Mechanical properties of nanoparticle chain aggregates by TEM, AFM and SEM: Isolated aggregates, networks and their role in reinforcing fillers and gas sensors

Nanoparticle chain aggregates (NCA) are branched structures composed of primary particles with diameters ranging from 1 to 50 nm. Interest in NCA stems from their importance in the manufacture of nanocomposite materials such as reinforced rubber, their use as planarization agents and their role in air pollution. The use of NCA as reinforcing fillers in rubber and other polymeric materials results in improved mechanical properties including increased tensile strength and Young's modulus. Although fillers constitute a significant volume fraction (30-40%) of the nanocomposite, the mechanism of interaction between NCA and the polymer chains is not well understood.; Our experimental studies have shown that NCA made of various materials, can be strained up to 100%; after breaking they contract to more compact structures. We have observed the behavior of NCA under strain (i) in the transmission electron microscope (TEM) where they can be stretched across holes that appear in carbon/formvar films on TEM grids, (ii) in a specially designed nanostructure manipulation device, (iii) using an atomic force microscope (AFM) to measure force displacement curves (force spectroscopy) for aggregates stretched between a cantilever tip and an aggregate-coated substrate and (iv) in combined AFM/SEM studies. The NCA were studied individually and as network films.; Similar stretching and elastic behavior was observed for NCA embedded in polystyrene and neoprene films. Reorientation of chains within the film indicated load transfer to the former through the polymer matrix, which may contribute to the enhanced mechanical properties. Our results therefore point to a possible mechanism of enhanced mechanical properties of carbon-black nanocomposites: namely separate contribution to the overall properties by the stretching and elastic properties of filler materials embedded in the polymer matrix.; Gas sensors based on tin dioxide nanoparticle chain aggregates show high sensitivity to reducing and oxidizing gases. Aerosol technology applying the flame spray pyrolysis was used for nanoparticle synthesis and direct deposition on sensor substrates. For the first time this technique has been used to synthesize a combination of two stacked porous layers. Sensors with improved behavior with regard to sensor signal and selectivity have been achieved.