AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Measuring Interfacial Tensions and Viscosities of Aqueous Aerosol Droplet Systems with Microfluidics
SHWETA NARAYAN, Archit Dani, Hallie Boyer, Cari Dutcher, University of Minnesota
Abstract Number: 378 Working Group: Aerosol Physics
Abstract Measurements of viscosity as well as surface and interfacial tensions of micron-sized aerosol droplets provide valuable information about the dynamic processes in these complex micro-environments. For liquid-liquid phase partitioning, thermodynamically favorable morphologies can be predicted with measurable quantities such as surface and interfacial tensions. In addition, the viscosity of aqueous aerosols is also important for determining particle mixing states, as the droplets may range from low viscosity dilute solutions to ultrahigh viscosity glassy states, depending on ambient conditions and solute concentrations. This work presents microfluidic techniques for measuring the viscosities and interfacial tensions of aqueous aerosol mimics using a microfluidic contraction-expansion geometry.
In the first part of this talk, biphasic micro-scale flows in PDMS devices are used to measure interfacial tensions of atmospheric aqueous aerosol mimics. Measurements are made at contracting microfluidic channels, which deform droplets of the aqueous phase by imposing an extensional flow field. Deformations are captured in videos by a high-speed camera and a force-balance equation is applied to the deforming droplet to calculate the interfacial tension. In the second part of this talk, viscosity is measured by studying droplet relaxation when these droplets emerge from the channel contraction in a microfluidic device and deform in a direction perpendicular to the flow. The relaxation is governed by the viscosity of the droplet. Low viscosity systems undergo periodic oscillations, whereas high viscosity systems relax to a spherical shape in an aperiodic manner. This shape relaxation is imaged, and the viscosity of the droplet calculated using existing theory for normal mode oscillations of a viscous liquid drop. Additionally, microfluidic hydrodynamic trapping, which can be used to confine single droplets generated on-chip, is demonstrated to measure the viscosity of the aqueous phase by inducing droplet oscillations.