Direct observation by laser scanning confocal microscopy of microstructure and phase migration of PVC gels in an applied electric field

The fluorescent probe lucigenin was incorporated in poly(vinyl chloride) (PVC) gels, and laser scanning confocal microscopy (LSCM) was used to clarify the internal structures of the gels. From the two-dimensional and three-dimensional information by LSCM, we first observed the internal structure of the PVC gel at a wet status, where the PVC gels comprised a polymer-rich phase and a polymer-poor phase uniformly with a three-dimensional network structure. After an electric field was applied, an effect of the electric field resulted in the change of internal structure in the gels. The polymer-poor phase moved from the cathode to the anode and the polymer-rich phase formed linelike arrangement between electrodes due to the attraction force. On the other hand, the freeze-dried PVC gels with/without in-situ dc voltage casting were particularly fabricated to confirm above results by the field emission scanning electron microscopy (FE-SEM). It was found that many craters remained on the surface of the gel near the anode due to sublimation in freeze-drying. This phenomenon did not appear on the surface near the cathode. The results of in-situ dc voltage casting also suggested that a substantial amount of polymer-poor phase was moved and fixed at the anode. Thus, results of both LSCM and in-situ dc voltage casting corresponded to the effect of electric field on PVC gels and provided a convincing evidence for the interpretation of the deformation mechanism of PVC gel actuators by an applied electric field.     

Biologically inspired path-controlled linear locomotion of polymer gel in air

A novel approach based on electrohydrodynamic behavior of a dielectric liquid pattern in electric field was developed to fabricate a poly(vinyl alcohol)/dimethyl sulfoxide (PVA/DMSO) gel electromechanical system. Driving experiments indicate that this system could be well-operated in air by using a direct current (DC) electric field, and the gel exhibits a long-range path-controlled snaillike or snakelike motion with a fast crawling speed of 14.4 mm/s. Some factors, such as the applied electric field and the mass of the gel on the average crawling speed of the gel at linear path and curvilinear path, are investigated. Furthermore, a transition between snaillike gaits and snakelike gaits of the gel is also further studied in this system. The mechanism analysis suggests that this path-controlled motion of the gel arises from the drag of the spatial varied shear force F originated from the electrohydrodynamic flow of the solvent in and out of the gel.     

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.     

On the role of electrostatic forces in the adhesion of polymer particles to solid surfaces

Simultaneous measurements have been made of the adhesive force and double electric charge of particles after their removal from a metal surface. For the systems investigated, the adhesive force and charge on the particles increase with particle diameter according to a power law with an exponent close to 2. Such dependence can be explained on the basis of the electrostatic nature of the adhesive forces. A double electric layer exists at the interface between the particles and the metal surface. A calculation was made of the surface density of charge for the polyvinyl chloride particle-steel system.     

Atomistic simulation on charge mobility of amorphous tris(8-hydroxyquinoline) aluminum (Alq3): origin of Poole-Frenkel-type behavior

The atomistic simulation of charge transfer process for an amorphous Alq(3) system is reported. By employing electrostatic potential charges, we calculate site energies and find that the standard deviation of site energy distribution is about twice as large as predicted in previous research. The charge mobility is calculated via the Miller-Abrahams formalism and the master equation approach. We find that the wide site energy distribution governs Poole-Frenkel-type behavior of charge mobility against electric field, while the spatially correlated site energy is not a dominant mechanism of Poole-Frenkel behavior in the range from 2x10(5) to 1.4x10(6) V/cm. Also we reveal that randomly meshed connectivities are, in principle, required to account for the Poole-Frenkel mechanism. Charge carriers find a zigzag pathway at low electric field, while they find a straight pathway along electric field when a high electric field is applied. In the space-charge-limited current scheme, the charge-carrier density increases with electric field strength so that the nonlinear behavior of charge mobility is enhanced through the strong charge-carrier density dependence of charge mobility.     

Effects of plasticizers on novel electromechanical actuations with different poly(vinyl chloride) gels

Four different plasticizers were applied to make different poly(vinyl chloride) (PVC) gels, poly(vinyl chloride)‐bis(2‐ethylhexyl)phthalate (PVC‐DOP), poly(vinyl chloride)‐di‐n‐butylphthalate, poly(vinyl chloride)‐bis(2‐ethylhexyl)adipate, and poly(vinyl chloride)‐tris(2‐ethylhexyl)trimellitate. In our previous work, we reported that PVC‐DOP gel exhibits novel and reversible deformations of creeping and jointlike bending induced by direct current electric fields. In this article, we scrutinize the effects of plasticizers on electromechanical actuations, that is, reversible creeping and bending actuation with four of the different aforementioned gels. We measured the relative creeping distance, creeping area, creeping velocity, current observed, and bending angle as a function of applied electric fields for different PVC gels and found significant differences among them. To explain these variations, we compared the utility of plasticizers on the basis of the properties of different PVC gels, such as plasticizer‐retention ability, bending modulus, elongation at break, and the dielectric constant. The mentioned properties of the PVC gels played vital roles on their electromechanical actuations. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2119–2127, 2003     

