Generation of Crystalline Hollow Needles: New Approach by Liquid-Liquid Phase Transformation

The formation of hollow crystalline needles by means of a solvent-mediated phase transformation takes place during the dehydration of hydrate crystals in methanol into hollow needle-shaped anhydrate crystals. Here, a special way of achieving needle growth is presented. When a saturated aqueous solution of sodium-2-ketogulonate is dropped into methanol, a simultaneous nucleation of monohydrate crystals and anhydrate needles takes place in the alcohol. It was proven by scanning electron microscope images that these needles are hollow. By means of the variation of the production method, it is for the first time possible to observe the needle growth in a more detailed manner, and to show that the nucleation can take place at impurities and surface roughnesses. The method helped to discuss and to deepen the understanding of the growth mechanism of the hollow crystalline needles.