INFLUENCE OF MICROFLUIDIC GEOMETRY ON MICRO-DROPLET FORMATION

Authors

Wilson Good, University of the Pacific
Isha Srivastava, University of the Pacific
Shelly Gulati, University of the PacificFollow

Introduction/Abstract

Micro-droplet technologies are a novel platform for performing chemical or biological analyses. These suspended micro-droplets (water-in-oil) that encapsulate reagents for chemical and biological reactions are generated by utilizing flow instabilities in microfluidic channel structures and are formed with controllable compositions and drop size, stably for long operating times. The nature of the device fabrication process however can introduce differences in identical microfluidic designs from device to device. These deviations in the droplet formation region, though seemingly minor, influence the drop formation process and droplet characteristics.

Purpose

The objective of this work is to characterize the micro-droplet formation process in six droplet formation structures with slight geometric differences. The influence of the microfluidic environments on droplet size and droplet formation is compared.

Method

Microfluidic devices were built using standard soft lithography techniques (Whitesides and coworkers, Electrophoresis, 2000). Water droplets were formed in oil by flow focusing – the oil phase surrounds and breaks off water droplets in the characteristic cross-junction structure. The micro-channels in each device are 100 μm wide and 100 μm deep. The rounding of the corners of the cross-junction was 0, 50, or 100 μm in all four corners (symmetric) or in only the two downstream corners (asymmetric). Droplet formation was studied over a range of flowrate ratios (oil to water flowrate). Micro-droplet flows were recorded using a high-speed imaging camera. Drop sizes were evaluated using image processing software.

Results

For both the symmetric and asymmetric geometries, there is little drop size difference between 0 and 50 μm rounding for each flowrate ratio, however the 100 μm rounding produces droplets with larger diameters. The pinch-off location for droplet formation for the symmetric junctions occurs farther downstream than asymmetric junctions indicating a different mechanism.

Significance

An increase in drop diameter for the largest rounding geometries implies higher drop volume as compared with smaller rounding at the same flowrates. Hence, if device fabrication cannot be held to strict tolerances, drop volumes may differ between devices which can be problematic when performing downstream operations where volume control is essential, such as a chemical reaction with carefully controlled reagent concentrations.

Location

DeRosa University Center, Stockton campus, University of the Pacific

Format

Poster Presentation