Mechanism of alkali thickening of acid-containing emulsion polymers. I. Examination of latexes by means of viscosity

Viscosity-versus-pH relationships for a large number of methacrylic acid-containing emulsion polymers have been measured. The monomers chosen for this study were so selected because they represent synthesized latexes of high and low T_g and comparative hydrophilicity. These were styrene, methyl methacrylate, ethyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate. The postulated mechanism involved in the transition from an unneutralized latex particle to the neutralized species is accounted for in terms of varying degrees of particle swelling. In the limiting case, particle swelling is followed by complete solution of the polymer. The most important variables are the per cent methacrylic acid and the polymer T_g and hydrophilicity as determined by the comonomers present. The degree of particle swelling ranges from none for high styrene-containing latexes to high degrees of swelling followed by polymer solubilization for high ethyl acrylate-containing latexes.     

Strong Completeness and Limited Canonicity for PDL

Propositional dynamic logic () is complete but not compact. As a consequence, strong completeness (the property ) requires an infinitary proof system. In this paper, we present a short proof for strong completeness of relative to an infinitary proof system containing the rule from [α; β ⁿ ]φ for all , conclude . The proof uses a universal canonical model, and it is generalized to other modal logics with infinitary proof rules, such as epistemic knowledge with common knowledge. Also, we show that the universal canonical model of lacks the property of modal harmony, the analogue of the Truth lemma for modal operators.     

Mathematical modeling of high-power-density insertion electrodes for lithium ion batteries

Theoretical calculations are compared with well-controlled experiments conducted on a high-surface area, small diameter lithiated-carbon electrodes. The electrodes are shown to yield very high current densities and exhibit little interfacial kinetics resistance or intercalate diffusion resistance. The mathematical treatment describes quantitatively a wide range of electrochemical experiments. The application of the model to the experimental data is facilitated by the use of a reference electrode. Initial cycling behavior of the high-surface-area electrode is elucidated, including clarification of the first-cycle coulombic inefficiency. Nitrogen absorbtion and scanning electron micrographs are utilized to ascertain the microstructural characteristics that distinguish the active electrode material. An asymptotic analysis is used to indicate when diffusion resistance within host particles is negligible; this fact simplifies model calculations and contributes to our overall understanding of insertion processes associated with host particles of very small dimensions.     

Composite electrodes of disordered carbon and graphite for improved battery state estimation with minimal performance penalty

Voltage based state of charge (SOC) estimation is challenging for lithium ion batteries that exhibit little open circuit voltage (OCV) change over a large SOC range. We demonstrate that by using a composite negative electrode composed of disordered carbon and graphite, we were able to introduce additional features to the OCV-SOC relationship that facilitate voltage-based SOC estimation. In contrast to graphite, the potential of disordered carbon is sensitive to the state of charge; this behavior, when manifested in a lithium ion battery, gives rise to additional beneficial features of the cell OCV-SOC relationship in terms of state estimation. We have demonstrated the effectiveness of the approach by comparing model simulations and corresponding experimental data of a cell composed of LiFePO₄ positives and graphite + disordered carbon composite negative electrodes. Last, we find that although the graphite material has a higher coulombic capacity, very little (dynamic) performance loss is manifest with the mixed graphite + disordered carbon composite is employed.     

A phase model for the gas-liquid equilibria in the ammonia-carbon dioxide-water-urea system in chemical equilibrium at urea synthesis conditions. III. Comparison of the phase model with an empirical thermodynamic model

Calculations using an empirical thermodynamic model for the ammonia-carbon dioxide-water-urea system in chemical equilibrium lead to phase equilibria results consistent and in good agreement with those following from a previously published ternary phase model for this system.     

Adaptive,multi-parameter battery state estimator with optimized time-weighting factors

We derive and implement a battery control algorithm that can accommodate an arbitrary number of model parameters, with each model parameter having its own time-weighting factor, and we propose a method to determine optimal values for the time-weighting factors. Time-weighting factors are employed to give greater impact to recent data for the determination of a system’s state. We employ the (controls) methodology of weighted recursive least squares, and the time weighting corresponds to the exponential-forgetting formalism. The output from the adaptive algorithm is the battery state of charge (remaining energy), state of health (relative to the battery’s nominal performance), and predicted power capability. Results are presented for a high-power lithium ion battery.     

Optimum Particle Size in Silicon Electrodes Dictated by Chemomechanical Deformation of the SEI

Nanostructured alloy-forming anode materials can resist fracture that is caused by extreme volume changes during cycling. However, the higher surface area per unit mass in nanomaterials increases exposure to the electrolyte reduction reactions that form a solid electrolyte interphase (SEI), which implies that capacity loss will increase as particle size decreases. This hypothesis is investigated with composite electrodes using different silicon nanoparticle sizes, and the expected particle size effect is not observed. Instead, there is an optimum particle size where capacity loss per volume is minimized. Finite element modeling demonstrates that the mechanical deformation of the SEI varies significantly with the silicon particle size. Smaller particles lead to the decrease of the tensile hoop strains in the outer portion of the SEI and simultaneously make the overall elastic strains in the inner portion more compressive. These results suggest that the SEI on smaller particles is more resistant to mechanical degradation, even though the higher specific surface areas increase initial SEI formation. The trade-off between these effects leads to the observed optimum particle size.