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Simulation of ion transport through poly(ethylene oxide) loaded with lithium perchlorate

100%

Munn R. W. , Eilmes A. , Scarle S. , Sterzel M.

tom Vol. 27, No. 3

637--647

A hierarchical approach is used to simulate lithium ion motion through poly(ethylene oxide) loaded with lithium perchlorate, alone and with a tungsten oxide (WO3) interface to model an electrochromic smart window assembly. The structure of the polymer is simulated using commercial software. Relaxation of the polymer is allowed on a lattice on which the lithium ions move as a lattice gas. Polarization and van der Waals energy changes are calculated for an added lithium ion at each lattice point. The structure and energy are also calculated in the presence of the WO3 interface. Ion transport is simulated in a kinetic Monte Carlo method, with and without an electric field. During runs at 300 K without the WO3 interface, with a field the lithium ions move 35 A along it and 3-7 A across it but without a field they move 2-5 A; these distances vary with temperature as expected for activated hopping. Ions explore their immediate neighbourhood, occasionally jumping to an adjacent neighbourhood along, across or sometimes against the field, thus circumventing regions where transport is hindered. With the WO3, the lithium ions tend to accumulate at the interface, producing a repulsive potential that reduces ion movement.

Studies on degradation of poly(ethylene oxide) by multistep pyrolysis/gas chromatography with a programmable temperature vaporization injector.

72%

Kaczmarek H. , Kowalonek J. , Janssen H. G. , Lieshout H. P. M. v.

tom T. 45, nr 6

433-438

The multistep pyrolysis/gas chromatography technique using a programmable temperature vaporization injector was used to study thermal and photochemical properties of polymers. Pure poly(ethylene oxide) (PEOX) and PEOX + 3% CoCl2 specimens, 20-mm films, were UV-irradiated (2.45 mW/cm2) for 2 and 4 h in air at room temperature and pyrolyzed/gas chromatographed at 200oC, 420oC and 500oC (Fig. 1, 2). The products evolved at 200oC included residual solvent, monomer, catalyst, polymerization additives, and processing aids. At 420oC, degradation attained maximum and the compound concentrations were maximum in PEOX UV-irradiated for 2 h. In the 4-irradiated PEOX, the 420oC chromatographic peaks were less intense. At 500oC, the intensity of the peaks rose as the irradiation time was prolonged. CoCl2 (3%) gave rise to new degradation products. At 420oC and 500oC, irradiation had negligible effect on degradation of PEOX + 3% CoCl2. Scheme 1 illustrates the major interactions accompanying thermal and photochemical degradation of PEOX in the presence of CoCl2.

In-situ study of the influence of crystallization on the ionic conductivity of polymer electrolytes

58%

Marzantowicz M. , Dygas J. R. , Krok F. , Zygadło-Monikowska E. , Florjańczyk Z.

Materials Science Poland

2006

tom Vol. 24, No. 1

195--203

Simultaneous impedance measurements and optical observations of polymer electrolytes were conducted in an automated experimental setup, combining an impedance analyser, polarizing microscope with a heating stage and a digital camera. The polymer film was placed between glasses with indium tin oxide conductive layers, forming a transparent cell mounted in a custom-designed holder, which preserved an argon atmosphere. Results of in-situ studies for various compositions of poly(ethylene oxide) (PEO) with LiN(CF3SO2)2 salt (LiTFSI), as well as pure PEO, are presented. In the investigated systems, crystallization had a strong impact on ionic conductivity. It was found that the initial growth of crystalline structures caused only a small fraction of the total decrease of conductivity. A large decrease in conductivity was observed during the second stage of crystallization, when no significant changes in microscope picture were observed. In pure PEO and the PEO:LiTFSI 6:1 system, a dense crystalline structure developed, resulting in a decrease in conductivity of over two orders of magnitude. In dilute PEO:LiTFSI systems, a "loose" structure was formed, with amorphous areas preserved between crystallites, and conductivity decreased by only a factor of about 6.