Quantifying Contact‐Electrification Induced Charge Transfer on a Liquid Droplet after Contacting with a Liquid or Solid

Abstract

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.202102886.Contact electrification (CE) is a common physical phenomenon, and its mechanisms for solid-solid and liquid-solid cases have been widely discussed. However, the studies about liquid-liquid CE are hindered by the lack of proper techniques. Here, a contactless method is proposed for quantifying the charges on a liquid droplet based on the combination of electric field and acoustic field. The liquid droplet is suspended in an acoustic field, and an electric field force is created on the droplet to balance the acoustic trap force. The amount of charges on the droplet is thus calculated based on the equilibrium of forces. Further, the liquid-solid and liquid-liquid CE are both studied by using the method, and the latter is focused. The behavior of negatively precharged liquid droplet in the liquid-liquid CE is found to be different from that of the positively precharged one. The results show that the silicone oil droplet prefers to receive negative charges from a negatively charged aqueous droplet rather than positive charges from a positively charged aqueous droplet, which provides a strong evidence about the dominant role played by electron transfer in the liquid-liquid CE.

Maxwell’s equations for a mechano-driven, shape-deformable, charged-media system, slowly moving at an arbitrary velocity field v( r ,t)

“…Besides the electrodynamics, the theory for fluid also include the mass and charge transport equations and Cauchy momentum equation for flowing fluid [31]. Furthermore, recent studies show that electron transfer and ion transfer do occur at liquid-solid interface [32,33] and even liquid-liquid interface [34]. This means that there are charges distributing at and in liquid media owing to contact-electrification effect.…”

Electrochemical On‐Site Switching of the Directional Liquid Transport on a Conical Fiber

“…interests for its broad applications in microfluidics, [2] liquid collection, [3] functional fabrics, [4] electricity generation, [5] and detection. [6] Particularly, DLT on a conical fiber (DLT-CF) enjoys advantages of low hydrodynamic resistance, high transport efficiency, and easy processing, [7] representing as the most frequently-used DLT system.…”

A Review: Contact Electrification on Special Interfaces

“…A new type of probe can be developed to study the charge behavior at the liquid-liquid interface. Tang et al (2021) cleverly designed a noncontact measurement method combining the electric field and sound field to quantify droplet charges, suspended droplets by field acoustic emitters, and used this method to study charge transfer behavior at the liquid-solid and liquid-liquid contact interfaces, as shown in Figure 9B. This method eliminates container interference, and for the liquid-solid interface, it is discovered that the amount of charge transfer between the solid and liquid decreases as ion concentration in the droplet increases, which is consistent with the previous reports.…”