Using a water-confined carbon nanotube to probe the electricity of sequential charged segments of macromolecules

The detection of macromolecular conformation is particularly important in many physical and biological applications. Here we theoretically explore a method for achieving this detection by probing the electricity of sequential charged segments of macromolecules. Our analysis is based on molecular dynamics simulations, and we investigate a single file of water molecules confined in a half-capped single-walled carbon nanotube (SWCNT) with an external electric charge of +e or -e (e is the elementary charge). The charge is located in the vicinity of the cap of the SWCNT and along the centerline of the SWCNT. We reveal the picosecond timescale for the re-orientation (namely, from one unidirectional direction to the other) of the water molecules in response to a switch in the charge signal, -e → +e or +e →-e. Our results are well understood by taking into account the electrical interactions between the water molecules and between the water molecules and the external charge. Because such signals of re-orientation can be magnified and transported according to Tu et al. [2009 Proc. Natl. Acad. Sci. USA 106 18120], it becomes possible to record fingerprints of electric signals arising from sequential charged segments of a macromolecule, which are expected to be useful for recognizing the conformations of some particular macromolecules.     

The mechanical property of single-walled carbon nanotube under combined electromechanical loading

The mechanical properties and failure process of single-walled carbon nanotube (SWCNT) under combined electric field and tensile loading are investigated using the semi-empirical quantum mechanical method. The local and global structural deformation and variation of mechanical properties of SWCNT under different directions and intensity of external electric field are discussed systematically. It is shown that the electric field induced deformation in the radial and axial directions of the SWCNT are strongly dependent on the direction of electric field. The analysis of mechanical properties shows that the structure stiffness, tensile strength and failure strain of the SWCNT all decrease with the increase of the field intensity, which is particularly evident under the longitudinal electric field. The Young's modulus of SWCNTs vary with the tube diameter and are affected by the electric field. The increase of the length of the tubes intensifies the charge concentration at the tube ends under the electric field and lead to the decrease of mechanical properties of SWCNTs. The failure process of SWCNTs under the coupling effect of electric field and tensile loading is found to be controlled by the field strength and also affected by the electric charge accumulation.     

Effects of O2 and N2/H2 plasma treatments on the neuronal cell growth on single-walled carbon nanotube paper scaffolds

The O₂ and N₂/H₂ plasma treatments of single-walled carbon nanotube (SWCNT) papers as scaffolds for enhanced neuronal cell growth were conducted to functionalize their surfaces with different functional groups and to roughen their surfaces. To evaluate the effects of the surface roughness and functionalization modifications of the SWCNT papers, we investigated the neuronal morphology, mitochondrial membrane potential, and acetylcholine/acetylcholinesterase levels of human neuroblastoma during SH-SY5Y cell growth on the treated SWCNT papers. Our results demonstrated that the plasma-chemical functionalization caused changes in the surface charge states with functional groups with negative and positive charges and then the increased surface roughness enhanced neuronal cell adhesion, mitochondrial membrane potential, and the level of neurotransmitter in vitro. The cell adhesion and mitochondrial membrane potential on the negatively charged SWCNT papers were improved more than on the positively charged SWCNT papers. Also, measurements of the neurotransmitter level showed an enhanced acetylcholine level on the negatively charged SWCNT papers compared to the positively charged SWCNT papers.     

Crystallisation of ice in charged Pt nanochannel

Using molecular dynamics simulations, we examine the crystallisation process of the extended simple point charge model (SPC/E) water confined in a charged Pt nanochannel. The presence of the external electric field enhances the surface layering of water and promotes the super-cooled water to crystallise into Ic ice within tens of nanoseconds. Ic ice is found to nucleate from the interior of the water lamina, and the Pt(111) surfaces do not show a remarkable promotion of Ic ice nucleation. Structural analysis reveals that a two-dimensional hydrogen-bond network is built among the water molecules absorbed on the charged Pt surfaces, which influences the bonding of the molecules between the first and the second layers, and disturbs the formation of tetrahedral structures that match Ic ice, finally resulting in the nucleation-free near the walls. Such arrangements of water molecules remain in the subsequent growth of Ic ice and cause the slowdown of growth velocity while approaching surfaces.     

Molecular dynamics simulations of electrostatic layer-by-layer self-assembly

Electrostatic assembly of multilayered thin films through sequential adsorption of polyions in layer-by-layer fashion utilizes the strong electrostatic attraction between oppositely charged molecules. We perform molecular dynamics simulations of multilayers of flexible polyelectrolytes around a charged spherical particle. Our simulations establish that the charge reversal after each deposition step is a crucial factor for the steady layer growth. The multilayers appear to be nonequilibrium structures.     

