Absence Of Electrostatic Forces Research Articles

Investigation of the surface roughness effect on the nonlinear size-dependent pull-in instability of the beam-type nano-actuator

In this paper, the effect of surface roughness on the pull-in behavior of beam-type nano-actuator in the presence of intermolecular Van der Waals force has been investigated. In order to model the surface roughness, the roughness has been modeled as a step on the fixed electrode. Based on the modified couple stress theory and by using Hamilton’s principle, the governing equation and boundary conditions have been derived for the Euler–Bernoulli beam model. The differential quadrature method has been used to solve the nonlinear governing equations of the system. The results showed that the presence of roughness on the fixed electrode leads to an increase in the displacement of the beam and a reduction in the pull-in voltage, especially when the roughness is at the end of the beam and has considerable height. In this case, the freestanding behavior of the nano-actuator and the effect of roughness on the critical intermolecular force in the absence of electrostatic force are also evaluated. The results revealed a decrease in the critical intermolecular force due to the presence of roughness. However, increasing the material length scale parameters leads to an increase in the pull-in voltage and the freestanding values. Also, the size effect parameter decreases the displacement at the end of the beam.

Influence of hydrophilic silica nanoparticles on the adsorption layer properties of non-ionic surfactants at water/heptane interface

There is a notable paucity of studies investigating the impact of charged nanoparticles on the interfacial behavior of nonionic surfactants, assuming that the interactions are negligible in the absence of electrostatic forces. Here, we argue about our observations and the existence of a complex interfacial behavior in such systems depending on the type and chemical structure of surfactant. This study set out to investigate the effects of interactions between hydrophilic silica nanoparticles (NP) and non-ionic surfactants on water/heptane dynamic interfacial properties using drop profile analysis tensiometry (PAT). Three surfactants were studied, namely Triton X-100 (significantly soluble in water phase), C12DMPO (well soluble in both phases) and SPAN 80 (oil-soluble). The different chemical structures and partition coefficients of the surfactants enabled us to cover possible interactions and differentiate between bulk and interfacial interactions. We observed that hydrophilic silica NPs had a negligible effect on the interfacial behavior of Triton X-100, that they increased the surface activity of C12DMPO when both compounds are initially in the aqueous phase. Most interestingly is that the added NPs generated unstable interfacial NP-surfactant complexes and reduced the pseudo-equilibrium interfacial tension of oil-soluble surfactant, Span 80, even though NPs and surfactants were in different bulk phases.

Directed self-assembly of nanogold using a chemically modified nanopatterned surface

Electron-beam lithography (EBL) was used to define an aminosilane nanopatterned surface in order to electrostatically self-assemble gold nanoparticles (Au NPs). The chemically modified nanopatterned surfaces were immersed into a Au NP solution to allow the Au NPs to self-assemble. Equilibrium self-assembly was achieved in only 20 min. The number of Au NPs that self-assembled on an aminosilane dot was controlled by manipulating the diameters of both the Au NPs and the dots. Adding salt to the Au NP solution enabled the Au NPs to self-assemble in greater numbers on the same sized dot. However, the preparation of the Au NP solution containing salt was sensitive to spikes in the salt concentration. These spikes led to aggregation of the Au NPs and non-specific deposition of Au NPs on the substrate. The Au NP patterned surfaces were immersed in a sodium hydroxide solution in order to lift-off the patterned Au NPs, but no lift-off was observed without adequate physical agitation. The van der Waals forces are too strong to allow for lift-off despite the absence of electrostatic forces.

Effect of thermal stresses on stability and frequency response of a capacitive microphone

This article deals with effects of thermal stresses on stability and frequency response of a fully clamped circular microplate, which acts as the diaphragm of a capacitive MEMS microphone. Static and dynamic pull-in phenomena limit the stable regions of a capacitive MEMS microphone. The results show that the non-dimensional static pull-in voltage of the studied case is about 5.23 (38.6 V). On the other hand, according to the results, the non-dimensional dynamic pull-in of the diaphragm is about 4.74 (34.98 V), which is as low as 90.63% of the static pull-in threshold. Because of the thermal expansion coefficient, diaphragm temperature increment leads to compressive thermal stresses and conversely, decrement of the diaphragm temperature creates tensile thermal stresses. The effect of temperature on the pull-in parameters is given by a design-correcting factor. As results demonstrate, the deflection of the diaphragm subjected to a given electrostatic force can be controlled by means of the temperature changes. In the absence of electrostatic force, as the results show, although temperature changes do not create any deflection, but for a critical temperature increment the diaphragm stiffness vanishes and the buckling phenomenon takes place. Effects of the electrostatic force and the temperature variation on the frequency response of the microphone subjected to a sound pressure wave are investigated. As the results illustrate, increment of the electrostatic force or increment of the diaphragm temperature increases the output level and sensitivity of the microphone and decreases the fundamental frequency of the microphone, limiting the upper band of its bandwidth. It is obvious that decrement of the diaphragm temperature acts conversely. In addition, the results show that in the presence of the electrostatic force sensitivity of the output level of the diaphragm to the temperature change increases.

Pull-in instability of nano-switches using nonlocal elasticity theory

This paper investigates the pull-in instability of nano-switches subjected to an electrostatic force due to an applied voltage and intermolecular force within the framework of nonlocal elasticity theory to account for the small scale effect. Both the nonlinear governing equation and boundary conditions with nonlocal effect are derived. A linear distributed load model is proposed to approximate the nonlinear intermolecular and electrostatic interactions. Closed-form solutions of critical pull-in parameters are obtained for cantilever and fixed–fixed nano-beams. The freestanding behaviour of nano-beams, which is a special case in the absence of electrostatic force, is also studied. It is found that the small scale effect contributes to the pull-in instability and freestanding behaviour of cantilever and fixed–fixed nano-beams in quite different ways. The effects of gap ratio, slenderness ratio and intermolecular force are discussed in detail as well.

