Effect of modified graphene oxide on properties of carbonyl iron composites

Abstract

In this study, wave absorption-heat conduction composites were prepared by modifying graphene oxide (GO), followed by ultrasonic mixing with carbonyl iron powder (CIP). The composites (0.1 wt% Cu-coated GO) exhibited a minimum reflection loss (RL_min) of −16.47 dB at 2.0 mm and an effective absorption bandwidth (EAB) exceeding 1.44 GHz, while the thermal conductivity reached 2.83 W/(m·K), surpassing that of pure carbonyl iron powder (2.66 W/(m·K)). Increasing the content of Cu-coated GO significantly enhanced the thermal conductivity but the absorption properties exhibited a slight decline. At the thickness of 1–2 mm, the reflection loss peaks for the composites are entirely within the S-band. Therefore, the CIP/Cu-coated GO composites demonstrate strong potential for S-band applications.

Keywords

Modifying graphene oxide carbonyl iron powder microwave absorption thermal conductivity S-band

Introduction

With the increase of communication devices and electronic equipment, the electromagnetic radiation (EMR) poses a potential threat to human health and surrounding electronic systems.^1–4 The electromagnetic wave (EMW) absorbing materials are capable of converting electromagnetic energy into heat or other forms, which can be considered a reliable method to resolve the hazards of EMR.^5,6

Excessive heat accumulation induces device overheating, which leads to the reduction of operational efficiency and long-term reliability of electronic devices.^7–9 Moreover, the high integration and miniaturization of electronic equipment further increase the demand for heat dissipation.^10,11 The thermal conductivity of materials has become a significant factor in the development of absorbing material.^12,13 Therefore, wave absorption-heat conduction composites with dual functionality are urgently needed in application fields such as microelectronic packaging and fifth-generation (5G) wireless systems.^14,15

The thermal conductivity of absorbing materials has been shown to be significantly enhanced by adjusting the type of materials, size, shape, and mass ratio of thermally conductive fillers, with interesting results.¹⁶ For instance, the ZnO/exfoliated graphite (EG)/epoxy composites have been prepared with integrated thermal conduction and EMW absorption, as reported by Singh et al..¹⁷ Li et al.¹⁸ also reported that the MXene/Co/PVDF composites with integrated thermal conduction by incorporating MXene and Co into the PVDF matrix. Pan et al. reported that the PMMA/Ni@GNP nanocomposites show a good EMW absorbing property. Notably, the composite with 30 wt% Ni@GNP displays the best EMW absorption performance and good thermal conductivities.¹⁹

Carbonyl iron powder (CIP) was widely used as materials for wave absorption due to moderate electrical conductivity and high saturation magnetization strength.^16,20 However, they suffer from the inherent drawback of relatively low thermal conductivity, excessive density, poor impedance matching.^16,21 Carbon-based materials such as graphite,²² graphene,²³ and carbon nanotubes (CNTs)²⁴ display a great potential as a thermal conductive filler due to their large thermal conductivity.

Although GO does not possess the high thermal conductivity of above carbon-based materials, its unique properties make it a highly promising thermal conductive filler.^25,26 GO is usually synthesized via the Hummers’ method, which involves exfoliating graphite in a concentrated acid and oxidizing environment.²⁷ In this way, the GO contains more oxygen-containing functional groups that lead to its excellent dispersibility, hydrophilicity and facile modification to produce other graphene-based materials.²⁸ Its excellent dispersibility ensures uniform distribution on the matrix and promotes the formation of an efficient thermal network. The ease of surface modification allows GO to be combined with other high thermal conductivity materials. Furthermore, its extremely high specific surface area enables it to bond tightly with high thermal conductivity materials, thereby enhancing the thermal conductivity of the composite. Additionally, GO offers low density and mechanical strength, which makes it particularly well-suited for advanced applications pursuing lightweight design and multifunctional integration.²⁵ Therefore, GO has been extensively used. For example, Liu et al.²⁹ reported that the SnS/GO hybrid was fabricated via a solvothermal method, which demonstrated excellent electromagnetic wave absorption capabilities. Similarly, Jiang et al.³⁰ fabricated low-density graphene@SiC aerogels through directional freeze-casting and thermal reduction of GO-coated SiC whiskers, enhancing microwave absorption. Xiao et al.³¹ prepared Fe₃O₄/graphene nanocomposites via solvothermal method by embedding Fe₃O₄ nanospheres into GO sheets to balance dielectric and magnetic properties.

GO also has some limitations. GO exhibits thermal instability and can readily undergo self-propagating disproportionation reactions to yield chemically modified graphene or reduced graphene oxide (r-GO) under mild heating conditions.³² Moreover, the presence of oxygen-containing functional groups on the surface of GO significantly diminishes π–π stacking interactions, which will reduce conductivity and introduces lattice defects within GO.³³

Electroless plating, a chemical deposition technology, enhances the oxidation resistance, corrosion resistance, conductivity, and wear resistance of the substrate material by depositing metals from solutions without external voltage.^34,35 Copper, with the second lowest resistivity in nature and a high free electron density, has attracted the attention of researchers due to its low cost, solderability, electro-migration resistance, and high electrical and thermal conductivity.³⁶ Electroless copper plating with its excellent conductivity, corrosion resistance and shielding capabilities is also widely used in absorbing materials. Li et al.³⁷ reported that ultrasonic electroless copper plating of CIP in non-woven FCAM effectively enhanced microwave absorption properties. Xie et al.³⁸ reported that the Cu-coated carbonyl iron/Co composite powders were prepared by ball milling and electroless plating, which enhanced absorbing stability and corrosion resistance. Li et al.³⁹ reported that the Fe/Cu composite samples, prepared by chemical plating of Cu particles on carbonyl iron sheets with the excellent microwave absorbing at an optimal plating time of 30 min.

To overcome the inherent limitations of GO, it is usually modified before practical application.⁴⁰ For instance, Yang et al.⁴¹ reported that the acidulated GO was synthesized through esterification followed by substitution of surface hydroxyl groups on graphene oxide. Bhunia et al.⁴² used hydrazine as a reducing agent to selectively remove hydroxyl groups and epoxy bonds from graphene oxide while retaining carboxyl anions. Bonanni et al.⁴³ eliminated oxygen-containing groups from GO via a reduction process and consequently reintroduced carboxyl groups onto the graphene surface.