Off-centre charge model of the planar electric double layer for asymmetric 2:1/1:2 valencies

ABSTRACT

Grand canonical Monte Carlo simulation results are reported for the structure and capacitance of a planar electric double layer containing off-centre charged rigid sphere cations and centrally charged rigid sphere anions. The ion species are assigned asymmetric valencies, +2:?1 and +1:?2, respectively, and set in a continuum dielectric medium (solvent) characterised by a single relative permittivity. An off-centre charged ion is obtained by displacing the ionic charge from the centre of the sphere towards its surface, and the physical double layer model is completed by placing the ionic system next to a uniformly charged, non-penetrable, non-polarizable planar electrode. Structural results such as electrode-ion singlet distribution functions, ionic charge density and orientation profiles are complemented by differential capacitance results at electrolyte concentrations of 0.2?mol/dm³ and 1?mol/dm³, respectively, and for various displacements of the cationic charge centre. The effect of asymmetry due to off-centre cations and valency asymmetry on the double layer properties is maximum for divalent counterions and when the cation charge is closest to the hard sphere surface.     

Polarization nonlinear optics of quadratically nonlinear azopolymers

The polarization properties of second harmonic and sum-frequency signals generated by femtosecond laser pulses in films of polymers containing covalent groups of an azobenzothiazole chromophore polarized by an external electric field are investigated. It is shown that the methods of polarization nonlinear optics make it possible to determine the structure of oriented molecular dipoles and reveal important properties of the motion of collectivized π electrons in organic molecules with strong optical nonlinearities. The polarization measurements show that the tensor of quadratic nonlinear optical susceptibility of chromophore fragments oriented by an external field in macromolecules of the noted azopolymers has a degenerate form. This is indicative of a predominantly one-dimensional character of motion of collectivized π electrons along an extended group of atoms in such molecules.     

Single-Walled Carbon Nanotubes Acting as Controllable Transport Channels

The motion and equilibrium distribution of water molecules adsorbed inside neutral and negatively charged singlewalled carbon nanotubes (SWNTs) have been studied using molecular dynamics simulations (MDSs) at room temperature based on CHARMM (Chemistry at HARvard Molecular Mechanics) potential parameters. We find that water molecules have a conspicuous electropism phenomenon and regular tubule patterns inside and outside the charged tube wall. The analyses of the motion behaviour of water molecules in the radial and axial directions show that by charging the SWNT, the adsorption efficiency is greatly enhanced, and the electric field produced by the charged SWNTs prevents water molecules from flowing out of the nanotube. However, water molecules can travel through the neutral SWNT in a fluctuating manner. This indicates that by electrically charging and uncharging the SWNTs, one can control the adsorption and transport behaviour of polar molecules in SWNTs for using as a stable storage medium or long transport channels. The transport velocity can be tailored by changing the charge on the SWNTs, which may have a further application as modulatable transport channels.     

Detection of positive and negative ions in a wire ionization counter filled with atmospheric air

The physical processes occurring during the detection of individual ions in a wire counter filled with atmospheric air are studied, and the amplitude distribution of electric pulses is measured. It is shown that a positive ion is detected due to electron emission from the surface of a negatively charged wire, whereas a negative ion is detected due to electron detachment near a positively charged wire. The secondary processes accompanying the neutralization of positive ions at a negatively charged external electrode and negatively charged wire are considered. It is established that, in contrast to standard proportional counters, these secondary processes result in an increase in the number of electric pulses rather than in an increase in the electric pulse amplitude. The wire counter allows the detection of both ions produced inside the detector and ions injected into the detector from the ambient air. Possible applications of air-filled wire detectors are described.     

Theoretical study of hydrogen adsorption in Ti-decorated capped carbon nanotube

We present ab initio study using dispersion-corrected density functional theory calculations to investigate the hydrogen interaction with Ti-coated, one end closed, single-walled carbon nanotube (SWCNT). Our results demonstrate that a single Ti atom binds up to five hydrogen molecules on SWCNT cap top, whereas adsorption of four hydrogen molecules is energetically more favourable. The analyses from adsorption energy profile, highest occupied molecular orbital–lowest unoccupied molecular orbital gap and Mulliken charge distribution show contrast in first hydrogen molecule adsorption compared with the rest of four configurations. This is clearly due to the strongly different bonding nature of first hydrogen adsorption among others, between hydrogen molecules and Ti-coated SWCNT. These results not only support our understanding of adsorption nature of hydrogen in Ti-coated SWCNTs but also suggest new directions for smart storage techniques.     

Pair Production of the Doubly Charged Leptons Associated with a Gauge Boson γ or Z in e~+e~-and γγ Collisions at Future Linear Colliders

In this paper,we investigate the production of a pair of doubly charged leptons associated with a gauge boson V(γ or Z) at future linear colliders via e~+e~-and γγ collisions.The numerical results show that the possible signals of the doubly charged leptons may be detected via the processes e~+e~→VX~(++)X~(--)and γγ→VX~(++)X~(--)at future ILC or CLIC experiments.     

