Growth control of sessile microbubbles in PDMS devices

TL;DR

This paper investigates how to control the size of microbubbles in PDMS microfluidic devices by analyzing gas transport mechanisms and using hydrostatic pressure regulation, with implications for device performance.

Contribution

It provides a quantitative model of gas exchange in PDMS devices and demonstrates how hydrostatic pressure and vapor pressure influence bubble size control.

Findings

Hydrostatic pressure can regulate bubble growth or shrinkage.

Vapor pressure significantly affects gas transport balance.

Controlling these factors enables stable bubble size management.

Abstract

In a microfluidic environment, the presence of bubbles is often detrimental to the functionality of the device, leading to clogging or cavitation, but microbubbles can also be an indispensable asset in other applications such as microstreaming. In either case, it is crucial to understand and control the growth or shrinkage of these bodies of air, in particular in common soft-lithography devices based on polydimethylsiloxane (PDMS), which is highly permeable to gases. In this work, we study the gas transport into and out of a bubble positioned in a microfluidic device, taking into account the direct gas exchange through PDMS as well as the transport of gas through the liquid in the device. Hydrostatic pressure regulation allows for the quantitative control of growth, shrinkage, or the attainment of a stable equilibrium bubble size. We find that the vapor pressure of the liquid plays an important role for the balance of gas transport, accounting for variability in experimental conditions and suggesting additional means of bubble size control in applications.