电场对(4, 0)Zigzag模型单壁碳纳米管的影响

The structural and electronic properties of a (4, 0) zigzag single-walled carbon nanotube (SWCNT) under parallel and transverse electric fields with strengths of 0-1.4×10~(-2) a.u. Were studied using the density functional theory (DFT) B3LYP/6-31G~* method. Results show that the properties of the SWCNT are dependent on the external electric field. The applied external electric field strongly affects the molecular dipole moments. The induced dipole moments increase linearly with increase in the electrical field intensities. This study shows that the application of parallel and transverse electric fields results in changes in the occupied and virtual molecular orbitals (Mos) but the energy gap between the highest occupied MO (HOMO) and the lowest unoccupied MO (LUMO) of this SWCNT is less sensitive to the electric field strength. The electronic spatial extent (ESE) and length of the SWCNT show small changes over the entire range of the applied electric field strengths. The natural bond orbital (NBO) electric charges on the atoms of the SWCNT show that increase in the external electric field strength increases the separation of the center of the positive and negative electric charges of the carbon nanotube.     

Theoretical study of a conjugated aromatic molecular wire

In this study, an organic conjugated molecule, 4,4′-[ethane-1,2-diylidenedi(nitrilo)] dibenzenthiol designed and is proposed as a molecular wire. Structural and electronic responses of this aromatic molecular wire to the static electric field with intensities −1.6 × 10⁻² to +1.6 × 10⁻² a.u., are studied using the DFT-B3LYP/6-31G* level of theory. Natural bond orbital atomic charge analysis shows that the imposition of static external electric field induces polarization—localization of charge on the two ends of molecule, especially on considered terminal contact sulfur atoms. The frontier molecular orbitals (MOs) energy levels including the highest occupied MO (HOMO) and the lowest unoccupied MO (LUMO) and the HOMO–LUMO gap (HLG) values are modified by the static electric field as well. The electric dipole moment and polarizability of the proposed molecular wire under the studied electric field strengths are considerably increased. The current–voltage characteristic curve is estimated for the proposed molecular wire.     

Electric field effects on the performance of a candidate multipole molecular switch: a quantum computational study

Structural and electronic responses of the organic molecule di(4-nitro-2-methylenamine phenyl) diazene a candidate molecular switch, as an active device in a nanoelectronic circuit, to the external electric fields with strengths 5 x 10(-4) - 1.8 x 10(-2) a.u. included explicitly in the Hamiltonian are studied using B3LYP/6-31G* method. This study shows that thermodynamic formation functions are not affected significantly by the applied field. Electronic spatial extent show a negligibly small change (<2%) over the studied range of the electric field strength. Calculated electric dipole moments show significant sensitivity to the external electric field, which result consequently in much stronger interactions with the electrodes (poles) of the mother nanoelectronic circuit at higher electric field strengths. Natural bond orbital atomic charges analysis shows different field effects on different atoms depending on their positions with respect to the direction of the field. The applied field increases HOMO, LUMO, and the Fermi level energies; however, decreases the HOMO-LUMO gap (HLG) values. Results of this study show that it is possible to control field-induced charge redistribution over the molecule by using push-pull effects of different substitution via their connection points to the extended pi-system.     

Single‐wall Boron Nitride Nanotube with Various Diameters under the Influence of Electric Field,A Computational Investigation

Structural and electrical response of the (4, 0), (5, 0) and (6, 0) zigzag model of single‐walled boron nitride nanotube (BNNT) with H‐terminated at the open ended, have been investigated under the external electric field (EF) with intensities 0–1.6 × 10^?2 a.u. using the DFT B3LYP/6‐31G* level of theory. Results of this study show that with increasing BNNTs diameter, the HOMO‐LUMO gap (HLG) values increase, and with increasing the EF intensity, the HLG values decrease. In both cases with increasing EF intensity and the BNNT diameters, the electric dipole moment is increased significantly. Also the calculated natural bond orbital (NBO) atomic charges on the atoms of the BNNT show that the separation of the center of the positive and the center of the negative electric charges of the boron nitride nanotubes are increases in both case. We have found that the properties of the BNNTs are dependent on their diameters and can be tuned by applied electric fields intensity.     

