Enhancement in Electromagnetic Wave Shielding Effectiveness through the Formation of Carbon Nanofiber Hybrids on Carbon-Based Nonwoven Fabrics

Round 1

Reviewer 1 Report

In this study, Kim et al. reported a new carbon based composites with enhanced EMI shielding effectiveness prepared by the CVD method. Their results are interesting. The manuscript described the process meticulously, going through every detail and discussion needed. After careful consideration, this reviewer does recommend publishing this manuscript in Nanomaterials. The following includes several comments that may be helpful to improve the manuscript further.

1. Details of preparation of specimen for electromagnetic parameters test should be given.
2. (a) should be marked in Figure 1.
3. More references concerning carbon based materials for EM absorption such as “Carbon, 2021, 175: 233-242”, “Ceramics International, 2021, 47(7): 10013-10018.” could be cited to highlight the theme and materials characterization.
4. Mechanism of EMI shielding is suggested to be further discussed, and the corresponding mechanism diagram is recommended to be provided.
5. Authors should carefully check the whole text to avoid some typos and grammar issues.

Author Response

Response to reviewer’s comments

 For (Reviewer # 1)’s comments

In this study, Kim et al. reported a new carbon based composites with enhanced EMI shielding effectiveness prepared by the CVD method. Their results are interesting. The manuscript described the process meticulously, going through every detail and discussion needed. After careful consideration, this reviewer does recommend publishing this manuscript in Nanomaterials. The following includes several comments that may be helpful to improve the manuscript further.

→ Thanks for your careful and cordial consideration.

1. Details of preparation of specimen for electromagnetic parameters test should be given. (a) should be marked in Figure 1.

→ We revised the manuscript concerning the issues raised by reviewers # 1 as his comments. Please see the following sentences and Fig. 1 in the revised manuscript.

Fig. 1a shows the details of preparation of specimen for electromagnetic parameters test. CMCs were formed in c-NFs using C₂H₂ + SF₆ gas flow in a thermal chemical vapor deposition system. The incorporation of H₂ gas flow into the C₂H₂ + SF₆ gas flow system caused the selective hybrid formation of numerous tiny CNFs in the c-NFs, where the CNFs formed only on the surfaces of the i-CFs constituting the c-NFs and not on the surfaces of the CMCs. For samples E–H, cyclic modulation of SF₆ gas flow was conducted by simply switching the gas flow on and off in continuous cycles. The source gas flow sequence mirrored the iterative order of the reaction processes: C₂H₂ + H₂ + SF₆ flow (C₂H₂ flow on, H₂ flow on, and SF₆ flow on) followed by C₂H₂ + H₂ flow (C₂H₂ flow on, H₂ flow on, and SF₆ flow off), as shown in Fig. 1b.

• "Please see the attachment."

Figure 1. (a) Samples before & after CVD process, (b) cyclic injection processes of C₂H₂, H₂, and SF₆ for samples E–H, and (c) waveguide test holders for vector network analyzer (VNA).

2. More references concerning carbon based materials for EM absorption such as “Carbon, 2021, 175: 233-242”, “Ceramics International, 2021, 47(7): 10013-10018.” could be cited to highlight the theme and materials characterization.

→ We revised the manuscript concerning the issues raised by reviewers # 1 as his comments. Please see the following Table 3 in the revised manuscript.

Table 3. EMI SE of carbon-based materials.

* CB: carbon black, *CNF: carbon nanofiber, *CNT: carbon nanotube, *ABS: acrylonitrile–butadiene–styrene, *SCF: short carbon fiber, *EVA: ethylene vinyl acetate, *MX: Mxene, *RGO: reduced graphene oxide, *3D G–CNT–Fe₂O₃: three-dimensional graphene–carbon nanotube–iron oxide, *GN: graphene, *THCS: triple-shell hollow carbon submicrospheres, *CNTsM: carbon nanotubes microspheres, *M40J SCF felt: M40J short-chopped carbon fibers felt, *CF-1200: carbon foams after carbonized at 1200℃, *c-NFs: native carbon-based nonwoven fabrics, *CMCs on c-NFs: carbon microcoils grown on c-NFs, *CNF–i-CF hybrids on c-NFs: hybrid of tiny CNFs on i-CFs in c-NFs, *CNF–CMC and CNF–i-CF hybrids in c-NFs: hybrids of both tiny CNFs on CMCs and tiny CNFs on i-CFs in c-NFs.