Carboxyl Terminus of Severe Acute Respiratory Syndrome Coronavirus Nucleocapsid Protein: Self-Association Analysis and Nucleic Acid Binding Characterization

Coronavirus nucleocapsid (N) protein envelops the genomic RNA to form long helical nucleocapsid during virion assembly. Since N protein oligomerization is usually a crucial step in this process, characterization of such an oligomerization will help in the understanding of the possible mechanisms for nucleocapsid formation. The N protein of severe acute respiratory syndrome coronavirus (SARS-CoV) was recently discovered to self-associate by its carboxyl terminus. In this study, to further address the detailed understanding of the association feature of this C-terminus, its oligomerization was systematically investigated by size exclusion chromatography and chemical cross-linking assays. Our results clearly indicated that the C-terminal domain of SARS-CoV N protein could form not only dimers but also trimers, tetramers, and hexamers. Further analyses against six deletion mutants showed that residues 343-402 were necessary and sufficient for this C-terminus oligomerization. Although this segment contains many charged residues, differences in ionic strength have no effects on its oligomerization, indicating the absence of electrostatic force in SARS-CoV N protein C-terminus self-association. Gel shift assay results revealed that the SARS-CoV N protein C-terminus is also able to associate with nucleic acids and residues 363-382 are the responsible interaction partner, demonstrating that this fragment might involve genomic RNA binding sites. The fact that nucleic acid binding could promote the SARS-CoV N protein C-terminus to form high-order oligomers implies that the oligomeric SARS-CoV N protein probably combines with the viral genomic RNA in triggering long nucleocapsid formation.

Electrostatic forces in fibrous filters—a review

Among various devices for removing submicrometer particles from a gas stream, fibrous filters have the advantages of providing high collection efficiencies at low-pressure drop. Even in the absence of electrostatic forces, a fibrous filter captures particles efficiently by inertial impaction, interception, and convective Brownian diffusion. Application of electrostatic forces can significantly increase the efficiency of collection. The process of aerosol filtration in the presence of electrostatic forces is complicated. Although past studies have led to a good understanding of the filtration process in clean filters, there is a marked gap between theory and experiment of the change in collection efficiency with particle loading in a filter in the presence of electrostatic forces. This paper gives a review on both theoretical and experimental studies on the application of electrostatic forces in filtration and discusses the needs for further studies on the effect of particle loading.

Toner Adhesion Force Estimation by Electric Field Activated Toner Jumping

Toner motion is controlled by electric force, adhesion force, mechanical force, and so on, in the electrophotographic printing process. Adhesion force is an important force. Adhesion force in the absence of electrostatic force is estimated by electric field forced toner jumping. Toner is sprayed on one of a pair of electrodes that are spaced parallel to each other. Voltage increasing at a constant rate is applied to the electrode, and toner jumping starts at the voltage where electric force overcomes adhesion and gravitation forces. From the toner jumping voltage, adhesion force is estimated. Toner diameter, substrate and toner application method dependencies are obtained.

Evidence for electrostatic channeling in a fusion protein of malate dehydrogenase and citrate synthase.

Brownian dynamics simulations were performed to investigate a possible role for electrostatic channeling in transferring substrate between two of the enzymes of the citric acid cycle. The diffusion of oxaloacetate from one of the active sites of malate dehydrogenase (MDH) to the active sites of citrate synthase (CS) was simulated in the presence and absence of electrostatic forces using a modeled structure for a MDH-CS fusion protein. In the absence of electrostatic forces, fewer than 1% of substrate molecules leaving the MDH active site are transferred to CS. When electrostatic forces are present at zero ionic strength however, around 45% of substrate molecules are successfully channeled. As expected for an electrostatic mechanism of transfer, increasing the ionic strength in the simulations reduces the calculated transfer efficiency. Even at 150 mM however, the inclusion of electrostatic forces results in an increase in transfer efficiency of more than 1 order of magnitude. The simulations therefore provide evidence for the involvement of electrostatic channeling in guiding substrate transfer between two of the enzymes of the citric acid cycle. Similar effects may operate between other members of the citric acid metabolon.

The double layer–capillary stability of an annular electrolyte fluid surrounding a dielectric-fluid core in a tube

In this paper we examine the linear stability of an annular film surrounding a dielectric-fluid core in a tube in the presence of double layers of charges at the film core and at the film–tube interfaces, when the fluid-fluid interface is of low tension. In the absence of electrostatic forces, the surface tension force arising from the circumferential curvature destabilizes, and that from the axial curvature stabilizes the system. The competition is such that waves larger than the unperturbed interface circumference are unstable and those shorter are stable. For charged layers in the film, two cases are examined: (i) double-layer repulsion where the volume charge density is everywhere of the same sign and (ii) double-layer attraction where the diffusive layers next to the film interfaces are of opposite signs. In the first case, double-layer repulsion and surface tension lowering stabilize the destabilizing action of the circumferential component of the surface tension force, and a window of stability can exist. In the case of double layers of opposite signs, double-layer attraction destabilizes the system, and growth rates larger than those caused by pure capillarity can arise. Finally, for the case of a core bounded by an infinite electrolyte, surface tension lowering stabilizes the destabilizing action of the circumferential component of the surface tension force and destabilizes the longitudinal one, although the magnitudes of these effects may differ. As a result the thread can become unstable to waves shorter than the interface circumference.

Electrostatic Persistence Length of a Wormlike Polyelectrolyte

Electrostatic Persistence Length of a Wormlike Polyelectrolyte