Conducting Polymeric Composites Based on Intrinsically Conducting Polymers as Electromagnetic Interference Shielding/Microwave Absorbing Materials—A Review

Round 1

Reviewer 1 Report

This manuscript presents a review on the electromagnetic interference shield effectiveness and microwave absorbing properties of conducting polymers and its composites. The related theory of electromagnetic attenuation mechanism is also briefly presented. However, minor revision is recommended before acceptance.

The following are some suggestions:

1. The Table content needs to be carefully checked to ensure consistency with the text. References cited in Tables are inconsistent with the descriptions in the text.
2. In line 334-335, is it appropriate to attribute molar mass, crystallinity, doping level and counter ion electronic structure (polarons and biopolarons) to the structure of intrinsically conductive polymers?
3. It is suggested that the Title of 2.2 should be revised to correspond to 2.1 and that it might be more appropriate to change it to “Absorption Mechanisms”.
4. There are many abbreviations in this manuscript, please note whether the full name given at the first appearance and note the unification of them in the full text. Recommends that the author review the full text.

For example:

1. “intrinsically conducting polymers (ICP)” in line 56, “ICPs” in line 65, “intrinsically conducting polymers” in line 81;
2. “PAni” in line 337 but “Pani” in line 646;

  ……

Author Response

We would like to thank the comments and suggestions of reviewer 1. We tried to make all modifications suggested, as explained:

This manuscript presents a review on the electromagnetic interference shield effectiveness and microwave absorbing properties of conducting polymers and its composites. The related theory of electromagnetic attenuation mechanism is also briefly presented. However, minor revision is recommended before acceptance.

The following are some suggestions:

1. The Table content needs to be carefully checked to ensure consistency with the text. References cited in Tables are inconsistent with the descriptions in the text.

Answer: Yes. Some mistakes have been made. We revised all references in the whole text and in Tables.

1. In line 334-335, is it appropriate to attribute molar mass, crystallinity, doping level and counter ion electronic structure (polarons and biopolarons) to the structure of intrinsically conductive polymers?

Answer: The paragraph may cause misunderstanding. We changed the sentence for this one “The most popular ICP is polyaniline due to its easy preparation, low cost of the reagents, redox tunability and reversible transformation of the insulating/ conducting form by a simple protonation/deprotonation process [68,72]. A huge amount of papers and reviews discusses different procedure for the synthesis of ICP [68-75]. The different methodologies including temperature, stirring, nature of protonting agent , doping level, solvent, etc exert great influence on the crystallinity and electronic structure (polarons and bipolarons) of ICP. Thus, by adjusting the synthesis conditions, a good level of conductivity and outstanding EMI shielding effectiveness may be easily achieved”.

1. It is suggested that the Title of 2.2 should be revised to correspond to 2.1 and that it might be more appropriate to change it to “Absorption Mechanisms”.

Answer: We changed the title to “Absorption Mechanism”

1. There are many abbreviations in this manuscript, please note whether the full name given at the first appearance and note the unification of them in the full text. Recommends that the author review the full text.

For example:

1. “intrinsically conducting polymers (ICP)” in line 56, “ICPs” in line 65, “intrinsically conducting polymers” in line 81;
2. “PAni” in line 337 but “Pani” in line 646;

Answer: We revised all text to avoid this type of mistakes.

Reviewer 2 Report

The review article reports on recent advances in microwave absorbing composites based on Intrinsically Conductive Polymers (ICPs). This is one of the interesting topics and continuous development going on in the field. Therefore, the review article may help the interested reader better understand the topic and recent developments. 

However, significant improvements needed technical aspects and proofreading—a considerable revision required before publication. 

Here are major comments.

- Title: The title indicates a broad coverage, but the actual coverage is narrow to few specific applications. The title is misleading and should be revised.

-Abstract: The abstract should provide a summary of the findings, rather than just providing an introduction. The author should emphasize the motivation of the review and what significant findings got through the study. And how this review article helps the readers.    

- In section 2: Introduction 

1. The author missed the several cited while claiming statements. The author should carefully cite every claim. For examples, page 1, line 27-29; line 31-35; line 41-42. It is requested to review the draft thoroughly and cite whenever needed. 
2. Introduction failed to develop the importance of the current review attempt. Therefore, it is suggested that the author should discuss the existing review articles and highlighted the importance of the current over the existing reviews on the topic.     

