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Smith, Kyle C.

Publications and source records attributed to Smith, Kyle C..

6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Realistic Ion Dynamics through Charge Renormalization in Nonaqueous Electrolytes

While many practically important electrolytes contain lithium ions, interactions of these ions are particularly difficult to probe experimentally because of their small X-ray and neutron scattering cross sections and large neutron absorption cross sections. Molecular dynamics (MD) is a powerful tool for understanding the properties of nonaqueous electrolyte solutions from the atomic level, but the accuracy of this computational method crucially depends on the physics built into the classical force field. In this study, we demonstrate that several force fields for lithium bistriflimide (LiTFSI) in acetonitrile yield a solution structure that is consistent with the neutron scattering experiments, yet these models produce dramatically different ion dynamics in solution. Such glaring discrepancies indicate that inadequate representation of long-range interactions leads to excessive ionic association and ion-pair clustering. We show that reasonable agreement with the experimental observations can be achieved by renormalization of the ion charges using a “titration” method suggested herewith. This simple modification produces realistic concentration dependencies for ionic diffusion and conductivity in <2 M solutions, without loss in quality for simulation of the structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Observation of Microheterogeneity in Highly Concentrated Nonaqueous Electrolyte Solutions

The development of models to describe structure and dynamics of nonaqueous electrolyte solutions is challenging, and experimental observations are needed to form a foundation. In this work, neutron scattering is used to probe molecular dynamics in nonaqueous organic electrolytes. Two solutions were compared: one contained symmetrical electrolyte molecules prone to crystallize, and one contained desymmetrized electrolyte molecules preferring disordered states. For the latter, calorimetry and neutron data show that a disordered fluid persists to very low temperatures at high concentrations. Upon heating, localized cold crystallization occurs, leading to burst nucleation of microcrystalline solids within fluid phases. Our results suggest molecular clustering and point to solvation inhomogeneities and molecular crowding in these concentrated fluids.

25 ENERGY STORAGE↗
DOE OSTI2019

Gravity induced flow cell

The flow cell includes first and second reservoirs having a selected volume containing a flowable redox electrode. A membrane separates charged and discharged material. An energy-extraction region includes electronically conductive porous current collectors through or adjacent to which the flowable redox electrodes flow and to which charge transfer occurs. Structure is provided for altering orientation of the flow cell whereby gravity induces flow of the flowable redox electrode between the first and second reservoirs to deliver power. By varying the angle of the cell, flow rate and power delivered on discharge or the charge rate on charge may be varied.

25 ENERGY STORAGE↗
DOE OSTI2018

Nanopore occlusion: A biophysical mechanism for bipolar cancellation in cell membranes

Highlights: • Cell experiments show that a first electrical pulse can be partially reversed by a second pulse. • Bipolar cancellation (BPC) of electrical effects in cells has defied biophysical mechanistic explanation. • For the first time we describe a successful model based on biophysical mechanisms. • The model's basis is {sup o}cclusion of nanopores{sup }by external molecules. • The model may be sufficiently general that BPC will prove to be essentially universal (BPC). Extraordinarily large but short electric field pulses are reported by many experiments to cause bipolar cancellation (BPC). This unusual cell response occurs if a first pulse is followed by a second pulse with opposite polarity. Possibly universal, BPC presently lacks a mechanistic explanation. Multiple versions of the “standard model” of cell electroporation (EP) fail to account for BPC. Here we show, for the first time, how an extension of the standard model can account for a key experimental observation that essentially defines BPC: the amount of a tracer that enters a cell, and how tracer influx can be decreased by the second part of a bipolar pulse. The extended model can also account for the recovery of BPC wherein the extent of BPC is diminished if the spacing between the first and second pulses is increased. Our approach is reverse engineering, meaning that we identify and introduce an additional biophysical mechanism that allows pore transport to change. We hypothesize that occluding molecules from outside the membrane enter or relocate within a pore. Significantly, the additional mechanism is fundamental and general, involving a combination of partitioning and hindrance. Molecules near the membrane can enter pores to block transport of tracer molecules while still passing small ions (charge number ±1) that govern electrical behavior. Our extension of the standard model accounts for key BPC behavior.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Versatile technique for assessing thickness of 2D layered materials by XPS

X-ray photoelectron spectroscopy (XPS) has been utilized as a versatile method for thickness characterization of various two-dimensional (2D) films. Accurate thickness can be measured simultaneously while acquiring XPS data for chemical characterization of 2D films having thickness up to approximately 10 nm. For validating the developed technique, thicknesses of few-layer graphene (FLG), MoS 2 and amorphous boron nitride (a-BN) layer, produced by microwave plasma chemical vapor deposition (MPCVD), plasma enhanced chemical vapor deposition (PECVD), and pulsed laser deposition (PLD) respectively, were accurately measured. The intensity ratio between photoemission peaks recorded for the films (C 1s, Mo 3d, B 1s) and the substrates (Cu 2p, Al 2p, Si 2p) is the primary input parameter for thickness calculation, in addition to the atomic densities of the substrate and the film, and the corresponding electron attenuation length (EAL). The XPS data was used with a proposed model for thickness calculations, which was verified by cross-sectional transmission electron microscope (TEM) measurement of thickness for all the films. The XPS method determines thickness values averaged over an analysis area which is orders of magnitude larger than the typical area in cross-sectional TEM imaging, hence provides an advanced approach for thickness measurement over large areas of 2D materials. The study confirms that the versatile XPS method allows rapid and reliable assessment of the 2D material thickness and this method can facilitate in tailoring growth conditions for producing very thin 2D materials effectively over a large area. Furthermore, the XPS measurement for a typical 2D material is non-destructive and does not require special sample preparation. Furthermore, after XPS analysis, exactly the same sample can undergo further processing or utilization.

2D film thickness↗