Composite nanostructures consisting of porous NiO nanosheets on carbon nanotubes (CNTs) are fabricated using a facile and low-cost electroless plating method. The CNTs, modified by a polymer, are adopted as the template upon which porous Ni nanosheets are grown using electroless plating. This is followed by removal of the polymer layer and oxidation of the Ni by controlled thermal annealing. The effect of reductant concentration on the morphology of the NiO nanosheets is studied. The electrochemical characteristics of the nanostructures are measured using chronopotentiometry. Experimental measurements show that the NiO nanosheet covered CNT composite nanostructures exhibit a relatively high specific capacitance of 1177 F g ⁻¹ at a discharge current density of 2 A g ⁻¹ , while retaining 89.2% of its initial capacitance at a current density of 2 A g ⁻¹ after 1000 cycles.

Molecular dynamics simulations were applied to study the wetting properties of nanoscale droplets on a polar silica solid substrate subjected to constant and alternative electric fields with various field frequencies. Results show that the external applied electric fields have significant effects on the wetting of the nanoscale droplet on a polar solid substrate. The droplet spreads asymmetrically under the effect of the external applied field, and this asymmetry culminates to the maximum when the electric field equals to 0.45 V nm⁻¹. For an electric field of 1.0 V nm⁻¹, the dynamic electro-wetting process undergoes two stages even with a symmetric equilibrium spreading state. The stage A–B transition happens suddenly when molecules on the leading edge drop onto the solid surface due to the strong attraction of the solid substrate. Furthermore, under the alternative electric field with a different GHz frequency range, it was observed that the spreading asymmetry was weakened by increasing the field frequency and the nanoscale water droplet shape changes very slightly above a threshold frequency. Accompanied by the shape variation of water droplets, the molecular dipole orientations of water molecules experience a remarkable change from a random disordered distribution to an ordered profile because of the realignment of water molecules induced by electric fields. In addition, the polar solid surface has significant effects on the rearrangement of water molecules compared with a single droplet. Thus, the electro-wetting behaviors of water droplets on a silica solid surface are determined by the competing intermolecular forces among water, solid and the electric field.

Molecular dynamic simulations were adopted to study the wetting properties of nanoscale droplets on rough silicon solid substrate subject to perpendicular electric fields. The effect of roughness factor and electric field strength on the static and dynamic wetting behaviors of a nano-droplet on a solid surface was investigated at the molecular level. Results show that the static contact angle tends to decrease slightly and show small difference with the increase of roughness factor, while it shows an obvious increase for the ramp-shaped surface because the appearing bottom space reduces the wettability of solid surface. Additionally, under the electric field, a nano-droplet was elongated in the field direction and the equilibrium contact angle increases with the increase of electric field strength. The nano-droplet was completely stretched to be column-shaped at a threshold value of the field. Besides, accompanied by the shape variation of water droplets, the molecular dipole orientations of water molecules experience a remarkable change from a random disordered distribution to an ordered profile because of the realignment of water molecules induced by electric fields.

A numerical analysis is presented of the Rayleigh–Taylor instability (RTI) in the presence of an external electric field, with an emphasis on nonlinear phenomena associated with the evolution of complex interfacial morphology. The Poisson equation for the electric field and the Navier–Stokes equation for fluid flow field are solved simultaneously along with the Cahn–Hilliard phase field equation for interface deformation and morphology development. Numerical model is validated against the existing data and the results of linear analysis. Extensive numerical simulations are carried out for a wide range of fluid flow and electric field conditions. Computed results show that, in both linear and nonlinear regimes, a horizontal field suppresses the RTI, while a vertical electric field aggravates it. However, the vertical field does not affect the secondary instability; specifically, it does not contribute to the baroclinical generation of vorticity and consequently does not affect the roll-up formation. Linear analysis predicts that the RTI remains the same with the interchange of the dielectric constants of the two fluids, which is also confirmed by the numerical model for small interface deformations. This prediction, however, does not hold true in the nonlinear regimes in that complex interfacial morphology may evolve quite differently if the dielectric constants of two fluids are interchanged.

A computational model is developed to study the manufacturing of micro/nanostructures by electrohydrodynamic (EHD) patterning processes. The computational methodology is based on the iterative coupling of the discontinuous boundary element method for electric field with the finite element method for free surface deformation. The model is capable of modeling fully nonlinear free surface deformations induced by an electric field. Geometric discontinuity resulting from the contact of the liquid film with the template is fully accounted for by introducing the short-range molecular forces. The critical voltage for liquid film instability is found by tracing the asymptote of the structural height vs. applied voltage curve, followed by a confirmation by the existence of an internal minimum of the total free energy. Computer codes are verified using the analytical solutions and available measurements. An important finding from the numerical simulations is that steady state structures can be electrohydrodynamically patterned when the applied voltage is either below or above a critical value. While linear analyses are useful, they may significantly over-predict the critical voltage, a crucial parameter for an EHD patterning process. The highly nonlinear phenomena of wetting the template above the critical voltage were considered to be unstable within the framework of linear perturbation. However, these phenomena can be very well predicted by the nonlinear boundary/finite element model enhanced by the short-range molecular forces. Finally, the computational model is flexible and may be modified with ease to analyze an EHD-patterning process for an air–polymer–polymer tri-layered system or other multiple-layered films for fabricating more complex nanostructures.