A large number of data on mobility and mass have been newly obtained or reanalyzed for clusters of a diversity of materials, with the aim of determining the relation between electrical mobility (Z) and mass diameter dm= (6m/)1/3 (m is the particle mass and the bulk density of the material forming the cluster) for nanoparticles with dm ranging from 1 nm to 6.5 nm. The clusters were generated by electrospraying solutions of ionic liquids, tetra-alkyl ammonium salts, cyclodextrin, bradykinin, etc., in acetonitrile, ethanol, water, or formamide. Their electrical mobilities Z in air were measured directly by a differential mobility analyzer (DMA) of high resolution. Their masses m were determined either directly via mass spectrometry, or assigned indirectly by first distinguishing singly (z = 1) and doubly (z = 2) charged clusters, and then identifying monomers, dimers, … n-mers, etc., from their ordering in the mobility spectrum. Provided that dm> 1.3 nm, data of the form dm vs. [z(1+mg/m)1/2/Z)]1/2 fall in a single curve for nanodrops of ionic liquids (ILs) for which is known (mg is the mass of the molecules of suspending gas). Using an effective particle diameter dp= dm+ dg and a gas molecule diameter dg= 0.300 nm, this curve is also in excellent agreement with the Stokes-Millikan law for spheres. Particles of solid materials fit similarly well the same Stokes-Millikan law when their (unknown) bulk density is assigned appropriately.
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Document Type: Research Article
Centers for Disease Control and Prevention (CDC), National Institute for Occupational Safety and Health (NIOSH), Cincinnati, Ohio, USA
Mechanical Engineering Department, Yale University, New Haven, Connecticut, USA
Publication date: 2009-03-01
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