First Principles Calculations of Electric Field Effect on the (6,0) Zigzag Single-Walled Silicon Carbide Nanotube for use in Nano-Electronic Circuits

Structural, electronic, and electrical responses of the H-capped (6,0) zigzag single-walled silicon carbide nanotube (SiCNT) was studied under the parallel and transverse electric fields with strengths 0–140 × 10^?4 a.u. by using density functional calculations. Analysis of the structural parameters indicates that resistance of the nanotube against the applied parallel electric field is more than resistance of the nanotube against the applied transverse electric field. The dipole moments, atomic charge variations, and total energy of the (6,0) zigzag SiCNT show increases with any increase in the applied external electric field strengths. The length, tip diameters, electronic spatial extent, and molecular volume of the nanotube do not change significantly with any increasing in the electric field strength. The energy gap of the nanotube increases with any increases in the electric field strength and its reactivity is decreased. Increase of the ionization potential, electron affinity, chemical potential, and HOMO and LOMO in the nanotube with increase of the applied external electric field strengths indicates that the properties of SiCNTs can be controlled by the proper external electric field for use in nano-electronic circuits.     

Linear viscoelastic properties of electro-rheological nano-suspension confined to narrow gap between electrodes

The linear viscoelastic properties of a suspension composed of titanium dioxide nanoparticles were measured under the direct current (dc) electric field with narrow gap distances between the electrodes. The yielding behavior under no external electric fields was also discussed. The wall slip at the interface between the parallel plates and the nano-suspension was briefly discussed. Under the dc electric field, a fine chain-like microstructure was optically found within a narrow gap of 50 μm between the electrodes in the quiescent state. The nano-suspension confined to a narrow gap of 65 μm between the parallel plates was rather viscoelastic even at the highest strength of the electric field of 16 kV·mm⁻¹. Furthermore, fast and slow relaxations of the dynamic moduli were found after removal of the electric field. It was pointed out that the linear viscoelasticity was an appropriate measure of the microstructure before yielding.     

Synthesis and characterization of alternating fluorene–thiophene copolymers bearing ethylene glycol side-chains

Abstract  

New alternating fluorene–thiophene copolymers are introduced bearing polar ethylene glycol-carboxylate functionalities on the thiophene ring to achieve enhanced solubility in polar solvents. Suzuki polycondensation was applied to synthesize a set of three polymers with differing lengths of the ethylene glycol side-chains. The polymers are thermally stable up to temperatures of 300 °C. Solutions of the polymers in CHCl₃ show an absorption maximum at approximately 397 nm and a luminescence maximum of 472 nm in solutions with quantum yield of 30%. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels have been determined to be at −5.7 and −2.6 eV, respectively.     

Polarization interaction of disperse particles with not thin Debye atmosphere

The electric field of the equilibrium double layer acts only at the distance of the Debye length. Therefore, the distances at which the electrostatic interaction forces act between particles in the absence of external fields are limited by the same length. As shown previously, the external electric field results in the appearance of volume charges outside DL. As a result, the long-range acting electric forces appear. In addition, the forces become anisotropic.

The polarization forces are proportional to at least the square of the external field. Previously we had shown that quadratic forces occurred not only as a result of the interaction of the charges being linear to an external field, but as a result of the interaction between the charges being quadratic to an external field as well as the equilibrium charges. We have described these quadratic charges in the theory of the double layer nonlinear polarization without any restrictions on the double layer thickness. This theory was developed by the method of successive approximations on the extemal field and the electrokinetic ς-potential. These results are obtained in analytical form and agree with the Fixman and Jagannathan's 1983 numerical solutions.

Our calculations of the polarization interaction energy showed: (a) in suspension of polar nonconductive particles in the less polar medium the orientation of the duplet perpendicular to field is more advantageous than along the field; (b) the attraction of the charged polar particles is substituted by the repulsion with the particle ς-potential increase both for longitude duplet (ς=2.5 mV) and for transverse duplet (ς=1.5 mV); (c) with the polar medium conductivity growth the repulsion forces between particles of the longitude duplet are changed by the attraction forces.     

MECHANISM OF ORIENTATION AND LINEAR DICHROISM OF PHOTOSYNTHETIC PARTICLES IN ELECTRIC FIELDS: CHLOROPLASTS AND CHLOROPHYLL-PROTEIN COMPLEXES

