Surface-charge effects on the electro-orientation of insulating boron-nitride nanotubes in aqueous suspension

Abstract

The alignment of hexagonal boron-nitride nanotubes (BNNTs) in aqueous KCl solutions under spatially uniform electric fields was examined experimentally, using direct optical visualization to probe the orientation dynamics of individual BNNTs for different electric-field frequencies. Different from most previously studied nanowires and nanotubes, BNNTs are wide-bandgap materials which are essentially insulating at room temperature. We analyze the electro-orientation of BNNTs in the general context of polarizable cylindrical particles in liquid suspensions, whose behavior can fall into different regimes, including alignment due to Maxwell-Wagner induced dipoles at high frequencies, and alignment due to fluid motion of the electrical double layer around the particles at lower frequencies. For BNNTs, the variation of the crossover frequencies in the electro-orientation spectra was studied in electrolytes of different conductivity. The effect of BNNT surface charge on electro-orientation was further studied by changing the pH of the aqueous solution. We find that the electric-field alignment of the BNNTs in the low-frequency regime is associated with the charging and motion of the electrical double layer around the particle. However, as BNNTs are non-conducting particles, the reasons for the formation of the electrical double layer are likely to be different than that of conducting particles. We discuss two possible mechanisms for the double-layer formation and alignment of 1D dielectric particles, and make comparison to those for the more commonly studied conducting particles.

Dynamic interphase–mediated assembly for deep cycling metal batteries

“…(ii) Under the electric field, excess counterions inside the EDL migrate and lead an electro-osmotic flow along the nanosheet surface, inducing an EDL polarization ( 37 ). Because of the anisotropic structure of nanosheets, excess polarization parallel to nanosheet surface can induce a torque to align the nanosheets with the electric field (text S1) ( 38 ). (iii) The vertically aligned nanosheets at the liquid-solid interface can further influence the orientation of Zn electrodeposits by preferential adsorption on (0002) Zn facet.…”

Emerging Applications of Boron Nitride Nanotubes in Energy Harvesting, Electronics, and Biomedicine

“…Centindag et al has started in some initiatives by aligning BNNTs in aqueous solution under spatially uniform electric fields. 20 Apparently, large-scale dispersion and integration of BNNTs into membranes are still challenging and would be an essential topic for the practical use of BNNTs in power production. In addition, condensation of salt crystals is reported within the channel of the t-BNNTs, 13 signifying an issue to continuously generate power by such an approach.…”

“…The next step would be to integrate arrays of BNNTs into fluidic membranes for practical usage. Centindag et al has started in some initiatives by aligning BNNTs in aqueous solution under spatially uniform electric fields . Apparently, large-scale dispersion and integration of BNNTs into membranes are still challenging and would be an essential topic for the practical use of BNNTs in power production.…”

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“…51 The interlayer formed by solution casting has a dense network structure and plays a vital role in hindering the migration of charge carrier. 52 In Fig. 6(b), the insulation resistivity of the lm was calculated according to leakage currents.…”