TY - JOUR
T1 - The mobility-volume relationship below 3.0 nm examined by tandem mobility-mass measurement
AU - Larriba, Carlos
AU - Hogan, Christopher J.
AU - Attoui, Michel
AU - Borrajo, Rafael
AU - Garcia, Juan Fernandez
AU - De La Mora, Juan Fernandez
PY - 2011/4
Y1 - 2011/4
N2 - The validity of the Stokes-Millikan equation is examined in light of mass and mobility measurements of clusters of the ionic liquid 1-ethyl-3-methyl- imidazolium tetrafluoroborate (EMI-BF4) in ambient air. The mobility diameter dZ based on the measured mobility and the Stokes-Millikan law is compared with the volume diameter dv, which generalizes the mass diameter for binary substances such as salts. dv is based on the sum of anion and cation volumes in the cluster corrected for the void fraction of the bulk ionic liquid. For dv 1.5 nm, dZ is within 1.4% of dv + 0.3 nm. For smaller clusters 3.84 and 14.3% deviations are observed at dv = 1.21 nm and 0.68 nm, respectively. These differences are smaller than expected due to a cancellation of competing effects. The increasing difference seen for dv 1.5 nm is due primarily to the interaction between the cluster and the dipole it induces in the gas molecules. Other potential sources of disagreement are non-globular cluster geometries, and departures of the cluster void fraction from the bulk value. These two effects are examined via molecular dynamics simulations, which confirm that the volume diameter concept is accurate for EMI-BF4 nanodrops with dv as small as 1.6 nm.
AB - The validity of the Stokes-Millikan equation is examined in light of mass and mobility measurements of clusters of the ionic liquid 1-ethyl-3-methyl- imidazolium tetrafluoroborate (EMI-BF4) in ambient air. The mobility diameter dZ based on the measured mobility and the Stokes-Millikan law is compared with the volume diameter dv, which generalizes the mass diameter for binary substances such as salts. dv is based on the sum of anion and cation volumes in the cluster corrected for the void fraction of the bulk ionic liquid. For dv 1.5 nm, dZ is within 1.4% of dv + 0.3 nm. For smaller clusters 3.84 and 14.3% deviations are observed at dv = 1.21 nm and 0.68 nm, respectively. These differences are smaller than expected due to a cancellation of competing effects. The increasing difference seen for dv 1.5 nm is due primarily to the interaction between the cluster and the dipole it induces in the gas molecules. Other potential sources of disagreement are non-globular cluster geometries, and departures of the cluster void fraction from the bulk value. These two effects are examined via molecular dynamics simulations, which confirm that the volume diameter concept is accurate for EMI-BF4 nanodrops with dv as small as 1.6 nm.
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U2 - 10.1080/02786826.2010.546820
DO - 10.1080/02786826.2010.546820
M3 - Article
AN - SCOPUS:78751618795
SN - 0278-6826
VL - 45
SP - 453
EP - 467
JO - Aerosol Science and Technology
JF - Aerosol Science and Technology
IS - 4
ER -