Graphene Oxide-Assisted Growth of Ultralong and Soft Single-Crystalline NaCl Ionic Nanowires for Potential Optical Nanodevices

Ionic crystals are composed of cations and anions by electrovalent bonding. Generally, the macroscopical ionic crystals are hard and brittle. Here, unexpectedly, we directly obtained ultralong and soft sodium chloride (NaCl) ionic nanowires on a mixed cellulose ester (MCE) membrane assisted by graphene oxide (GO), which are up to 4000 μm with diameters of approximately 0.58 μm and can be bent 180°. In contrast to the pristine MCE membrane, GO coverage significantly improves NaCl nanowire growth by affecting competition between evaporation and transportation of pore fluid. Transmission electron microscopy studies show that these nanowires are typical face-centered cubic single crystals; they grow along the crystal orientation of ⟨100⟩. Interestingly, we note that the soft property of NaCl nanowires is relative to their diameters, and the flexibility increases as the diameter decreases. Our findings provide novel potential material for optical nanodevices and help understand ionic crystal properties with size effect.