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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Fundamental aspects of electric double layer force-distance measurements at liquid-solid interfaces using atomic force microscopy

In this paper, atomic force microscopy (AFM) force-distance measurements are used to investigate the layered ion structure of Ionic Liquids (ILs) at the mica surface. The effects of various tip properties on the measured force profiles are examined and reveal that the measured ion position is independent of tip properties, while the tip radius affects the forces required to break through the ion layers as well as the adhesion force. Force data is collected for different ILs and directly compared with interfacial ion density profiles predicted by molecular dynamics. Through this comparison it is concluded that AFM force measurements are sensitive to the position of the ion with the larger volume and mass, suggesting that ion selectivity in force-distance measurements are related to excluded volume effects and not to electrostatic or chemical interactions between ions and AFM tip. Finally, the comparison also revealed that at distances greater than 1 nm the system maintains overall electroneutrality between the AFM tip and sample, while at smaller distances other forces (e.g., van der waals interactions) dominate and electroneutrality is no longer maintained.

25 ENERGY STORAGE↗
DOE OSTI2012

General solution to the electric double layer with discrete interfacial charges

We provide extensive molecular dynamics simulations of counterion and coion distributions near an impenetrable plane with fixed discrete charges. The numerical results are described by an explicit solution that distinguishes the plasma (math/σ>3) and the binding regime (math/σ<3) where σ is the ion diameter and Ac = |e/ν| (ν is the surface charge density). In the plasma regime, the solution consists of a product of two functions that can be computed from simpler models and reveals that the effects of the discreteness of the charge extends over large distances from the plane. The solution in the binding regime consists of a Stern layer of width σ and a diffuse layer, but contrary to standard approaches, the strong correlations between ions within the Stern layer and the diffuse layer require a description in terms of a “displaced” diffuse layer. The solution is found to describe electrolytes of any valence at all concentrations investigated (up to 0.4M) and includes the case of additional specific interactions such as van der Waals attraction and other generalizations. We discuss some open questions.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Coupled double-layer Fano resonance photonic crystal filters with lattice-displacement

We present here ultra-compact high-Q Fano resonance filters with displaced lattices between two coupled photonic crystal slabs, fabricated with crystalline silicon nanomembrane transfer printing and aligned e-beam lithography techniques. Theoretically, with the control of lattice displacement between two coupled photonic crystal slabs layers, optical filter Q factors can approach 211 000 000 for the design considered here. Experimentally, Q factors up to 80 000 have been demonstrated for a filter design with target Q factor of 130 000.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Analysis of carrier behavior in C60/P(VDF-TrFE) double-layer capacitor by using electric-field-induced optical second-harmonic generation measurement

By using displacement current measurement (DCM) and electric-field-induced optical second-harmonic generation (EFISHG) measurement, we studied the carrier behavior in the indium-tin oxide (ITO)/Poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE))/C60/Au(or Al) capacitors. Two DCM peaks appeared asymmetrically at around −35.5 V and +30.0 V in the dark. Correspondingly, the EFISHG response from the C60 layer was observed, but the peak positions were different with respect to DCM ones. The results show that the spontaneous polarization of the ferroelectric P(VDF-TrFE) polymeric layer directly affects the electric field in the C60 layer, and thus governs the carrier motion in this layer. As a result, the C60 layer serves like an insulator in the dark, while electrons and holes are captured and released at the interface in response to the turn-over of spontaneous polarization of ferroelectric layer. On the other hand, under white light illumination, C60 layer serves like a conductor due to the increase of photogenerated mobile carriers, and these carriers dominate the carrier motions therein. Our findings here will be helpful for analyzing carrier behaviors in organic electronic devices using ferroelectric polymers.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Electric double layer for a size-asymmetric electrolyte around a spherical colloid

We have studied the structure of a size-asymmetric electrolyte on charged colloids by a density functional perturbation theory. The hard-sphere contribution has been approximated as the direct pair correlation function with the coupling parameter, whereas the electronic contribution has been approximated as the mean-spherical approximation in the bulk phase. The calculated results for the ionic density distributions and mean electrostatic potentials are in very good agreement with the computer simulations over a wide range of colloid sizes and electrolyte concentrations. The present theory provides better structural results than the hypernetted-chain equation based on the mean spherical approximation. We have confirmed that the overcharging appears when the counterions are larger than the coions. The overcharging disappears everywhere when the electrostatic repulsion becomes strong enough, while the charge reversal is observed when the coions are larger than the counterions, and the reversal effect appears for a size-asymmetric electrolyte at high surface charge densities. The charge reversal occurs even for the point of zero charge, mainly due to the depletion force between two ions. The present theory is able to provide interesting insights about the charge reversal and overcharging phenomena occurring at the interface.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