- In section 2: EM Shielding Mechanism

1. The author discussed the various equations to quantify the mechanism. However, it failed to discuss the shielding mechanism. For example, Figure 1 represents the different mechanisms. However, they are not appropriately addressed in the text. The author should discuss the importance of these mechanisms and explain each parameter label in figure 1. 
2. In general, it is essential to mention the units while mentioning variables in an equation. Unfortunately, the author failed to mention all equations. Nevertheless, it is very much important, especially for equations 3 and 4.      
3. It is unclear what is the meaning of the term mention in the brackets on Page 4, lines 28 and 35 while discussing the dielectric and magnetic loss. 
4. ‘Skin depth’ is one of the critical parameters associated with the EM shielding study; the author failed to discuss it. Please discuss it properly. The author can refer to to the paper. [Das, S., Sharma, S., Yokozeki T., & Dhakate, S.; Conductive layer-based multifunctional structural composites for electromagnetic interference shielding. Composite Structures. 20201110 DOI: https://doi.org/10.1016/j.compstruct.2020.113293]

- In section 3: Techniques for measuring

1. Labels in Figures 2 and 3 are hard to readable. Please relabel with visible font size.
2. ‘NRW algorithmic’ reference missing on Page 8,, line 93.
3. Equations 14 and 15 need to be verified. The mentioned reference didn’t show such an equation. S21 and S11 are the S-parameter that can’t use directly to calculate the SE and SL. Please review the corresponding theories. The author also can refer to the above mention paper for the conversion.       

- In section 4: EMI SE and microwave …

1. The summary of the paper is not the only what the reader expects to read from the review paper. It is recommended to highlight each paper's limitation and significant findings, and the further scope of those studies. So that ready can find an idea for future research in the field. 
2. EMI SE is always associated with frequency range, which is missed on Page 10, Line 56. 

- Although some summary tables are included, the paper lacks a comparative narrative. The different solutions offered should be compared in terms of some standard metrics (e.g., conductivity) to facilitate drawing some general conclusions on where the most significant improvement is provided to drive future development.

- Sanjay Dhakate and the group significantly contributed to Polyaniline-based EMI shielding; the author should review their works for more comparison data.

‘Multi-walled carbon nanotube–graphene–polyaniline multiphase nanocomposite with superior electromagnetic shielding effectiveness, TK Gupta, BP Singh, RB Mathur, SR Dhakate, Nanoscale 6 (2), 842-851’

- In thermoset polymer development for EMI shielding, the below work shows interesting findings and discussed the dielectric properties; the author should review for a comparison with other similar works.  

‘Frequency independent AC electrical conductivity and dielectric properties of polyaniline-based conductive thermosetting composite, V Kumar, S Das, T Yokozeki - Journal of Polymer Engineering, 2018.’

- Lastly, please reconsider the grammatical mistakes. 

- Also, please consistent with acronyms. Once defined, keep using the rest of the paper. Don’t reintroduce at every section. ICP has been reintroduced several times. Please check all the others also.

- Define acronyms before using them. For example, DBSA is not defined before use. Please check for all others.

Author Response

Review 2

We would like to thank the comments and suggestions of reviewer 1. We tried to make all modifications suggested, as explained:

The review article reports on recent advances in microwave absorbing composites based on Intrinsically Conductive Polymers (ICPs). This is one of the interesting topics and continuous development going on in the field. Therefore, the review article may help the interested reader better understand the topic and recent developments. 

However, significant improvements needed technical aspects and proofreading—a considerable revision required before publication. 

Here are major comments.

- Title: The title indicates a broad coverage, but the actual coverage is narrow to few specific applications. The title is misleading and should be revised.

Answer: We changed the title. Additionally, we added some other examples in the text related to hybrid materials to make a broader covering of the subject.

-Abstract: The abstract should provide a summary of the findings, rather than just providing an introduction. The author should emphasize the motivation of the review and what significant findings got through the study. And how this review article helps the readers.

Answer: we added some new information in the abstract. We hope to properly answer the reviewer’s suggestion.

- In section 2: Introduction 

1. The author missed the several cited while claiming statements. The author should carefully cite every claim. For examples, page 1, line 27-29; line 31-35; line 41-42. It is requested to review the draft thoroughly and cite whenever needed. 

Answer: we included different references to state the claims proposed in the Introduction.

2. Introduction failed to develop the importance of the current review attempt. Therefore, it is suggested that the author should discuss the existing review articles and highlighted the importance of the current over the existing reviews on the topic.

Answer: We included some discussion related to other reviews and tried to emphasize the importance of the present document for helping the reader with the importance of using intrinsically conducting polymer as filler and coatings for polymer composites.      

- In section 2: EM Shielding Mechanism

1. The author discussed the various equations to quantify the mechanism. However, it failed to discuss the shielding mechanism. For example, Figure 1 represents the different mechanisms. However, they are not appropriately addressed in the text. The author should discuss the importance of these mechanisms and explain each parameter label in figure 1. 

