Effect of Graphite Nanoplatelets Content and Distribution on the Electromagnetic Shielding Attenuation Mechanisms in 2D Nanocomposites

Round 1

Reviewer 1 Report

The paper describes an experimental study of the shielding properties of some composite materials.  The motivation is explained clearly, and the paper covers background theory, methods and results, followed by a sensible discussion and conclusion.  The results will be of practical interest to readers, particularly the effects of porosity and compaction on the reflective and absorptive components of shielding effectiveness.

The paper could be improved in places by providing more details.  Specific comments are:

The authors state (line 37) that 'To date, this function [i.e. shielding] is performed by metals,' but in fact the shielding properties of carbon-fibre composites have been studied since the 1990's and probably earlier, e.g.

Ramadin, Y., Jawad, S.A., Musameh, S.M., Ahmad, M., Zihlif, A.M., Paesano, A., Martuscelli, E. and Ragosta, G., 1994. Electrical and electromagnetic shielding behavior of laminated epoxy–carbon fiber composite. Polymer international, 34(2), pp.145-150.

Having defined shielding effectiveness as SE, you could then use this abbreviation consistently to make the paper more compact.

Line 80, please explain the term 'specific shielding effectiveness', and give an indication of how high this parameter needs to be, for it to be deemed 'outstanding', 'very high' etc. (the term is explained later in lines 216-221).

Table 1, how do you know that these values of percentage filler content are correct?  Could some of the polymer have evaporated during the manufacturing process?

Lines 131-140, the method looks reasonable, but please estimate the accuracy of R, A and T values obtained using this technique.  How was the sample fixed in the waveguide, and how did you prevent waves from diffracting around its edge?  Did you calibrate the instrument with a sample of known SE?

Figure 4, it would be useful to present the SE values here (or at least the T values) as well as the R and A components.

Line 90, you state 'According to this observation, by making the nanostructure porous (i.e., chaotic), the EM waves are partly absorbed, and the reflection mechanism is not the primary.'  But looking at Fig 4, R is still higher than A for the porous samples (although you do correct state that R has decreased and A increased with respect to the compact samples).

Figure 6, caption only covers left-hand part (a), and should also describe right-hand part (b)

Line 217, SEE_T should be SSE_T.

Author Response

The paper describes an experimental study of the shielding properties of some composite materials.  The motivation is explained clearly, and the paper covers background theory, methods and results, followed by a sensible discussion and conclusion. The results will be of practical interest to readers, particularly the effects of porosity and compaction on the reflective and absorptive components of shielding effectiveness.

The paper could be improved in places by providing more details. Specific comments are:

• The authors state (line 37) that 'To date, this function [i.e. shielding] is performed by metals,' but in fact the shielding properties of carbon-fibre composites have been studied since the 1990's and probably earlier, e.g.

Ramadin, Y., Jawad, S.A., Musameh, S.M., Ahmad, M., Zihlif, A.M., Paesano, A., Martuscelli, E. and Ragosta, G., 1994. Electrical and electromagnetic shielding behavior of laminated epoxy–carbon fiber composite. Polymer international, 34(2), pp.145-150.

According to the reviewer comment, the introduction has been updated also including the suggested citation.

• Having defined shielding effectiveness as SE, you could then use this abbreviation consistently to make the paper more compact.

We would like to thank the reviewer for this suggestion. The manuscript has been reviewed by using the abbreviation.

• Line 80, please explain the term 'specific shielding effectiveness', and give an indication of how high this parameter needs to be, for it to be deemed 'outstanding', 'very high' etc. (the term is explained later in lines 216-221).

The term SSE has been explained at lines 242-248 and the Eq. (6) has been added in order to clarify this concept. It describes the shielding capability of the material regardless its thickness and weight. For this reason, the SSE is useful parameter to directly compare the shielding capability of different materials. Thus, the higher the SSE, the higher the shielding capacity of the material.

• Table 1, how do you know that these values of percentage filler content are correct?  Could some of the polymer have evaporated during the manufacturing process?

The percentage reported in Table 1 were checked by thermogravimetric analysis. However, they were not reported in the manuscript initially. The table 2 and table 3 have been updated by including the nominal and actual filler content according to the reviewer comment and the method has been described (lines 126-132).

• Lines 131-140, the method looks reasonable, but please estimate the accuracy of R, A and T values obtained using this technique. How was the sample fixed in the waveguide, and how did you prevent waves from diffracting around its edge? Did you calibrate the instrument with a sample of known SE?

The measures have been repeated 5 times for each sample in order to estimate their accuracy. The standard deviation is very low (<0.005 for all measures). Samples were glued on a polystyrene support of 1 cm thickness of the dimension of the waveguide (22.86 mm x 10.16 mm) and placed in a short rectangular guide (2 cm length) in order to avoid the rupture of the specimen during the mounting and for inhibit vibration.  Here no diffraction effects are present since the sample can be modelled as a dielectric slab inside the waveguide, orthogonal to the waveguide axis. Accordingly, the standard description of propagation inside a rectangular waveguide can be applied.