References

36. Wang Y.; Zhou W.; Zeng G.; Chen H.; Luo H.; Fan X.; Li Y. Rational design of multi-shell hollow carbon submicrospheres for high-performance microwave absorbers. Carbon 2021, 175, 233–242.
37. Zhang Y.; Zhou W.; Chen H.; Duan G.; Luo H.; Li Y. Facile preparation of CNTs microspheres as improved carbon absorbers for high-efficiency electromagnetic wave absorption. Ceramics International 2021, 47, 10013-10018.
38. Liang J.; Gu Y.; Bai M.; Wang S.; Li M.; Zhang Z. Electromagnetic shielding property of carbon fiber felt made of different types of short-chopped carbon fibers. Composites Part A 2019, 121, 289–298.
39. Li J.; Ding Y.; Yu N.; Gao Q.; Fan X.; Wei X.; Zhang G.; Ma Z.; He X. Lightweight and stiff carbon foams derived from rigid thermosetting polyimide foam with superior electromagnetic interference shielding performance. Carbon 2020, 158, 45-54.
40. Mechanism of EMI shielding is suggested to be further discussed, and the corresponding mechanism diagram is recommended to be provided.

→ We revised the manuscript concerning the issues raised by reviewers # 1 as his comments. Please see the following sentences and Fig. 12 in the revised manuscript.

Fig. 11c shows the SE values for the reflection loss of the native and hybridized c-NFs. For the reflection loss, the SE values of the hybridized c-NFs were lower than that of the native c-NFs throughout the entire range of operating frequencies. At lowest operating frequency (8.0 GHz) in this work, the difference between the SE values of sample A, with the highest electrical conductivity, and sample H, with the lowest electrical conductivity value, was the largest. The combined results of Table 2 and Fig. 11c confirm the dependence of reflection SE of the samples on their electrical conductivity values.

The schematic in Fig. 12 explains the reasons behind the enhancement in total SE for the nonselective hybrid formation of numerous tiny CNFs in c-NFs (sample H). It reveals the improvement in the total SE values for the nonselective hybridized sample owing to the enhanced absorption SE originating from the numerous intersections of tiny CNFs, although hybrid formation reduced the electrical conductivity of the sample.

• "Please see the attachment."

Figure 12. Schematic explaining the enhancement in total SE for the nonselective hybrid formation of numerous tiny CNFs in c-NFs (sample H).

4. Authors should carefully check the whole text to avoid some typos and grammar issues.

→ We revised the manuscript concerning the issues raised by reviewers # 1 as his comments. Please see the following corrections in the revised manuscript.

Line 83 & 86 : CNF hybrids → CNF-hybrids

Line 211 & 213 : on the i-CF → on the i-CFs

Line 260 : more → much more

Author Response File: Author Response.pdf

Reviewer 2 Report

Authors reported the synthesis of Carbon microcoils by using thermal chemical vapor deposition method, and investigated their electromagnetic wave shielding effectiveness. Materials realization and experimental characterization are properly given; the results are clearly presented. However, some issues should be addressed.

1, The narrative in Abstract section was too tedious. Authors should focus on the what you have done and the related description should be refined to highlight your viewpoints. In addition, authors should figure out the significance and real-life application of the present paper.

2, Herein, the preparation method of the composites is thermal chemical vapor deposition. As far as I am concerned, it is just to meet the test conditions of waveguide test, and how to achieve the strength requirements in practical application, please give more details. What is important is that the sample used for SE value test is powders or films? If the powders were used for test, what is content of the effective filler? Authors should replenish the relevant measurement condition.

Author Response

Response to reviewer’s comments

 For (Reviewer # 2)’s comments

Authors reported the synthesis of Carbon microcoils by using thermal chemical vapor deposition method, and investigated their electromagnetic wave shielding effectiveness. Materials realization and experimental characterization are properly given; the results are clearly presented. However, some issues should be addressed.

1. The narrative in Abstract section was too tedious. Authors should focus on the what you have done and the related description should be refined to highlight your viewpoints. In addition, authors should figure out the significance and real-life application of the present paper.

