Rheology nanoparticles

These materials have possible utility in a number of specialty applications and are being explored by Guan et al. [37], They have used these catalysts, and their unique chain-walking characteristics to synthesize a variety of dendritic materials (Fig. 4), which could find potential application as processing aids, rheological modifiers, and amphiphilic core-shell nanoparticles for drug delivery and dye formulation. 

Overall, the key element in many of these approaches is the complex needs of the ink to meet the needs of the deposition technique, to facilitate the formation of the desired material with appropriate properties and to facilitate the desired thickness, roughness, line resolution, and uniformity. This set of constraints will in most cases require an appropriate combination of precursors, solvents, surfactants, adhesion promoters, and rheology control agents (e.g., see Chapter 12 for more discussion).29 For new metal organic and nanoparticle precursors, the fabrication of inks is still an emerging science. 

It is also important to emphasize that conventional consciousness of colloid or fine particle technology, like better dispersion and control of rheological properties of dipping solution, are not to be overlooked. The growth of nanoparticles in liquid phase is almost exactly regulated by the nuclei-growth theory as well as stability of lyophobic colloids suggested half a century ago. 

Vekas, L., Rasa, M., and Bica, D., Physical properties of magnetic fluids and nanoparticles from magnetic and magneto-rheological measurements, J. Colloid Interface Sci., 231, 247, 2000. 

Nanoparticles may also be important within planetary interiors. For example, phase transitions within the deep Earth may generate materials that are composites of nanoparticles (e.g., within the spinel phase at the olivine-spinel transition at the 400-km discontinuity). These grain sizes may affect both kinetics and rheology (e.g., of ice in planetary interiors Stern et al. 1997). Chemical reactions in the deep Earth, perhaps between metal and silicate near the core-mantle boundary, may be impacted by nanocrystals. 

Keywords Colloidal dispersions Colloidal glasses Dynamics Grafted particles Hairy particles Micelles Nanoparticle-polymer hybrids Phase diagrams Polymers Rheology Soft colloids- Softness Stars... 

J, Ndmeth and 1, Ddkdny, The effect of nanoparticle growth on rheological properties of silica and silicate dispersions. Colloid Polym Sci., 278 211-219, 2000... 

The rheological behavior of these materials is still far from being fully understood but relationships between their rheology and the degree of exfoliation of the nanoparticles have been reported [73]. An increase in the steady shear flow viscosity with the clay content has been reported for most systems [62, 74], while in some cases, viscosity decreases with low clay loading [46, 75]. Another important characteristic of exfoliated nanocomposites is the loss of the complex viscosity Newtonian plateau in oscillatory shear flow [76-80]. Transient experiments have also been used to study the rheological response of polymer nanocomposites. The degree of exfoliation is associated with the amplitude of stress overshoots in start-up experiment [81]. Two main modes of relaxation have been observed in the stress relaxation (step shear) test, namely, a fast mode associated with the polymer matrix and a slow mode associated with the polymer-clay network [60]. The presence of a clay-polymer network has also been evidenced by Cole-Cole plots [82]. 

Since nanoparticles in PNC are orders of magnitude smaller than conventional reinforcements, the models developed for composites are not applicable to nanocomposites. However, development of a universal model for PNC is challenging since the shape, size, and dispersion of the nanoparticles vary widely from one system to another. On the one hand, exfoliated clay provides vast surface areas of solid particles (ca. 800 m /g) with a large aspect ratio that adsorb and solidify a substantial amount of the matrix polymer, but on the other hand, the mesoscale intercalated clay stacks have a much smaller specific surface area and small aspect ratio. However, in both these cases the particle-particle and particle-matrix interactions are much more important than in conventional composites, affecting the rheological and mechanical behavior. Thus, the PNC models must include the thermodynamic interactions, often neglected for standard composites. 

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