2/RO,m) value, the more effective is the costabilizer in stabilizing miniemulsion droplets against the diffusional degradation process. Correlations of the K1/RO,m (or K2/RO,m) data with the water solubility (or solubility parameter) of the bulk costabilizer were established. Polymeric costabilizers showed quite different behavior in stabilizing miniemulsions compared to low molecular weight costabilizers. Incorporation of hydrophilic functional groups into the costabilizer structures greatly reduced their capabilities to enhance the storage stability of miniemulsion products.
Characterizations of styrene miniemulsions stabilized by a series of n-alkane costabilizers (CnH2n+2, n = 10, 12, 16, 18, 20, 24 and 32) were also studied in this work. The semi-empirical model was capable of predicting the Ostwald ripening rate data over a wide range of the volume fraction of n-alkanes within submicron monomer droplets. It was shown that the Ostwald ripening rate (or the water solubility of n-alkane) decreased with increasing n-alkane molecular weight. A correlation between the water solubility and the molecular weight of n-alkanes was established accordingly.

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