Nanoparticles dynamic mobility

Here we briefly discuss the dynamic mobility of particles that do not have thin double layers, that is systems in which the double layer thickness is more than about l/20th of the particle radius. In Section 4.4 we pointed out that double layers are usually thin in aqueous based systems, for the salt concentration is often higher than 1 mM and so double layers are typically less then 10 nm thick. However, such double layers are not thin compared to nanoparticle radii and it is these systems that we are concerned with here. 

Manglesdorf and White [12] have produced a computer program for calculating the dynamic mobility of a particle with an arbitrary double layer thickness, and this can be used for determining zeta from the measured mobility spectrum, provided Ka is known. Thus, an independent measure of particle size is required to obtain the zeta in nanoparticle systems. Once again, the attenuation sizing in the AcoustoSizer can be used for this determination. 

In the case of the particles accommodating amine ligands, a new phenomenon has been evidenced, namely, a dynamic exchange at the NMR timescale between free and coordinated amines. It has been correlated to the TEM and HREM results, which show that, at the early stage of the reaction, the particles display a spherical aspect and a small size (ca. 2-3 nm), and that after a few hours, the particles coalesce into elongated wormlike particles, still constituted of pure, unoxidized hep ruthenium. This NMR observation is particularly interesting since it evidences for these particles a fluxionality similar to that of molecular clusters, which is well documented. The ruthenium nanoparticles contain coordinated mobile surface hydrides, as recently demonstrated by a combination of NMR techniques in solution, gas phase, and in the solid state. ... 

Solid state NMR techniques not only allow a characterization of the immobilization of a homogeneous catalyst, but permit under favomable conditions also a monitoring of reaction intermediates and their dynamics. In particular for hydrogenation reactions the study of the mobility and bonding situation of hydrogen/deuterium ligands on the surface of the nanoparticles stabilized by mesoporous systems is essential. 

Mixing of fillers into a polymer containing polar groups alters mechanical, thermal, and electrical properties of the polymer matrix, to a degree determined primarily by the nature and amount of the filler and the interaction between the two components. Several dielectric studies concentrated on monitoring composition-dependent perturbations in the sidechain (noncooperative) and the segmental (cooperative) relaxation dynamics of the thermoplastic component. The relaxational response of the polymeric matrix could sometimes be modified by a competition between several factors. One of them is the looser packing of the polymer chains, due to the presence of nanoparticles and interactions with them. This factor leads to increased free volume and enhanced molecular mobility. Another factor is the formation of a layer of modified polymer around the nanoparticles, which leads to decreased molecular mobility [e.g., see Mohomed et al. (2005)]. 

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