Low External Force Research Articles

Reversible Mechanochemistry Enabled Autonomous Sustaining of Robustness of Polymers—An Example of Next Generation Self-healing Strategy

Even under low external force, a few macromolecules of a polymer have to be much more highly stressed and fractured first due to the inherent heterogeneous microstructure. When the materials keep on working under loading, as is often the case, the minor damages would add up, endangering the safety of use. Here we show an innovative solution based on mechanochemically initiated reversible cascading variation of metal-ligand complexations. Upon loading, crosslinking density of the proof-of-concept metallopolymer networks autonomously increases, and recovers after unloading. Meanwhile, the stress-induced tiny fracture precursors are blocked to grow and then restored. The entire processes reversibly proceed free of manual intervention and catalyst. The proposed molecular-level internal equilibrium prevention mechanisms fundamentally enhance durability of polymers in service.

Molecular Dynamics Study of Graphene Nanoflake Shuttle Device on Graphene Nanoribbon with Carbon Nanotube Blocks.

Superlubric motions of graphene nanoflakes (GNFs) on graphene have opened up more applications of graphene for micromachines and nanomachines. Here, we investigate the dynamic behavior of a GNF shuttle on a graphene nanoribbon (GNR) with carbon nanotube (CNT) blocks via molecular dynamics simulations. The GNF moves on a GNR superlubrically, and the CNTs as building blocks induce bistable potential wells so that the GNF is stabilized. MD simulation results indicate that when a GNF shuttle approaches the CNTs, a potential well is created by an increase in the attractive van der Waals energy between the GNF and CNTs, and bistability at the local energy minima positions can be achieved near the CNTs. In order for the GNF shuttle to escape the local energy minima positions, a high external force must be applied to overcome the potential energy barrier. However, after the GNF shuttle escapes from one of the bistable positions, only a low external force is required to stabilize the GNF shuttle. This work explicitly demonstrates that a GNF-GNR/CNT system could be applied to alternative nonvolatile memory and high-speed mass storage by using GNR-CNT arrays.

Enlightening the role of critical parameters for the determination of the tensile strength by means of the Circular Semi Ring test

Analytic formulae for stresses and displacements are provided for the Circular Semi Ring under either compression or tension. The respective expressions for the tensile strength for both tests are obtained and compared to existing ones. In addition, it is shown that smooth contact between the specimen and the loading device should be preferred. The suggested tests seem to remove some drawbacks of existing methods for obtaining the tensile strength of brittle materials: Fracture is achieved at points where the stress field is purely tensile and, also, very low external force is required thus avoiding premature fracturing at the specimen-loading device contact region. From the theoretical point of view the tension test appears to be more advantageous regarding the very low fracture load and the fact that the maximum tensile stress is higher in absolute value from the respective compressive one.

Aluminosilicate Nanotubes Embedded Polyamide Thin Film Nanocomposite Forward Osmosis Membranes with Simultaneous Enhancement of Water Permeability and Selectivity.

Nanocomposite membranes are strongly desired to break a trade-off between permeability and selectivity. This work reports new thin film nanocomposite (TFN) forward osmosis (FO) membranes by embedding aluminosilicate nanotubes (ANTs) into a polyamide (PA) rejection layer. The surface morphology and structure of the TFN FO membranes were carefully characterized by FTIR, XPS, FESEM and AFM. The ANTs incorporated PA rejection layers exhibited many open and broad “leaf-like” folds with “ridge-and-valley” structures, high surface roughness and relatively low cross-linking degree. Compared with thin film composite (TFC) membrane without ANTs, the TFN membrane with only 0.2 w/v% ANTs loading presented significantly improved FO water permeability, selectivity and reduced structural parameters. This promising performance can be mainly contributed to the special ANTs embedded PA rejection layer, where water molecules preferentially transport through the nanochannels of ANTs. Molecular dynamic simulation further proved that water molecules have much larger flux through the nanotubes of ANTs than sodium and chloride ions, which are attributed to the intrinsic hydrophilicity of ANTs and low external force for water transport. This work shows that these TFN FO membranes with ANTs decorated PA layer are promising in desalination applications due to their simultaneously enhanced permeability and selectivity.