Label-free detection of charged macromolecules by using a field-effect-based sensor platform: Experiments and possible mechanisms of signal generation

The possibilities and limitations of a direct electrical detection of charged macromolecules using a field-effect-based sensor platform is evaluated, mainly focusing on capacitive EIS (electrolyte-insulator-semiconductor) devices. The experimentally obtained results on the detection of DNA immobilisation and hybridisation as well as the monitoring of layer-by-layer adsorbed charged polyelectrolyte (PE) multilayers have been discussed by using two basic possible mechanisms of signal generation, namely the intrinsic charge of the macromolecules and the charge redistribution within the intermolecular spaces or in the multilayer. The effects of the layer-by-layer adsorption conditions (unbuffered and pH buffer solution), and the number and polarity of charged layers on the sensor response have been systematically investigated by means of capacitance–voltage (C–V), constant–capacitance (ConCap) and impedance spectroscopy (IS) methods. PACS 82.47.Rs; 82.80.Fk; 85.30.Tv; 87.15.Kg; 87.14.Gg     

曲率对Rh在锯齿型单壁碳纳米管内外吸附影响的研究

利用密度泛函理论系统的研究了单壁碳纳米管的曲率对Rh原子在锯齿型碳管内外的吸附行为, 发现Rh原子在管外吸附比管内稳定; 随着碳管管径的增加, 曲率减小, 管内外吸附能的差值逐渐减小, 接近Rh原子在石墨烯上的吸附能. 电荷密度分析表明, 由于卷曲效应使碳纳米管管外的电荷密度大于管内, 随着曲率减小, 这种差别逐渐减小. 管内外吸附Rh原子的Bader电荷差值及局域态密度差别亦随着曲率的下降而减小, 这与Rh原子在管内外吸附能的变化规律相一致.     

Compton scattering of 59.5 keV gamma rays from p-Si sample in an external electric field

This study is related to Compton scattering of photons from a p-Si sample whose surface charge density distributions are changed by an external electric field. The external electric field intensity in the range 0-75 kV/m was used to change the surface charge density distributions of the sample. The sample surface perpendicular to the electric field was selected as the scattering surface. The p-Si sample was bombarded by 59.5 keV γ-photons emitting from an Am-241 point source. The Compton scattered photons at an angle of 90^o were detected by an Si(Li) detector. The Compton scattering intensity suddenly increased with the application of the electric field since the applied electric field distorts both the negatively charged scattering center (free electron, bound electron, ionized acceptor) and the positively charged scattering center (hole) and their momentum distribution in the sample. There is a good third-order polynominal relation between the Compton scattering intensity and the increasing (or decreasing) electric field intensity. The results show that the positively charged scattering centers behave like negatively charged scattering centers, but the latter are slightly more effective than the former in the Compton scattering of γ-rays from the sample in the electric field.     

Water contact angles on charged surfaces in aerosols

Interactions between water and solid substrates are of fundamental importance to various processes in nature and industry. Electric control is widely used to modify interfacial water, where the influence of surface charges is inevitable. Here we obtain positively and negatively charged surfaces using LiTaO₃ crystals and observe that a large net surface charge up to 0.1 C/m² can nominally change the contact angles of pure water droplets comparing to the same uncharged surface. However, even a small amount of surface charge can efficiently increase the water contact angle in the presence of aerosols. Our results indicate that such surface charges can hardly affect the structure of interfacial water molecular layers and the morphology of the macroscopic droplet, while adsorption of a small amount of organic contaminants from aerosols with the help of Coulomb attraction can notably decrease the wettability of solid surface. Our results not only provide a fundamental understanding of the interactions between charged surfaces and water, but also help to develop new techniques on electric control of wettability and microfluidics in real aerosol environments.     

Electric dispersion of fluid under the oscillatory instability of its free surface

A semiphenomenological analysis is performed of possible modes of electric dispersion of drops and menisci at the end of the capillary used to deliver the liquid into the discharge system under an oscillatory instability of the charged liquid surface. The instability is assumed to be induced by a time-dependent external force acting on the liquid surface, a finite rate of charge redistribution over the surface under virtual deformations, and tangential discontinuity of the velocity field across the interface.     

Tunneling Radiation of Charged and Magnetized Particles from the Reissner-Nordstr?m-de Sitter Black Holes with Magnetic Charges

We extended the Parikh-Wilczek’s method to calculate the tunneling radiation of charged and magnetized particles from the event horizon and the cosmological horizon of the Reissner-Nordstr?m-de Sitter black hole with magnetic charges. We reconstructed the electromagnetic field tensor and recalculated the Lagrangian of the field corresponding to the source with electric and magnetic charges. By viewing the eclectic and magnetic charges as an equivalent electric charge, we obtained the tunneling rate of the charged and magnetized particles. Our calculation supports the conclusion given by Parikh and Wilczek that the emission spectrum is no longer purely thermal, and the emission process supports the information conservation.     