→ We revised the manuscript concerning the issues raised by reviewers # 1 as his comments. Please see the following Abstract in the revised manuscript.

Abstract: The selective hybrid formation of numerous tiny carbon nanofibers (CNFs) in carbon-based nonwoven fabrics (c-NFs), namely CNFs formed only on the surfaces of individual carbon fibers (i-CFs) constituting c-NFs and not on the surfaces of carbon microcoils (CMCs), could be formed by the incorporation of H₂ gas flow into the C₂H₂ + SF₆ gas flow in a thermal chemical vapor deposition system. On the other hand, the nonselective hybrid formation of numerous tiny CNFs in c-NFs, that is, tiny CNFs formed on the surfaces of both i-CFs and CMCs, could be achieved by simply modulating the SF₆ gas flow on and off in continuous cycles during the reaction. Detailed mechanisms are suggested for the selective or nonselective formation of tiny CNFs in c-NFs. Furthermore, the electromagnetic wave shielding effectiveness (SE) values of the samples were investigated across operating frequencies in the 8.0–12.0 GHz range. Compared with previously reported total SE values, the presently measured values rank in the top tier. Although hybrid formation reduced the electrical conductivity of the native c-NFs, the total SE values of the native c-NFs greatly increased following hybrid formation. This dramatic improvement in the total SE values is ascribed to the increased thickness of c-NFs after hybrid formation and the electromagnetic wave absorption enhancement caused by the intrinsic characteristics of CMCs and the numerous intersections of tiny CNFs.

2. Herein, the preparation method of the composites is thermal chemical vapor deposition. As far as I am concerned, it is just to meet the test conditions of waveguide test, and how to achieve the strength requirements in practical application, please give more details.

→ We revised the manuscript concerning the issues raised by reviewers # 1 as his comments. Please see the following sentences and Fig. 1 in the revised manuscript.

Fig. 1a shows the details of preparation of specimen for electromagnetic parameters test. CMCs were formed in c-NFs using C₂H₂ + SF₆ gas flow in a thermal chemical vapor deposition system. The incorporation of H₂ gas flow into the C₂H₂ + SF₆ gas flow system caused the selective hybrid formation of numerous tiny CNFs in the c-NFs, where the CNFs formed only on the surfaces of the i-CFs constituting the c-NFs and not on the surfaces of the CMCs. For samples E–H, cyclic modulation of SF₆ gas flow was conducted by simply switching the gas flow on and off in continuous cycles. The source gas flow sequence mirrored the iterative order of the reaction processes: C₂H₂ + H₂ + SF₆ flow (C₂H₂ flow on, H₂ flow on, and SF₆ flow on) followed by C₂H₂ + H₂ flow (C₂H₂ flow on, H₂ flow on, and SF₆ flow off), as shown in Fig. 1b.

→ Indeed, we can use the stacking type, namely woven-nonwoven-woven type, fabrics to achieve the strength requirements in practical application. However, we can’t expose the details at this point, because this technique has been recently applied as Korean Patent (Application # 10-2020-0108268). Please see the following sentences in the revised manuscript.

Apart from its excellent SE values, the hybridized c-NFs fabricated in this study could give remarkable mechanical strength when they were manufactured as a stacking type, namely woven-nonwoven-woven type, fabrics. The details for the fabrication of the stacking type fabrics were applied as Korean Patent (application number 10-2020-0108268) [40]. In addition, its production process may be scaled up in a cost-effective manner. These results strongly suggest that the hybridized c-NFs fabricated in this study are applicable for the manufacture of effective and highly flexible EM shielding materials.

References

40. Yu J. D.; Kim H.J.; Kim D.Y.; Choi J.W.; Ji W.J.; Sim W.D.; Lee C.O.; Yu J.H. Electromagnetic wave shielding material and method for producing the same. Korea Patent 10-2020-0108268,

3. What is important is that the sample used for SE value test is powders or films?

If the powders were used for test, what is content of the effective filler? Authors should replenish the relevant measurement condition.

→ Actually, our sample is like a film. Accurately, it is a numerous nanofibers incorporated fabrics. So, we did not need the filler.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Authors have addressed my concerns well. This paper with current form can be accepted for publication.

Reviewer 2 Report

All issues were well addressed, and this work can be accepted.