Effect of diameter and height of electrochemically-deposited ZnO nanorod arrays on the performance of piezoelectric nanogenerators

We investigated the performance of zinc oxide (ZnO) nanorod arrays (NRAs)-based piezoelectric nanogenerators (NGs) by controlling their diameter and height which are closely related to piezoelectric output current. The ZnO NRAs as a nanostructured piezoelectric material were synthesized on flexible indium tin oxide (ITO)-coated polyethylene terephthalate (PET) (i.e., ITO/PET) substrates by a facile electrochemical deposition (ED) method. As the zinc nitrate concentration and growth time increased, the diameter and height of ZnO NRAs also increased. Based on the ZnO NRAs on ITO/PET, piezoelectric NGs were fabricated with an opposite electrode of gold-coated PET film (i.e. Au/PET). At 10 mM of zinc nitrate concentration and 1 h of growth time, the ZnO NRAs exhibited relatively regular and higher output currents, leading to an estimated average value of ∼10.4 nA/cm2 under a low external pushing force of 0.98 N. For the samples at 1 and 100 mM, piezoelectric currents were relatively low (∼4.34 and 1.45–5.21 nA/cm2, respectively). It was found that the ZnO NRAs with high diameter/height uniformity and good alignment tend to be bent more easily for efficiently generating piezoelectric currents. The bending efficiency of ZnO NRAs was also analysed theoretically by calculating the strain distribution of ZnO NRAs-based NGs with different diameters and heights of the nanorods.

High transparency and triboelectric charge generation properties of nano-patterned PDMS

Triboelectric charge generation and high transparency properties of the nano-patterned PDMS, which was stamped by silicon subwavelength grating structures as a mold, on indium tin oxide (ITO) coated polyethylene terephthalate (PET) were investigated for triboelectric nanogenerators. At visible wavelengths, the nano-patterned PDMS on ITO coated PET (i.e., ITO/PET) exhibited high transmittances of >85%, together with a theoretical analysis using the RCWA simulation. When the ITO/PET was compressed onto the nano-patterned PDMS on ITO/PET, the output voltage and current density were reliably generated with a short interval time of 0.17 s, which yielded −5.2/5.4 V and −0.57/0.74 μA cm−2, respectively, under a low external pushing force. The effect of pushing frequency on the output voltage and current density was also investigated.

Efficient piezoelectric ZnO nanogenerators based on Au-coated silica sphere array electrode

We reported ZnO nanorod-based piezoelectric nanogenerators (NGs) with Au-coated silica sphere array as an efficient top electrode. This electrode can readily bend the ZnO nanorods due to its enhanced surface roughness, thus resulting in more increased and regular piezoelectric charge output. Under a low external pushing force of 0.3 kgf, the output current and voltage were increased by approximately 2.01 and 1.51 times, respectively, in comparison with a conventional Au top electrode without silica spheres. Also, the effect of Au-coated silica spheres on the bending radius of ZnO nanorods was theoretically investigated.

Experimental Research on the Quantitative Characterizations of Elasticity and Viscosity of Polyacrylamide Solution

Through creep-recovery and dynamic experiments, the viscoelasticity of polyacrylamide solutions (in short polymer) with different mass concentration are studied, the proportions of elastic part and viscous part in the polymer solution are calculated and the limit of mass concentration called high concentration polymer solution is given. It is indicated that the elastic part of the polymer solution increases firstly and tends to be constant with the increase in mass concentration under low external force condition. The minimum mass concentration of the polymer solution keeping constant elastic part is 1500mg/L. Under low stress and low shear rate conditions, the viscous part of the polymer solution is greater than that of elastic part; but under oil reservoir shear rate (6.283s-1) condition, the elastic part is greater than viscous part, and its elastic part increases with the increase in mass concentrations and the increment becomes smaller.

Nanoscale Poiseuille flow and effects of modified Lennard–Jones potential function

Numerical simulation of Poiseuille flow of liquid Argon in a nanochannel using the non-equilibrium molecular dynamics simulation (NEMD) is performed. The nanochannel is a three-dimensional rectangular prism geometry where the concerned numbers of Argon atoms are 2,700, 2,550 and 2,400 at 102, 108 and 120 K. Poiseuille flow is simulated by embedding the fluid particles in a uniform force field. An external driving force, ranging from 1 to 11 PN (Pico Newton), is applied along the flow direction to inlet fluid particles during the simulation. To obtain a more uniform temperature distribution across the channel, local thermostating near the wall are used. Also, the effect of other mixing rules (Lorenthz–Berthelot and Waldman–Kugler rules) on the interface structure are examined by comparing the density profiles near the liquid/solid interfaces for wall temperatures 108 and 133 K for an external force of 7 PN. Using Kong and Waldman–Kugler rules, the molecules near the solid walls were more randomly distributed compared to Lorenthz–Berthelot rule. These mean that the attraction between solid–fluid atoms was weakened by using Kong rule and Waldman–Kugler rule rather than the Lorenthz–Berthelot rule. Also, results show that the mean axial velocity has symmetrical distribution near the channel centerline and an increase in external driving force can increase maximum and average velocity values of fluid. Furthermore, the slip length and slip velocity are functions of the driving forces and they show an arising trend with an increase in inlet driving force and no slip boundary condition is satisfied at very low external force (<1 PN).

