Fabrication and Elastic Properties of TiO₂ Nanohelix Arrays through a Pressure-Induced Hydrothermal Method

Abstract

TiO₂ nanohelices (NHs) have attracted extensive attention owing to their high aspect ratio, excellent flexibility, elasticity, and optical properties, which endow promising performances in a vast range of vital fields, such as optics, electronics, and micro/nanodevices. However, preparing rigid TiO₂ nanowires (TiO₂ NWs) into spatially anisotropic helical structures remains a challenge. Here, a pressure-induced hydrothermal strategy was designed to assemble individual TiO₂ NWs into a DNA-like helical structure, in which a Teflon block was placed in an autoclave liner to regulate system pressure and simulate a cell-rich environment. The synthesized TiO₂ NHs of 50 nm in diameter and 5-7 mm in length approximately were intertwined into nanohelix bundles (TiO₂ NHBs) with a diameter of 20 μm and then assembled into vertical TiO₂ nanohelix arrays (NHAs). Theoretical calculations further confirmed that straight TiO₂ NWs prefer to convert into helical conformations with minimal entropy (<i>S</i>) and free energy (<i>F</i>) for continuous growth in a confined space. The excellent elastic properties exhibit great potential for applications in flexible devices or buffer materials.