Investigating Influence of Particle Size on Viscosity

SUNANDAN MAHANT, Jefferson Snider, Markus Petters, North Carolina State University

     Abstract Number: 145
     Working Group: Aerosol Chemistry

Abstract
Many atmospheric aerosol particles can be said to be amorphous and with physical compositions defined as liquid, semisolid, or glassy. The phase state influences gas-particle partitioning, chemical aging, and ice nucleation, and in turn modulates the role of aerosols on human health and climate. The amorphous phase state has been known to be highly dependent on particle composition, temperature and relative humidity for (secondary) organic aerosols. This study focuses on understanding the effect of particle diameter on the phase state. A differential mobility analyzer coupled with an optical particle spectrometer and a tandem differential mobility analyzer were used to probe the transition temperature of organic aerosol mimics. The temperature at which phase state changes is referred to as the transition temperature, and corresponds to where the viscosity is ~10⁷ Pa s. Using the Angel scaled fragility, it is shown that viscosity decreases by 4 orders of magnitude as the size of sucrose particles decreases from 200 nm to 30 nm. The decrease in viscosity is anticipated by recent theoretical models describing the dependence of viscosity as a function of particle size. These measurements are expected to improve overall understanding of aerosols and refine existing phase state models.