To date, experimental studies on the modification of GO via electroless copper remain limited. In this work, the Cu-coated GO/CIP composite as a dual-functionalized composite for wave absorption and thermal conductivity was successfully designed and prepared by electroless copper plating process and ultrasonic mixing. This work aims to investigate the relationship between the wave absorption/thermal conductivity properties and the GO filler. The effect of doping content of GO filler on the microstructure, wave-absorbing, and thermal conductive properties was also studied.

GO was modified by chemical copper plating as the thermal filler. The chemical copper plating can modulate dielectric, thermal conductivity property of GO. The filler can reduce contact between CIP particles, leading to increased interface losses and polarization losses. Moreover, at low filler levels (≤1 wt%), slightly impact on wave absorption properties, maximized the thermal conductivity of the absorbing composites. In summary, the cost-effective and easy preparation method for wave absorption-heat conduction materials was provided in this work, which is also suitable for engineering applications.

The whole manuscript is divided into four sections. The background, motivation, and the novelty of the work were described in the introduction (section 1). The experiment steps, technique parameters, measurement methods were described in experiment (section 2). The results and discussions (section 3) are composed of the experimental results and related discussions, covering the morphological characteristics, absorption properties, and thermal conductivity of the composites. Finally, the conclusions (section 4) summarize the experimental results and potential applications.

Experiment

Materials

The graphene oxide (GO) powders were purchased from Jiangsu XFNANO Materials Tech Co., Ltd (Nanjing, China). EDTA-2Na, sodium hydrate (NaOH), hydrochloric acid (HCl), Formaldehyde (HCHO), Tin chloride (SnCl₂), Palladium chloride (PdCl₂) and Copper sulfate pentahydrate (CuSO₄·5H₂O) were purchased from Sinopharm Chemical Reagent Co., Ltd The Anhydrous ethanol was purchased from Wuxi City Yasheng Chemical Co., Ltd The carbonyl iron powder (CIP) was purchased from Jiangsu Tianyi Ultra-fine Metal Powder Co., Ltd

Preparation of electroless copper plating Go

The GO powders (0.5 g) were put in deionized water (1 L), after that the ultrasonic dispersion was operated for 5 min. The dispersed GO powders were filtrated and dried at 50°C for 2 h. The sensitizing solution consisting of 40 mL/L HCl and 20 g/L SnCl₂ was used. The GO and the sensitizing solution at a ratio of 0.5 g:1 L were placed into a beaker for GO sensitization. With magnetic stirring, the beaker was immersed in a water bath maintained at 85°C for 60 min. After that, the sensitized GO was washed with deionized water, and dried at 50°C for 2 h.

The activating solution was prepared by 40 ml/L HCl and 0.5 g/L PdCl_2. The sensitized GO and the activating solution at a ratio of 0.5 g:1 L were placed into a beaker. The temperature, magnetic stirring, and the process time for activation are similar to those of sensitization. After that, the activated GO was washed with deionized water, and dried at 50°C for 2 h.

The copper plating solution was prepared with the following components: 10 g/L CuSO₄·5H₂O, 15 g/L EDTA-2Na and 15 g/L NaKC₄H₄O₆. The activated GO and the copper plating solution at a ratio of 0.5 g:1 L were placed into a beaker. Under the temperature of 80°C, the electroless plate was started by maintaining the pH range of 12.0 to 12.5, which is tuned by titrating NaOH solution. Moreover, the 10 mL/L HCHO was titrated during plating process. The reaction was continued for 10 min. After that, the plated products were washed three times with anhydrous ethanol and dried at 50°C for 2 h. Then, the Cu-coated GO was obtained.

Synthesis of thermal conductive wave-absorbing composites

The CIP was thoroughly blended with the Cu-coated GO by the ultrasonic mixing in anhydrous ethanol (120 W, 10 min). After that, the mixture was dried under vacuum at 50°C for 8 h. The thermal conductive wave-absorbing composite was obtained. By repeating the above steps, the series of composite materials (0.1 wt%, 0.3 wt%, 0.5 wt%, 0.8 wt%, and 1.0 wt%) were fabricated.

Characterizations

The crystal structures of the samples were detected by X-ray diffraction (XRD). The morphology was characterized by scanning electron microscopy (SEM, Zeiss EVO-18). The complex permittivity and complex permeability were measured by using Vector Network Analyzer (VNA) in the range of 1–18 GHz. The thermal conductivity of the absorbing materials was measured by using Quick Thermal Conductivity Meter. Thermal conductivity measurements were conducted on the disk of composite (5 wt% paraffin, 30 mm diameter × 2 mm thickness), which is molded under the pressure of 20 MPa. The composite powders for electromagnetic measurements were wax composites at a mass ratio of 85 wt%,and then the powder/paraffin composites were die-pressed to form cylindrical toroidal specimens with 7.0 mm outer diameter, 3.04 mm inner diameter and 3 mm thickness. Based on the transmission line theory, the reflection loss (RL) can be calculated by the following equation.⁴⁴

R L (d B) = 20 \log | (Z_{i n} - Z_{0}) / (Z_{i n} + Z_{0}) |

(1)

Z_{i n} = Z_{0} \sqrt{μ_{r} / ε_{r}} \tanh [j (\frac{2 π f d}{c}) \sqrt{μ_{r} ε_{r}}]

(2)

Here, $Z_{i n}$ is the input impedance, $Z_{0}$ is the impedance of free space, f is electromagnetic wave frequency, d is the thickness, and c is the light velocity.

Results and discussion

The XRD pattern of the composites is shown in Fig. 1. The XRD pattern of Cu-coated GO sample exhibits three different distinct diffraction peaks compared to that of GO. The first diffraction peak appears approximately at 25.08°, which is significantly different from the characteristic (001) peak of GO at 10.9°. The notable variation in diffraction angles can be attributed to the electroless copper plating process, which impacts the interlayer spacing ( $d$ ) of GO and consequently affects the diffraction angle.^45,46 Additionally, two diffraction peaks are observed at approximately 36.5° and 43.3°. The diffraction peak at 36.5° was attributed to the (111) plane of Cu₂O.⁴⁷ The diffraction peak may result from the presence of dissolved oxygen in the plating solution during the chemical copper plating process, which could have induced a side reaction resulting in the formation of Cu₂O.⁴⁸ The diffraction peak at 43.3° corresponds to the (111) plane of Cu.⁴⁹ No diffraction peak associated with Cu-coated GO was observed in the doped composites, which due to the low concentration of Cu-coated GO.⁵⁰ Moreover, the CIP/Cu-coated GO composites show three distinct diffraction peaks at approximately 44.5°, 65.0°, and 82.5°, corresponding to the (110), (200), and (211) crystal planes of $α$ -Fe, respectively. The position and sharpness of diffraction peaks show no significant change compared with that of CIP, indicating that the addition of Cu-coated GO did not alter the internal crystal and phase structure of the CIP.⁵¹

Figure 1.

