Ultrafast, electric field-induced fingers in an anticlinic liquid crystal

Propagating fingers of synclinic liquid crystalline phase were observed to invade the anticlinic phase for applied electric fields E larger than a characteristic threshold field E_th. The front velocity was found to be highly non-linear in E, with enormous velocities of at least 10 cm s^-1, and perhaps as high as 400 cm s^-1 for the maximum applied field. These are by far the largest velocities ever observed for a liquid crystal. The results are discussed theoretically, including the possibilities of a field-dependent molecular interaction coefficient and shear thinning.     

Electrorheological properties of polyaniline suspensions: field-induced liquid to solid transition and residual gel structure

Polyaniline (PANI) was synthesized via oxidative coupling polymerization in acid conditions and de-doped in solution of ammonia. The electrorheological (ER) properties of the PANI/silicone oil suspensions were investigated in oscillatory shear as functions of electric field strength, particle concentration, and host fluid viscosity. Consistent with literature, the PANI ER fluid exhibits viscoelastic behavior under the applied electric field and the ER response is strongly enhanced with increasing electric field strength and particle concentration. The dynamic moduli, G' and G' increase dramatically, by 5 orders of magnitude, as the electric field strength is increased to 2 kV/mm. A viscoelastic liquid to solid transition occurs at a critical electric field strength, in the range Ec = 50-200 V/mm, whose value depends on particle concentration and host fluid viscosity. The fibrillar structure formed in the presence of the applied field has a static yield strength tau(y), whose value scales with electric field strength as tau(y) approximately E(1.88). When the field is switched off a residual structure remains, whose yield stress increases with the strength of the applied field and particle concentration. When the applied stress exceeds the yield stress of the residual structure, fast, fully reversible switching of the ER response is obtained.     

Ultrafast,electric field-induced fingers in an anticlinic liquid crystal

Propagating fingers of synclinic liquid crystalline phase were observed to invade the anticlinic phase for applied electric fields E larger than a characteristic threshold field E_th. The front velocity was found to be highly non-linear in E, with enormous velocities of at least 10 cm s^-1, and perhaps as high as 400 cm s^-1 for the maximum applied field. These are by far the largest velocities ever observed for a liquid crystal. The results are discussed theoretically, including the possibilities of a field-dependent molecular interaction coefficient and shear thinning.     

A 2D electrohydrodynamic model for electrorotation of fluid drops

A theoretical analysis of spontaneous electrorotation of deformable fluid drops in a DC electric field is presented with a 2D electrohydrodynamic model. The fluids in the system are assumed to be leaky dielectric and Newtonian. If the rotating flow is dominant over the cellular convection type of electrohydrodynamic flow, closed-form solutions for drops of small deformations can be obtained. Because the governing equations are in general nonlinear even when drop deformations are ignored, the general solution for even undeformed drop takes a form of infinite series and can only be evaluated by numerical means. Both closed-form solutions for special cases and numerical solutions for more general cases are obtained here to describe steady-state field variables and first-order drop deformations. In a DC electric field of strength beyond the threshold value, spontaneous electrorotation of a drop is shown to occur when charge relaxation in the surrounding fluid is faster than the fluid inside the drop. With increasing the strength of the applied electric field from the threshold for onset of electrorotation, the axis of drop contraction deviates from from that of the applied electric field in the direction of the rotating flow with an angle increasing with the field strength.     

