Volume 72, Issue 10

We are largely unable to predict the composition and crystal structure of new extended structure compounds. Yet we find that as materials become more complex in stoichiometry and structure, new, interesting, and perhaps useful, phenomena are encountered. The need for improved experimental and theoretical approaches to seize more rapidly the opportunities provided in this complexity is discussed.

Reference materials have long been considered essential for both calibration and checking the correct operation of equipment used for the determination of physicochemical properties. Up until the 1970s, the maintenance of pure reference materials and the means to verify their properties through measurement using state-of-the-art equipment was the prerogative of many national standards laboratories. Over the last 30 years, many of the standards laboratories have either limited or eliminated their activity in maintaining both reference materials and state-of-the-art measuring equipment. One reason is the ready availability of high-purity materials from commercial sources and the ease with which one can now determine purity. A second reason is the ready availability of instruments to measure digitally fundamental quantities such as time, temperature, length, frequency, and voltage accurately has enabled chemical calibration using reference materials to be replaced in many instruments by electrical calibration. At the same time, digitization has enabled the computerization of the whole measurement process. Such automated devices, if not checked with reference materials, can give highly reproducible results but have large systematic errors, leading to poor values. The role of physicochemical reference materials in the past and the present will be outlined, and their status in the future will be explored.

At liquid-like densities, molecules of complex fluids can assume a variety of structures (or positions) in space; when the molecules contain many atoms as, for example, in polymers, that variety becomes very large. Further, when confined to a narrow space, it is possible to achieve structures that are not normally observed. Thanks to recent advances in statistical mechanics and molecular physics, and thanks to increasingly fast computers, it is now possible to calculate a fluid's structure, that is, the positions of molecules at equilibrium under given conditions. Calculation of fluid structure is useful because thermodynamic properties depend strongly on that structure, leading to possible applications for new materials. Three examples illustrate some recent developments; each example is presented only schematically (with a minimum of equations) to indicate the physical basis of the mathematical description. The first example considers the effect of branching on self-assembly (micellization) of copolymers (with possible long-range applications in medicine). The second and third examples consider the effect of confinement on fluid structure: first, crystallization in a narrow, confined space to produce a desired crystal structure (with possible applications for light-emitting diodes) and second, suppression of micellization of a diblock copolymer in a thin film (with possible application in lithography). Whenever possible, theoretical calculations are compared with experimental results.

Life is almost always associated with the generation of heat. Thus far, all chemotrophic life forms that have been studied in calorimeters were found to be exothermic. Certain literature reports have even cast doubt on the existence of endothermic growth, even though thermodynamic principles do not rule it out. The present report describes the first experiments demonstrating the actual existence of chemotrophic life forms that take up heat rather than produce it.

Thermochemical analyses related with development of advanced nuclear fuels (i.e., metalic, nitride, and hydride fuels) with respect to the transmutation of transuranium elements and relevant pyrochemical reprocessing and fabrication processes, which have been carried out mainly in Japan, are summarized. In addition, application of atmosphere-controlled high-temperature mass spectrometry on solid-gas reactions, in particular on the prediction of gas-interacting behaviors of cesium and lithium on respective oxide ceramics, are delineated in relation to nuclear material-relevant researches.

Potentiometric selectivity coefficients have been collected for ionophore-based ion-selective electrodes (ISEs) for inorganic cations reported from 1988-1997. In addition to numerical values of K (A,B) pot together with the methods and conditions for their determination, response slopes, linear concentration ranges, chemical compositions, and ionophores structures for the ISE membranes are tabulated.