Elastic behavior of nanoparticle chain aggregates: A hypothesis for polymer-filler behavior

Abstract

Electron microscopy studies in our laboratory have shown that nanoparticle chain aggregates (NCAs) of inorganic oxides have elastic properties. Measurements were made with titania, alumina, and iron oxide NCAs generated by laser ablation. Primary particles were 5–10 nm in diameter, and the mobility diameters of the NCAs studied were about 0.5 μm. NCA stretching appeared to begin with the rotation and/or sliding of adjacent nanocrystals. This led to a small change in the NCA length but allowed for chain straightening. Most of the NCA lengthening resulted from the separation of kinked chain segments held together by weak, probably van der Waals (vdw), forces. NCA strains up to 90% were observed. Calculated values for NCA deformation energies per unit volume were compared with those for conventional polymers; under certain conditions, the two deformation energies were of the same order of magnitude. These results may help explain the remarkable effects that nanoparticle reinforcing fillers such as carbon black and silica have on commercial rubber. It may be possible to improve the properties of composites of molecular polymers and NCAs through the use of NCAs with prescribed primary particle sizes, vdw-bond numbers, chain lengths, and morphological properties. Synthesizing such NCAs will require the use of modern concepts of aerosol aggregate formation. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2658–2665, 2000