|Jean-Christophe Daigle and Jerome P. Claverie report a method for fabricating materials composed of inorganic nanoparticles encased in organic polymer shells.|
Reviewed by Dr. Michael Steigerwald, Columbia University
Jean-Christophe Daigle and Jerome P. Claverie, "A Simple Method for Forming Hybrid Core-Shell Nanoparticles Suspended in Water, Journal of Nanomaterials," Journal of Nanomaterials, Volume 2008 (2008), Article ID 609184. DOI: 10.1155/2008/609184
Daigle and Claverie report an interesting, versatile, and potentially valuable method for the large-scale fabrication of composite nanomaterials: inorganic nanoparticles encased in organic polymer shells. Starting with commercially available inorganic nanoparticulate materials, they first conduct a particle-attached polymerization to solubilize the particles and then a second polymer-attached polymerization to construct the organic shell. The most clever feature of the authors' method is the use of Reversible Addition Fragmentation chain Transfer (RAFT) as the first polymerization step. This allows them to restart the polymerization at their discretion, thereby allowing the second polymerization step to be selectively localized around the solubilized nanoparticle.
This manuscript, which includes a thorough review of the recent literature in the hybrid core-shell nanoparticle field, shows that the authors can solubilize a variety of nanoparticle materials (e.g., barium titanate, zirconia, several varieties of titania, and silicon nitride) with polyacrylic acid, PAA, using a RAFT process. The resulting dispersed particle-cum-surfactant is chemically active in the sense that it contains the restartable RAFT polymerization initiator. In the second step a second monomer (or a second set of monomers) is added and the sleeping RAFT initiator is reawakened. The resulting polymer grows attached to the PAA that is itself attached to the inorganic particle. The authors note specifically that if this “living” polymer system is not used (that is, if the PAA coating is a “dead” polymer), no polymeric shell forms around the inorganic core.
It is intriguing that the authors' process does not rely on a very strong adsorption of the initial PAA coating on the particle surface. A strong interaction does lead to the core-shell structure, but it is apparently not required. Instead, if there is only a comparatively weak interaction between the PAA and the particle, then as the second polymer grows it becomes more and more hydrophobic, and it is therefore trapped more and more strongly on the particle--effectively being pressed onto the surface by its unfriendly aqueous surroundings.
The simplicity, generality, and scalability of this method should make it attractive to manufacturing.
Image from J.-C. Daigle and J. P. Claverie, "A Simple Method for Forming Hybrid Core-Shell Nanoparticles Suspended in Water," Journal of Nanomaterials, Volume 2008 (2008), Article ID 609184. Reprinted under a Creative Commons Attribution License