A surprising mechanism by which polymers form nanocomposite particles could provide researchers with a new tool for controlling the growth of such materials.

Because the properties of nanoparticles depend so closely on their size, size distribution, and morphology, techniques for controlling the growth of these tiny structures is of great interest to materials researchers today.

According to researchers at the Georgia Institute of Technology and Drexel University, growing nanoparticles within the confinement of a polymer-based structure is now a common technique for controlling particle growth. After the particles are produced, the templating polymer matrix is simply removed by melting it away resulting in nanocomposites for various applications, such as optical and photonics devices.

Rina Tannenbaum and her colleagues carried out a series of experiments and discovered that there is a strong relationship between the chemical reactivity of the polymer and the size and shape of the resulting nanoparticles. "We have concentrated on the reactivity of the polymeric matrix and how that influences the growth of particles," explains Tannenbaum, "We found that in the melt, the key parameter influencing particle size is actually the type of interaction with the polymer. The molecular weight of the polymer and the synthesis temperature are almost insignificant."

The researchers prepared iron oxide nanoparticles within polymer films of different types, including polystyrene, poly(methyl methacrylate), bisphenol polycarbonate, poly(vinylidene di-fluoride), and polysulfone. They characterized the particles using transmission electron microscopy.

"These polymers spanned a variety of functional groups that differed in the strength and nature of their interactions with the iron oxide particles and in their position along the polymer chain," Tannenbaum adds, "We found that the characteristic nanoparticle size decreased with the increasing affinity - the strength of the interaction - between the polymer and the iron oxide particles."

Tannenbaum and Drexel's Nily Dan charted the relationship between average particle size and the reactivity of the polymer interface. That information should help other scientists as they attempt to regulate the growth of nanoparticles using polymer reactivity. The results are likely to be applicable to other nanoparticles types too.

Macromolecules, 2005; 38, 4254-4259; http://dx.doi.org/10.1021/ma048317x
 
American Chemical Society Meeting & Exposition, August 28 - September 1, 2005 Washington, DC USA http://www.chemistry.org/meetings/washington2005