Abstract View
The Effect of Potential Interaction and Atomic Mass on the Nature of the Scattering and Accommodation of Gas Molecules from the Surface of Charged Particles. Transitioning from Specular to Diffuse Reemission
VIRAJ GANDHI, Jayden Pothoof, Carlos Larriba-Andaluz, IUPUI
Abstract Number: 543
Working Group: Aerosol Physics
Abstract
Stokes-Millikan’s (SM) slip correction equation has been shown to provide an accurate description of a charged particle’s electrical mobility throughout a vast range of Knudsen numbers. The equation asymptotically agrees with the Stokes’ flow in the continuum regime and with kinetic theory derivations in the free molecular regime, but only when a 91% diffuse/ 9% specular reemission law is chosen for colliding gas molecules. While this choice of reemission law has been shown to be valid for different gases, its universal validity remains in question. From a kinetic theory perspective, it is known that SM cannot hold for all molecules. Given that monoatomic collisions must be specular, the percentage of diffuse reemissions must become smaller as the number of atoms in the charged particle is reduced. This sets the 91%/9% reemission law as an asymptotic behaviour from two very different perspectives: 1) when reducing the size from the transition regime and 2) when increasing the size from the free molecular. This work focuses on the latter behaviour, i.e. trying to understand how the gas molecule reemission evolves into a predominantly diffuse scattering. Previously, our work has shown that this evolution occurs at various rates for different gases. Here, the effects of potential interaction and distinct atomic masses are observed through the study of alkali metal salts. Iodine salts of increasing cation masses are compared under Nitrogen environments. It is shown as the mass of the cation increases, the collisions seem to become more specular. This is tested by using IMoS, a mobility calculator that is able to predict electrical mobilities of all-atom entities to about 4% error. IMoS is also used to predict the Lennard-Jones gas-cation parameters that would be required to agree with the experimental results. Results suggest a correlation between increasing masses and decreasing potential well-depths, leading to the observation that smaller long-range interactions lead to more specular reemissions. Finally, MD simulations within IMoS are used to check whether the increasing specular reemissions may be regarded as due to the loss of scattering from increasing masses, due to smaller potential interactions, or perhaps due to a mixed of both.