ABSTRACT

The formation of polymeric nanoparticles actually contains two main parts: 1) the micronization of a material into nanoparticles and 2) the stabilization of the resultant nanoparticles. As for the rnicronization, one can start with either small monomers or long chain polymers. Emulsion including mini-and micro-emulsion polymerization as a conventional method can make polymeric particles in the size range 10-104 nm. Miller and El-Aasser (1997) have summarized recent advances in this area. It is well known that in microemulsion polymerization, a large amount of surfactant/co-surfactant has to be added to make small nanoparticles. The addition of surfactant limits not only the solid content in the dispersion but also their applications. The removal of surfactant from a resultant dispersion without affecting its stability is extremely difficult, if not impossible. Much effort has been spent on how to increase the solid content and reduce the amount of surfactant added. Up to now, it still remains a challenge to prepare concentrated uniform surfactant-free polymeric nanoparticles (10-50 nm in size) stable in water. Besides using surfactant, protein and other natural polyelectrolytes are often used in food and pharmaceutical industries to stabilize nanoparticles. Polymeric nanoparticles in water can also be stabilized by ionic groups introduced by copolymerization, initiation, and surface modification, and by hydrophilic polymer chains adsorbed or grafted on the particle surface.