The XRD pattern of the composites and filler.

The SEM images of the Cu-coated GO and CIP/Cu-coated GO composites are shown in Fig. 2. As illustrated in Fig. 2(a), the Cu-coated GO samples exhibit a relatively small particle size ranging from 30 to 40 µm. The particles of Cu-coated GO displayed the sheet-like structure, which is similar to that of GO.^52,53 It is well known that a flake-like absorbing material exhibiting shape anisotropy can exceed the Snoek limit.⁵⁴ It is indicated that the chemical plating process primarily affects GO by modifying its functional groups and interlayer interactions, rather than altering its microstructural characteristics.⁵⁵ Meanwhile, the surface roughness of GO particles increases after chemical copper plating. Figure 2(b)–(f) show the CIP/Cu-coated GO composites with varying mass fraction of Cu-coated GO. The particle size of composites is approximately 10–20 µm, as measured by the Nano Measurer. It can be seen that after ultrasonic mixing, the shape of the composites is significantly different from that of pure CIP.⁵⁶ The composites also exhibit a flake structure, demonstrating a localized agglomeration phenomenon.

Figure 2.

SEM images of the composites: (a) Cu-coated GO and (b)-(f) CIP/Cu-coated GO composites.

The Raman spectra of all samples, CIP and Cu-coated GO are shown in Fig. 3. The Cu-coated GO composites only display one strong signal centered at 1303 cm⁻¹, which corresponds to the D band (the vibration of sp³ defects and the disorder sites) of carbon.⁵¹ Compared to carbon, the composites after the chemical copper plating process exhibit the absence of the G band (the ordered state of sp²-hybridized carbon lattice).⁵⁷ The phenomenon may be attributed to the reducing agents in the chemical plating solution, which leads to the decrease of sp² domain size after the reduction process.⁵⁸ The Raman spectra of the composites in this work exhibit characteristics that differ from those reported in previous studies. For instance, Liu et al.²⁹ reported that SnS/GO hybrids show both D and G bands with an ID/IG ratio of about 1.06, and this change suggests the presence of increased defects and relevant lattice deformation on GO plates. Similarly, Jiang et al.³⁰ reported that the clear D and G bands were shown in GO@SiC aerogels, with an ID/IG ratio of 1.15, which is close to that of pristine GO. Moreover, the CIP with different doping contents has also one characteristic Raman peak near 1303 cm⁻¹, which also corresponds to the D band of carbon. The D band of CIP with different doping contents may originate from carbonyl groups in CIP.⁵⁹

Figure 3.

Raman spectra of the CIP/Cu-coated GO composites, Cu-coated GO and CIP.

The complex permittivity and complex permeability of all samples within the frequency range of 1–18 GHz are shown in Fig. 4. The complex permittivity is expressed as $ε_{γ} = ε^{'} - j ε^{″}$ , while the complex permeability is expressed as $μ_{γ} = μ^{'} - j μ^{″}$ . These metrics are crucial for analyzing the electromagnetic properties and understanding the mechanisms behind electromagnetic wave (EMW) attenuation in the material.⁶⁰ The parameters $ε^{'}$ and $μ^{'}$ reflect the energy stored in the electromagnetic field, whereas $ε^{″}$ and $μ^{″}$ reflect the energy dissipation tendencies.⁶¹

Figure 4.

Complex permittivity of the CIP and CIP/Cu-coated GO composites: (a) real $ε^{'}$ ; (b) imaginary $ε^{″}$ and Complex permeability of the CIP and CIP/Cu-coated GO composites: (c) real $μ^{'}$ ; (d) imaginary $μ^{″}$ .

The real permittivity ( $ε^{'}$ ) values of the composites is shown in Fig. 4(a). As the frequency increases, the values of $ε^{'}$ for all samples exhibit slight fluctuations within small ranges, which can be attributed to interfacial polarization for multi-phase composites.⁶² Furthermore, the increase in $ε^{'}$ values with Cu-coated GO doping up to 0.3 wt% can be attributed to the enhanced ferroelectric characteristics and improved dipole alignment within the material.⁶³ However, as Cu-coated GO doping continued up to 0.5 wt%, the dielectric constant rapidly declines. This decline can be explained by the introduction of structural defects and disorder in the crystal lattice at higher doping concentrations.⁶³ These defects can impact the mobility of charge carriers and reduce the material's capacity for effective polarization, leading to a deterioration of its dielectric properties.

The imaginary permittivity ( $ε^{″}$ ) values of the composites are shown in Fig. 4(b). It is observed that the imaginary permittivity for all samples gradually increases with slight fluctuations in frequency within the 2–18 GHz range, which is attributed to the enhancement of space-charge polarization at the interfaces of particles as the surface area increases.^64,65 Notably, the $ε^{″}$ value for samples (0.8 wt% doped) is higher than that of the other samples, which is due to domain wall displacement in the CIP magnetic components.⁶⁶ Additionally, the curve exhibits several absorption peaks, which may result from the dispersion of multiploidization linked to interfacial polarization relaxation and dielectric relaxation.⁶⁷ The minor fluctuations in the curve at lower frequencies are influenced by leakage conduction, while the more significant fluctuations at higher frequencies are due to both relaxation polarization loss and conduction loss affecting high-frequency dielectric loss.⁶⁸

Figure 4(c) shows the frequency dependence of $μ^{'}$ for the samples in the 2–18 GHz band. For all samples, the value of $μ^{'}$ decreases dramatically as the frequency increases, which is consistent with the dispersion characteristics.⁶⁹ The value of $μ^{'}$ for the doped composites are lower than that of pure CIP, which is due to the fact that Cu-coated GO is non-magnetic, thus its doping inevitably reduces the magnetic permeability of the composites.⁷⁰ As shown in Fig. 4(d), for all samples, the values of $μ^{″}$ show one peak around 4.2 GHz, which is similar to the findings reported by Ji et al. regarding the jump of $μ^{″}$ ..⁷¹ The jump of $μ^{″}$ can be attributed to the flake-like particles of the composites and the exchange coupling between the refined particles.^72,73

The parameter $α$ associated with the amplitude decay of the incident electromagnetic wave, which reflects the dissipation characteristics and the overall attenuation capacity of the absorbers. It can be expressed as⁷⁴

α = \frac{\sqrt{2} π f}{c} \times \sqrt{(μ^{″} ε^{″} - μ^{'} ε^{'}) + \sqrt{{(μ^{″} ε^{″} - μ^{'} ε^{'})}^{2} + {(μ^{'} ε^{″} + μ^{″} ε^{'})}^{2}}}

(3)

Here, f represents the frequency, while c represents the speed of light in free space.

