Tuning the 1D-to-2D transition in lepidocrocite titanate nanofilaments via polymer wrapping

Abstract

Recently, a solution-based method was developed to synthesize sub-nm thin one-dimensional (1D) lepidocrocite (1DL) titanium-oxide-based nanofilaments as a colloidal suspension. When converted into the solid state, these 1DL nanofilaments self-assemble into 2D layered structures. Herein, we show how a polymer—branched polyethyleneimine (bPEI)—can be used to wrap individual 1DL surfaces and arrest this 1D-to-2D structural transition. X-ray diffraction (XRD) confirmed that the polymer molecules coated onto individual 1DL surfaces. More interestingly, the bPEI-coated 1DLs form a columnar hexagonal liquid crystalline structure in the solid state, and the inter-1DL distances can be readily tuned from 1.66 to 3.00 nm by controlling the polymer-to-1DL volume ratio. Combining the XRD results and density functional theory (DFT) calculations, we conclude that the 1D nanofilaments, on average, are comprised of 2 × 2 edge-shared TiO₆ octahedra roughly 0.6 nm in diameter. The tunable liquid crystalline phase could open new opportunities to realize 1DL in multiple applications.