KCl crystallization within the space between carbon nanotube walls

Crystallization in Confinement

Many crystallization processes of great importance, including frost heave, biomineralization, the synthesis of nanomaterials, and scale formation, occur in small volumes rather than bulk solution. Here, the influence of confinement on crystallization processes is described, drawing together information from fields as diverse as bioinspired mineralization, templating, pharmaceuticals, colloidal crystallization, and geochemistry. Experiments are principally conducted within confining systems that offer well-defined environments, varying from droplets in microfluidic devices, to cylindrical pores in filtration membranes, to nanoporous glasses and carbon nanotubes. Dramatic effects are observed, including a stabilization of metastable polymorphs, a depression of freezing points, and the formation of crystals with preferred orientations, modified morphologies, and even structures not seen in bulk. Confinement is also shown to influence crystallization processes over length scales ranging from the atomic to hundreds of micrometers, and to originate from a wide range of mechanisms. The development of an enhanced understanding of the influence of confinement on crystal nucleation and growth will not only provide superior insight into crystallization processes in many real-world environments, but will also enable this phenomenon to be used to control crystallization in applications including nanomaterial synthesis, heavy metal remediation, and the prevention of weathering.

ZnO-coated carbon nanotubes: inter-diffusion of carboxyl groups and enhanced photocurrent generation

ZnO is a defect-governed oxide and emits light at both visible and UV regimes. This work employs atomic layer deposition to produce oxide particles on oxygenated carbon nanotubes, and the composites only show emission profiles at short wavelengths. The quenching of defect-related emissions at long wavelengths is verified, owing to carboxyl diffusion into oxygen vacancies, and doping is supported by ZnCO3 formation in oxide lattice. Fully coated tubes display an increased photocurrent and the quantum efficiency increases by 22 % relative to the bare nanotubes.

Polyethylene crystallization nucleated by carbon nanotubes under shear

Polyethylene crystallization under shear has been studied in the presence of single-wall, few-wall, and multiwall carbon nanotubes (SWNT, FWNT, and MWNT). Polyethylene crystal d-spacings for (110) and (200) planes in polyethylene/carbon nanotubes (CNT) are smaller than in the control polyethylene without CNT and the polymer chain is oriented along the CNT axis. The single-wall carbon nanotube templated polyethylene crystals do not redissolve in boiling xylenes; instead, the chain morphology transforms to an amorphous conformation but remains oriented along the nanotube axis. SWNT crystal peaks were also observed in polyethylene/SWNT fibers.

Morphology of potassium chloride in aqueous and in formamide solution — An experimental and computational investigation

The morphology of potassium chloride grown in pure water as well as in water–formamide solution was investigated. Surface morphology of the crystals was examined by using scanning electron microscopy. It has been observed that the potassium chloride crystals are largely grown with {100} face at different concentrations in pure water, which contradicts earlier reports. Experimental results show that the potassium chloride crystals grown in formamide are also cubic in nature. However, it has been found that the sodium chloride crystals are octahedrons under similar conditions. The difference in the morphological behavior of these two alkali halides with formamide was investigated with computational methods. The calculated results revealed that formamide is largely preferred to adsorb on the {111} surface of NaCl, which can lead to octahedrons. However, the energetics is not substantially different for the adsorption of additives to the important surfaces of potassium chloride and results in the formation of a competing stable {100} surface.