Ostwald process polymerization

Classical theories of emulsion stability focus on the manner in which the adsorbed emulsifier film influences the processes of flocculation and coalescence by modifying the forces between dispersed emulsion droplets. They do not consider the possibility of Ostwald ripening or creaming nor the influence that the emulsifier may have on continuous phase rheology. As two droplets approach one another, they experience strong van der Waals forces of attraction, which tend to pull them even closer together. The adsorbed emulsifier stabilizes the system by the introduction of additional repulsive forces (e.g., electrostatic or steric) that counteract the attractive van der Waals forces and prevent the close approach of droplets. Electrostatic effects are particularly important with ionic emulsifiers whereas steric effects dominate with non-ionic polymers and surfactants, and in w/o emulsions. The applications of colloid theory to emulsions stabilized by ionic and non-ionic surfactants have been reviewed as have more general aspects of the polymeric stabilization of dispersions. ... 

Miniemulsion is a special class of emulsion that is stabilized against coalescence by a surfactant and Ostwald ripening by an osmotic pressure agent, or costabilizer. Compared with conventional emulsion polymerization process, the miniemulsion polymerization process allows all types of monomers to be used in the formation of nanoparticles or nanocapsules, including those not miscible with the continuous phase. Each miniemulsion droplet can indeed be treated as a nanoreactor, and the colloidal stability of the miniemulsion ensures a perfect copy from the droplets to the final product. The versatility of polymerization process makes it possible to prepare nanocapsules with various types of core materials, such as hydrophilic or hydrophobic, liquid or solid, organic or inorganic materials. Different techniques can be used to initiate the capsule wall formation, such as radical, ionic polymerization, polyaddition, polycondensation, or phase separation from preformed polymers. 

However, it is difficult to control the micelle formation during microemulsion polymerization, hi general, polymerization process is kinetically and thermodynamically unstable because of Ostwald ripening, the growth by collision between monomer droplets and monomer consumption during polymerization [154,155]. It is noteworthy that precise control of the micelle is essential to produce monodisperse and nano-sized conducting polymer nanomaterials. 

Microsuspension polymerization is a process used in the PVC industry to produce resins for plastisols [125], In this process, which resembles miniemulsion polymerization, a mixture of monomer and an oil-soluble initiator are dispersed in an aqueous solution of surfactants using intensive shear. The monomer droplets are polymerized yielding particles usually <2 pm, which are normally isolated by spray drying as they cannot be separated by centrifuging or filtering. These particles are solid and nonporous. The polymer particles are larger than the monomer droplets (0.1-2 pm) because the combined effect of the Ostwald ripening (as no costabilizer is used in the formulation) and droplet/particle coalescence. 

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