SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Electrostatics

136

Magnesium silicate as a high-performance adsorption material has attracted increasing attention for the removal of organic dye pollution. Here, we prepared a series of magnesium silicate hydrates (MSH) in a hydrothermal route, and carefully investigated the corresponding adsorption behavior towards methylene blue (MB) as well as the effect of surface charge on adsorption capacity. The results show that surface charge plays a key role in the adsorption performance of MSH for MB, a negative surface charge density follows the increase of Si/Mg feeding ratio from 1.00 to 1.75, and furthermore the higher negative charge favors the improvement of the adsorption capacity. Among four investigated samples (MSH = 1.00, 1.25, 1.50, and 1.75), MSH-1.75 has the highest negative surface charge and shows the largest adsorption capacity for MB. For example, the equilibrium adsorption quantity is 307 mg·g−1 for MSH-1.75, which is 35% higher than that of 227 mg·g−1 for MSH-1.00. Besides, for MSH-1.75, the as-prepared sample with negative charge exhibits ca. 36% higher adsorption quantity compared to the sample at the zero point of charge (pHZPC). Furthermore, magnesium silicate hydrate material with Si/Mg feeding ratio = 1.75 demonstrates the promising removal efficiency of beyond 98% for methylene blue in 10 min, and the maximum adsorption capacity of 374 mg·g−1 calculated from the Langmuir isotherm model.

Concepts: Electric charge, Fundamental physics concepts, Density, Electrostatics, Adsorption, Surface chemistry, Charge density, Current density

35

Honeybees, like other insects, accumulate electric charge in flight, and when their body parts are moved or rubbed together. We report that bees emit constant and modulated electric fields when flying, landing, walking and during the waggle dance. The electric fields emitted by dancing bees consist of low- and high-frequency components. Both components induce passive antennal movements in stationary bees according to Coulomb’s law. Bees learn both the constant and the modulated electric field components in the context of appetitive proboscis extension response conditioning. Using this paradigm, we identify mechanoreceptors in both joints of the antennae as sensors. Other mechanoreceptors on the bee body are potentially involved but are less sensitive. Using laser vibrometry, we show that the electrically charged flagellum is moved by constant and modulated electric fields and more strongly so if sound and electric fields interact. Recordings from axons of the Johnston organ document its sensitivity to electric field stimuli. Our analyses identify electric fields emanating from the surface charge of bees as stimuli for mechanoreceptors, and as biologically relevant stimuli, which may play a role in social communication.

Concepts: Electron, Electromagnetism, Electric charge, Electromagnetic field, Fundamental physics concepts, Electrostatics, Electric field, Coulomb's law

29

Triboelectrification is an effect that is known to each and every one probably ever since the ancient Greek time, but it is usually taken as a negative effect and is avoided in many technologies. We have recently invented a triboelectric nanogenerator (TENG) that is used to convert mechanical energy into electricity by a conjunction of triboelectrification and electrostatic induction. As for this power generation unit, in the inner circuit, a potential is created by the triboelectric effect due to the charge transfer between two thin organic/inorganic films that exhibit opposite tribo-polarity; in the outer circuit, electrons are driven to flow between two electrodes attached on the back sides of the films in order to balance the potential. Since the most useful materials for TENG are organic, it is also named organic nanogenerator, which is the first of using organic materials for harvesting mechanical energy. In this paper, we review the fundamentals of the TENG in the three basic operation modes: vertical contact-separation mode, in-plane sliding mode, and single-electrode mode. Ever since the first report of the TENG in January 2012, the output power density of TENG has been improved for five orders of magnitude within 12 months. The area power density reaches 313 W/m2, volume density reaches 490 kW/m3, and a conversion efficiency of ~60% has been demonstrated. The TENG can be applied to harvest all kind mechanical energy that is available but wasted in our daily life, such as human motion, walking, vibration, mechanical triggering, rotating tire, wind, flowing water and more. Alternatively, TENG can also be used as a self-powered sensor for actively detecting the static and dynamic processes arising from mechanical agitation using the voltage and current output signals of the TENG, respectively, with potential applications for touch pad and smart skin technologies. To enhance the performance of the TENG, besides the vast choices of materials in the triboelectric series, from polymer to metal and to fabric, the morphologies of their surfaces can be modified by physical techniques with the creation of pyramids-, square- or hemisphere-based micro- or nano-patterns, which are effective for enhancing the contact area and possibly the triboelectrification. The surfaces of the materials can be functionalized chemically using various molecules, nanotubes, nanowires or nanoparticles, in order to enhance the triboelectrific effect. The contact materials can be composites, such as embedding nanoparticles in polymer matrix, which may change not only the surface electrification, but also the permittivity of the materials so that they can be effective for electrostatic induction. Therefore, there are numerous ways for enhancing the performance of the TENG from the materials point of view. This gives an excellent opportunity for chemists and materials scientists to do extensive study both in the basic science and in practical applications. We anticipate that a much more enhancement of the output power density will be achieved in the next few years. The TENG is possible not only for self-powered portable electronics, but also as a new energy technology with a potential of contributing to the world energy in the near future.

