Paper Number
MM10 

Session
Microrheology and Microfluidics

Title
Microfluidics measurements of interfacial tension and viscosity of complex emulsions

Presentation Date and Time
October 10, 2017 (Tuesday) 1:30

Track / Room
Track 6 / Aspen

Authors (Click on name to view author profile)

1. Narayan, Shweta (University of Minnesota, Mechanical Engineering)
2. Dutcher, Cari (University of Minnesota, Mechanical Engineering)

Author and Affiliation Lines (in printed abstract book)
Shweta Narayan and Cari Dutcher
Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455

Speaker / Presenter 
Narayan, Shweta

Text of Abstract
The stability of complex emulsions, which depends on both liquid-liquid interfacial tension and viscosity, is relevant to a variety of technological applications that deal with these systems, ranging from oil recovery to food and cosmetics. Conventional measurement techniques include Wilhelmy plates and pendant drop tensiometry for interfacial tension and rheometers for viscosity measurements. However, these are macro-scale measurement techniques which require at least a few milliliters of sample volume and have characteristic length scales on the order of a few millimeters. In contrast, microfluidic techniques offer a viable alternative for probing properties of emulsions at much smaller length scales. Here, we employ biphasic microfluidics to study complex emulsions, using contraction-expansion geometries as well as hydrodynamic traps. Monodisperse droplets of a dispersed phase deform as they enter or exit a contraction in a microfluidic device under the influence of an elongational flow field. High-speed videos of these deforming droplets are analyzed to extract the deformation of the droplets in complex emulsions, and used to calculate the interfacial tension between the two phases and viscosity of the inner or outer phase using existing theory. Microfluidic interfacial tensiometry using is particularly effective in measuring dynamic interfacial tension, since the length and time-scales involved in microfluidic measurements are more representative of real systems. Additionally, hydrodynamic traps are used in this work to confine and perturb single droplets generated on a microfluidic chip. Perturbed droplets with low viscosities undergo periodic oscillations before returning to a spherical shape, whereas high viscosity droplets will relax back to a spherical shape in an aperiodic manner. High-speed videos of such trapped droplet shape oscillations can also be used to extract fluid properties.