The increased values of $μ^{″} and ε^{″}$ can improve the attenuation characteristics of absorbing materials.⁷⁵ However, the emphasis on maximizing these parameters ( $μ^{″}$ , $ε^{″}$ ) does not yield optimal absorption properties. The disparity between $μ^{″}$ and $ε^{″}$ may lead to low impedance matching at the medium interface, resulting in a majority of incident electromagnetic waves being reflected from the medium interface.⁵⁹

The attenuation constant ( $α$ ) of the samples is shown in Fig. 5(a). The value of $α$ increases steadily with increasing frequency. The value of $α$ for the sample (0.3 wt% doped) is larger than that of other samples. Notably, the sample (0.8 wt% doped) exhibiting the largest values of $μ^{″}$ and $ε^{″}$ does not demonstrate the largest value of $α$ , which is consistent with the aforementioned analysis. However, the absorbing properties of materials depend not only on the attenuation constant ( $α$ ) but also on the impedance matching ratio ( $Z r$ ) of the sample.^76,77 The parameter $Z_{γ}$ represents the impedance matching ratio, which can be expressed as

Z_{r} = | \frac{Z_{i n}}{Z_{0}} | = \sqrt{\frac{μ_{r}}{ε_{r}}}

(4)

where

ε_{r}

represents the complex permittivity value and

μ_{r}

represents permeability value. Generally speaking, the higher the

Z r

value, the better the impedance matching that can be achieved.

Figure 5.

(a) Attenuation constant ( $α$ ) and (b) frequency dependence of the impedance matching ratio ( $Z_{γ}$ ) of the CIP and CIP/Cu-coated GO composites.

The impedance matching ratio ( $Z_{r}$ ) of the samples is shown in Fig. 5(b). The values of $Z_{r}$ for all samples decrease monotonically with increasing frequency, which is consistent with the analysis of interfacial polarization.⁷⁸ Notably, the sample (0.1 wt% doped) has low attenuation and the best impedance matching. In contrast, the sample (0.3 wt% doped) exhibits the best attenuation properties and the worst impedance matching performance, which can be explained by its high complex permittivity. The result is similar to the analysis of electromagnetic parameters, as shown in Fig. 4(a) and (b).

The eddy current loss ( $C_{0}$ ) is used to describe the magnetic loss mechanism, which can be expressed as⁷⁹

C_{0} = μ^{″} (μ^{'})^{- 2} f^{- 1} = \frac{2}{3} π μ_{0} d^{2} σ

(5)

The eddy current loss contribution to the imaginary part permeability is related to thickness ( $d$ ), electric conductivity ( $γ$ ) and the permeability of vacuum ( $μ_{0}$ ).

The values of $C_{0}$ for all samples are shown in Fig. 6. It can be seen that the values of $C_{0}$ for the samples are almost constant in the 2–8 GHz range, which is indicated that the eddy current loss is the main loss mechanism for samples in these frequency regions.⁸⁰ However, the values of $C_{0}$ for the samples change drastically after 12 GHz, indicating that the magnetic loss is not only attributed to eddy current losses but are also significantly influenced by natural resonance.^81,82 In addition, the peaks observed after 12 GHz correspond to broadened natural resonance, which may be attributed to the effects of small particle size and the structural characteristics of the flake particles.^83–85

Figure 6.

$μ^{″} (μ^{'})^{- 2} f^{- 1}$ values of the CIP and CIP/Cu-coated GO composites.

Figure 7 shows the reflection loss (RL) VS frequency for all samples. The RL peaks for all samples are located within S-band. It can be seen from Fig. 7(a) that with the increase in Cu-coated GO doping content, the values of RL_min first decrease and then increase, and the RL peaks shift to the higher frequency. At the thickness of 1.5 mm, the CIP has an RL_min value of −12.13 dB at 3.28 GHz. It can be seen that the composite (0.1 wt% doped) achieves a minimum reflection loss (RL_min) of −12.32 dB at 3.76 GHz. Moreover, the composites (0.3%, 0.5%, 0.8% and 1%) demonstrate higher RL_min values with peaks around 3.28 GHz, as shown in Figure 7(a). An RL value below −10 dB indicates that the material dissipates 90% of the incoming electromagnetic wave energy.⁸⁶

Figure 7.

The reflection loss of the CIP and CIP/Cu-coated GO composites at thicknesses of 1.5 and 2 mm.

Additionally, at the thickness of 2 mm, the values of RL_min for all samples are below −14 dB within the S-band. It is evident that the doping content does not alter the frequency range of the RL peaks of the CIP, which remains within the S-band. Moreover, the influence of doping content on the values of RL_min is the same as that in Fig.7(a). In contrast to the CIP@TiO2 composite reported by Su et al.,⁸⁷ which achieved an RLmin of −46.07 dB at 5.04 GHz but required a high filler loading of 50 wt% and a thickness of 3.1 mm. The sample with only 0.1 wt% filler also exhibits good absorptive performance in the S-band (−16.47 dB at 2.8 GHz). It is indicated that the samples in this study possess significant advantages for practical lightweight applications. Lai et al.⁸⁸ reported that the CIP/ABS composite exhibits a broader EAB of 4.1 GHz (below −10 dB), the narrower EAB (1.44 GHz) observed in our sample enables more precise absorption in the S-band. In summary, the samples exhibit excellent absorption performance in the S-band.

To further explore the RL characteristics of samples at varying thicknesses in the S-band, the 3D relationship map of the RL versus frequency and thicknesses for samples is shown in Fig. 8. The thickness varies from 1.0 mm to 2.0 mm, and the frequency ranges from 2 GHz to 18 GHz. It can be seen that the RL peaks of all the samples decrease with increasing of thickness, which can be explained by the quarter matching model.⁸⁹ Additionally, the peak frequency consistently falls within the S-band (2–4 GHz). It is indicated that the absorption properties of the samples can be modulated by varying both the thickness and the content of Cu-coated GO. The properties of the composites facilitate precise control of the wave-absorbing performance in the S-band.

Figure 8.

Frequency dependence of RL values at different thicknesses for the CIP and CIP/Cu-coated GO composites: 3D plot.

