![]() ![]() There is a separate monomer phase in intervals I. The particle number increases with time in interval I and particle nucleation occurs in interval I. At the end of this stage most of surfactants are exhausted (i.e. Emulsion polymerization carried out through three main intervals as shown in Figure 2. Schematic representation of emulsion polymerization shown in Figure 1. As polymerization continue inside micelle, the micelle grow by monomer addition from monomer droplets outside and latex are formed. In general, monomer droplets are not effective in competing with micelles in capturing free radicals generated in the aqueous phase due to their relatively small surface area, so the micelle act as a meeting site of water-soluble initiators and hydrophobic vinyl monomers. Water-soluble initiators enter into the micelle where free radical propagation start. Typical micelles have dimensions of 2–10 nm, with each micelle containing 50–150 surfactant molecules. When surfactant concentration exceeds critical micelle concentration (CMC) it aggregate in the form of spherical micelles, so surface tension at the surface decrease, as a result hydrophobic monomers enter in to the vicinity of micelle and reaction continue until all monomer droplets are exhausted and micelle containing monomers increase in size. The dispersion medium is water in which hydrophobic monomers is emulsified by surface-active agents (surfactant). The main components of emulsion polymerization media involve monomer(s), dispersing medium, emulsifier, and water-soluble initiator. Components of heterogeneous emulsion polymerization Many articles discuss different types of emulsion polymerization found in literature. Miniemulsion, microemulsion and conventional emulsion polymerizations show quite different particle nucleation and growth mechanisms and kinetics. ![]() (3) Mini emulsion polymerization involves systems with monomer droplets in water with much smaller droplets than in emulsion polymerization and characterized by monomer droplet =50–1000 nm, surfactant concentration CMC, polymer particles = 10–50 nm, water-soluble initiator are commonly used. These two polymerization types known as oil-in-water (o/w) and water-in-oil (w/o) emulsions. (2) Inverse emulsion polymerization, where organic solvents of very low polarity as paraffin or xylene used as a polymerization media to emulsify hydrophilic monomers, then initiation proceed with the aid of hydrophobic initiator. Systems of emulsion polymerization involve (1) conventional emulsion polymerization, in which a hydrophobic monomer emulsified in water and polymerization initiated with a water-soluble initiator. Aside from other polymerization techniques, emulsion polymerization affords increasing molecular weight of the formed latexes through decreasing polymerization rate by either decreasing initiator concentration or lowering reaction temperature. Emulsion polymerization is a rather complex process because nucleation, growth and stabilization of polymer particles are controlled by the free radical polymerization mechanisms in combination with various colloidal phenomena. These emulsion polymers find a wide range of applications such as synthetic rubbers, thermoplastics, coatings, adhesives, binders, rheological modifiers, plastic pigments. Typical polymerization monomers involve vinyl monomers of the structure (CH 2=CH-). ![]() 2,2-azobisisobutyronitrile (AIBN)) in the presence of stabilizer which may be ionic, nonionic or protective colloid to disperse hydrophobic monomer through aqueous solution. potassium persulfate (K 2S 2O 8) or an oil-soluble initiator (e.g. Emulsion polymerization is a unique process involves emulsification of hydrophobic monomers by oil-in water emulsifier, then reaction initiation with either a water soluble initiator (e.g. ![]()
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