Answer: We changed some paragraphs to include this discussion Just after the Figure 1 is cited. We hope this new version is clearer.

1. In general, it is essential to mention the units while mentioning variables in an equation. Unfortunately, the author failed to mention all equations. Nevertheless, it is very much important, especially for equations 3 and 4. 

Answer: We added the unit in all equations. We believe we have not forgotten any equations.

1. It is unclear what is the meaning of the term mention in the brackets on Page 4, lines 28 and 35 while discussing the dielectric and magnetic loss.

Answer: The terms are related to loss tangent. But we eliminated to avoid misunderstanding.

1. ‘Skin depth’ is one of the critical parameters associated with the EM shielding study; the author failed to discuss it. Please discuss it properly. The author can refer to to the paper. [Das, S., Sharma, S., Yokozeki T., &Dhakate, S.; Conductive layer-based multifunctional structural composites for electromagnetic interference shielding. Composite Structures. 20201110 DOI: https://doi.org/10.1016/j.compstruct.2020.113293]

Answer: We included this discussion and also the references suggested (ref 29 in this new version).

- In section 3: Techniques for measuring

1. Labels in Figures 2 and 3 are hard to readable. Please relabel with visible font size.

Answer: The Figures were re-drawn to emphasize the labels

2. ‘NRW algorithmic’ reference missing on Page 8,, line 93.

Answer: We included the reference (ref 65 in this new version of the manuscript)

3. Equations 14 and 15 need to be verified. The mentioned reference didn’t show such an equation. S21 and S11 are the S-parameter that can’t use directly to calculate the SE and SL. Please review the corresponding theories. The author also can refer to the above mention paper for the conversion. 

Answer: We changed the equations to better correlate the S-parameters with the SET, SER and SEA. (Equations 15, 16 and 17 in this new version)

- In section 4: EMI SE and microwave …

1. The summary of the paper is not the only what the reader expects to read from the review paper. It is recommended to highlight each paper's limitation and significant findings, and the further scope of those studies. So that ready can find an idea for future research in the field.

Answer: We tried to include some discussion. However, it is hard to compare the results from different groups due to different parameters used to prepare the samples, the different frequency, etc 

1. EMI SE is always associated with frequency range, which is missed on Page 10, Line 56. 

Answer: We try to associate the EMI SE with the frequency range in the whole document.

- Although some summary tables are included, the paper lacks a comparative narrative. The different solutions offered should be compared in terms of some standard metrics (e.g., conductivity) to facilitate drawing some general conclusions on where the most significant improvement is provided to drive future development.

Answer: We tried to make some comparison, but somewhat it is difficult to make because of different systems, different matrices, different frequency range, etc

- Sanjay Dhakate and the group significantly contributed to Polyaniline-based EMI shielding; the author should review their works for more comparison data.

‘Multi-walled carbon nanotube–graphene–polyaniline multiphase nanocomposite with superior electromagnetic shielding effectiveness, TK Gupta, BP Singh, RB Mathur, SR Dhakate, Nanoscale 6 (2), 842-851’

Answer: We have taken into consideration the suggestion of the reviewer and added the suggested reference with some discussion.

- In thermoset polymer development for EMI shielding, the below work shows interesting findings and discussed the dielectric properties; the author should review for a comparison with other similar works.  

‘Frequency independent AC electrical conductivity and dielectric properties of polyaniline-based conductive thermosetting composite, V Kumar, S Das, T Yokozeki - Journal of Polymer Engineering, 2018.’

Answer: We revised the part related to thermosetting materials and include this paper and other related to the same subject and the same research group.

- Lastly, please reconsider the grammatical mistakes. 

Answer: We made a careful revision in the whole document. We hope to correct all mistakes and typos.

- Also, please consistent with acronyms. Once defined, keep using the rest of the paper. Don’t reintroduce at every section. ICP has been reintroduced several times. Please check all the others also.

- Define acronyms before using them. For example, DBSA is not defined before use. Please check for all others.

 Answer: We made a careful revision in order to use the same acronym and also define it when appears for the first time.

Reviewer 3 Report

Intrinsically conducting polymers are widely used in EMI shielding and MA. This article is a meaningful summary of the latest research results of ICPs in this field. The structure is reasonable and the classification is clear. Therefore, this article can be accepted for publication after addressing the following comments.