In wave-absorbing materials, the thickness of the sample is a critical factor influencing the property of wave absorption. In the instance of electromagnetic waves traversing wave-absorbing material, a fraction of the energy is absorbed by the material, while the remainder is reflected. Many studies have demonstrated that the thickness of the sample has a significant effect on the reflection and absorption of electromagnetic waves. For example, the sample with a thickness of 20 mm had the best electromagnetic wave absorption characteristics among the three sets of thickness samples was reported by Xie et al.⁹⁰ Chai et al.,⁹¹ also reported that the effect of sample thickness on the electromagnetic wave absorption properties of wave-absorbing materials. In general, an increase in thickness of the sample results in an enhancement of the absorption effect.⁹² However, this is accompanied by an increase in the weight and cost of the material.

The matching thickness of the wave absorbing material is an important factor affecting the absorption effect. By selecting the correct thickness, the best absorption effect can be realized, and the matching thickness can be calculated by the following equation.⁹³

d = \frac{λ_{0}}{4 \sqrt{| ε | | μ |}}

(6)

where

| ε |

is the modulus of the complex permittivity,

| μ |

is the modulus of the complex permeability, and

λ_{0}

is the wavelength in free space.

Figure 9 shows the frequency dependence of the matching thickness at 2–18 GHz. The matching thickness of all samples decreases with increasing frequency, with small differences among the curves. Notably, the sample (0.1 wt%) has the largest matching thickness value. This indicates that Cu-coated GO does not significantly alter the matching thickness of the composites.

Figure 9.

Correlation between the matching thickness and frequency of the CIP and CIP/Cu-coated GO composites.

When the thickness is 1.5 mm, the frequency of minimum RL is 3.76 GHz. From Fig. 9, the frequency corresponding to a matching thickness of 1.5 mm is 4.56 GHz. The significant discrepancy is mainly due to the mismatch at the air-material interface, as the matching thickness is based on ideal reflection conditions ( $(1 / 4) λ$ ) which differ from the theoretical models of thin films and transmission lines.⁹⁴ However, when the thickness is 2 mm, the frequency of minimum RL is 2.8 GHz, and the frequency corresponding to a matching thickness of 2 mm is 3.04 GHz, which are relatively close. The reflection values in both cases are near the ideal value.

The thermal conductivity of composites is primarily influenced by the matrix properties and microscopic structures.⁹⁵ However, the thermal conductivity can be enhanced by doping fillers that have thermal conductivities higher than those of metals.⁹⁶ In this study, Cu-coated GO composites are used as thermally conductive fillers to enhance the thermal conductivity of the composites.

Figure 10 shows a bar graph that depicts the correlation between thermal conductivity and the level of doping content. The thermal conductivity of the CIP is 2.66 W/m·K VS that of composites increases to 2.83, 3.02, 3.25, 3.51, and 3.73 W/m·K, with the doping content of Cu-coated GO is 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.8 wt%, and 1.0 wt%, respectively. It is indicated that the thermal conductivity of the composites is positively correlated with the weight fraction of Cu-coated GO. Although the Cu-coated GO significantly enhanced the thermal conductivity, at the low filler content range (≤1 wt%), the thermal conductivity of the composites remains limited by the relatively low thermal conductivity of the CIP matrix itself (2.66 W/m·K) and the persistent interfacial resistance.⁹⁷

Figure 10.

Thermal conductivity of the CIP and CIP/Cu-coated GO composites.

In practical applications, the main approach for enhancing the thermal conductivity of composites is utilizing high filler concentrations (50 wt%–95 wt%). The high content addition of thermal conductivity fillers, such as h-BN,⁹⁸ NICFs⁹⁹ and Al₂O₃@AgNPs,¹⁰⁰ can significantly enhance the thermal conductivity of composites. However, the excessive incorporation of thermally conductive fillers in composites may result in the decline in material's processability, mechanical and absorbing properties..^101,102 As the thermal conductive wave-absorbing materials, it is should avoid excessively pursuing any single properties.

In this study, the results indicated that the lower filler content (ranging from 0.1 wt% to 1 wt%) could still significantly enhance the thermal conductivity of the CIP/Cu-coated GO composites. Meanwhile, the influence on the absorption properties is negligible. Therefore, the absorbing materials with excellent thermal conductivity and absorption properties have been obtained, achieving an optimal balance between these properties.

Conclusions

In summary, the wave absorption-heat conduction composites have been successfully synthesized by a two-step synthesis route, which combines chemical copper plating with ultrasonic mixing. The microstructure, wave absorption properties and thermal conductivity of the CIP/Cu-coated GO composites were studied. From XRD spectra, the composites all exhibit the $α$ -Fe phase. The results of SEM confirmed that the lamellar structure of the absorbing composites with the average size measured to be within the range of 10 to 20 μm. The dielectric constant among all composites reaches its maximum value when the doping mass fraction is 0.3%. Moreover, the wave absorption properties and thermal conductivity of CIP/Cu-coated GO composites can be easily controlled by adjusting the thickness and the doping content of Cu-coated GO. The composites, with a thickness of 2 mm and a doping concentration of 0.1 wt%, exhibit the best absorption properties compared with all other samples, achieving an RL_min value of −16.47 dB at 2.8 GHz. The EAB is 1.44 GHz, ranging from 2.1 to 3.54 GHz, which falls entirely within the S-band. Compared with pure CIP, the composites show a modest enhancement in absorption properties, accompanied by a concurrent increase in thermal conductivity. The composites (1.0 wt% doped) exhibit excellent thermal conductivity, reaching the maximum value of 3.73 W/(m·K) among all the samples, whereas its wave absorption properties have only slightly declined. Therefore, the CIP/Cu-coated GO composites with excellent wave absorption properties and thermal conductivity can serve as a promising candidate for microwave absorption in the S-band.

Footnotes

Nomenclature

ORCID iD

Zekai Li

Author contribution(s)

Zekai Li: Investigation; Validation; Visualization.

Guozhi Xie: Formal analysis; Methodology; Resources.

Yaqi Li: Investigation; Validation; Visualization.

Jing Chen: Resources; Supervision.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: National Natural Science Foundation of China (NSFC) (11974188 and 11304159); QingLan Project of Jiangsu Province.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Data availability statement

All data generated or analyzed during this study are included in this published article.

References

Chen

Wang

Xiong

, et al. Fiber materials for applications of electromagnetic wave absorption. Adv Fiber Mater 2025; 7: 1320–1349.