Abstract— The mechanisms of orientation in pulsed and alternating electric fields of thylakoids (derived from the sonication of spinach chloroplasts) and of light-harvesting chlorophyll a/b-protein complexes (CPII) were investigated by utilizing linear dichroism techniques. Comparisons of the linear dichroism spectra of thylakoids and CPII particles suggest that the latter are oriented with their directions of largest electronic polarizabilities (and thus probably their largest dimensions) within the thylakoid membrane planes. At low electric field strengths (< 12 V cm^?1), and at low frequencies of alternating electric fields (< 0.25 Hz), thylakoid membranes tend to align with their normals parallel to the direction of the applied electric field; the mechanism of orientation involves a permanent dipole moment of the thylakoids which is oriented perpendicular to the planes of the membranes. However, at high field strengths and high frequencies of the applied alternating electric fields, the thylakoids tend to orient with their planes parallel to the applied field, thus exhibiting an inversion of the sign of the linear dichroism as the electric field strength is increased. At the higher frequencies and at higher field strengths, the orientation mechanisms of the thylakoids involve induced dipole moments related to anisotropies in the electronic polarizabilities. The polarizability is higher within the plane than along a normal to the plane, thus accounting for the inversion of the dichroism as the electric field strength is increased. The CPII particles align with their largest dimension parallel to the applied field at all field strength, indicating that the induced dipole moment dominates the orientation mechanisms in pulsed electric fields. The magnitude of the absolute linear dichroism of CPII suspensions increases with increasing dilution, indicating that aggregates of lower symmetry are formed at higher concentrations of the CPII complexes.     

Automatic Geometry Optimization and Vibrational Analysis in External Electric Field: Ethylene

Stationary points of the INDO energy hypersurface for various orientations of ethylene in external electric fields of the strength F=0, 2, 4, 6, 8 and 10 × 10¹⁰ V m^?1 were found and their characteristics studied by the force constant matrix analysis. Energies, structural parameters, charges, Wiberg indices and dipole moments are presented. The only stable orientation of the ethylene molecule is that for which the C? C bond is parallel to the field direction up to F=6 × 10¹⁰ V m^?1 (orientation (a) in Fig. 1). Above this value the molecule is structurally unstable and it decomposes to the hydride anion and the C₂H₃⁺ cation. Rotational instability was found for two perpendicular orientations of the C? C bond with respect to the field vector, in which the field vector was parallel and perpendicular to the molecular plane. Pseudorotations with negative eigenvalues of force constant matrices lead to the stable orientation (a). No stationary points were found when the angle between the C? C bond and the field vector was between 0 and 90°. The five longest wavelength vibrational bands are presented for selected orientations and field strengths.     

Conductivity of flowing polyaniline suspensions in electric field

The formation of chain structures by polarized polyaniline (PANI) particles suspended in silicone oil in the electric field has been monitored by recording suspension conductivity in the course of time. For that purpose, three types of PANI particles differing in the conductivity (3.1 × 10⁻³, 1.7 × 10⁻¹, and 2.0 × 10⁻¹ S cm⁻¹) have been chosen out of a series of nine samples prepared by controlled protonation of PANI base in orthophosphoric acid solutions. Relaxation times reflecting this process and characterizing the rate of the response to the electric field decreased with particle conductivity, indicating a higher polarizability of particles. At the same time, the maximum conductivity of suspension increased as a consequence of the electric and shear forces acting on the particles. In the shear fields, shorter relaxation times appeared than at rest. The simultaneous measurement of the shear stress confirmed that the conductivity investigation can reliably characterize the development of electrorheological structures.     

Effects of electric and magnetic fields on the electronic properties of zigzag carbon and boron nitride nanotubes

We have investigated the electronic properties of zigzag CNTs and BNNTs under the external transverse electric field and axial magnetic field, using tight binding approximation. It was found that after switching on the electric and magnetic fields, the band modification such as distortion of the degeneracy, change in energy dispersion, subband spacing and band gap size reduction occurs. The band gap of zigzag BNNTs decreases linearly with increasing the electric field strength but the band gap variation for CNTs increases first and later decreases (Metallic) or first hold constant and then decreases (semiconductor). For type (II) CNTs, at a weak magnetic field, by increasing the electric field strength, the band gap remains constant first and then decreases and in a stronger magnetic field the band gap reduction becomes parabolic. For type (III) CNTs, in any magnetic field, the band gap increases slowly until reaches a maximum value and then decreases linearly. Unlike to CNTs, the magnetic field has less effects on the BNNTs band gap variation.     

Investigation on specific adsorption of hydrogen on lithium-doped mesoporous silica

This paper reports the synthesis, structure, and hydrogen adsorption property of Li-doped mesoporous silica (MPS) with a 2D hexagonal structure. The Li-doping is achieved by impregnation of the cylindrical mesopores with an ethanol solution of lithium chloride followed by heat treatment. Detailed characterization by solid-state NMR, TG-MS, and FT-IR suggests that, during the heat treatment, lithium chloride reacts with surface ethoxy groups (≡Si-OEt) to form ≡SiOLi groups, while ethyl chloride is released into the gas phase. The hydrogen uptake at 77 K and 1 atm increases from 0.68 wt% for the undoped MPS to 0.81 wt% for Li-doped MPS (Li-MPS). The isosteric heat of adsorption is 4.8 kJ mol⁻¹, which is consistent with the quantum chemistry calculation result (5.12 kJ mol⁻¹). The specific hydrogen adsorption on Li-MPS would be explained by the frontier orbital interaction between HOMO of hydrogen molecules and LUMO of ≡SiOLi. These findings provide an important insight into the development of hydrogen storage materials with specific adsorption sites.     