Effect of a few repeating stereosequences on electrical space charge behavior of poly(methyl methacrylate)

Three films of poly(methyl methacrylate) (PMMA) (samples X, Y, and Z) were prepared by compression molding of purified polymers as polymers having different tacticities. They were exhaustively characterized by ¹H NMR spectroscopy so as to be able to evaluate the differences in content of the repeating stereosequences:… mmrm … (termini of isotactic sequences); …. rrrmr (breaking off syndiotactic sequences; pure heterotactic … mrmr … moistures; and atactic parts. By applying the so‐called thermal step method, the behavior in space charge showed a priority charge injection from both electrodes and some polarization at the cathode. Some strong differences between the samples were evidenced and they accurately agree with the variations in the above repeating stereosequences for the samples. The results allow to define every stereosequence as specific trap of the distinct sorts of space charge, namely injection from the anode or the cathode and polarization. These attributions are common with those proposed for poly(vinyl chloride) (PVC) and poly(propylene) (PP) in earlier work. Conversely, whether the priority charge is of injection or polarization type, depends markedly on the type of polymer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 633–639, 2009     

Effect of solvent type on formation of PVC‐solvent complex

The effect of solvent type on the structural features of PVC gels prepared from the solutions of dibutyl phthalate(DBP) and butyl benzoate(BB) were investigated. The influence of solvent type, i.e., diester solvent or monoester solvent, on the mechanical responses was characterized by dynamic viscoelastic measurements as a function of temperature, aging time, and PVC concentration. In the case of PVC/DBP aged gels, the transition phenomenon appeared close to 50°C, whereas no such transitions were observed for PVC/BB aged gels. This transition is considered to be associated with polymer‐solvent complex which can be accounted for electrostatic interaction between C=O bond of solvent and H‐C‐Cl part of PVC. While BB solvent molecules can not form polymer‐solvent complex due to no capacity to act as a bridge between PVC molecular chains. FT‐IR spectroscopy and DSC investigation on either PVC/DBP gels or PVC/BB gels was reported and discussed together with the mechanical behavior. Electron micrographs of the dried gel prepared from the critical point drying technique reveal that the gel morphology consists of well developed three dimensional fibrous network structure independent of solvent type.     

脉冲电场O/W乳状液破乳的分子动力学模拟

采用分子动力学方法研究了水包油(O/W)型乳状液体系中重油油滴在脉冲电场中的聚集行为. 通过改变电场占空比的模拟参数, 探讨了一定电场强度下的油滴聚集行为, 以及电场破乳时电场强度参数与占空比参数之间的联系. 同时利用静电势分布、 相互作用势能以及结合构象统计等分析方法, 从微观角度说明在电场作用下油滴的电荷分布与聚集机制. 模拟结果表明, 在近0.40~0.75 V/nm范围内电场强度下, 距离一定的重油滴聚集, 低电场强度可通过增加占空比促使油滴聚集, 且占空比随电场强度的增大而减小; 油滴在电场中发生形变, 油滴电荷出现两极化分布, 带负电沥青质分子引导油滴朝电场反方向移动; 无电场下聚集过程中沥青质处于两油滴界面, 范德华作用力为油滴聚集的主要作用力, 同时油滴界面沥青质分子与周围分子形成π-π结合构象, 增强了油滴间的相互作用力.     

Electrochemical impedance study of GaAs surface charge modulation through the deprotonation of carboxylic acid monolayers

Modifications to the space charge region of p+ and p-GaAs due to surface charge modulation by the pH-induced deprotonation of bound carboxylic acid terminal monolayers were studied by electrochemical impedance spectroscopy and correlated to flat-band potential measurements from Mott-Schottky plots. We infer that the negative surface dipole formed on GaAs due to monolayer deprotonation causes an enhancement of the downward interfacial band bending. The space charge layer modifications were correlated to intermolecular electrostatic interactions and semiconductor depletion characteristics.     

Fourier transform infrared study of segmental orientation in polymer blends

The effect of the macromolecular plasticizer poly(-methyl--n-propyl--propiolactone), PMPPL, on the orientation of poly(vinyl chloride), PVC, has been studied by FTIR spectroscopy. The addition of PMPPL to PVC does not change significantly the degree of orientation of PVC segments. In blends, PMPPL chains are more oriented when the matrix is richer in PVC but the PMPPL orientation function always remains smaller than that of PVC segments.     

