Ordered mesostructured porous silicas that are also macroscopically structured were created by control of the interface on two different length scales simultaneously. Micellar arrays controlled the nanometer-scale assembly, and at the static boundary between an aqueous phase and an organic phase, control was achieved on the micrometer to centimeter scale. Acid-prepared mesostructures of silica were made with the p6, Pm3n, and the P63/mmc structures in the form of porous fibers 50 to 1000 micrometers in length, hollow spheres with diameters of 1 to 100 micrometers, and thin sheets up to 10 centimeters in diameter and about 10 to 500 micrometers in thickness. These results might have implications for technical applications, such as slow drug-release systems or membranes, and in biomineralization, where many processes are also interface-controlled.

A temperature‐dependent small‐angle x‐ray scattering and electron microscopic study on a sample of low‐density polyethylene affords a determination of the structure changes in a heating and cooling cycle and suggests a new model of partial crystallization and melting. The analysis of SAXS data is based upon some general properties of the electron‐density correlation function. Electron micrographs are obtained from stained sections γ irradiated at elevated temperatures and are analyzed quantitatively by statistical means. According to the model proposed here the thickness distribution in the amorphous layers, rather than that of the crystalline regions, is the essential factor governing the crystallization and melting behavior. The temperature‐dependent changes in this thickness distribution provide a natural explanation for the large reversible changes in long‐spacing.

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The melting temperatures and phase structures of a series of hydrogenated polybutadienes with fixed co-unit content (2.3 mol % branch points) and varying molecular weights have been studied. These copolymers represent molecular weight and composition fractions of randomly ethyl-branched ethylene copolymers. Also studied were a set of random ethylene-hexene copolymers with a lower co-unit content. The observed melting temperatures, after a variety of crystallization procedures, were found to decrease with increasing molecular weight for both copolymer types. This unusual result could be attributed to the decreasing crystallite thickness in the chain direction with molecular weight. At the higher molecular weights, M = 4.6 X 10®, the crystallite thickness is reduced to about 30 A. Associated with the crystallite is a relatively large disordered overlayer. Although small-angle X-ray measurements and thin-section transmission electron microscopy give results that are in quantitative agreement for the crystallite thickness, the Raman LAM measurement give significantly higher values in the low-size range. The conventional extrapolative method of plotting the observed melting temperature against the crystallization temperature, in order to obtain the equilibrium melting temperature, failed for the random copolymers at low levels of crystallinity. A straight line resulted that paralleled the 45°line. Therefore, extrapolation to the equilibrium melting temperature could not be accomplished. Although the extrapolation could be made for higher levels of crystallinity, this procedure was arbitrary and lead to unreasonable values for the equilibrium melting temperature.

Replicas and thin‐section electron microscopic studies were made of fractions of linear polyethylene covering the molecular weight range 2.78 × 104 to 6.0 × 106 for a variety of crystallizing conditions. Lamellar crystallites were found under all circumstances; and the supermolecular structure, or crystalline morphology, is in agreement with that previously reported from an analysis of the small‐angle light‐scattering patterns of the same samples under similar crystallization conditions. Details of the crystalline microstructure are also described, which range from truncated hollow pyramids which degenerate as the molecular weight or the undercooling are increased. From these results, it is possible to describe the mechanism of formation of polyethylene spherulites.