Physical Methods for the Preparation of Hybrid Nanocomposite Polymer Latex Particles

In this chapter, we will highlight conceptual physical approaches towards the fabrication of nanocomposite polymer latexes in which each individual latex particle contains one or more "hard" nanoparticles, such as clays, silicates, titanates, or other metal(oxides). By "physical approaches" we mean that the "hard" nanoparticles are added as pre-existing entities, and are not synthesized in situ as part of the nanocomposite polymer latex fabrication process. We will narrow our discussion to focus on physical methods that rely on the assembly of nanoparticles onto the latex particles after the latex particles have been formed, or its reciprocal analogue, the adhesion of polymer onto an inorganic nanoparticle. First, will discuss the phenomenon of heterocoagulation and its various driving forces, such as electrostatic interactions, the hydrophobic effect, and secondary molecular interactions. We will then address methods that involve assembly of nanoparticles onto or around the more liquid precursors (i.e., swollen/growing latex particles or monomer droplets). We will focus on the phenomenon of Pickering stabilization. We will then discuss features of particle interaction with soft interfaces, and see how the adhesion of particles onto emulsion droplets can be applied in suspension, miniemulsion, and emulsion polymerization. Finally, we will very briefly mention some interesting methods that make use of interface-driven templating for making well-defined assembled clusters and supracolloidal structures

An Ethylene-Mediated Increase in Sensitivity to Auxin Induces Adventitious Root Formation in Flooded Rumex palustris Sm.

The hormonal regulation of adventitious root formation induced by flooding of the root system was investigated in the wetland species Rumex palustris Sm. Adventitious root development at the base of the shoot is an important adaptation to flooded conditions and takes place soon after the onset of flooding. Decreases in either endogenous auxin or ethylene concentrations induced by application of inhibitors of either auxin transport or ethylene biosynthesis reduced the number of adventitious roots formed by flooded plants, suggesting an involvement of these hormones in the rooting process. The rooting response during flooding was preceded by increased endogenous ethylene concentrations in the root system. The endogenous auxin concentration did not change during flooding-induced rooting, but a continuous basipetal transport of auxin from the shoot to the rooting zone appeared to be essential in maintaining stable auxin concentrations. These results suggest that the higher ethylene concentration in soil-flooded plants increases the sensitivity of the root-forming tissues to endogenous indoleacetic acid, thus initiating the formation of adventitious roots

Aerenchyma formation in the wetland plant Juncus effusus is independent of ethylene

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Evidence that ethylene signalling is not involved in selective root placement by tobacco plants in response to nutrient-rich soil patches

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