Concepts: Electric charge, Electricity, Electrostatics, Friction, Static electricity, Electrical phenomena, Triboelectric effect, Electrophorus

28

Self organization of large-scale structures in nature - either coherent structures like crystals, or incoherent dynamic structures like clouds - is governed by long-range interactions. In many problems, hydrodynamics and electrostatics are the source of such long-range interactions. The tuning of electrostatic interactions has helped to elucidate when coherent crystalline structures or incoherent amorphous structures form in colloidal systems. However, there is little understanding of self organization in situations where both electrostatic and hydrodynamic interactions are present. We present a minimal two-component oil-in-oil model system where we can control the strength and lengthscale of the electrohydrodynamic interactions by tuning the amplitude and frequency of the imposed electric field. As a function of the hydrodynamic lengthscale, we observe a rich phenomenology of exotic structure and dynamics, from incoherent cloud-like structures and chaotic droplet dynamics, to polyhedral droplet phases, to coherent droplet arrays.

Concepts: Electric charge, Fundamental physics concepts, Fluid dynamics, Magnetohydrodynamics, Electrohydrodynamics, Structure, Electrostatics, Electric field

27

The influence of the shape of a polyelectrolyte (PE) on its electrophoretic behavior in a nanofluidic channel is investigated by considering the translocation of a deformable ellipsoidal PE along the axis of a cylindrical nanochannel. A continuum model comprising a Poisson equation for the electric potential, Nernst-Planck equations for the ionic concentrations, and modified Stokes equations for the flow field is adopted. The effects of the PE shape, boundary, bulk ionic concentration, counterion condensation, electroosmotic retardation flow, and electroosmotic flow (EOF) on the PE mobility are discussed. Several interesting behaviors are observed. For example, if the nanochannel is uncharged and the double layer is thick, then the PE mobility increases (decreases) with increasing double-layer thickness for a smaller (larger) boundary, which has not been reported previously. If the nanochannel is negatively charged and the double layer is thick, then a negatively charged PE moves in the direction of the applied electric field. The results gathered provide necessary information for both the interpretation of experimental data and the design of nanochannel-based sensing devices.

Concepts: Electromagnetism, Electric charge, Electric potential, Electrostatics, Maxwell's equations, Capillary electrophoresis, Faraday's law of induction, Zeta potential

26

Mechnosensational human-machine interfaces (HMIs) can greatly extend communication channels between human and external devices in a natural way. The mechnosensational HMIs based on biopotential signals have been developing slowly owing to the low signal-to-noise ratio and poor stability. In eye motions, the corneal-retinal potential caused by hyperpolarization and depolarization is very weak. However, the mechanical micromotion of the skin around the corners of eyes has never been considered as a good trigger signal source. We report a novel triboelectric nanogenerator (TENG)-based micromotion sensor enabled by the coupling of triboelectricity and electrostatic induction. By using an indium tin oxide electrode and two opposite tribomaterials, the proposed flexible and transparent sensor is capable of effectively capturing eye blink motion with a super-high signal level (~750 mV) compared with the traditional electrooculogram approach (~1 mV). The sensor is fixed on a pair of glasses and applied in two real-time mechnosensational HMIs-the smart home control system and the wireless hands-free typing system with advantages of super-high sensitivity, stability, easy operation, and low cost. This TENG-based micromotion sensor is distinct and unique in its fundamental mechanism, which provides a novel design concept for intelligent sensor technique and shows great potential application in mechnosensational HMIs.

