Slip Correction Measurements of Polystyrene and Polyvinyltoluene Aerosol Particles Using AN Improved Millikan Apparatus.
Abstract
A slip correction equation of the form C(Kn) = 1 + Kn{(alpha) + (beta)exp((gamma)/Kn)} with Kn the particle Knudsen number is routinely used to correct Stokes' law for progressively lower than predicted drag force as Kn increases. The published values of the parameters ((alpha), (beta), and (gamma)) are based on Millikan's original values corrected with an improved value of mean free path for gas molecules in dry air. In this work, Millikan's most accurate raw data were carefully reviewed and the slip correction parameters were reevaluated using the latest published values of physical constants and nonlinear least squares function fitting. The values of (alpha), (beta), and (gamma) given by Millikan in 1923 adjusted for a modern value of the mean free path ((lamda) = 0.0673 (mu)m at 23(DEGREES)C and 760 mm of Hg) were 1.209, 0.406, and 0.893, respectively. Improved values of these parameters calculated by least squares using Millikan's most accurate raw data are 1.155, 0.471, and 0.596, respectively. Though these two sets of values appear significantly different, the maximum percentage difference in the calculated correction factor is less than 2.0% over the Knudsen number range of 0.001 to 100. This error is small when compared to differences which may be caused by different particle surfaces and gas compositions. An improved version of the Millikan oildrop apparatus was built and slip correction measurements were made on ninety solid, spherical particles in air. Measurements were made on eleven polystyrene latexdivinylbenzene particles, twentyfive polyvinyltoluene particles, and fiftyfour polystyrene latex particles, spanning a Knudsen number range from 0.03 to 7.2. The values of (alpha), (beta), and (gamma) computed using nonlinear least squares function fitting for a mean free path at 23(DEGREES)C of 0.0673 (mu)m and a viscosity of 1.83245 x 10('4) gcm('1)s(' 1) were 1.142, 0.558, and 0.99 respectively. The value of (alpha) agrees very closely with Millikan's result. The sum of (alpha) + (beta) applicable in the free molecular regime is 4.45 percent higher than Millikan's value; this is probably due to the fact that a higher percentage of molecules undergo specular reflections from the surface of a solid particle compared to an oil droplet. Dynamic shape factors were measured for eight doublet aggregates and six triangular triplet aggregates. For the doublets, (kappa) = 1.0721 (S.D. = (+OR) 0.0082) and, for the triplets, (kappa) = 1.0833 ((+OR) 0.0053). The fact that these dynamic shape factors are lower than the values measured by earlier authors for random orientations, and the consistency of the data, indicate a specific orientation with the long axis of the aggregate aligned with the lines of force of the electric field. The triplet aggregates seemed to undergo almost complete vertical orientation, whereas the double aggregates appeared to be unaffected as much by the electric field.
 Publication:

Ph.D. Thesis
 Pub Date:
 1983
 Bibcode:
 1983PhDT........66A
 Keywords:

 Physics: General