10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Dual-Beam Optical Tweezers Development for Measuring the Dynamic Evolution of Aerosol Surface Tension and Viscosity
Aidan Rafferty, KYLE GORKOWSKI, Thomas Preston, McGill University
Abstract Number: 512 Working Group: Instrumentation
Abstract Understanding the evolution of glassy particles in the atmosphere has important implications when modeling mixtures of inorganic and organic particles. A glassy state of organic particles affects the particle to gas phase partitioning of organic species, diffusion of oxidants into the particle and the phase state of clouds, as they can serve as heterogeneous ice nucleating particles. To better understand how glassy states, evolve in the atmosphere as humidity and aerosol composition changes we have built a dual-beam optical tweezers (D-BOT).
The D-BOT system has two optical potential wells which trap a single droplet in-between them. The optical potential wells balance each other, pulling equally on opposite sides of the droplet. By increasing the laser power in the traps, the optical force pulling on opposite sides of the droplet causes it to deform into an ellipse. The surface tension of the droplet balances the optical force resulting in the elliptical deformation. We use the equilibrium deformation at high laser power to measure the surface tension of the droplet. Then after a viscous system has been deformed to an ellipse, the droplet viscosity is measured from the relaxation back to a sphere when the laser power is lowered. The physical dimensions of the ellipse and effective refractive index are retrieved from a newly developed fitting program for the measured elliptical whispering gallery modes (WGMs). The differences between the optical pathlengths for the major and minor axis of the ellipse result in shifts in the WGMs. These shifts in the WGMs are used to retrieve the ellipse deformation in the major and minor axis. We will present the new WGM analysis method for elliptical WGMs and with it, we will present results on surface tension and viscosity measurements for simple chemical systems.