Cation Environment in Molten Lithium Iodide Doped Poly(ethylene oxide)

Abstract

We present neutron diffraction isotopic substitution (NDIS) and molecular dynamics (MD) simulation results on molten poly(ethylene oxide) doped with LiI in a molar ratio of five ether oxygens per Li + ion. The NDIS and the MD studies yield estimates of the partial radial distribution function about the Li + ion. Using a quantum chemistry based atomistic force field, excellent agreement between simulation and experiment is obtained. The agreement between NDIS and MD is improved significantly if ion/ion and ion/polymer polarization effects are introduced in the simulations, indicating the importance of polarization effects in this system. Results indicate a strong coordination between the Li + cations and the ether oxygen atoms. The simulation results suggest a value of nO(r < 3 Å) = 3.5 for the coordination number of oxygens about Li + . The variation of nO with Li-O separation to 2.5 Å is similar from simulation and experiment, although experimentally beyond 2.5 Å this function is impossible to determine.

The dynamics in polyethyleneoxide–alkali iodide complexes investigated by neutron spin-echo spectroscopy and molecular dynamics simulations

“…The most probable explanation is the reduction in the MD simulation of the Coulomb charge of the Na ϩ and I Ϫ in order to take into account polarization interactions. It was shown earlier 5 and also in the present MD simulations that without this reduction NaI clustering occurs, which contradicts with measurements by Fauteux et al, 22 and thus the polarization interactions should really be included in the MD simulation. This is a subject for further study, but it is worthwhile to note that a reduction of the ion charge by a factor of 1/2 might lead to a decrease of the relaxation time by an factor of approximately 5.…”

“…Quasielastic neutron scattering measurements on the PPO-LiClO 4 complex have confirmed this effect, but because of the limited energy resolution it was impossible to obtain quantitative results for the effect of solvated salt on the structural relaxation. 4 Londono et al 5 have performed neutron diffraction with isotopic Li substitution in combination with MD simulations in order to determine the partial pair distribution function g Li,O (r). They obtained a Li-O coordination number of about 3.5 for PEOLiI ͑O:Mϭ5, which is the number of ether oxygens of the polymer chain per metal ion͒, confirming crosslinking between cations and ether oxygens.…”

“…4 Londono et al 5 have performed neutron diffraction with isotopic Li substitution in combination with MD simulations in order to determine the partial pair distribution function g Li,O (r). They obtained a Li-O coordination number of about 3.5 for PEOLiI ͑O:Mϭ5, which is the number of ether oxygens of the polymer chain per metal ion͒, confirming crosslinking between cations and ether oxygens.…”

High internal phase CO2-in-water emulsions stabilized with a branched nonionic hydrocarbon surfactant

“…The excess of negatively charged bicarbonate anions on these droplets was balanced by excess hydronium ions in the cores of the microemulsion droplets in the double layer surrounding the macroemulsion droplets. The preferential adsorption of hydronium ions to EO groups [53] of 5b-C 12 E 8 in W/C microemulsions was consistent with wellknown adsorption of cations such as Li to EO [62]. It should be noted that the concentrations of hydronium and bicarbonate ions in the bulk water are on the order of 10 −3 M (pH 3) [63].…”

Simulation insights on the structure of nanoscopically confined poly(ethylene oxide)

“…19 and 20, with a cutoff radius of 0.9 nm and a distance-dependent dielectric constant. 23 The initial simulation box size was chosen to match the average PEO density to experimental values 24 at each temperature. Periodic boundary conditions were used in all three directions.…”