Effect of external fields applied during hot-water treatment on the aspect ratio of nanocrystallites formed on SiO<Subscript>2</Subscript>·TiO<Subscript>2</Subscript> coatings derived from sol–gel techniques

SiO₂·TiO₂ coatings were prepared by a sol–gel route. The effect of the external fields including mechanical vibration and electric charge applied during hot-water treatment on titania precipitation at the surface of the coatings was investigated. The shape of the resulting precipitates tended to elongate by applying vibration in a parallel or perpendicular direction, or by applying an electric charge. The organization of titania nanocrystallites possibly occurs because of the concentration gradient of dissolved titania species generated by the external fields during the hot-water treatment. A maximum aspect ratio of 38.1 was achieved for the precipitate prepared by hot-water treatment performed under parallel vibration for 5 h. The shape of the resulting precipitates was also influenced by the content of TiO₂ in the SiO₂·TiO₂ coating, with a smaller proportion of TiO₂ increasing the aspect ratio of the resulting precipitate.     

Integrated microfluidic device with an electroplated palladium decoupler for more sensitive amperometric detection of the 8-hydroxy-deoxyguanosine (8-OH-dG) DNA adduct

8-Hydroxy-deoxyguanosine (8-OH-dG) DNA adduct is one of the most frequently used biomarkers reporting on the oxidative stress that leads to DNA damage. More sensitive and reliable microfluidic devices are needed for the detection of these biomarkers of interest. We have developed a capillary electrophoresis (CE)-based microfluidic device with an electroplated palladium decoupler that provides significantly improved detection limit, separation efficiency, and resolving power. The poly(dimethylsiloxane) (PDMS)/glass hybrid device has fully integrated gold microelectrodes covered in situ with palladium nanoparticles using an electroplating technique. The performance and coverage of the electrodes electroplated with palladium particles were evaluated electrochemically and via scanning electron microscope (SEM) imaging, respectively. The performance of the device was tested and evaluated with different buffer systems, pH values, and electric field strengths. The results showed that this device has significantly improved resolving power, even at separation electric field strengths as high as 600 V cm⁻¹. The detection limit for the 8-OH-dG adduct is about 20 attomoles; the concentration limit is on the order of 100 nM (S/N = 3). A linear response is reported for both 8-OH-dG and dG in the range from 100 nM to 150 μM (≈100 pA μM⁻¹) with separation efficiencies of approximately 120,000–170,000 plates m⁻¹.     

Adsorption properties of SCN? on (6,0), (7,0), (8,0), and Al-doped (6,0) zigzag single-walled carbon nanotubes: a density functional study

Abstract  

The behavior of the thiocyanate anion (SCN⁻) adsorbed on the external surface of H-capped (6,0), (7,0), (8,0), and Al-doped (6,0) zigzag single-walled carbon nanotubes was studied by using density functional calculations. Geometry optimizations were carried out at the B3LYP/6-31G* level of theory using the Gaussian 03 suite of programs. We present the nature of the SCN⁻ interaction in selected sites of the nanotubes. Our results show that the pristine carbon nanotubes cannot significantly detect SCN⁻. The calculated binding energy of the Al-doped (6,0) single-walled carbon nanotubes indicated that SCN⁻ can be adsorbed significantly on the C and Al sites and these nanotubes can therefore be used for SCN⁻ storage. Binding energies corresponding to adsorption of SCN⁻ on the Al site in the Al-doped (6,0) single-walled carbon nanotubes was calculated as −286.38 kJ mol⁻¹. The calculated binding energies for SCN⁻ in N-down orientation are higher than those in S-down orientation for all of the configurations. More efficient binding could not be achieved by increasing the nanotube diameter. We also report the effects of SCN⁻ adsorption on the electronic properties of the nanotubes.     

Electrically induced anisotropy in a colloidal dispersion of nanospheres as measured by electric birefringence

Electrically induced birefringence experiments were performed on dispersions consisting of sulfate latex nanospheres of two different sizes and charges dispersed in an electrolyte solution, at various ionic strengths. The induced birefringence was found to have an important contribution increasing as a quadratic power law of the volume fraction of the spheres. This shows that interparticle interactions play a role in the observed birefringence. The data were analyzed, using a theory from Hafkenscheid and Vlieger [Physica 75 (1974) 57], in terms of the changes of the interparticle separations in the directions parallel and perpendicular to the applied electric field.