Direct Visualization of Dynamic Mobility of Li2O2 in Li-O2 Batteries: A Differential Interference Microscopy Study

The reversibility and the discharge/charge performance in nonaqueous lithium-oxygen (Li-O₂) batteries are critically dependent on the kinetics of interfacial reactions. However, the interfacial reaction dynamic behaviors, especially the quantitative analysis, are still far from deep understanding. Using the method of laser confocal microscopy combined with differential interference contrast microscopy (LCM-DIM), we monitored the Li-O₂ interfacial reaction and in situ traced the Li₂O₂ migration processes promoted by the solution catalyst. Different dynamic behaviors exist when regulating the concentration of the redox mediator. Quantitative analysis of the discharged Li₂O₂ particles shows high mobility at the early discharge stage and decayed motion in the subsequent process, indicating the solution-mediated pathway participating Li₂O₂ formation in the low-concentration redox mediator addition, while particles/aggregates confined into the amorphous film demonstrate simultaneous solution and surface route-mediated pathway participation in the high-concentration case. These distinctive observations of Li₂O₂ formation and decomposition processes present the advantage of LCM-DIM to fundamentally understand the dynamic evolution in Li-O₂ batteries.

AC Electrokinetics of Salt-Free Multilayered Polymer-Grafted Particles

Interest in the electrical properties of the interface between soft (or polymer-grafted) nanoparticles and solutions is considerable. Of particular significance is the case of polyelectrolyte-coated particles, mainly taking into account that the layer-by-layer procedure allows the control of the thickness and permeability of the layer, and the overall charge of the coated particle. Like in simpler systems, electrokinetic determinations in AC fields (including dielectric dispersion in the 1 kHz-1 MHz frequency range and dynamic electrophoresis by electroacoustic methods in the 1-18 MHz range) provide a large amount of information about the physics of the interface. Different models have dealt with the electrokinetics of particles coated by a single polymer layer, but studies regarding multi-layered particles are far scarcer. This is even more significant in the case of so-called salt-free systems; ideally, the only charges existing in this case consist of the charge in the layer(s) and the core particle itself, and their corresponding countercharges, with no other ions added. The aims of this paper are as follows: (i) the elaboration of a model for the evaluation of the electrokinetics of multi-grafted polymer particles in the presence of alternating electric fields, in dispersion media where no salts are added; (ii) to carry out an experimental evaluation of the frequency dependence of the dynamic (or AC) electrophoretic mobility and the dielectric permittivity of suspensions of polystyrene latex spherical particles coated with successive layers of cationic, anionic, and neutral polymers; and (iii) finally, to perform a comparison between predictions and experimental results, so that it can be demonstrated that the electrokinetic analysis is a useful tool for the in situ characterization of multilayered particles.

Violet Fox: A Clinical View of Vertebral Fractures

Had Violet's abdominal MR not been performed, or its findings not appreciated, the cause of her clinical event might never have been known because our current concept of osteoporotic vertebral fracture (VF) is substantially predicated on a change in either vertebral height or shape on lateral or sagittal spine imaging. The intention of this commentary is to stimulate a multidisciplinary conversation of osteoporotic VFs from an integrated clinical, physiological, and imaging perspective. For research and epidemiological purposes, osteoporotic VFs have been defined as a reduction in anterior, middle, or posterior vertebral height although the required minimum height reduction (e.g., 15% or 20%) varies among definition schemes. We further classify osteoporotic VFs to be "clinical" when they are accompanied by back pain and "morphometric" when they are not, and we have generally accepted the assertion that most of the osteoporotic VFs are painless, that is, morphometric. This dichotomous VF definition scheme has been the foundation of osteoporosis epidemiology and the primary endpoint in most pivotal osteoporosis pharmaceutical trials. Although, having served the osteoporosis community well, our clinical experience, refined by recent insights into vertebral anatomy and spinal biomechanics, advances in vertebral imaging, and 2 decades of vertebral augmentation suggest that the spectrum of osteoporotic VFs is more complicated than this scheme suggests.