The Research of Biomedical Intelligent Polymer Materials

The properties of biomedical intelligent polymer materials can be changed obviously when there is a little physical or chemical change caused by external condition. They are in the forms of solids, solutions and the polymers on the surface of carrier, and include water solution of hydrophilic polymers, cross-linking hydrophilic polymers(i.e. hydrogels) and the polymers on the surface of carrier. The environmental stimulating factors are temperature, pH value, composition of solution, ionic intention, light intention, electric field, stress field and magnetic field etc.. The properties of intelligent polymer are those of phase, photics, mechanics, electric field, surface energy,reaction ratio, penetrating ratio and recognition etc..Stimulation-response of intelligent water-soluble polymerWater-soluble intelligent polymer can be separated out from solution under special external condition. It can be used as the switch of temperature or pH indicator. When water-soluble intelligent polymer is mixed with soluble-enzyme matter or cell suspension, the polymer can bring phase separation and react with soluble-enzyme matter or cell membrane through accepting some external stimulation. Other water-soluble intelligent polymer is that can make the main chemical group of some natural biomolecular recognition sequence section to arrange on skeleton of polymer at random. It is the same ratio as natural biomolecules.Stimulation-response of intelligent polymer of carrier surface Intelligent polymer can be fixed on the surface of solid polymer carrier through chemical grafting or physical adsorption. When the external conditions are changed, the thickness, humidity and electric field of the surface layer will be changed. Intelligent polymer can be preparated the permanence switch by precipitating into the hole of porous surface, and it can control on-off state of the hole. When protein or cell interacts with intelligent polymer surface to be placed in to open or close, they can be selectively absorbed on hydrophobic surface.Stimulation-response of intelligent polymer hydrogelIntelligent polymer hydrogel's construction, physical property, and chemical property can change with the changing of external environmental conditions. When environmental stimulation signal, for example, solution composition, pH value, ionic intention, temperature, light intention, electric field,magnetic field and substance etc. changes, the intelligent polymer will occur to break of volume.This is the intelligence of polymer hydrogel.The intelligence of these polymers will be widely applied in biomedical fields.     

SERS detection of the vibrational Stark effect from nitrile-terminated SAMs to probe electric fields in the diffuse double-layer

The vibrational Stark effect is observed in the surface-enhanced Raman scattering spectra of self-assembled monolayers functionalized with pendant nitrile groups. Stark tuning of the nitrile-stretching frequency serves as a localized probe of the electric field in the diffuse double layer of a SAM-modified electrochemical interface. Stark-tuning rates at low ionic strength correspond to reasonable values of the local electric (E) field in the double layer. The nitrile-stretching frequency converges on its isotropic value at applied potentials approaching the PZC, which indicates that Stark-tuning of the frequency is a direct probe of the E field at the interface. Loss of the local electric field at high ionic strengths shows that the probe responds to changes in the Debye length of the double layer. The results demonstrate the applicability of this electric-field probe for characterizing the diffuse double-layer region.     

Tissue engineering with electric fields: investigation of the shape of mammalian cell aggregates formed at interdigitated oppositely castellated electrodes

The shape of aggregates of cells formed by positive dielectrophoresis (DEP) at interdigitated oppositely castellated electrodes under different conditions was investigated and compared with calculations of the electric field gradient |nablaE(2)|, and the electric field E, and E(2). The results confirm that at low field strength the cells predominantly accumulate above the tips of the electrodes, but at higher electric field strengths the cells predominantly accumulate in the middle of the aggregate. For a given electrode size, a higher applied voltage significantly increases the aggregate footprint. Higher flow rates distort this pattern, with more cells accumulating at the electrodes that are upstream. Calculation of the electric field strength E, E(2) and the electric field strength gradient |nablaE(2)| in the interdigitated oppositely castellated electrode array shows that, at low flow rates, there is a strong correlation between the aggregate shape and the distribution of the electric field E and E(2), but not so between the aggregate shape and |nablaE(2)|. The results indicate that interparticle forces such as pearlchain formation strongly affect the aggregation process, but that, when positive DEP is used to make the aggregates, the distribution of the electric field E, or better E(2), can be used as a useful guide to the final aggregate shape.     

