Membrane separation technology is dictated by the permeability-selectivity trade-off rule, because selectivity relies on membrane pore size being smaller than that of hydrated ions. We discovered a previously unknown mechanism that breaks the permeability-selectivity trade-off in using a rotating nanoporous graphene membrane with pores of 2 to 4 nanometers in diameter. The results show that the rotating membrane exhibits almost 100% salt rejection even when the pore size is larger than that of hydrated ions, and the surface slip at the liquid/graphene interface of rotating membrane enables concurrent ultra-selectivity and unprecedented high permeability. A novel concept of “temporal selectivity” is proposed to attribute the unconventional selectivity to the time difference between the ion’s penetration time through the pore and the bypass time required for ion’s sliding across the pore. The newly discovered temporal selectivity overcomes the limitation imposed by pore size and provokes a novel theory in designing high-performance membranes.

Controllable directional transport of liquid droplets on a functionalized surface has been a challenge in the field of microfluidics because it does not require energy supply, and the physical mechanism of such self-driving transport exhibits extraordinary contribution to fundamental understanding of some biological processes and the design of microfluidic apparatus. In this paper, we report a novel design of a surface microstructure that can realize unidirectional self-driving liquid mercury (Hg) droplet transport on a graphene-covered copper (Cu) substrate with a three-dimensional surface microstructure. We have demonstrated that a liquid Hg droplet spontaneously propagates on a grooved Cu substrate covered by a monolayer graphene without any external force fields. Classical molecular dynamics results provide a profound insight on the self-driving process of Hg droplets. It shows that the Hg droplet undergoes acceleration, deceleration, and return stages successively from the narrow to wide ends of the gradient groove. Intriguingly, Hg droplets can move continuously and unidirectionally on the three-dimensional graphene-covered surface microstructure when they accumulate enough kinetic energy from the gradient groove to break the energy barrier at the step junctions between the two neighboring unit cells. The design of the zigzag textured surface covered by a monolayer graphene artfully uses the facts; (1) the monolayer graphene can effectively reduce the droplet pinning on the textured surface, (2) the hydrophobic graphene layer reduces the friction between Hg droplets and the substrate, and (3) the textured surface can permeably interact with the droplets through the monolayer graphene to achieve a continuous self-driving process. The findings reported here open a door to explore the graphene-covered functional surface to directional transport of liquid droplets and provide an in-depth understanding of the self-driving mechanism for liquid droplets on graphene-covered textured substrates.

Carbon nanotubes (CNTs) are frequently used as torsional devices in nanoelectromechanical systems; thus it is necessary to gain a thorough understanding of the mechanical behavior of tubes under torsion. In this paper, molecular dynamics simulations are carried out to investigate the torsional buckling of single-walled CNTs completely filled with copper atoms. Results show that, due to metal filling, the torsional rigidity of tubes can be dramatically enhanced and the critical torsional angles of filled tubes can be 2–4 times as high as those of empty ones. Furthermore, due to structural asymmetry in chiral metal-filled tubes, there exists a dependence of the torsional behavior on loading directions. The torsional response of metal-filled tubes is dependent on both tube chirality and loading direction. The microstructure of metal atoms may have a strong influence on the mechanical deformation of metal-filled tubes. These results can provide useful guidelines on the application of CNTs as torsional devices, especially in the case where high torsional stability is required.

No abstract

Conducting polypyrrole (PPy) films doped with p‐toluene solfonate (pTS−), perchlorate (ClO4−) and polyphosphate (PP−) were electrochemically synthesized on the stainless steel SS‐304 and the Indium Tin Oxide (ITO) glass substrates successfully. The conducting polymer composite films were studied by Fourier transform infrared spectra, integrated thermal analysis system and scanning electron microscopy, respectively. Four‐point probe measurements and in situ nanotribolab system equipped with a nanoscale electrical contact resistance package were employed to analyze their electrical and mechanical properties. Results indicate that the film doped with PP− ion showed the best thermal stability. For the ClO4− ion doped films, the glass transition occurred at 274.8 °C. The pTS− ion doped film on the SS‐304 steel had a good conductivity, and there was a voltage barrier that ranged from −1.25 to 1.9 V according to the current–voltage curves. Nanoindentation tests show that the mechanical properties of the PPy/pTS− film and the PPy/PP− film were better than that of PPy/ClO4− films. Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, a carbon nanotube-based charge-controlled speed-regulating nanoclutch (CNT-CC-SRNC), composed of an inner carbon nanotube (CNT), an outer CNT, and the water confined between the two CNT walls, is proposed by utilizing electrowetting-induced improvement of the friction at the interfaces between water and CNT walls. As the inner CNT is the driving axle, molecular dynamics simulation results demonstrate that CNT-CC-SRNC is in the disengaged state for the uncharged CNTs, whereas water confined in the two charged CNT walls can transmit the torque from the inner tube to the outer tube. Importantly, the proposed CNT-CC-SRNC can perform stepless speed-regulating function through changing the magnitude of the charge assigned on CNT atoms.

Mechanical energy harvesters are widely studied because of their diverse applications, such as harvesting of ocean wave energy, self-powered wireless sensors, portable power supplies and so on. To be feasible,...

Articles you may be interested inLinear relationship between water wetting behavior and microscopic interactions of super-hydrophilic surfaces Ab initio and classical molecular dynamics studies of the structural and dynamical behavior of water near a hydrophobic graphene sheet J. Chem. Phys. 138, 204702 (2013); 10.1063/1.4804300Droplet contact angle behavior on a hybrid surface with hydrophobic and hydrophilic properties A study on the dynamic behaviors of water droplets impacting nanostructured surfaces Wetting dynamics and motion behaviors of a water droplet on graphene are characterized under the electric-thermal coupling field using classical molecular dynamics simulation method. The water droplet on graphene can be driven by the temperature gradient, while the moving direction is dependent on the electric field intensity. Concretely, the water droplet on graphene moves from the low temperature region to the high temperature region for the relatively weak electric field intensity. The motion acceleration increases with the electric field intensity on graphene, whereas the moving direction switches when the electric field intensity increases up to a threshold. The essence is the change from hydrophilic to hydrophobic for the water droplet on graphene at a threshold of the electric field intensity. Moreover, the driven force of the water droplet caused by the overall oscillation of graphene has important influence on the motion behaviors. The results are helpful to control the wettability of graphene and further develop the graphene-based fluidic nanodevices.