Structural Formation of Oil-in-Water (O/W) and Water-in-Oil-in-Water (W/O/W) Droplets in PDMS Device Using Protrusion Channel without Hydrophilic Surface Treatment.

Dong Yoon,Shuichi Shoji,Daiki Tanaka,Tetsushi Sekiguchi

doi:10.3390/mi9090468

Abstract

This paper presents a simple method of droplet formation using liquids that easily wet polydimethylsiloxane (PDMS) surfaces without any surface treatment. Using only structural features and uniform flow focusing, Oil-in-Water (O/W) and Water-in-Oil-in-Water (W/O/W) droplets were formed in the full PDMS structure. Extrusion channel and three-dimensional flow focusing resulted in effective fluidic conditions for droplet formation and the droplet size could be precisely controlled by controlling the flow rate of each phase. The proposed structure can be utilized as an important element for droplet based research, as well as a droplet generator.

Highlights

Microdroplet technologies have been developed for quantitative volume control and the efficient isolation of samples in various chemical [1,2], biological [3,4,5,6], and material [7,8] research fields
An external shear force from the surrounding fluid greater than the surface tension of the target liquid is essential for drop separation
In the case of the W/O/W droplet formation device, the first unit includes an injection channel and the second unit consists of two layers: a cylindrical junction layer and an injection layer consisting of four branch channels for uniform flow focusing

Summary

Introduction

Microdroplet technologies have been developed for quantitative volume control and the efficient isolation of samples in various chemical [1,2], biological [3,4,5,6], and material [7,8] research fields. The target liquid should be detached from solid phase wall surfaces These two conditions are fundamental requirements for droplet formation. Rotem et al [34] discussed the limitations placed on the types of formable liquids, including contact angle or wettability on the solid structure. It seems that the structure requires the assistance of specific materials and techniques still. The most critical cause of insufficient formation results is the fact that wetting between the dispersed phase liquid and the wall surface stronger than the hydrodynamic shear or drag forces prevents the liquid from being isolated from the wall. This study is a technique for producing multi-phase and -layer droplets, but it describes the development of a functional device element that is used in droplet based research

Principle and Computational Analysis

C For multi-layer droplet formation

Device Design and Fabrication

B Side view

Results and Discussion