Global existence for a forced dispersive dissipative equation via the I-method

In this paper, we first investigate the Korteweg-de Vries-Burgers(KdV-Burgers) equation with low regularity external force $f$, where$f$ is a space-time function. We show that we can adapt the I-methodto study the global well-posedness of our problem on a Sobolevspace of negative index when a low regularity space-time externalforce occurs.

Molecular dynamics study on the field effect ion transport in carbon nanotube

We investigated potassium ion transport in the (5, 5) carbon nanotube by using classical molecular dynamics simulations under applying external force fields. This can be applied to nanoscale ionic-field-effect devices. As the applying external force field increases, the potassium ions rapidly go through the nanochannel. Under the low external force fields, the thermal fluctuation of the nanochannel affected on the tunneling of the potassium ions, whereas the effects of the thermal fluctuation were negligible under the high external force fields.

Talin B is required for force transmission in morphogenesis of Dictyostelium.

Talin plays a key role in the assembly and stabilisation of focal adhesions, but whether it is directly involved in force transmission during morphogenesis remains to be elucidated. We show that the traction force of Dictyostelium cells mutant for one of its two talin genes talB is considerably smaller than that of wild-type cells, both in isolation and within tissues undergoing morphogenetic movement. The motility of mutant cells in tightly packed tissues in vivo or under strong resistance conditions in vitro was lower than that of wild-type cells, but their motility under low external force conditions was not impaired, indicating inefficient transmission of force in mutant cells. Antibody staining revealed that the talB gene product (talin B) exists as small units subjacent to the cell membrane at adhesion sites without forming large focal adhesion-like assemblies. The total amount of talin B on the cell membrane was larger in prestalk cells, which exert larger force than prespore cells during morphogenesis. We conclude that talin B is involved in force transmission between the cytoskeleton and cell exterior.

Mechanical state of airway smooth muscle at very short lengths.

Although the shortening of smooth muscle at physiological lengths is dominated by an interaction between external forces (loads) and internal forces, at very short lengths, internal forces appear to dominate the mechanical behavior of the active tissue. We tested the hypothesis that, under conditions of extreme shortening and low external force, the mechanical behavior of isolated canine tracheal smooth muscle tissue can be understood as a structure in which the force borne and exerted by the cross bridge and myofilament array is opposed by radially disposed connective tissue in the presence of an incompressible fluid matrix (cellular and extracellular). Strips of electrically stimulated tracheal muscle were allowed to shorten maximally under very low afterload, and large longitudinal sinusoidal vibrations (34 Hz, 1 s in duration, and up to 50% of the muscle length before vibration) were applied to highly shortened (active) tissue strips to produce reversible cross-bridge detachment. During the vibration, peak muscle force fell exponentially with successive forced elongations. After the episode, the muscle either extended itself or exerted a force against the tension transducer, depending on external conditions. The magnitude of this effect was proportional to the prior muscle stiffness and the amplitude of the vibration, indicating a recoil of strained connective tissue elements no longer opposed by cross-bridge forces. This behavior suggests that mechanical behavior at short lengths is dominated by tissue forces within a tensegrity-like structure made up of connective tissue, other extracellular matrix components, and active contractile elements.

Motion of laser-cooled atoms in an optical potential.

The motion of laser-cooled $^{85}\mathrm{Rb}$ atoms along a one-dimensional optical potential under the influence of an external force is investigated. The transition from a region of low external force, where the motion is dominated by the optical potential, to one of a strong force, where the presence of the optical potential is hardly felt, is demonstrated. An unexpected discrepancy is found between the measured and expected value of the drift velocity induced by an applied magnetic field on a one-dimensional ${\mathrm{\ensuremath{\sigma}}}^{+}$-${\mathrm{\ensuremath{\sigma}}}^{\mathrm{\ensuremath{-}}}$ optical molasses.