Partitioning future research

Distribution of organic chemicals among environmental compartments can be defined in terms of simple equilibrium expressions. Partition coefficients between water and air, water and soil, and water and biota can be combined to construct model environments which can provide a framework for preliminary evaluation of expected environmental behavior. This approach is particularly useful when little data is available since partition coefficients can be estimated with reasonable accuracy from correlations between properties. In addition to identifying those environmental compartments in which a chemical is likely to reside, which can aid in directing future research, these types of models can provide a base for more elaborate kinetic models. 

One of the interests in confined polymers arises from adsorption behavior— that is, the intake or partitioning of polymers into porous media. Simulation of confined polymers in equilibrium with a bulk fluid requires simulations where the chemical potentials of the bulk and confined polymers are equal. This is a difficult task because simulations of polymers at constant chemical potential require the insertion of molecules into the fluid, which has poor statistics for long chains. Several methods for simulating polymers at constant chemical potential have been proposed. These include biased insertion methods [61,62], novel simulation ensembles [63,64], and simulations where the pore is physically connected to a large bulk reservoir [42]. Although these methods are promising, so far they have not been implemented in an extensive study of the partitioning of polymers into porous media. This is a fruitful avenue for future research. 

The tube models a concrete folding mechanism by following the center of the tube and the fluctuations near that center. This concrete mechanism can be examined with respect to the overall funnel picture. For example, if the rate in the tube is exceptionally slow compared to the experimental rate, it is unlikely that the sampled tube is important. Computationally and conceptually, we should partition the funnel to tubes and analyze them one by one. We note that all the tubes meet at the folded state. Therefore the weight of each tube can be measured by overlapping the equilibrium flux into the reactant with the flux from a tube. The calculation of weights of tubes is a topic for future research. 

In the Preface to this handbook we argued that the subject of mass transfer is a poor relation compared to the sciences of chemical partitioning and reactivity in the environment. The science of mass transfer is less mature in its development. Uncertainties about transport rates are, we believe, a significant cause of error in simulations of chemical fate in the environment. In this final chapter we present a personal perspective assessing the state-of-the-art for chemical transport coefficient estimation and we offer a cursory review of the deficiencies in the field of environmental mass transfer that should be the focus for future research endeavors. 

A number of attempts have been made to understand the mechanism of the adsorption of chelates on oxide minerals. For instance, IR spectroscopic studies10 have indicated the presence of a basic monosalicylaldoximate copper complex as well as the bis-salicylaldoximate complex on the surface of malachite (basic copper carbonate) treated with salicylaldoxime. However, other workers4 have shown that the copper chelate is partitioned between the surface and dispersed within the solution, and that a dissolution-precipitation process is responsible for the formation of the chelate. Research into the chemistry of the interaction of chelating collectors with mineral surfaces is still in its infancy, and it can be expected that future developments will depend on a better understanding of the surface coordination chemistry involved. 

Herczeg, J.W. 2002. The Advanced Fuel Cycle Initiative The future path for advanced spent fuel treatment and transmutation research in the United States. 7th Information Exchange Meeting on Actinide and Fission Product Partitioning and Transmutation, October, Jeju, Repubhc of Korea. 

Lee (1995) has proposed a model for fast-track diffusion to explain the effects of combined lattice diffusion and diffusion along fast diffusion pathways through the lattice such as defects. Lee proposed that the combined diffusion could be modeled as two parallel diffusion mechanisms with argon atoms partitioning between the two. The mathematical model produces realistic release patterns, but does not currently take account of the distances between fast track pathways and the time taken for atoms to reach one (cf. Arnaud and Kelley 1995). Future development of the fast track model may provide very fruitful avenues for research. 

Electrokinetic and electrohydrodynamic instability mixing in microsystems is a complex phenomenon which researchers are only beginning to exploit and understand. Future work requires a further development of experimental models and expansion of computational simulations to better understand how the instabilities form and grow. Specific applications of electrokinetic and electrohydrodynamic instabilities are still limited. The application of these instabilities to improve mixing between components should be explored. One example is through the use of multiphase systems where electrohydrodynamic instabilities are utilized to improve component partitioning for liquid extraction devices. 

Bipolar electrodes are stacked to produce a battery of cells connected at the partitions. If the cells in a bipolar battery are not rigorously sealed around the edges, electrolyte leaks can provide a shunt current path between cells, which reduces the battery performance. Researchers continue to look at new materials and designs for commercial bipolar batteries. Recent work to develop bipolar batteries is discussed further in Future Development at the end of this article (Fig. 5.1). 

---