Search

Abstract: Reproducibility of repeated crystallization experiments from melts is obtained after annealing the melt at a sufficiently high temperature for short time, or at lower temperatures for longer time. This annealing process erases the polymer melt memory. Its physical origin remains elusive, but it is linked to precursor structures for crystallization. What precursor structures are, and how they are affected by shear flow and melt temperature is also unclear. We identify in this work two well-defined melt states: the fully relaxed melt and the melt sheared up to a steady state. Crystallization from fully relaxed melts is slowest while from melts sheared up to the steady state is fastest. We demonstrate that polymers crystallized at the same temperature from the two different melt states have similar average spherulite size, but melts sheared up to steady state have lower viscosity and low number of entanglements, this being the reason for the acceleration of crystallization kinetics in these melts. Annealing of the melts sheared up to the steady state slows down the crystallization kinetics until it becomes comparable with that of fully relaxed melts. [ABSTRACT FROM AUTHOR]

Abstract: The facilitated transport of Cr(VI) through a bulk liquid membrane (BLM) is investigated, using the commercially available solvent tri-n-butyl phosphate (TBP) as mobile carrier. The influences of the carrier concentration in the liquid membrane phase, the HCl concentration of the feed phase, and the stripping concentration on the mass transfer process are studied. The transport rate of Cr(VI) increases with increasing the TBP concentration and HCl concentration. The increasing of the stripping concentration improves the stripping process until a plateau is reached. A kinetic model is used to describe the Cr(VI) transport behavior, assuming that it obeys the kinetic laws of two consecutive irreversible first-order reactions. The experimental data fits reasonable well with the derived model. The analysis of the accumulation of Cr(VI) in the liquid membrane phase and the discussion of the rate-controlling step under different experimental conditions are carried out. The magnitude of the value of k e and k s is found to be 10−4–10−5 s−1, and is well in agreement with other studies. [Copyright &y& Elsevier]

A better conversion enhancement of esterification between acetic acid and n-butanol was achieved in a catalytically active membrane reactor ( p CAMR) when compared to that in a traditional inert membrane reactor (IMR). This enhancement was attributed to a novel composite catalytically active membrane in which a highly porous catalytic layer was introduced. SEM images showed that the membrane consisted of three layers: the top layer was a highly porous catalytic layer with massive macrovoids and “sponge-like” pores, the middle layer was a dense polyvinyl alcohol selective layer, and the bottom layer was a porous polyethersulfone support layer. The preparation of a highly porous catalytic layer instead of a dense one in the composite membrane greatly decreased the overall mass transfer resistance of the reactor from 6.7 × 10 5 to 5.6 × 10 5 s/m, a value which is even comparable to that of IMR (5.1 × 10 5 s/m) where the additional catalytic layer was absent. The effects of operational parameters on the esterification-pervaporation coupling performance in p CAMR were systematically evaluated. Through a reasonable match between reaction rate and water removal rate, a genuine in-situ water removal at a molecular lever was realized. For comparison, coupling performances in an IMR and a catalytically active membrane reactor with a dense composite membrane ( d CAMR) were also investigated. Results showed that the coupling performance in p CAMR outperformed both IMR and d CAMR due to a combination of much lower overall mass transfer resistance and higher mass transfer driving force for water removal in p CAMR. After 45 h at 85 °C, the acid conversion in p CAMR reached almost completion, an approximately 43% of conversion enhancement was achieved when compared to equilibrium conversion. [ABSTRACT FROM AUTHOR]

Uniform minor Mn-doped LiFePO 4 /C cathode materials are synthesized and their electrochemical performances are investigated systematically. Via tuning the doping amount of Mn, it is found that the well crystallized LiFePO 4 /C doped with 11000 ppm Mn gives the highest discharge capacity of 165 mAh g −1 at 0.1 C at room temperature. Remarkably, it holds a quite stable cycling performance at 45 °C, with capacity retention of 97.4% after 200 cycles using a high rate of 3.0 C, and its low-temperature (−20 °C) specific capacity maintains at high up to 131.4 mAh g −1 at 0.1 C, higher than that of the majority reports. The higher or lower Mn-doping amount than 11000 ppm is found to have less positive impact on the performance of LiFePO 4 /C. Such phenomenon may be attributed to the negative cooperative effect of Mn doping, which enlarges the crystal space for improving the Li + transfer under low dose due to the large radius of Mn, but increases the charge transfer resistance and declines the performance under high dose owing to its poor intrinsic kinetics. [ABSTRACT FROM AUTHOR]

Abstract: To study the pharmacokinetics of Chan Su, a sensitive and selective method was developed and validated for the determination of five main bufadienolides (cinobufagin, resibufogenin, bufalin, bufotalin and arenobufagin) in rat plasma. The analytes were extracted by liquid–liquid extraction with ethyl acetate after internal standard (IS, caudatin) spiked. The separation was performed by a ZORBAX SB-C18 column (3.5μm, 2.1mm×100mm) and a C18 guard column (5μm, 4.0mm×2.0mm) with an isocratic mobile phase consisted of acetonitrile–water–formic acid (50:50:0.05, v/v/v) at a flow rate of 0.3mL/min. The Agilent G6410A triple quadrupole LC/MS system was operated under the multiple reaction monitoring mode (MRM) using the electrospray ionization technique in positive mode. The nominal retention times for cinobufagin, resibufogenin, bufalin, bufotalin, arenobufagin and caudatin were 3.07, 3.55, 2.30, 1.62, 1.22 and 3.43min, respectively. All analytes showed good linearity in a wide concentration range (r >0.995) and their lower limits of quantification (LLOQ) were all 1.0ng/mL. The method was linear for all analytes with correlation coefficients >0.995 for all analytes. The average extract recoveries of the five analytes from rat plasma were all over 85%, the precisions and accuracies determined were all within 15%. This method has been successfully applied to pharmacokinetic study of Chan Su in rats following oral administration. [Copyright &y& Elsevier]