Copyright (C) JCPDS-International Centre for Diffraction Data

Abstract The structure refinement of X-ray powder data using the Rietveld method often results in false minima, i.e. not necessarily the energetically favored result. By introducing force fields as a new type of constraint into the recently developed BGMN program, a fully featured X-ray Rietveld system was created. With the model of bonding and nonbonding interactions, it was finally possible to refine the crystal structure of an aromatic trimer. By means of simple powder diffraction measurements, a set of structural data was obtained which was fitted mathematically to a structural model containing the geometry optimization by ab initio calculations, the indexing of diffraction pattern, the search of reasonable space group and the structure refinement under force field constraints. As an example, it was found that cycle-tris(2,6-pyridyl formamidine) crystallizes in a monoclinic unit cel

Ion exchange membranes derived from sulfonated polyaramides

Homo- and both random and block copolyaramides of high molecular weights, with sulfonated moieties in the backbone, were obtained by low temperature polycondensation technique in a dipolar aprotic solvent (NMP) using (a) free aromatic diamines in the presence of pyridine as acid acceptor and (b) N,N ′-bis-trimethylsilyl derivatives of the diamines without additional acid acceptor. The addition of low molecular weight electrolytes (LiCl or CaCl2) and in some cases trimesoyl chloride to the reaction mixture was found to be favorable for the synthesis of high molecular weight polyamides. The materials had a theoretical ion exchange capacity of up to 3.14 meq/g. The membranes were characterized in terms of morphology, thermal stability, water-uptake, and ion exchange capacities.Fil: Taeger, A.. Institute of Polymer Research Dresden; AlemaniaFil: Vogel, C.. Institute of Polymer Research Dresden; AlemaniaFil: Lehmann, D.. Institute of Polymer Research Dresden; AlemaniaFil: Jehnichen, D.. Institute of Polymer Research Dresden; AlemaniaFil: Komber, H.. Institute of Polymer Research Dresden; AlemaniaFil: Meier Haack, J.. Institute of Polymer Research Dresden; AlemaniaFil: Ochoa, Nelio Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich". Universidad Nacional de San Luis. Facultad de Ciencias Físico Matemáticas y Naturales. Instituto de Física Aplicada "Dr. Jorge Andrés Zgrablich"; ArgentinaFil: Nunes, S.P.. GKSS Research Center; AlemaniaFil: Peinemann, K.-V.. GKSS Research Center; Alemani

Enthalpy of formation and disordering temperature of transient monotropic liquid crystals of poly(butylene 2,6-naphthalate)

© 2018 Elsevier Ltd Melt-crystallization of poly(butylene 2,6-naphthalate) (PBN) at temperatures lower than about 160 °C follows Ostwald's rule of stages via intermediate formation of a smectic liquid crystalline phase (LC-phase). The transient LC-phase has been isolated by interruption of the isothermal crystallization process at 140 °C at sub-second timescale, and then its disordering was analyzed on heating at a rate of 2000 K/s, which suppresses the transition into α-crystals. The disordering temperature of the LC-mesophase is slightly lower than 200 °C, and as such 20–30 K lower than the melting temperature of α-crystals formed from the LC-phase at 140 °C. Analysis of the bulk enthalpy of formation of the LC-phase revealed that it covers only 20–25% of the total bulk enthalpy of crystallization, which is considered further proof of its smectic nature

An efficient two-polymer binder for high-performance silicon nanoparticle-based lithium-ion batteries: A systematic case study with commercial polyacrylic acid and polyvinyl butyral polymers

Silicon is one of the most promising anode materials for high energy density lithium ion batteries (LIBs) due to its high theoretical capacity and natural abundance. Unfortunately, significant challenges arise due to the large volume change of silicon upon lithiation/delithiation which inhibit its broad commercialization. An advanced binder can, in principle, reversibly buffer the volume change, and maintain strong adhesion toward various components as well as the current collector. In this work, we present the first report on the applicability of polyvinyl butyral (PVB) polymer as a binder component for silicon nanoparticles-based LIBs. Characteristic binder properties of commercial PVB and polyacrylic acid (PAA) polymers are compared. The work focuses on polymer mixtures of PVB polymers with PAA, for an improved binder composition which incorporates their individual advantages. Different ratios of polymers are systematically studied to understand the effect of particular polymer chains, functional groups and mass fractions, on the electrochemical performance. We demonstrate a high-performance polymer mixture which exhibits good binder-particle interaction and strong adhesion to Cu-foil. PAA/PVB-based electrode with a Si loading of ∼1 mg/cm2 tested between 0.01 and 1.2 V vs. Li/Li+ demonstrate specific capacities as high as 2170 mAh/g after the first hundred cycles. © The Author(s) 2019