Hou

Wang

Gao

, et al. A novel approach to electromagnetic wave absorbing material design: utilizing nano-antenna arrays for efficient electromagnetic wave capture. Chem Eng J 2023; 471: 144779.

Zhang

Wang

, et al. Metal single-atoms toward electromagnetic wave-absorbing materials: insights and perspective. Adv Funct Mater 2024; 34: 2405972.

Wang

Jin

Guo

, et al. Lightweight waterproof magnetic carbon foam for multifunctional electromagnetic wave absorbing material. Carbon N Y 2023; 202: 464–474.

Cheng

Zhang

Ning

, et al. Emerging materials and designs for low-and multi-band electromagnetic wave absorbers: the search for dielectric and magnetic synergy. Adv Funct Mater 2022; 32: 2200123.

Liu

Cao

Fang

, et al. Green building materials lit up by electromagnetic absorption function: a review. J Mater Sci Technol 2022; 112: 329–344.

Lin

Huang

Guo

, et al. Hydrophobic multilayered PEG@ PAN/MXene/PVDF@ SiO2 composite film with excellent thermal management and electromagnetic interference shielding for electronic devices. Small 2024; 20: 2402938.

. Multifunctional antimony tin oxide/reduced graphene oxide aerogels with wideband microwave absorption and low infrared emissivity. Compos Part B Eng 2022; 231: 109565.

Yin

Xiu

Wang

. Flexible mille-feuille structure electromagnetic interference shielding film with excellent thermal conductivity and Joule heating. Nano Res 2024; 17: 4544–4554.

10.

Lin

Zhong

Chen

. Reinforcement of microwave absorption and thermal conductivity of polydimethylsiloxane achieved by metal-organic framework-derived carbon nanotube/boron nitride flake heterogeneous structure. Carbon N Y 2024; 227: 119242.

11.

Liu

Wei

. Facile synthesis of nickel ferrite decorated carbon nanotube/cellulose aerogel for efficient electromagnetic wave absorption. Small Methods 2025; 9: 2402260.

12.

Luo

Fei

Zhou

. Silver particle-modified BN@C composites for thermal management and microwave absorption. Ceram Int 2024; 50: 22252–22265.

13.

Guo

Ruan

Wang

. Advances and mechanisms in polymer composites toward thermal conduction and electromagnetic wave absorption. Sci Bull 2023; 68: 1195–1212.

14.

Chen

Liu

, et al. Recent advances in polymer-based composites for thermal management and electromagnetic wave absorption. Adv Compos Hybrid Mater 2025; 8: 210.

15.

Mou

Zhao

Wang

, et al. BCN Nanosheets derived from coconut shells with outstanding microwave absorption and thermal conductive properties. Chem Eng J 2022; 437: 135285.

16.

Zhang

. High electromagnetic wave absorption and thermal conductivity of vertically oriented boron nitride/carbonyl iron/silicone rubber composites. J Alloys Compd 2024; 1008: 176567.

17.

Singh

Akhtar

Kar

. Impact of Al2O3, TiO2, ZnO and BaTiO3 on the microwave absorption properties of exfoliated graphite/epoxy composites at X-band frequencies. Compos Pt B-Eng 2019; 167: 135–146.

18.

Gao

Xing

. Lightweight, multifunctional MXene/polymer composites with enhanced electromagnetic wave absorption and high-performance thermal conductivity. Carbon N Y 2021; 183: 301–312.

19.

Pan

Yang

Jia

. Enhanced thermally conductive and microwave absorbing properties of polymethyl methacrylate/Ni@ GNP nanocomposites. Ind Eng Chem Res 2021; 60: 12316–12327.

20.

Sista

Dwarapudi

Kumar

. Carbonyl iron powders as absorption material for microwave interference shielding: a review. J Alloys Compd 2021; 853: 157251.

21.

Song

Hou

, et al. Heterogeneous interfaces of magnetic CIP and binary dielectric carbon-based material toward high-efficiency microwave attenuation. Frontiers in Materials 2022; 9: 950399.

22.

Zhao

Sun

Huang

, et al. Constructing multi-layer heterogeneous interfaces in liquid metal graphite hybrid powder: towards microwave absorption enhancement. J Colloid Interface Sci 2025; 677: 79–89.

23.

Liu

Lin

, et al. Perspectives for electromagnetic wave absorption with graphene. Carbon N Y 2024; 223: 119017.

24.

Wei

Bachagha

. Component optimization and microstructure design of carbon nanotube-based microwave absorbing materials: a review. Carbon N Y 2024; 217: 118651.

25.

Farooq

Islam

Danish

, et al. Synergistic effects of Li-based ferrite and graphene oxide in microwave absorption applications. Synth Met 2024; 307: 117674.

26.

Zhang

Meng

. Active/passive protection and anti-UV waterborne epoxy coatings based on low defect functionalized PDA-GO-CeO2 material for excellent corrosion control. Chem Eng J 2023; 479: 147859.

27.

Anuwongsa

Yawai

Ananpreechakorn

. A simple preparation of graphene oxide with a modified Hummer's method. J Mater Sci Appl Energy 2023; 12: 251664–251664.

28.

Aixart

Diaz

Llorca

, et al. Increasing reaction time in Hummers’ method towards well exfoliated graphene oxide of low oxidation degree. Ceram Int 2021; 47: 22130–22137.

29.

Liu

. Amorphous SnS nanosheets/graphene oxide hybrid with efficient dielectric loss to improve the high-frequency electromagnetic wave absorption properties. Appl Surf Sci 2019; 486: 344–353.

30.

Jiang

Chen

Liu

. Lightweight spongy bone-like graphene@SiC aerogel composites for high-performance microwave absorption. Chem Eng J 2018; 337: 522–531.

31.

Zeng

Yang

. Solvothermal synthesis and good microwave absorbing properties for magnetic porous-Fe3O4/graphene nanocomposites. AIP Adv 2017; 7: 056605.

32.

Krishnan

Kim

Luo

. Energetic graphene oxide: challenges and opportunities. Nano Today 2012; 7: 137–152.

33.

Yadav

Singh Raman

Meena

. An update on graphene oxide: applications and toxicity. ACS Omega 2022; 7: 35387–35445.

34.

Lin

Yen

. Effects of additives and chelating agents on electroless copper plating. Appl Surf Sci 2001; 178: 116–126.

35.

Hou

Ren

. Research progress on the removal, recovery and direct high-value materialization of valuable metal elements in electroplating/electroless plating waste solution. J Water Process Eng 2022; 46: 102577.

36.