Concepts: Electricity, Electrostatics, Indium tin oxide, Indium(III) oxide, Indium, Signal-to-noise ratio, Optical coating, Triboelectric effect

26

The implementation of contact mode Kelvin probe force microscopy (KPFM) utilizes the electrostatic interactions between tip and sample when the tip and sample are in contact with each other. Surprisingly, the electrostatic forces in contact are large enough to be measured even with tips as stiff as 4.5 N/m. As for traditional non-contact KPFM, the signal depends strongly on electrical properties of the sample, such as the dielectric constant, and the tip-properties, such as the stiffness. Since the tip is in contact with the sample, bias-induced changes in the junction potential between tip and sample can be measured with higher lateral and temporal resolution compared to traditional non-contact KPFM. Significant and reproducible variations of tip-surface capacitance are observed and attributed to surface electrochemical phenomena. Observations of significant surface charge states at zero bias and strong hysteretic electromechanical responses at non-ferroelectric surface have significant implications for fields such as triboelectricity and piezoresponse force microscopy.

Concepts: Electromagnetism, Electric charge, Electricity, Fundamental physics concepts, Electrostatics, Scanning probe microscopy, Electric and magnetic fields in matter, Kelvin probe force microscope

26

Strong interactions, or correlations, between the d or f electrons in transition-metal oxides lead to various types of metal-insulator transitions that can be triggered by external parameters such as temperature, pressure, doping, magnetic fields and electric fields. Electric-field-induced metallization of such materials from their insulating states could enable a new class of ultrafast electronic switches and latches. However, significant questions remain about the detailed nature of the switching process. Here, we show, in the canonical metal-to-insulator transition system V2O3, that ultrafast voltage pulses result in its metallization only after an incubation time that ranges from ∼150 ps to many nanoseconds, depending on the electric field strength. We show that these incubation times can be accounted for by purely thermal effects and that intrinsic electronic-switching mechanisms may only be revealed using larger electric fields at even shorter timescales.

Concepts: Electromagnetism, Electric charge, Magnetic field, Quantum mechanics, Fundamental physics concepts, Electrostatics, Maxwell's equations, Magnetism

25

A negatively charged copolymer poly (MPC-co-AMPS) of 2-methacryloyloxyethyl phosphorylcholine (MPC) and 2-acrylamide-2-methyl propane sulfonic acid (AMPS) was designed and synthesized. Chitosan nanoparticles with cell outer membrane mimetic structure were prepared by electrostatic interaction between the sulfonic acid groups of poly (MPC-co-AMPS) and the protonated amino groups of chitosan. Effects of factors on influencing the particle size, distribution and stability were investigated.The experimental results showed that cell membrane mimetic chitosan nanoparticles with controllable and homogeneous size ranged from 100 to 300 nm were prepared at the concentration of 0.1~2.0 mg/mL and the charge ratio of 0.5~1.1. Chitosan nanoparticles prepared can exist stably for more than 45 days placed at 4℃ and pH < 7.5. The cytotoxicity of chitosan nanoparticles reduced significantly after surface modification with cell membrane mimetic structure, meeting the basic requirements of biomedical materials. The results suggest cell membrane mimetic chitosan nanoparticles prepared with polyanion and polycation obtain good biological compatibility and immune stealth ability, which has important academic significance and great application prospect.

Concepts: Protein, Cell, Electric charge, Amino acid, Amine, Cell membrane, Electrostatics, Sulfonic acid

25

The peptide drug enfuvirtide (T20) is the only HIV-1 fusion inhibitor in clinical use, but it easily induces drug-resistance, calling for new strategies for developing next-generation drugs. On the basis of the M-T hook structure, we recently developed highly potent short-peptide HIV-1 fusion inhibitors (MTSC22 and HP23), which mainly target the conserved gp41 pocket and possess high genetic barriers to resistance. Here, we focused on the selection and characterization of HIV-1 escape mutants to MTSC22, which revealed new resistance pathways and mechanisms. Two mutations, E49K and L57R, located at the inhibitor-binding site, and two mutations, N126K and E136G, located at the C-terminal heptad repeat region of gp41, were identified as conferring high resistance either singly or in combinations. While E49K reduced the C-terminal binding of inhibitors via an electrostatic repulsion, L57R dramatically disrupted the N-terminal binding of M-T hook structure and pocket-binding domain. Different from E49K and N126K that enhanced the stability of endogenous viral six-helical bundle core (6-HB), L57R and E136G conversely destabilized the 6-HB structure. We also demonstrated that both primary and secondary mutations caused the structural changes of 6-HB and severely impaired the ability of HIV-1 entry. Collectively, our data provide novel insights into the mechanisms of short-peptide fusion inhibitors targeting the gp41 pocket site and help our understanding for the structure and function of gp41 and HIV-1 evolution.

Concepts: HIV, Protein, Michael Faraday, Electrostatics, Electric field, CCR5, Inhibitor, Entry inhibitor