Ambipolar diffusion in multicomponent plasmas

A recently described self-consistent effective binary diffusion approximation is applied to ambipolar diffusion in a neutral multicomponent plasma in zero magnetic field, where forced diffusion due to the electric field E plays an essential role. The field E is determined by the constraint that the net current flow produced by the diffusion fluxes must be zero. The resulting effective binary diffusion fluxes are the sum of those that would obtain for E=0 and ambipolar correction terms proportional to E. The formulation is .self=consistent with respect to both mass and charge, the net diffusional fluxes of which are both identically zero. The results may be further simplified due to the small mass of the electrons. The effective binary diffusivity D_e of the electrons no longer appears in the simplified expressions. They are therefore well suited to numerical calculations, where the large value of D_e, might otherwise have resulted in unacceptable stability or accuracy restrictions. The well-known effective doubling of ion diffusivities due to ambipolar diffusion occurs in simple situations but is not a general feature.     

Dielectric relaxation studies and electro‐optical measurements in poly(triethylene glycol dimethacrylate)/nematic E7 composites exhibiting an anchoring breaking transition

Electric field driven anchoring breakage in poly(triethylene glycol dimethacrylate)/nematic E7 composites was studied using dielectric spectroscopy and transmittance measurements. The transmittance hysteresis observed on increasing and decreasing an applied electric field, associated with different alignment states of the liquid crystal (LC), was monitored through dielectric loss. Essential changes are felt mainly in the δ‐peak, i.e. the dielectric response of the nematic when the director lies parallel to the applied electric field. An irreversible effect persists after the field had exceeded a critical value, which was manifest in a higher transmittance and a higher dielectric strength of the δ‐peak in the OFF state. The initial scattering/opaque state of the sample can only be recovered by heating to the clearing temperature of the nematic LC. The effect referred, commonly called memory effect, is rationalized in terms of anchoring breakage of the LC at the polymer–LC interfaces. The electro‐optical response was tested for different poly(triethylene glycol dimethacrylate)/nematic E7 composites in different composition ratios prepared by polymerisation‐induced phase separation. The lowest threshold field was observed for the 30:70 composite.     

A Survey of Chemical Nonequilibrium in Argon Arc Plasma

The widespread application of electric arcs is closely related to the continuous research interest over the course of many years. The present survey is concerned with chemical and excitation nonequilibrium in atmospheric pressure argon plasma generated between a sharpened tungsten cathode and a flat copper anode at current levels of 35–200 A. Advanced fully nonequilibrium modelling is applied to simulate the combination of the wall-confined arc plasma column and the open region in front of the anode in a self-consistent manner in order to pay tribute to the tremendous research work that E. Pfender has done. The new modelling results are presented along with experimental and modelling results of the studies of E. Pfender and his group and other works of relevance.     

Long-range self-governing motion of polymer gel on a gradiently charged insulating substrate.

Herein, we report a special poly(vinyl alcohol)/dimethylsulfoxide (PVA/DMSO) gel electromechanical system with great self-governed capability. The system is operated in air by applying a noncontacted DC electric field. When the applied electric field exceeds a certain critical value, the gel exhibits fast and self-governing locomotion on the gradiently charged glass substrate. In contrast to field-controlled gel systems developed earlier, the crawling direction of the gel is independent of the direction of the applied electric field and can be actively controlled. The maximum crawling velocity can reach 3.22 mm s(-1), which is much larger than that of the actuators described earlier. Furthermore, some factors that influence the critical driving electric field and the average crawling speed of the gel were studied. The mechanism analysis indicates that, the self-governing linear motion of the gel is due to the spatially and temporally varying electrostatic interaction between the gel and the applied electric field in response to the gradient change of the charge density and the charge polarity on the substrate.     

