Key Takeaways & Executive Findings
- •• Deep eutectic gels with tunable hydrogen bond (HB) density were synthesized by varying the ChCl:EG molar ratio, enabling systematic study of HB effects on EMW absorption. • The optimal gel (G22-CE2.4) achieved an effective absorption bandwidth of 8.50 GHz at 2.54 mm thickness, attributed to enhanced conduction loss and impedance matching from optimal HB content. • This work is the first to elucidate the role of hydrogen bonds in dielectric loss, providing a new mechanism for designing high-performance EMW absorbers. • The findings offer a rational strategy for optimizing supramolecular polymer absorbers by controlling intermolecular interactions, with potential applications in electromagnetic pollution mitigation.
Abstract
Gels and conductive polymer composites, including hydrogen bonds (HBs), have emerged as promising materials for electromagnetic wave (EMW) absorption across various applications. However, the relationship between conduction loss in EMW-absorbing materials and charge transfer in HB remains to be fully understood. In this study, we developed a series of deep eutectic gels to fine-tune the quantity of HB by adjusting the molar ratio of choline chloride (ChCl) and ethylene glycol (EG). Owing to the unique properties of deep eutectic gels, the effects of magnetic loss and polarization loss on EMW attenuation can be disregarded. Our results indicate that the quantity of HB initially increases and then decreases with the introduction of EG, with HB-induced conductive loss following similar patterns. At a ChCl and EG molar ratio of 2.4, the gel labeled G22-CE2.4 exhibited the best EMW absorption performance, characterized by an effective absorption bandwidth of 8.50 GHz and a thickness of 2.54 mm. This superior performance is attributed to the synergistic effects of excellent conductive loss and impedance matching generated by the optimal number of HB. This work elucidates the role of HB in dielectric loss for the first time and provides valuable insights into the optimal design of supramolecular polymer absorbers.
1. Introduction
With the advancement of microwave technology, electromagnetic (EM) pollution has become increasingly severe. One of the key strategies to mitigate this pollution is the application of high-performance electromagnetic wave (EMW) absorbers [1–2]. However, the inadequate understanding of EMW loss mechanisms at the microscale restricts the optimization design of these absorbers. Many researchers suggest that changes in chemical bonds can affect charge transfer and the formation of electric dipoles in materials, thereby modulating their EMW absorption through increased dielectric loss. This enhancement is achieved via interface engineering [3–4], defect engineering [5–6], lattice distortion engineering [7], and their combined designs [8–9]. Hydrogen bonds (HBs), a type of intermolecular interaction distinct from chemical bonds, are widely present in gel-based absorbers. They not only facilitate charge transfer but also change the electron structure of materials [10–12]. However, the specific role of HB in the EM loss mechanism of absorption materials needs to be elucidated to improve understanding of EMW loss mechanisms.
Given that gel-based absorbers contain HBs, they serve as an ideal medium to investigate the response mechanism of HBs to EMWs. While current research predominantly focuses on defects and interfaces to explore the EMW loss mechanisms, the regulatory mechanism of HBs on the EMW absorption performance remains unclear. Furthermore, the coupling effect of HBs with conduction loss on the EMW response mechanism is still unexplored. Consequently, it is essential to develop the following research framework: 1) Establishing the relative motion regularity of electrons and protons at the molecular level to investigate how HB affects electron transmission. It has been demonstrated that HB can promote electron transfer [10–12]. 2) Owing to the abundant conductive network within gel-based absorbers, it is necessary to demonstrate how conduction loss contributes to EMW absorption and the synergy between conductive loss and impedance matching to explore the optimal range of EMW attenuation [13]. 3) Exploring the factors influencing the crosslink density of hydrogen-bonded networks and the variation in the number of HB and examining the impact of the number of HB on electromagnetic parameters. 4) The orbital interaction of HBs, as compared to covalent bonds, can be viewed as the interaction between the orbitals of the HB donor and acceptor (X–H...Y), with Y contributing to the anti-bonding orbital of X–H. This characteristic endows HB with a distinct energy dissipation mechanism, with strength between electrostatic interactions and covalent bonds [10,14–15]. It is necessary to explore the impact of the orbital interaction between HB and covalent bonds on the energy dissipation mechanism of gels.
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Yuntong Wang, Shengchong Hui, Zhaoxiaohan Shi, Zijing Li, Geng Chen, Tao Zhang, Xinyue Xie, Limin Zhang, Hongjing Wu (2025). Hydrogen bond-induced conduction loss for enhanced electromagnetic attenuation in deep eutectic gel absorbers. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-024-2938-0
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Frequently Asked Questions
What is the main contribution of this study?
The study is the first to elucidate the role of hydrogen bonds (HBs) in dielectric loss for electromagnetic wave absorption, demonstrating that HB-induced conduction loss can be tuned to enhance absorption performance.
How were the deep eutectic gels prepared?
The gels were prepared by adjusting the molar ratio of choline chloride (ChCl) and ethylene glycol (EG), which allowed fine-tuning of the hydrogen bond quantity.
What was the best performing gel and its absorption properties?
The gel labeled G22-CE2.4, with a ChCl:EG molar ratio of 2.4, exhibited the best performance with an effective absorption bandwidth of 8.50 GHz at a thickness of 2.54 mm.
Why is the role of hydrogen bonds important in EMW absorbers?
Hydrogen bonds facilitate charge transfer and influence the electron structure, thereby affecting conduction loss and impedance matching, which are critical for efficient EMW absorption.
What are the practical implications of this research?
The findings provide a new design strategy for supramolecular polymer absorbers by controlling hydrogen bond density, which could lead to more effective materials for mitigating electromagnetic pollution.
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