Surface tension effects on immersed electrosprays

TL;DR

This paper investigates how surface tension influences immersed electrosprays in liquid baths, especially with surfactants, revealing complex behaviors relevant for biomedical and microfluidic applications.

Contribution

It provides a comprehensive review and systematic analysis of immersed electrosprays with varying surfactant concentrations, highlighting new phenomenological insights.

Findings

Different regimes of electrospray behavior identified with surfactant variation

Reduced surface tension leads to lower electrification states

Rich phenomenology observed with varying surface tension levels

Abstract

Electrosprays are a powerful technique to generate charged micro/nanodroplets. In the last century, the technique received extensive study and successful applications, including a Nobel price in Chemistry. However, nowadays its use in microfluidic devices is still limited mainly due to a lack of knowledge of the phenomenon when the dispersing fluid is immersed in another inmiscible liquid. The "immersed electrosprays" share almost identical properties as their counterparts in air. Things however change when surface active agents are added to the host liquid, which are normally used in lab-on-chip applications to stabilize the generated emulsions. In this work, we review the main properties of the immersed electrosprays in liquid baths with no surfactant, and we methodically study the behavior of the system for increasing surfactant concentrations. The different regimes found are then analyzed and compared with both classical and more recent experimental, theoretical and numerical studies. A very rich phenomenology is found when the surface tension is allowed to vary in the system. More concretely, the lower states of electrification achieved with the reduced surface tension regimes might be of interest in biological or biomedical applications in which the free charge is normally hazardous for the encapsulated entities.