1. Equation 8 is unfinished.
2. EMI SE is the abbreviation for electromagnetic interference shielding efficiency. The word “interference” is missing in Line 91 and Line 318.
3. Section 4 is too long and it is better to be divided into several subsections.
4. There is an inaccurate understanding of reflection loss (RL) in Line 555-557. RL describes the loss due to reflection, according to the Equation 11. So RL < -10 dB only means less than 10% of the electromagnetic energy is dissipated by reflection. The rest of the electromagnetic waves are absorbed or permeated. The rest electromagnetic waves may be absorbed or may pass through the material.
5. In addition, the RL value is always negative, while the EMI SE value is positive. Please make modifications to Line 445, 827, and 665.
6. Effective absorption bandwidth is also an important parameter to describe the absorbing ability of materials, which is missing in this manuscript.
7. A summarizing discussion on the pros and cons of the different preparation methods should be added in Section 5.1.
8. The prospect of ICPs in the field of EMI shielding or MA is weak.

Author Response

We would like to thank the comments and suggestions of reviewer 1. We tried to make all modifications suggested, as explained:

Intrinsically conducting polymers are widely used in EMI shielding and MA. This article is a meaningful summary of the latest research results of ICPs in this field. The structure is reasonable and the classification is clear. Therefore, this article can be accepted for publication after addressing the following comments.

1. Equation 8 is unfinished.

Answer: We must apologize for this mistake. The equation was completed.

1. EMI SE is the abbreviation for electromagnetic interference shielding efficiency. The word “interference” is missing in Line 91 and Line 318.

Answer: We included the word “interference” in all sentences related to EMI SE.

1. Section 4 is too long and it is better to be divided into several subsections.

Answer: We agree with the reviewer and make some division.  We also included some informations related to hybrid materials.

1. There is an inaccurate understanding of reflection loss (RL) in Line 555-557. RL describes the loss due to reflection, according to the Equation 11. So RL < -10 dB only means less than 10% of the electromagnetic energy is dissipated by reflection. The rest of the electromagnetic waves are absorbed or permeated. The rest electromagnetic waves may be absorbed or may pass through the material.

Answer: We agree with the reviewer. In fact, the RL was measured using a metal backed plaque. Thus, one measures only the amount of reflected radiation. We correct the signal in all document and use negative value for RL and positive value for SET, etc.  

1. In addition, the RL value is always negative, while the EMI SE value is positive. Please make modifications to Line 445, 827, and 665.

Answer: We made a revision in the whole document and corrected the signal.

1. Effective absorption bandwidth is also an important parameter to describe the absorbing ability of materials, which is missing in this manuscript.

Answer: We included this parameter, mainly for the systems using hybrid materials.

1. A summarizing discussion on the pros and cons of the different preparation methods should be added in Section 5.1.

Answer: We try to include some little discussion related to the different methods of preparing the composites.

1. The prospect of ICPs in the field of EMI shielding or MA is weak.

Answer: Yes, we agree with the reviewer. However, they should be important, for example to achieve a balance of absorption properties without increasing density. Moreover, the presence of ICP, mainly in coatings may provide multi-functions to the material, for example, as anti-corrosion agent and also absorbing material. As observed in some systems, the presence of ICP resulted in synergetic effect in terms of microwave absortivity when using hybrid materials.

Reviewer 4 Report

Recent Advances in Microwave Absorbing Composites Based on Intrinsically Conducting Polymers- A Review by   B. G. Soares et al., has elaborated the recent Intrinsically Conducting Polymers based EMI shielding studies where the focus was more on the commonly used ICP Polyaniline and polypyrrole. This review has highlighted the various method to increase the EMI shielding effectiveness of the shielding layer via chemical doping and experimental processing. Overall, the manuscript written in systematically. There are few suggestions and concern about this review which are listed below:

1. The title of the manuscript is about Intrinsically Conducting Polymers.However, the manuscript has focused on various doped and chemically tunned Polymers. Therefore, the intrinsic term is misleading to the readers.
2. There are various grammatical error and few sentences need to reframe. Please check the grammar again.
3. Line 118 change sielectric to dielectric.
4. Equation 8 remove the = after the equation.
5. Could you mention about the reason behind the higher conductivity for PAni CSA sample as mention in figure 5.
6. The mechanism of EMI shielding need to highlight more. In particular, how the polyaniline and polypyrrole can influence the electrical conductivity of the composites. There are always an trade in between high conductivity and impedance matching of the layer. Also, when used as composite filler, the synergetic effect of the conductivity of ICP and the dielectric or magnetic loss arise from the dielectric and magnetic filler leads to higher SE. So the optimum % of the filler need to determined. Please follow the recent articles ( K. Choudhary, R. Kumar, S. P. Pawar, A. V. Anupama, S. Bose, B. Sahoo, ChemistrySelect 2018, 3, 2120. And H. K. Choudhary, S. P. Pawar, R. Kumar, A. V. Anupama, S. Bose, B. Sahoo, ChemistrySelect 2017, 2, 830.).
7. Recently, the applications of carbonaceous fillers such as multiwall carbon nanotubes carbon coated metallic particles and graphene are used as filler for EMI shielding applications and they are shown a good alternative to the ICP for the EMI Shielding and microwave absorption owing to their low cost production ( in recent years), low percolation threshold ( ~5 % ) and higher conductivity than the ICP. There should be an paragraph in this review about where the ICP stand in the competition to these carbonaceous fillers.  Furthermore, the thermal and mechanical stability of these ICP is poor in comparison to the carbonaceous fillers, which make them second choice for microwave absorbing filler. A comparison studies between them will help the reader to choose between them

