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

Abstract

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 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 a rational strategy is executed. Here, we report that in shearing processes dopants such as 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.

Aqueous Coassembly of Small TiO2 Nanorods with Cellulose Nanocrystals into Transparent, Uniaxially Aligned Inorganic Thin Films for Waveplates

“…It has been previously reported that CNCs can aid in aligning high-aspect-ratio nanowires by preventing aggregation and enhancing orientational order. 34,35 In our case, CNCs facilitate the alignment of much smaller nanorods under shear. Our observation of uniaxial alignment of coassembled composite system is consistent with oriented, low-aspect-ratio gold nanorods mixed with CNCs as demonstrated by Liu et al 20 Although Liu's study was limited to low loading of gold nanorods, they did not calcine the material to remove organics.…”

Integration of PEGylated Polyaniline Nanocoatings with Multiple Plastic Substrates Generates Comparable Antifouling Performance

“…48 Although the detailed mechanism of in situ, oxidative polymerization remained in debate, 49 our previous studies have verified that individual V 2 O 5 •nH 2 O nanofibers functioned as sacrificing templates for the formation of nanofibrous PANI. 46,50 Based on the hydrophobic interparticulate interactions between nanofibrillar PANI, multiple structural forms such as thin films, 46 fibers, 51 and 3D networks 50,52 could be permanently maintained after oxidative polymerization using V 2 O 5 •nH 2 O dispersions or (thin) films as oxidant agents. It is worth noting that the method based on in situ, oxidative polymerization was equally valid for the fabrication of other conducting polymers including polypyrrole 50,53 and poly(3,4-ethylenedioxythiophene).…”

“…Therefore, the interactions between V 2 O 5 · n H 2 O nanofibers are so strong that adjacent nanofibers tend to be mutually oriented in each nematic polydomain in a spontaneous manner. The ordering can be preserved or enhanced permanently in continuous V 2 O 5 · n H 2 O films and thin films , after solvent removal. In short, both extreme aspect ratios and rich interfacial hydroxy groups guarantee strong interparticulate interactions between V 2 O 5 · n H 2 O nanofibers.…”

Nanowires in Flexible Sensors: Structure is Becoming a Key in Controlling the Sensing Performance

“…Certainly, it has been challenging to arbitrarily arrange nanowire into compact and desired geometry, but the recently reported bottom-up technologies endow the ability to assemble well-aligned nanowire arrays in a predesigned way with higher precision for practical applications. [117,118] There have been very good review focused on NWs assembly in recent years; [31,119,120] hence, we only provide a brief introduction on NWs assembly and pay close attention to analyzing the effect of the macrostructures on the sensing performances of the devices. Briefly, the choice for the method of transferring NWs onto flexible substrates is mainly determined by the synthesis process of the NWs.…”