Solid Contact Nitrate Ion‐Selective Electrode Based on Ionic Liquid with Stable and Reproducible Potential

A simple, fast and cheap method of preparation of solid contact nitrate ion‐selective electrode is proposed. The electrode membrane phase consist of only three components: PVC, plasticizer and ionic liquid (IL).The ionic liquid trihexyltetradecylphosphonium chloride is used in triple function as ionophore, as lipophilic ionic component in order to reduce membrane resistance, and as transducer media in order to stabilize the potential of internal Ag/AgCl electrode. The electrical properties of the membrane were studied by electrochemical impedance spectroscopy and the influence of the interfacial water film was evaluated by potentiometric water layer test.     

高效的CdS/Ti-Fe2O3异质结光阳极:研究Z型电荷迁移机制增强光电化学水氧化活性

近年来以Z型机制为转移的光催化体系成微光电化学分解水领域的研究热点.相比较传统的异质结,Z型异质结能够保留具有高氧化能力与高还原能力的位点,从而提高光电化学效率.其中,证明电荷的Z型迁移机制成为研究人员努力的方向,比较有效的证明方法包括自由基捕获、XPS分析和检测还原位点等.对于Z型异质结,界面电场处电荷的迁移行为是至关重要的,但目前常用的证明手段对界面电场处电荷的迁移行为研究还比较少.因此,本文精心设计了CdS/Ti-Fe₂O₃异质结光阳极来探索光电化学分解水中的电荷转移行为.采用开尔文探针测试、表面光电压谱测试和瞬态光电压谱测试等光物理测试手段监测CdS/Ti-Fe₂O₃Z型异质结光阳极界面电场中光生电荷的迁移行为.其中,开尔文探针和表面光电压测量表明,CdS/Ti-Fe₂O₃界面驱动力有利于激发电子快速迁移至CdS;由于Z型异质结是一个双光子的过程,因此在瞬态光电压的过程中采取了双光束策略,即用不同波长的光分别从两个半导体侧进行照光,以充分发挥内层CdS的电子传输层的作用.结果表明,在双光束照射下界面电场增强,使得更多Ti-Fe₂O₃电子与CdS空穴结合,使得更多Ti-Fe₂O₃电子与CdS空穴结合,更多的空穴迁移到Ti-Fe₂O₃的表面去参与反应,充分证明了CdS/Ti-Fe₂O₃光阳极的Z型迁移机制.基于界面电场有效的电荷迁移与分离的分析,对Z型异质结光阳极进行了光电化学的测试,与单纯Ti-Fe₂O₃光阳极相比,CdS/Ti-Fe₂O₃光阳极表现出优异的光电化学性能.其中,25CdS/Ti-Fe₂O₃光阳极的光电流密度在1.23V(相对于标准氢电极)达到1.94 mA/cm²,比单纯Ti-Fe₂O₃光电流高出两倍.阻抗测试结果表明,CdS/Ti-Fe₂O₃光阳极能够减小电荷传输阻力,从而加快电荷分离效率,这也间接证明了Z型光阳极的成功构筑,因此,本文提供了一个有效且新颖的手段来证明光电化学分解水中光催化系统的Z型电荷转移机制.     

Surface electric field manipulation of the adsorption kinetics and biocatalytic properties of cytochrome c on a 3D macroporous Au electrode

Upon adsorbing on a solid-state substrate, water-soluble proteins are prone to denaturation and deterioration of their functions due to the conformation change. The surface electric field of a conductive substrate is one of the important factors that influence the character of adsorbed proteins. In this work, a 3D macroporous gold electrode has been prepared and served as the working electrode to study the influence of surface electric field on the adsorption kinetics and conformation of the adsorbed cytochrome c (cyt-c) with the help of electrochemical, in situ electrochemical IR spectroscopic, atomic force microscopic, and contact angle measurements. The external electric field creates excess surface charge which can manipulate the adsorption rate of proteins on the substrate by the enhanced electrostatic interactions between the electrode and protein patches by coupling with complementary charges. The amount of immobilized cyt-c with electrochemical activity on the 3D macroporous gold electrode showed a minimum at potential of zero charge (PZC) and it increased with increasing net excess surface charge. Higher electric field could influence the conformation and the corresponding properties such as direct electrochemistry, bioactivity, and surface character of the adsorbed cyt-c molecules. However, high external electric field leads to damage of the protein secondary structure. This study provides fundamentals for the fabrication of biomolecular devices, biosensors, and biofuel cells through electrostatic interactions. Figure Two cases are illustrated for the protein immobilized on electrode surfaces: a retention of protein structure under moderate excess surface charge, b denaturation and conformation change of proteins adsorbed at high excess surface charge, e.g., due to the higher external electric field.     