Peng

Tan

Venkataraman

. Effects of ultrasonic-assisted nickel pretreatment method on electroless copper plating over graphene. Sci Rep 2022; 12: 21159.

37.

Zhu

. Microwave absorption properties of fabric coated absorbing material using modified carbonyl iron power. Compos Part B-Eng 2011; 42: 626–630.

38.

Xie

Chen

. Study on the corrosion and electromagnetic properties of carbonyl iron/Co composites by electroless plating Cu. J Mater Sci: Mater Electron 2023; 34: 2293.

39.

. Microwave absorbing properties and enhanced infrared reflectance of Fe/Cu composites prepared by chemical plating. J Magn Magn Mater 2014; 355: 65–69.

40.

Liu

Chen

Liu

. Progress in preparation, characterization, surface functional modification of graphene oxide: a review. J Saudi Chem Soc 2022; 26: 101560.

41.

Yang

Wang

. “Clicking” graphite oxide sheets with well-defined polystyrenes: a new strategy to control the layer thickness. Polymer 2011; 52: 3046–3052.

42.

Bhunia

Hwang

Min

. A non-volatile memory device consisting of graphene oxide covalently functionalized with ionic liquid. Chem Commun 2012; 48: 913–915.

43.

Bonanni

Chua

Pumera

. Rational design of carboxyl groups perpendicularly attached to a graphene sheet: a platform for enhanced biosensing applications. Chem-Eur J 2014; 20: 217–222.

44.

Zhang

Wang

Chen

, et al. A rational route towards dual wave-transparent type of carbonyl iron@SiO2@heterogeneous state polypyrrole@paraffin composites for electromagnetic wave absorption application. J Colloid Interface Sci 2021; 581: 84–95.

45.

Tan

Fan

Song

. Effects of interlayer spacing and oxidation degree of graphene oxide nanosheets on water permeation: a molecular dynamics study. J Mol Model 2022; 28: 57.

46.

Bragg

. The diffraction of short electromagnetic waves by a crystal. Scientia 1929; 23: 153.

47.

Kunya

Abdu

Mustafa

. Cuprous oxide (Cu2O) based solar cell thickness dependence. Brit J Phys Stud 2022; 1: 01–07.

48.

Yang

Marchal

Radisic

. Role of oxygen and cuprous ions in copper electroplating. In 22nd Materials for advanced metallization conference, 2013.

49.

Dong

Wang

Tan

. Synthesis and characterization of pure copper nanostructures using wood inherent architecture as a natural template. Nanoscale Res Lett 2018; 13: –8.

50.

Wang

Shi

Huang

. Synthesis and degradation kinetics of TiO2/GO composites with highly efficient activity for adsorption and photocatalytic degradation of MB. Sci Rep 2019; 9: 18744.

51.

Chen

Xie

Zhang

. Broadband microwave absorption for thin FeSiCr/rGO composites. J Magn Magn Mater 2024; 596: 171979.

52.

Oliveira

AEF

Braga

Tarley

CRT

. Thermally reduced graphene oxide: synthesis, studies and characterization. J Mater Sci 2018; 53: 12005–12015.

53.

Xiaoyu

Guozhi

Ningyan

, et al. Fabrication and microwave absorption properties of the flaky carbonyl iron/graphene oxide composite in S-band. J Mater Sci: Mater Electron 2023; 34: 09.

54.

Yang

R-B

Liang

W-F

. Microwave properties of high-aspect-ratio carbonyl iron/epoxy absorbers. J Appl Phys 2011; 109: 07A311.

55.

Joshi

Koduru

Malek

. Surface modifications and analytical applications of graphene oxide: a review. TrAC, Trends Anal Chem 2021; 144: 116448.

56.

Xie

Zhang

, et al. Facile constructing core-shell F–CIP@ O/N-SWCNHs composites for high-performance microwave absorption and anti-corrosion. Carbon N Y 2024; 230: 119632.

57.

Song

. Preparation of Cu-graphene coating via electroless plating for high mechanical property and corrosive resistance. J Alloys Compd 2019; 777: 877–885.

58.

Zhao

Wang

. Fabrication and tensile properties of graphene/copper composites prepared by electroless plating for structrual applications. Phys Status Solidi A 2014; 211: 2878–2885.

59.

Xie

. Microwave absorbing properties of flaky carbonyl iron powder prepared by rod milling method. J Electron Mater 2019; 48: 2495–2500.

60.

Shen

. Promoting electromagnetic wave absorption performance by integrating MoS₂@ Gd₂O₃/MXene multiple hetero-interfaces in wood-derived carbon aerogels. Small 2024; 20: 2306915.

61.

Cao

Zhang

. Regulating the electromagnetic balance of materials by electron transfer for enhanced electromagnetic wave absorption. J Mater Sci Technol 2024; 195: 63–73.

62.

Tang

Zhao

Tian

. Synthesis, characterization and microwave absorption properties of titania-coated barium ferrite composites. J Phys Chem Solids 2006; 67: 2442–2447.

63.

Esmaeili

Ehsani

Toghraie

. Sr-doping effects on piezoelectric and dielectric properties of lead-free barium titanate via molecular dynamics approach. Sci Rep 2025; 15: 8404.

64.

Wen

Zuo

. Microwave-absorbing properties of shape-optimized carbonyl iron particles with maximum microwave permeability. Physica B 2009; 404: 3567–3570.

65.

Cho

Kim

, et al. Study of electromagnetic wave-absorbing materials made by a melt-dragging process. Phys Status Sol (a) 2004; 201: 1942–1945.

66.

Zhang

Xie

Chen

. Preparation and microwave absorption properties of FeCoV/GO/coupling agent composites in S band. J Electron Mater 2024; 53: 4071–4080.

67.

Min

Qingze

Yun

. Preparation of NiFe2O4 nanorod-graphene composites via an ionic liquid assisted one-step hydrothermal approach and their microwave absorbing properties. J Mater Chem A 2013; 1: 5577–5586.

68.

Singh

Shukla

Patra

. Microwave absorbing properties of a thermally reduced graphene oxide/nitrile butadiene rubber composite. Carbon N Y 2012; 50: 2202–2208.

69.

Feng

Qiu

Shen

. Absorbing properties and structural design of microwave absorbers based on carbonyl iron and barium ferrite. J Magn Magn Mater 2007; 318: 8–13.

70.

Trukhanov

Tishkevich

Podgornaya

. Impact of the nanocarbon on magnetic and electrodynamic properties of the ferrite/polymer composites. Nanomaterials-Basel 2022; 12: 68.

71.