稳定图的测定与矩形离子阱质谱性能分析

从理论上讲, 离子阱质谱仪的性能是由阱内电场分布决定的,而电场分布又是由组成离子阱的电极几何结构和离子阱工作电压决定的. 对于矩形离子阱, 即使不考虑其几何结构的偏差, 其阱内的电场分布一般也很复杂. 在矩形离子阱内, 除四极电场外, 还包含多种成分的其他各种高阶场, 它们直接影响离子在阱内的运动轨迹和离子阱质谱的性能. 由于各种电场成分对离子阱内离子运动的影响非常复杂, 还很难从数学上给出精确的解析解, 使得目前从理论上还无法预测高阶场成分对质谱性能的影响. 本工作通过测定不同几何结构的矩形离子阱的稳定图, 从实验上比较了不同场半径, 即不同电场分布条件下的离子阱质谱性能的差别. 实验中, 通过改变离子阱的几何比例结构, 详细测定了不同结构的矩形离子阱的稳定图特征, 并与实验测得的质谱分析结果进行比较. 同时, 我们还详细介绍了矩形离子阱质谱的稳定图的测定方法, 并根据得到的不同情况下的稳定图结构分析了离子阱的质谱性能. 研究结果表明： 可以通过比较试验得到的稳定图结构来判断其离子阱质谱仪的性能如质量分辨能力等. 此外, 实验结果还发现： 对于y方向拉伸结构的矩形离子阱, 其实验绘制得到的是不完整的稳定图. 但根据稳定图边界的特点, 通过采用四极直流电压调制的方法, 可以对y方向拉伸结构的矩形离子阱的性能进行改善, 极大地提高了阱的质量分辨能力.     

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.     

An ab initio study of electrochemical vs. electromechanical properties: the case of CO adsorbed on a Pt(111) surface

We have studied electrochemical vibrational and energy properties of CO/Pt(111) in the framework of periodic density functional theory (DFT) calculations. We have used a modified version of the previously developed Filhol-Neurock method to correct the unphysical contributions arising from homogeneous background countercharge in the case of thick metallic slabs. The stability of different CO adsorption sites on Pt(111) (Top, Bridge, Hcp, Fcc) has been studied at constant electric field. The energies are dominated by the surface dipole interaction with the external electric field: a strong positive electric field favors the surfaces with the lower dipole moment (that correspond to the ones with the lower coordination). The Stark tuning slope of the CO stretching frequency for a Top site was calculated for different surface coverages in very good agreement with both experimental and other theoretical results. Finally, we have performed an analysis of the origin of Stark shifts showing that the total Stark effect can be split into two competing components. The first one corresponds to the direct effect of charging on the C-O chemical bond: it is referred as an electrochemical effect. The second is the consequence of the surface dipole interaction with the applied electric field that modifies the C-O distance, inducing a change of the C-O force constant because of C-O bond anharmonicity: it is referred as the electromechanical effect. In the CO/Pt(111) case, the dominant contribution is electromechanical. The electrochemical contribution is very small because the electronic system involved in the surface charging is mostly non-bonding as analyzed by looking at the surface Fukui function.     

Methods to electrophoretically stretch DNA: microcontractions, gels, and hybrid gel-microcontraction devices

The ability to controllably and continuously stretch large DNA molecules in a microfluidic format is important for gene mapping technologies such as Direct Linear Analysis (DLA). We have recently shown that electric field gradients can be readily generated in a microfluidic device and the resulting field is purely elongational. We present a single molecule fluorescence microscopy analysis of T4 DNA (169 kbp) stretching in the electric field gradients in a hyperbolic contraction microchannel. In addition, we are able to selectively pattern a crosslinked gel anywhere inside the microchannel. With an applied electric field, DNA molecules are forced to reptate through the gel and they moderately stretch as they exit the gel. By placing a gel immediately in front of the hyperbolic contraction, we bypass "molecular individualism" and achieve highly uniform and complete stretching of T4 DNA.     

Front motion in an A+B-->C type reaction-diffusion process: effects of an electric field

We study the effects of an external electric field on both the motion of the reaction zone and the spatial distribution of the reaction product, C, in an irreversible A- + B+ -->C reaction-diffusion process. The electrolytes A identical with (A+,A-) and B identical with (B+,B-) are initially separated in space and the ion-dynamics is described by reaction-diffusion equations obeying local electroneutrality. Without an electric field, the reaction zone moves diffusively leaving behind a constant concentration of C's. In the presence of an electric field which drives the reagents towards the reaction zone, we find that the reaction zone still moves diffusively but with a diffusion coefficient which slightly decreases with increasing field. The important electric field effect is that the concentration of C's is no longer constant but increases linearly in the direction of the motion of the front. The case of an electric field of reversed polarity is also discussed and it is found that the motion of the front has a diffusive as well as a drift component. The concentration of C's decreases in the direction of the motion of the front, up to the complete extinction of the reaction. Possible application of the above results to the understanding of the formation of Liesegang patterns in an electric field is briefly outlined.     

