Free volume in imidazolium triflimide ([C{sub 3}MIM][NTf{sub 2}]) ionic liquid from positron lifetime: Amorphous, crystalline, and liquid states

Journal Article · Tue Sep 28 00:00:00 EDT 2010 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.3487522· OSTI ID:21559920

Dlubek, G ^[1]; Yu, Yang; Krause-Rehberg, R ^[1]; Beichel, W; Bulut, S; Pogodina, N; Krossing, I; Friedrich, Ch ^[2]

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1. Institut fuer Physik, Martin-Luther-Universitaet Halle-Wittenberg, Von-Danckelmann-Platz 3, 06120 Halle (Germany)
2. Freiburger Materialforschungszentrum (FMF), Albert-Ludwigs-Universitaet Freiburg, Stefan-Meier-Strasse 21, Germany and Institut fuer Anorganische Chemie, Albert-Ludwigs-Universitaet Freiburg, Albertstrasse 21, D-79104 Freiburg i. Br. (Germany)

Positron annihilation lifetime spectroscopy (PALS) is used to study the ionic liquid 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide [C{sub 3}MIM][NTf{sub 2}] in the temperature range between 150 and 320 K. The positron decay spectra are analyzed using the routine LifeTime-9.0 and the size distribution of local free volumes (subnanometer-size holes) is calculated. This distribution is in good agreement with Fuerth's classical hole theory of liquids when taking into account Fuerth's hole coalescence hypothesis. During cooling, the liquid sample remains in a supercooled, amorphous state and shows the glass transition in the ortho-positronium (o-Ps) lifetime at 187 K. The mean hole volume varies between 70 A{sup 3} at 150 K and 250 A{sup 3} at 265-300 K. From a comparison with the macroscopic volume, the hole density is estimated to be constant at 0.20x10{sup 21} g{sup -1} corresponding to 0.30 nm{sup -3} at 265 K. The hole free volume fraction varies from 0.023 at 185 K to 0.073 at T{sub m}+12 K=265 K and can be estimated to be 0.17 at 430 K. It is shown that the viscosity follows perfectly the Cohen-Turnbull free volume theory when using the free volume determined here. The heating run clearly shows crystallization at 200 K by an abrupt decrease in the mean <{tau}{sub 3}> and standard deviation {sigma}{sub 3} of the o-Ps lifetime distribution and an increase in the o-Ps intensity I{sub 3}. The parameters of the second lifetime component <{tau}{sub 2}> and {sigma}{sub 2} behave parallel to the o-Ps parameters, which also shows the positron's (e{sup +}) response to structural changes. During melting at 253 K, all lifetime parameters recover to the initial values of the liquid. An abrupt decrease in I{sub 3} is attributed to the solvation of e{sup -} and e{sup +} particles. Different possible interpretations of the o-Ps lifetime in the crystalline state are briefly discussed.

• OSTI ID: 21559920
• Journal Information: Journal of Chemical Physics, Vol. 133, Issue 12; Other Information: DOI: 10.1063/1.3487522; (c) 2010 American Institute of Physics; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
36 MATERIALS SCIENCE
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
AMORPHOUS STATE
ANNIHILATION
BETA-PLUS DECAY
COALESCENCE
COMPARATIVE EVALUATIONS
CRYSTALLIZATION
CRYSTALS
DISTRIBUTION
HEATING
HOLES
HYPOTHESIS
LIFETIME
LIQUIDS
MOLTEN SALTS
ORGANIC COMPOUNDS
PARTICLES
POSITRONS
SPECTROSCOPY
SUPERCOOLING
TEMPERATURE RANGE
ANTILEPTONS
ANTIMATTER
ANTIPARTICLES
BETA DECAY
COOLING
DECAY
ELEMENTARY PARTICLES
EVALUATION
FERMIONS
FLUIDS
INTERACTIONS
LEPTONS
MATTER
NUCLEAR DECAY
PARTICLE INTERACTIONS
PHASE TRANSFORMATIONS
SALTS