A standard Thru-Reflect Line (TRL) calibration has been performed to reduce the effects of the systematic errors [24]. This is a calibration procedure, typically adopted when dealing when waveguides, introduced to overcome the problems associated with non-coaxial measurements. Indeed, a set of three distinct well characterized impedance standards are often impossible to produce for non-coaxial transmission media, and this compromises the accuracy of the results, when adopting a standard calibration method. This problem is solved, in the TRL calibration method, by adopting a formulation requiring a very little knowledge about the standards. The calibration is performed in three steps: step 1 requires a thru connection, step 2 the use of unknown high reflective terminations, while step 3 the connection of a line of unknown length and propagation constant, but known characteristic impedance. Due to the simplicity of the calibration standards, TRL can be easily applied in dispersive transmission media such as microstrip, stripline and waveguide.

[24] Hewlett Packard, “Network Analysis: Applying the HP 8510 TRL Calibration for Non-coaxial Measurements,” Product Note 8510-8A, 1992.

The manuscript has been modified by adding details on the measure procedure and the calibration procedure within the Materials and Methods section.

• Figure 4, it would be useful to present the SE values here (or at least the T values) as well as the R and A components.

The picture has been modified by adding T values for compact and porous samples as function of filler content (Figure 4c).

• Line 90, you state 'According to this observation, by making the nanostructure porous (i.e., chaotic), the EM waves are partly absorbed, and the reflection mechanism is not the primary. But looking at Fig 4, R is still higher than A for the porous samples (although you do correct state that R has decreased and A increased with respect to the compact samples).

The statement has been reformulated, the sentence was changes as follows:

“… According to this observation, by making the nanostructure porous (i.e., chaotic), the EM waves are partly absorbed. Although the reflection mechanism is still the primary, an increase in absorption capacity has been found. ….”

• Figure 6, caption only covers left-hand part (a), and should also describe right-hand part (b)

The caption was modified by including the description of the part b)

“Figure 6. Shielding effectiveness SE_T (a) and SSE_T (b) at 10 GHz for samples with 50 wt%, 70 wt% and 90 wt% GNPs contents”

• Line 217, SEE_T should be SSE_T.

Fixed.

Author Response File: Author Response.pdf

Reviewer 2 Report

SUMMARY

The authors deal with the issue of the EMI shielding properties in the X band of high-content graphene nanoplatelets nanocomposites. The authors investigated the effect of filler content and the nanoarchitecture of the shielding material. The authors prepared self-made samples with two configurations, compact and porous, with variable filler content and thickness. The filler content used varies from 10 wt% to 90 wt%. The authors tested four different systems: thin (i) and thick (ii) compact laminates and thin (iii) and thick (iv) porous coatings. The morphology of the material prepared was investigated using scanning electron microscopy. Based on the experiments, the authors found the well-known fact that the material morphology significantly influences its electromagnetic response in terms of reflection and absorption in the X band. The authors declare that in the X band, the disordered structures predominate absorption, while highly aligned structures predominate reflection.

POSITIVE ASPECTS

1. Based on a literature review, the authors point out the issues associated with electromagnetic interference, the material properties necessary for good shielding efficiency, and the advantages of graphene for efficient EMI shielding.
2. The authors investigated the EMI shielding properties of graphene nanoplatelets in the X band.
3. The authors considered in the experiment two different configurations, compact and porous, varying the filler content and the thickness of the sample.
4. The authors tested four different systems: thin (i) and thick (ii) compact laminates and thin (iii) and thick (iv) porous coatings.
5. The authors comment on which structures absorption or reflection in the microwave band of the electromagnetic spectrum in the range of 8-12 GHz is predominant.

ISSUES

My comments are merely editorial (of minor type). I have a few comments that can be used to improve the article.

Minor issues
1. On line 81, the authors introduce an unusual physical unit, but not explained until later on lines 217 to 218. Each lesser-known physical unit (SEET) must be explained the first time it is mentioned.
2. The meaning of the acronym “GO” is not explained at all. Correct accordingly throughout the article.

CONCLUSION

I find this article helpful. Regretfully, the paper cannot be accepted in its present form. The authors of the present article have to correct the issues.

Author Response

The authors are gratefully to the reviewer for his suggestions and comments. Please find below a point by point response to the issues detected within the paper.

• On line 81, the authors introduce an unusual physical unit, but not explained until later on lines 217 to 218. Each lesser-known physical unit (SEET) must be explained the first time it is mentioned.

According to the reviewer comment, the SSE parameter has been explained in the text when it is introduced within the manuscript (lines 87-88). The manuscript has changed as follows:

“… These materials are able to block and absorb 99.99995% of the incident radiation, and exhibit a SE of 63.0 dB and a very high specific shielding effectiveness (SSE, namely SE divided by specimen density and thickness) of 49750 dB cm²/g….”

• The meaning of the acronym “GO” is not explained at all. Correct accordingly throughout the article.

