Elsevier

Nano Energy

Volume 81, March 2021, 105618
Nano Energy

Communication
Stability and decay of surface electrostatic charges in liquids

https://doi.org/10.1016/j.nanoen.2020.105618Get rights and content

Highlights

  • Ionization and polarity of the liquid molecule are two key parameters that lead to the neutralization of electrostatic charges.

  • Adding small amount of matter that can ionize in non-polar and aprotic liquid can speed up the decay of charges.

  • Air-bubble-structured electret is designed and can recover the surface charges after water wet-dry process.

Abstract

Understanding the mechanism of the stability and decay of surface electrostatic charges in different liquid environments is critical for the reliability of devices based on electrostatic functions or preventing the damage from electrostatic charge accumulation. In this work, the influences of surface electrostatic charges in polar and protic (Ethanol and Water), polar and aprotic (Tetrahydrofuran and Chloroform), and non-polar and aprotic (Benzene and Hexane) liquids have been investigated. Results prove that ionization in liquid or polarity of the liquid molecules can determine the electrostatic charges neutralization, and adding small amount of matter (1% Vol) that can ionize in non-polar and aprotic liquids can avoid the electrostatic charges accumulation. Moreover, air-bubble-structured electret is designed to improve the water-against ability for surface electrostatic charges.

Graphical Abstract

This work provides strategies for improving the durability of electrostatic-based devices in liquids and preventing the risk caused by electrostatic charges accumulation.

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Introduction

In recent years, devices based on the electrostatic induction processes have drawn heavy attentions, such as the triboelectric generators/sensors [1], [2], [3], [4], [5], electret-based sensors/actuators [6], [7], [8], and elastomer actuators [9], [10], etc. for energy harvesting, wearable electronics, and human-machine interaction applications etc. [11], [12], [13], Although triboelectrification effect caused by the relative movement between liquid-solid or liquid-liquid interfaces could generate electrostatic charges [14], [15], [16], normal electrostatic-based devices which rely on the pre-charged electrostatic charges would have bad stability performance when directly exposed to liquid environments [17]. Since the amounts of the surface electrostatic charges depend heavily on the environmental conditions, these devices require good package or special material design for long-term and stable operations [18], [19]. On the other hand, the accumulation of surface electrostatic charges is a common problem in a variety of scenarios. For instance, possible sparks as the result of high electrostatic charges in organic liquids, such as gasoline, are dangerous and should be avoided [20]. As such, understanding the stability and decay of surface electrostatic charges in different liquid environments is an important topic for various electrostatic-based applications.

Here, we study the stability and decay of surface electrostatic charges on Fluorinated Ethylene Propylene (FEP) electret films in 3 types of liquids: (1) polar and protic (Ethanol and Water), (2) polar and aprotic (Tetrahydrofuran and Chloroform), and (3) non-polar and aprotic (Benzene and Hexane). It’s found that surface electrostatic charges only have good long-term stability in non-polar and aprotic liquid. This result implies that not only the ionization in liquid but also the polarity of the liquid molecule are two key parameters that lead to the neutralization of electrostatic charges. To speed up the decay of the electrostatic charges in non-polar and aprotic liquid, a simple strategy is adding small amount of matter (1% Vol) that can ionize in such liquids. Furthermore, in order to improve water against property of the surface electrostatic charges, air-bubble-structured electret is designed and has the ability to recover the surface electrostatic charges in continuous 20 times of wet-dry process.

Section snippets

Surface electrostatic charges stability in 3 types of testing liquids

Based on their polarity and ionization (conductivity) properties, liquids can be divided into 3 key categories: polar and protic, polar and aprotic, and non-polar and aprotic liquids [21]. In this work, Water and Ethanol are tested as the polar and protic liquid, Tetrahydrofuran and Chloroform as polar and aprotic liquid, and Benzene and Hexane as non-polar and aprotic liquid in all tests, respectively. As shown in Fig. 1(a), we immerse FEP electret films with electrostatic charges on the

Conclusion

In summary, by directly immersing the charged FEP electret films into different liquids and verifying the electricity generation of electret generator in different liquids, it’s found that both of the ionization in liquid and polarity of the liquid molecule can determine the surface electrostatic charges neutralization or stability, and proving that adding small amount of matter (1%) that can ionize in non-polar and aprotic liquids can avoid the electrostatic charges accumulation. On the other

Experimental section

The FEP electret film (thickness of 50 µm) was purchased from American Dura Film. The porous water-proof tape (300 µm) as purchased from 3 M company. Corona charging method was used to generate the surface electrostatic charges. The surface potential of the electret films was measured by the Trek Model 347 electrostatic meter. After the liquid treating process, electret films were dried in the fuming cupboard first and then the surface potential was measured. A 50 µm thick FEP film sticks on

CRediT authorship contribution statement

Zhaoyang Li: Conceptualization, Investigation, Writing. Yu Long: Conceptualization, Investigation, Writing - review & editing. Junwen Zhong: Conceptualization, Supervision, Writing - review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

Z. Li and Y. Long contributed equally to this work. We acknowledge the funding support from University of Macau, China and the help from Prof. Liwei Lin in University of California Berkeley, USA.

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