Kenya Ogawa

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

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.

Elasticity of nanoparticle chain aggregates: implications for polymer fillers and surface coatings

Abstract Nanoparticle chain aggregates (NCA) of inorganic oxides have elastic properties. The NCA of titania, alumina and iron oxide generated by laser ablation were deposited on an electron microscope grid. Expanding holes in the films on the grid produced by the electron beam caused the chains to stretch up to about twice their original length before snapping back. The NCA were several tenths of a micron long and were composed of 5–10 nm primary particles. Mechanisms for NCA elasticity are proposed. The application of these concepts to improving the properties of composites of NCA and molecular polymers (e.g., rubber) and to NCA coatings with special optical properties is discussed. The need to develop methods for the synthesis of NCA with prescribed primary particle size, chain length and other properties follows from these applications.