Publications

Resource constraints have become critical for the Li-ion industry. Spinel LiMn 2 O 4 presents a cheaper, more sustainable alternative to traditional layered Li-ion cathodes, but its capacity is constrained by a two-phase transition at ~3V associated with a large, inhomogeneous volume change that leads to particle cracking and poor cycling stability. In contrast, the partially disordered spinels (PDS) have more sloping, solid-solution-like behavior, resulting in better rate capability and more homogeneous volume change. In this talk, we demonstrate that PDS achieves this by introducing cation disorder, which can shrink, and even fully remove, the two-phase region. By analyzing samples from cluster expansion-based Monte Carlo simulations, we identify the mechanisms that increase Li solubility in the LiMn 2 O 4 phase and lead to this shortened ~3V plateau. These results provide guidance on the optimal level of disorder in spinels to achieve both solid-solution behavior and good Li mobility and also highlight more generally how disorder can be utilized to reduce the effects of problematic phase transformations in ordered frameworks.

Abstract Previous studies have demonstrated both energy restriction (ER) and higher protein (HP), lower carbohydrate (LC) diets downregulate hepatic de novo lipogenesis. Little is known about the independent and combined impact of ER and HP/LC diets on tissue‐specific lipid kinetics in leptin receptor‐deficient, obese rodents. This study investigated the effects of ER and dietary macronutrient content on body composition; hepatic, subcutaneous adipose tissue (SAT), and visceral AT (VAT) lipid metabolic flux ( 2 H 2 O‐labeling); and blood and liver measures of cardiometabolic health in six‐week‐old female obese Zucker rats (Lepr fa+/fa+ ). Animals were randomized to a 10‐week feeding intervention: ad libitum (AL)‐HC/LP (76% carbohydrate/15% protein), AL‐HP/LC (35% protein/56% carbohydrate), ER‐HC/LP, or ER‐HP/LC. ER groups consumed 60% of the feed consumed by AL. AL gained more fat mass than ER (P‐energy = 0.012) and HP/LC gained more fat mass than HC/LP (P‐diet = 0.025). Hepatic triglyceride (TG) concentrations (P‐interaction = 0.0091) and absolute hepatic TG synthesis (P‐interaction = 0.012) were lower in ER‐HP/LC versus ER‐HC/LP. ER had increased hepatic, SAT, and VAT de novo cholesterol fractional synthesis, absolute hepatic cholesterol synthesis, and serum cholesterol (P‐energy≤0.0035). A HP/LC diet, independent of energy intake, led to greater gains in fat mass. A HP/LC diet, in the context of ER, led to reductions in absolute hepatic TG synthesis and TG content. However, ER worsened cholesterol metabolism. Increased adipose tissue TG retention with the HP/LC diet may reflect improved lipid storage capacity and be beneficial in this genetic model of obesity.

Performance improvements of perfluorosulfonic acid membranes, such as Nafion and Flemion, underline a need for dielectric characterization of these materials toward a quantitative understanding of the dynamics of water molecules and protons within the membranes. In this Article, a two-port transmission line technique for measuring the complex permittivity spectra of polymeric electrolytes in the microwave region is described, and the algorithms for permittivity determination are presented. The technique is experimentally validated with liquid water and polytertrafluoroethylene film, whose dielectric properties are well-known. Further, the permittivity spectra of dry and hydrated Flemion SH150 membranes are measured and compared to those of Nafion 117. Two water relaxation modes are observed in the microwave region (0.045-26 GHz) at 25 degrees C. The higher-frequency process observed is identified as the cooperative relaxation of bulk-like water, whose amount was found to increase linearly with water content in the polymer. The lower-frequency process, characterized by longer relaxation times in the range of 20-70 ps, is attributed to water molecules that are loosely bound to sulfonate groups. The loosely bound water amount was found to increase with hydration level at low water content and levels off at higher water contents. Flemion SH150, which has an equivalent weight of 909 g/equiv, displays higher dielectric strengths for both of these water modes as compared to Nafion 117 (equivalent weight of 1100 g/equiv), which probably reflects the effect of equivalent weight on the polymers' hydrated structure, and in particular its effect on the extended ionic cluster domains.

Polymer chemistry offers the possibility of synthesizing multifunctional nanoparticles which incorporate moieties that enhance diagnostic and therapeutic targeting of cargo delivery to the lung. However, since rules for predicting particle behavior following modification are not well-defined, it is essential that probes for tracking fate in vivo are also included. Accordingly, we designed polyacrylamide-based hydrogel particles of differing sizes, functionalized with a nona-arginine cell-penetrating peptide (Arg(9)), and labeled with imaging components to assess lung retention and cellular uptake after intratracheal administration. Radiolabeled microparticles (1-5 microm diameter) and nanoparticles (20-40 nm diameter) without and with Arg(9) showed diffuse airspace distribution by positron emission tomography imaging. Biodistribution studies revealed that particle clearance and extrapulmonary distribution was, in part, size dependent. Microparticles were rapidly cleared by mucociliary routes but, unexpectedly, also through the circulation. In contrast, nanoparticles had prolonged lung retention enhanced by Arg(9) and were significantly restricted to the lung. For all particle types, uptake was predominant in alveolar macrophages and, to a lesser extent, lung epithelial cells. In general, particles did not induce local inflammatory responses, with the exception of microparticles bearing Arg(9). Whereas microparticles may be advantageous for short-term applications, nanosized particles constitute an efficient high-retention and non-inflammatory vehicle for the delivery of diagnostic imaging agents and therapeutics to lung airspaces and alveolar macrophages that can be enhanced by Arg(9). Importantly, our results show that minor particle modifications may significantly impact in vivo behavior within the complex environments of the lung, underscoring the need for animal modeling.