Kinetics of Mass Transfer in the Melt Polycondensation of Poly(Ethylene Terephthalate)

For a four-parameter reaction-mass transport model of melt polycondensation, the constants of polycondensation, thermolysis, and diffusion were determined by means of experiments in thin-layer polycondensation. Based on these constants, the convectional mass transport and efficient melt thickness in polycondensation systems under conditions of compelled mixing can be estimated. However, for stirred polycondensation systems a reaction-mass transfer model proves more suitable. The constants of polycondensation and thermolysis obtained by the diffusion model can be transferred to the reaction-mass transfer model. Thus, only the mass transfer coefficient has to be determined.     

Li ion diffusion in the anode material Li12Si7: ultrafast quasi-1D diffusion and two distinct fast 3D jump processes separately revealed by 7Li NMR relaxometry

The intermetallic compounds Li(x)Si(y) have attracted considerable interest because of their potential use as anode materials in Li ion batteries. In addition, the crystalline phases in the Li-Si phase diagram turn out to be outstanding model systems for the measurement of fast Li ion diffusion in solids with complex structures. In the present work, the Li self-diffusivity in crystalline Li(12)Si(7) was thoroughly probed by (7)Li NMR spin-lattice relaxation (SLR) measurements. Variable-temperature and -frequency NMR measurements performed in both the laboratory and rotating frames of reference revealed three distinct diffusion processes in Li(12)Si(7). The diffusion process characterized by the highest Li diffusivity seems to be confined to one dimension. It is one of the fastest motions of Li ions in a solid at low temperatures reported to date. The Li jump rates of this hopping process followed Arrhenius behavior; the jump rate was ~10(5) s(-1) at 150 K and reached 10(9) s(-1) at 425 K, indicating an activation energy as low as 0.18 eV.     

Miscibility Behavior of Binary Monolayers in Dependence on the Chain Length Differences and Film States of the Phosphatidylcholine/Phosphatidylethanolamine Mixtures

The comparison of the miscibility behavior in binary monolayers of type phosphatidylcholine/phosphatidylethanolamine [system 1, dilauroylphosphatidylcholine / dilauroylphosphatidylethanolamine; system 2, dilauroylphosphatidylcholine/dimyristoylphosphatidylethanolamine; system 3, dilauroylphosphatidylcholine/dipalmitoylphosphatidylethanolamine] leads to the essential results that both the differences in the number of CH₂units of the hydrocarbon chains and the film state (liquid-expanded film M^eor condensed film M^C) in the monolayers are responsible for miscibility or immiscibility of the components in the mixed films. The investigations of the binary monolayers were carried out by application of a variety of surface and spreading techniques (mixed spreading, separated spreading, spreading pressure, compression isotherms, long-time investigations). From these studies of the compression and spreading properties of the above mentioned three binary systems and the application of the surface-phase rule we obtained the phase diagrams of the mixed monolayers. In system 1 we found that both components are completely miscible in the film state M^eand only partially miscible in the film state M^C. The same situation characterizes system 2. In the mixed monolayers of system 3 we found only partial miscibility of the phospholipids.     

Photoelimination of nitrogen from cyclic azo alkanes. An exceptionally labile and an exceptionally reluctant diazabicyclo[2.2.2]octene

The photochemistry of an unusually reactive diazabicyclo[2.2.2]octene has been found to be extremely solvent and temperature dependent; an exceptionally stable diazabicyclo[2.2.2]octene has been found to undergo a novel fragmentation as a result of vapor phase photoexcitation.