Nanocombing Effect Leads to Nanowire-Based, In-Plane, Uniaxial Thin Films.

The fabrication of thin films comprising ordered nanowire assemblies with emerging, precisely defined properties and adjustable functionalities enables highly integrated technologies in the fields of microelectronics and micro system technology, as well as for efficient power generation, storage, and utilization. Shear force, theoretically, is deemed as the most promising method for obtaining in-plane, uniaxial thin films comprising nanowires. The success depends largely on the assembly process, and uniform structural control throughout multiple length scales can be achieved only if the rational strategy is executed. Here, we report that in shearing processes, dopants like lyotropic cellulose nanorods can give rise to the uniaxial alignment of V2O5·nH2O nanowires. Our systematic study indicates that this finding, namely the nanocombing effect, can be a general principle for the continuous production of uniaxial thin films comprising densely-packed nanowires varying in chemical composition and aspect ratios. Conversion of the V2O5·nH2O constituents via in situ oxidative polymerization leads to in-plane, uniaxial polyaniline (PANI) thin films with anisotropic electric and optical properties, which are otherwise difficult to fabricate due to the poor processability of PANI. The uniaxial PANI thin films can be utilized to fabricate flexible gas sensors for distinguishing various analytes, including similar homologues such as methanol and ethanol. We expect the methodology to be applied to a broad spectrum of synthetic and biogenic nanowires for the integration of their collective properties in high-performance electronic devices.