Nature of a high-conductivity state of poly(diphenylene phthalide)

For thin films prepared from non-conjugated polymer, including poly(diphenylene phthalide) (PDP), a rather enigmatic transition to a metal-like high-conductivity state is observed. The existing models of the HCS in wide-band polymers were examined. The main feature of these models is a significant (often highly improbable) rearrangement of the electronic structure of part of the macromolecules under the action of external factors (an electric field, light, injected electrons, etc.). The model of the HCS in PDP proposed in the current work is based on the results of studying the electron-acceptor properties of fragments of PDP macromolecules and the concepts of molecular electronics. Electron-acceptor unoccupied orbitals of the fragments of macromolecules and the corresponding energy levels are assumed to act as transport nodes for the resonance coherent tunneling of electrons. Since PDP has no intrinsic charge carriers, the key role in the formation of the HCS is played by the injection of electrons from the electrodes and, hence, the processes occurring in the interface. The resonance injection of electrons from the Fermi level of the electrode immediately onto the transport levels of the polymer is achieved due to the applied electric field, chemical connection of macromolecules to the electrodes, and ensuing modification of the interface dipole. The connection of PDP macromolecules to the electrodes occurs via defective hydroxyl and carboxyl groups. Carboxylate ions, which interact with the electrode metal, can also be formed because of the dissociative capture of injected electrons by phthalide cycles adjacent to the electrode. Since a conducting channel in a 1-μm-thick film should be composed of at least ten PDP macromolecules, it is necessary to assume that an efficient electron transfer occurs between macromolecules. The proposed concept was additionally substantiated by invoking the published data on the conductivity of DNA molecules and the field emission of electrons from metals coated with a PDP film.     

Elastic charge density representation of the interaction via the nematic director field

The interaction between particle-like sources of the nematic director distortions (e.g., colloids, point defects, macromolecules in nematic emulsions) allows for a useful analogy with the electrostatic multipole interaction between charged bodies. In this paper we develop this analogy to the level corresponding to the charge density and consider the general status of the pairwise approach to the nematic emulsions with finite-size colloids. It is shown that the elastic analog of the surface electric charge density is represented by the two transverse director components on the surface imposing the director distortions. The elastic multipoles of a particle are expressed as integrals over the charge density distribution on this surface. Because of the difference between the scalar electrostatics and vector nematostatics, the number of elastic multipoles of each order is doubled compared to that in the electrostatics: there are two elastic charges, two vectors of dipole moments, two quadrupolar tensors, and so on. The two-component elastic charge is expressed via the vector of external mechanical torque applied on the particle. As a result, the elastic Coulomb-like coupling between two particles is found to be proportional to the scalar product of the two external torques and does not directly depend on the particles' form and anchoring. The real-space Green function method is used to develop the pairwise approach to nematic emulsions and determine its form and restrictions. The pairwise potentials are obtained in the familiar form, but, in contrast to the electrostatics, they describe the interaction between pairs (dyads) of the elastic multipole moments. The multipole moments are shown to be uniquely determined by the single-particle director field, unperturbed by other particles. The pairwise approximation is applicable only in the leading order in the small ratio particle size-to-interparticle distance as the next order contains irreducible three-body terms.     

工业中粉体颗粒的荷电机理及数值模拟方法

工业过程中粉体颗粒不可避免地会相互摩擦碰撞而荷电. 荷电颗粒的存在可能会危害正常的工业生产过程, 也可能对工业过程起促进作用. 因此, 荷电粉体颗粒及其特性受到了广泛的关注, 但目前对粉体颗粒的荷电机理依然缺乏透彻的了解, 尤其是在气固两相流动中的粉体颗粒荷电现象. 事实上, 工业中存在的粉体颗粒的运动都受到流体的影响, 是典型的气固两相流系统, 流体对粉体颗粒的作用使粉体颗粒接触的荷电现象变得更为复杂, 因此从两相流动的观点来研究粉体颗粒荷电的物理本质就显得越来越重要. 本文介绍了工业过程中的几种不同类型的粉体颗粒荷电行为, 回顾了颗粒的荷电机理与描述颗粒荷电的数学模型. 对于工业过程中颗粒的荷电现象及颗粒在多相流体中的动力学行为, 介绍了研究颗粒受流体影响时荷电特性的数值模拟方法. 本文旨在对粉体颗粒的荷电机理、应用以及研究方法进行梳理与探讨, 为正确认识工业过程中粉体颗粒的荷电现象并加以控制利用提供理论借鉴.