一种基于导体尖端效应的无针式静电纺丝方法

基于导体的尖端效应原理提出一种静电纺丝法, 将探针阵列有序嵌入并垂直于聚合物溶液槽底部, 保持针头与液面高度相近, 当给溶液施加高电压时, 会在针头附近区域形成峰值电场, 由于流体在电场中具有不稳定性, 射流能够在溶液表面的峰值电场处自发形成, 进而拉伸细化、 劈裂成丝, 固化在收集板上. 但有序排列的探针阵列之间也存在电场相互干扰问题. 为了得到最佳的纺丝电场环境, 需对工作电场进行模拟及优化. 利用COMSOL Multiphysics 5.0建立几何模型, 分析嵌入探针的长短、 数量、 针间距及几何排布方式对溶液表面场强峰值的影响. 当溶液槽中嵌入一排探针时, 凸弧形的几何排布方式能提高中间区域的场强峰值; 对于两排探针, 交错的排布方式有利于改善溶液表面电场的均匀性, 而并列排布和对角线排布对均衡场强的效果不显著.     

Strain-controlled switching of hierarchically wrinkled surfaces between superhydrophobicity and superhydrophilicity

Recent years have witnessed intense interest in multifunctional surfaces that can be designed to switch between different functional states with various external stimuli including electric field, light, pH value, and mechanical strain. The present paper is aimed to explore whether and how a surface can be designed to switch between superhydrophobicity and superhydrophilicity by an applied strain. Based on well-established theories of structure buckling and solid-liquid contact, we show that this objective may be achieved through a hierarchically wrinkled surface. We derive general recursive relations for the apparent contact angle at different levels of the hierarchical surface and investigate the thermodynamic stability of different contact states. Our study may provide useful guidelines for the development of multifunctional surfaces for many technological applications.     

Transient response of an electrorheological fluid under square-wave electric field excitation

The transient process of an electrorheological (ER) fluid based on zeolite and silicone oil sheared between two parallel plates to which a square-wave electric field is applied has been experimentally studied. The transient shear stress response to the strain or time is tested. The characteristic constants of time under different applied electric fields and shear rates have been determined. The response time is found to be proportional to shear rate with an exponent of about -0.75 in the tested shear rate range, which agrees with the theoretical predictions made by others. But it only shows a small dependence on the strength of the applied electric field. The results show that the transient process of ER fluids is related to the structure formation in the shearing. When the required shear strain is reached, the shear stress rises to a stable value under constant electric field. Although the electric field strength greatly affects the yield strength, it shows little effect on the stress response time. Also, experiments showed the electric field-induced shear stress decreased with an increase of shear rate.     

Small Janus dimer as electric field manipulated molecular clam switch and electric information storage unit

A small Janus molecular dimer, as external electric field (F_z) manipulated both a molecular clam switch and a novel electric information storage unit, is found by quantum chemical computations for the first time. The molecular clam switching is intriguing and reversible. A critical F_z value of 95 × 10⁻⁴ au causes a dramatically open change in conformation from Closed form to Open form. And a small reversed electric field of F_z = −10 × 10⁻⁴ au performs a close change from Open form to Closed form. In the switching process, owing to the existence of a great electric dipole moment (μ) contrast between 0 and 22.13 D, the molecular clam switch may serve as an electric information storage unit. Gratifyingly, the reading, writing, and erasing of binary information on the electric information storage unit are easy. And further calculations show that Janus graphene fragment dimer can also serve as a molecular clam switch. Thus, this work proposes a new molecular switch prototype in the invention of artificial molecular machines, and a novel electric information storage unit in the field of molecular electronics.