Electrically induced linear locomotion of polymer gel in air

A electromechanical gel, which could be driven in air by a DC electric field, was developed using poly(vinyl alcohol)/dimethylsulfoxide gel. When the applied electric field exceeds a certain threshold, the gel exhibited a continuous and linear crawling motion. The result indicated that, under the applied electric field of 275 V/mm, the maximum crawling velocity of the gel could reach v = 1.63 mm/s, which is about 80 times larger than that reported in earlier works. At a proper range of the driving time, the average crawling speed and crawling direction could be well controlled by the external electric field. Furthermore, some factors, which have influence on the critical driving electric field of the gel, such as the swelling degree of the gel and the apparent contact area between the gel and substrate, were studied. For the first time, a mechanism based on the strong electrostatic interaction between the external electric field and the charges accumulated in the gel–air and substrate–gel interfacial regions was put forward to explain the novel motion. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1187–1197, 2007     

Fourier-transform infrared study of orientation in pure and plasticized poly(vinyl chloride)

Fourier-transform infrared spectroscopy has been used for the study of orientation of pure and plasticized PVC. The results show that orientation is independent of experimental conditions (temperature, strain rate, plasticizer) in the homogeneous deformation range. Such behavior is explained by the existence of a fringe micellar-type network with physical crosslinks. The network is partially destroyed during stretching. Furthermore, the orientation of the carbonyl group of the plasticizer is connected with PVC chain orientation.     

力化学降解对聚氯乙烯加工流变行为的影响

采用Brabender塑化仪和毛细管流变仪研究了经力化学降解制得的聚氯乙烯(PVC)的加工流变行为。结果表明,降解的PVC塑化时间比未降解的PVC明显缩短,塑化速度和熔化效率也明显加快,熔体粘度及玻璃比温度降低。     

旋转模塑过程中PVC溶胶物理凝胶化转变的有限元分析

采用有限元法,数值模拟了成型过程中镍制模具和PVC材料的非稳态温度场,进而得到了PVC材料结构参数的时间演变和空间分布规律,再由结构-性能关系获得了PVC材料的溶胶黏度及其演变特点,在此基础上比较分析了不同增塑剂对PVC材料物理凝胶化转变过程的影响.结果表明,由于热阻不同,靠近模具壁的PVC溶胶升温速率较大,首先发生凝胶化转变;加热过程中,PVC材料的黏度首先降低至最小值,凝胶化转变开始后,PVC树脂和增塑剂之间的相互作用增强,材料黏度迅速升高;不同增塑剂对材料结构参数和溶胶黏度的演变规律有着不同影响.     

Integrated Micro Space Electrostatic Field in Aqueous Zn-Ion Battery: Scalable Electrospray Fabrication of Porous Crystalline Anode Coating

The inhomogeneous consumption of anions and direct contact between electrolyte and anode during the Zn-deposition process generate Zn-dendrites and side reactions that can aggravate the space-charge effect to hinder the practical implementation of zinc-metal batteries (ZMBs). Herein, electrospray has been applied for the scalable fabrication (>10 000 cm² in a batch-experiment) of hetero-metallic cluster covalent-organic-frameworks (MCOF-Ti₆Cu₃) nanosheet-coating (MNC) with integrated micro space electrostatic field for ZMBs anode protection. The MNC@Zn symmetric cell presents ultralow overpotential (≈72.8 mV) over 10 000 cycles at 1 mAh cm⁻² with 20 mA cm⁻², which is superior to bare Zn and state-of-the-art porous crystalline materials. Theoretical calculations reveal that MNC with integrated micro space electrostatic field can facilitate the deposition-kinetic and homogenize the electric field of anode to significantly promote the lifespan of ZMBs.     

Interfacial properties for real rough MEMS/NEMS surfaces by incorporating the electrostatic and Casimir effects–a theoretical study

This paper studied the adhesive properties of real rough micro/nano‐electromechanical systems (MEMS/NEMS) surfaces by considering the electrostatic force and the Casimir force theoretically, and an improved model has been proposed. A statistical approach for characterizing surface topography was used by taking the surface standard deviation, the asperity density and the radius of curvature into account. The effects of surface roughness on the electrostatic force and the Casimir force were analysed individually, and a comparison between the proposed model and existing models has been conducted. The whole adhesive force increases with the surface standard deviation, and the prediction by the proposed model becomes more in agreement with the one by existing models when the surface standard deviation is increased. The contribution of the Casimir force to the total adhesive force tends to vanish when the surface standard deviation is relatively large. The electrostatic force and the Casimir force contribute more to the total adhesive forces calculated based on the proposed model with the increase of the asperity density and the radius of curvature. Copyright © 2009 John Wiley & Sons, Ltd.