Yoshida

Ando

Shimada

. Crystal structure and microwave permeability of very thin Fe–Si–Al flakes produced by microforging. J Appl Phys 2003; 93: 6659–6661.

72.

Jiao

Zhao

. Vapor diffusion synthesis of CoFe₂O₄ hollow sphere/graphene composites as absorbing materials. J Mater Chem A 2014; 2: 735–744.

73.

Deng

Zhou

Xie

. Characterization and microwave resonance in nanocrystalline FeCoNi flake composite. J Appl Phys 2007; 101: 2733610.

74.

Cheng

Guo

Zhang

, et al. Achieving the broader frequency electromagnetic absorber by development of magnetic core-shell composite with tunable shell/core sizes. Appl Surf Sci 2018; 434: 763–770.

75.

Wang

Shu

, et al. Confinedly tailoring Fe3O4 clusters-NG to tune electromagnetic parameters and microwave absorption with broadened bandwidth. Chem Eng J 2018; 332: 321–330.

76.

Wang

Zhang

, et al. Porous carbon polyhedrons coupled with bimetallic CoNi alloys for frequency selective wave absorption at ultralow filler loading. J Mater Sci Technol 2022; 103: 34–41.

77.

Jiao

, et al. One-dimensional core–shell CoC@CoFe/C@PPy composites for high-efficiency microwave absorption. J Colloid Interface Sci 2023; 650: 2014–2023.

78.

Zhang

Wei

Yang

. Effect of shape of Sendust particles on their electromagnetic properties within 0.1-18 GHz range. Phys B Condens Matter 2011; 406: 3896–3900.

79.

Zhang

. Coxfey@C composites with tunable atomic ratios for excellent electromagnetic absorption properties. Sci Rep 2015; 5: 18249.

80.

Zhang

Cao

Xue

, et al. Microwave absorption performance of the absorber based on epsilon-Fe3N/epoxy and carbonyl iron/epoxy composites. J Magn Magn Mater 2015; 374: 755–761.

81.

Deng

Gao

, et al. Scalable 3D textile with hierarchically functionalized pyramidal units using nanostructured polyamide@carbon/Fe3O4 fibers for tunable microwave absorption. Chem Eng J 2023; 473: 145040.

82.

Sun

Dong

Cao

, et al. Hierarchical dendrite-like magnetic materials of Fe3O4, γ-Fe₂O₃, and Fe with high performance of microwave absorption. Chem Mater 2011; 23: 6.

83.

Zhao

Cheng

Zhu

, et al. Ultralight CoNi/rGO aerogels toward excellent microwave absorption at ultrathin thickness. J Mater Chem C 2019; 7: 2.

84.

Jian

Mahmood

. Facile synthesis of Fe3O4/GCs composites and their enhanced microwave absorption properties. J Am Chem Soc 2016; 8: 9.

85.

Ding

Wang

, et al. Rational design of core-shell Co@C microspheres for high performance microwave absorption. Carbon N Y 2017; 111: 722–732.

86.

Wang

Gao

Tang

. Microwave absorption properties of carbon nanocoils coated with highly controlled magnetic materials by atomic layer deposition. J Am Chem Soc 2012; 6: 11009–11017.

87.

Wang

. Preparation of CIP@TiO2 composite with broadband electromagnetic wave absorption properties. Int J Miner Metall Mater 2024; 31: 197–205.

88.

Lai

Wang

. Effects of carbonyl iron powder (CIP) content on the electromagnetic wave absorption and mechanical properties of CIP/ABS composites. Polymers (Basel) 2020; 12: 1694.

89.

Liu

Yao

Zhou

, et al. Small magnetic co-doped NiZn ferrite/graphene nanocomposites and their dual-region microwave absorption performance. J Mater Chem 2016; C.4: 9738–9749. 10.1039/C6TC03518C

90.

Xie

. Electromagnetic wave absorption properties of helical carbon fibers and expanded glass beads filled cement-based composites. Compos Part A-Appl Sci Manuf 2018; 114: 360–367.

91.

Chai

Cheng

Zhang

. Enhancing electromagnetic wave absorption performance of Co3O4 nanoparticles functionalized MoS2 nanosheets. J Alloys Compd 2020; 829: 154531.

92.

Tripathi

Sandha

. Impact of thickness and wt% on the dielectric properties of sugarcane bagasse and MWCNT composite material as microwave absorber. Waste Biomass Valorization 2023; 14: 2009–2024.

93.

Ning

Dong

Luo

, et al. Ultra-broadband microwave absorption by ultra-thin metamaterial with stepped structure induced multi-resonances. Results Phys 2020; 18: 103320.

94.

Xie

Gao

, et al. Absorbing properties of melt spun FeSi alloy with the addition of Co in 5G bang. J Mater Sci: Materials in Electronics 2019; 30: 18065–18069.

95.

Zhai

Zhang

Xian

. Effective thermal conductivity of polymer composites: theoretical models and simulation models. Int J Heat Mass Transfer 2018; 117: 358–374.

96.

Abbas

Septevani

Yurid

. Thermal interface polymer-based composites materials: a critical review. Multiscale and Multidiscip Model Exp and Des 2025; 8: 1–25.

97.

Chen

Zhou

. Thermal conductivity of polymers and their nanocomposites. Adv Mater 2018; 30: 1705544.

98.

Cha

Hong

Pang

. Maximizing filler content and manufacturing highly thermal conductive composite materials through eutectic liquefaction of epoxy resin. J Ind Eng Chem 2024; 140: 376–384.

99.

Zhang

Zhou

Xie

. Thermal interface materials with sufficiently vertically aligned and interconnected nickel-coated carbon fibers under high filling loads made via preset-magnetic-field method. Compos Sci Technol 2021; 213: 108922.

100.

Huang

Drummer

. Multi-contact hybrid thermal conductive filler Al2O3@ AgNPs optimized three-dimensional thermal network for flexible thermal interface materials. J Appl Polym Sci 2021; 138: 50889.

101.

Ye W, Wang Z, Zeng X, Ren L, Sun R, Wen Z, Zeng X. Study on the influence of different filler fractions on the properties of thermal interface materials. IEEE 22nd International Conference on Electronic Packaging Technology (ICEPT), 2021: 1–4. 10.1109/ICEPT52650.2021.9568054

102.

Kruželák

Kvasničáková

Hložeková

. Mechanical, thermal, electrical characteristics and EMI absorption shielding effectiveness of rubber composites based on ferrite and carbon fillers. Polymers (Basel) 2021; 13: 2937.