The acronym GO has been explicated in the text (line 87). The manuscript has changed as follows:

“… Finally, Lai et al. [19] investigated the SE of graphene oxide (GO) paper with porous architecture….”

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript is one of many papers related to EMI shieling efficiency of graphene nano platelets-based composites vs the concentration of nano-filler as well as samples porosity.

The paper does not comprise enough new information to be accepted for publication in its present view.

How and why porosity influence the electromagnetic performance? do you think there is crytical porosity when reflective composite becomes absorptive?

What is the role of GNP dispersion state? What if they are agglomerated? Whether they will work with the same efficiency as well-dispersed nanoparticles?

What is the role of GNP parameters (the number of layers in it, lateral dimensions)?

What is the role of composutes thickness? Is it possible to suppress reflection for certain thicknesses?

Can you reconstruct dielectric permittivity from the measurements data, which will help to understand better the possible advantages of the fabricated composites?

Author Response

• How and why porosity influence the electromagnetic performance? do you think there is critical porosity when reflective composite becomes absorptive?

The shields mostly reflect back signals due to the mismatch of impedance between the propagating signal medium and the shield surface. The relative volume of air entrapped within the porous framework facilitates better impedance matching. The porous network of conducting nanofillers also provides multiple filler–polymer interfaces that will result in multiple internal scatterings or reflections [Ref]. The quest for a critical configuration for triggering the behaviour from reflective to absorptive is suggestive, nevertheless we believe that such an analysis could be performed after an electromagnetic model of the material has been assessed. We are currently working on this point.

[Ref] Pai AR, Azeez NP, Thankan B, Gopakumar N, Jaroszewski M, Paoloni C, et al. Recent Progress in Electromagnetic Interference Shielding Performance of Porous Polymer Nanocomposites&mdash;A Review. Energies 2022, Vol 15, Page 3901 2022;15:3901. https://doi.org/10.3390/EN15113901.

• What is the role of GNP dispersion state? What if they are agglomerated? Whether they will work with the same efficiency as well-dispersed nanoparticles?

In the present work, we presented nanocomposites made by spray coating, the hierarchical ordered structure is obtained as results of a deposition stage and a further calendering process. The “porous state” discussed is related to the semifinished system including nanoplatelets, deposited through the spray process, bonded by a low amount of polymer and cured in order to freeze the structure. In nanocomposites at high filler content (>50%wt), there are empty interstitial volumes inside the material due to the lack of compaction. In the author’s opinion, agglomerates could contribute in creating filler–polymer interfaces that can contribute to internal scatterings or reflections. On the other hand, agglomerates reduce the electrical conductivity affecting the overall shielding property.

• What is the role of GNP parameters (the number of layers in it, lateral dimensions)?

Graphite nanoplatelets used in the present work have a lateral size of 30 µm and a thickness of 14 nm (about 40 layers). The supplier and the geometrical parameters of nanoplatelet are reported in the Material and Methods section.

• What is the role of composites thickness? Is it possible to suppress reflection for certain thicknesses?

In general, the amplitude of the reflection coefficient can vary as function of the sample thickness, exhibiting minima. These minima can be very small depending on the configuration, particularly when the sample can be assumed lossless.

• Can you reconstruct dielectric permittivity from the measurements data, which will help to understand better the possible advantages of the fabricated composites?

We are currently working on reconstructing the dielectric permittivity of the material.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

SUMMARY

The authors deal with the issue of the EMI shielding properties in the X band of high-content graphene nanoplatelets nanocomposites. The authors investigated the effect of filler content and the nanoarchitecture of the shielding material. The authors prepared self-made samples with two configurations, compact and porous, with variable filler content and thickness. The filler content used varies from 10 wt% to 90 wt%. The authors tested four different systems: thin (i) and thick (ii) compact laminates and thin (iii) and thick (iv) porous coatings. The morphology of the material prepared was investigated using scanning electron microscopy. Based on the experiments, the authors found the well-known fact that the material morphology significantly influences its electromagnetic response in terms of reflection and absorption in the X band. The authors declare that in the X band, the disordered structures predominate absorption, while highly aligned structures predominate reflection.

POSITIVE ASPECTS

1. Based on a literature review, the authors point out the issues associated with electromagnetic interference, the material properties necessary for good shielding efficiency, and the advantages of graphene for efficient EMI shielding.
2. The authors investigated the EMI shielding properties of graphene nanoplatelets in the X band.
3. The authors considered in the experiment two different configurations, compact and porous, varying the filler content and the thickness of the sample.
4. The authors tested four different systems: thin (i) and thick (ii) compact laminates and thin (iii) and thick (iv) porous coatings.
5. The authors comment on which structures absorption or reflection in the microwave band of the electromagnetic spectrum in the range of 8-12 GHz is predominant.

CONCLUSION

The authors have addressed all the reviewers comments properly and this present revised manuscript is suitable for publication.

Reviewer 3 Report

I am satisfed with the revised version of manuscript and thisnk it can be published.