Author Response

We would like to thank the comments and suggestions of reviewer 1. We tried to make all modifications suggested, as explained:

Recent Advances in Microwave Absorbing Composites Based on Intrinsically Conducting Polymers- A Review by   B. G. Soares et al., has elaborated the recent Intrinsically Conducting Polymers based EMI shielding studies where the focus was more on the commonly used ICP Polyaniline and polypyrrole. This review has highlighted the various method to increase the EMI shielding effectiveness of the shielding layer via chemical doping and experimental processing. Overall, the manuscript written in systematically. There are few suggestions and concern about this review which are listed below:

1. The title of the manuscript is about Intrinsically Conducting Polymers.However, the manuscript has focused on various doped and chemically tunned Polymers. Therefore, the intrinsic term is misleading to the readers.

Answer: We changed the title to avoid misunderstanding. This review intends to focus on the composite prepared by blending conventional insulating polymers with ICP used as conducting fillers.

1. There are various grammatical error and few sentences need to reframe. Please check the grammar again.

Answer: We made a careful revision in the whole document to correct some grammatical errors and typos.

1. Line 118 change sielectric to dielectric.

Answer: The word was corrected.

1. Equation 8 remove the = after the equation.

Answer: The equation was completed.

1. Could you mention about the reason behind the higher conductivity for PAni CSA sample as mention in figure 5.

Answer: The PAni.CSA presented slightly higher crystallinity, which, according to the authors, should contributed for an increase of conductivity. The authors suggest that the hydroxyl group of CSA generates an electron repulsion effect. However, the conductivity of PAni.HCl and PAni.CSA may be considered similar if one takes into account the error of the measure.

1. The mechanism of EMI shielding need to highlight more. In particular, how the polyaniline and polypyrrole can influence the electrical conductivity of the composites. There are always an trade in between high conductivity and impedance matching of the layer. Also, when used as composite filler, the synergetic effect of the conductivity of ICP and the dielectric or magnetic loss arise from the dielectric and magnetic filler leads to higher SE. So the optimum % of the filler need to determined. Please follow the recent articles ( K. Choudhary, R. Kumar, S. P. Pawar, A. V. Anupama, S. Bose, B. Sahoo, ChemistrySelect 2018, 3, 2120. And H. K. Choudhary, S. P. Pawar, R. Kumar, A. V. Anupama, S. Bose, B. Sahoo, ChemistrySelect 2017, 2, 830.).

Answer: We added some section including hybrid materials and tried to better discuss the effect of conductivity and EMI SE. We also included the suggested references.

1. Recently, the applications of carbonaceous fillers such as multiwall carbon nanotubes carbon coated metallic particles and graphene are used as filler for EMI shielding applications and they are shown a good alternative to the ICP for the EMI Shielding and microwave absorption owing to their low cost production ( in recent years), low percolation threshold ( ~5 % ) and higher conductivity than the ICP. There should be an paragraph in this review about where the ICP stand in the competition to these carbonaceous fillers.  Furthermore, the thermal and mechanical stability of these ICP is poor in comparison to the carbonaceous fillers, which make them second choice for microwave absorbing filler. A comparison studies between them will help the reader to choose between them.

Answer: The use of ICP in composites is still interesting because one can improve the absortivity of the system without increasing density too much as normally occurs with ferrite. Carbonaceous materials present high conductivity, and in some case, this feature contributes for an increase of the reflection mechanism. Also, some combination of ICP with other dielectric and/or magnetic materials should give rise to outstanding EMI SE and absortivity  as discussed in several papers in the literature. We try to highlight these advantages in the Conclusion. .

Round 2

Reviewer 2 Report

The current version of the draft is well organized and addresses all the recommendations. 

Reviewer 3 Report

It is now suitable for publication.