Polymer Coatings Based on Polyisobutylene, Polystyrene and Poly(styrene-block-isobutylene-block-styrene) for Effective Protection of MXenes

Round 1

Reviewer 1 Report

The manuscript ‘Polymer Coatings Based on Polyisobutylene, Polystyrene and Poly(styrene-block-isobutylene-block-styrene) for Effective Protection of MXenes’ by Hanna Maltanava et al. devoted to the production of the protective coatings of perspective 2D materials of the MXene family has a significant value for industry-oriented research as it simplifies the transfer of MXene-based technologies to large-scale production allowing the preservation of conductivity of the proposed structures through prevention of MXene oxidation which is one of the challenges in successful MXene applications. The presentation of the research is consistent, logical, without significant errors. The experimental methods correspond to the goals set by the authors. Illustrative material reflects the main results and is well perceived when reading. However, it is worth making a few changes that will improve the perception of research results but will not lead to a significant change in the manuscript itself (mentioned below).

This manuscript can be recommended to be published in MDPI Coatings.

Major remark:

1. Figure 4 represents Raman spectra of MXene films when excited with two different wavelengths. However, it is not clear what reason the spectrum collected at 532 nm is presented for. It is not discussed in the text. It would be also useful to explain whether these spectra reveal any information about the state of the MXene films (number of layers, interlayer distance, orientation, etc.). Are there any differences in spectra of MXene films after the polymer deposition? Could Raman spectra of MXene films with PSt prove the hypothesis of additional stress arising from the polymer? Please, provide corresponding spectra or, at least, discussion in the text.

 Minor remarks:

1. The term MXene is written differently throughout the text. Please, use the common spelling (‘MXene’ instead of ‘Mxene’ in Lines 24, 78, 207. And ‘MXene particles’ instead of ‘MXenes particles’ in Line 68; ‘for’ instead of ‘of’ in Line 211. It is not clear, why ‘RAMAN’ is written in capitals (Line 259).

2. Some misprints, like ‘of’ in ‘to protect of MXene films’ in Line 72. Misprint in units in Line 97 8.65×10^-17 m²∙s^‒1∙Pa^‒17.

3. Please, unify the mathematical signs and the way of writing complex units (Lines 96-100), use ‘L’ instead of ‘l’ for volume in Lines 133, 153; pay attention to subscripts (Lines 147, 180 – subscripts instead of lower case)

4. Figure 3 (b) needs to be mentioned in the text.

5. Excitation wavelengths for Raman measurements mentioned in methods and in Figure 4 differ (785nm vs. 784 nm). Please, unify.

6. Unification of the Figure representations and axes labels should be done (units, etc.).

7. Please, remove extra brackets in the caption of Figure 5.

8. Figure 6 includes two plots, but there is no explanation and no (a)/(b) labels. Please, clarify.

9. Please, remove the duplicates of abbreviations (Lines 262-263) and Line 261.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

In the abstract, Mxene should be replaced with MXene. Kindly make this correction throughout the manuscript.

The introduction needs a significant improvement. It should be precise and well aligned with the topic of the manuscript.

More results are focused on the characterization of MXene and thin films, while it is only one result to study the oxidation of MXene thin films.

What are the possible interactions between the MXene thin films and polymers?

To what extent could the degree of oxidation be controlled by using this protection method?

What is the rate of oxidation for MXene thin films? How do the authors control the environment to study the oxidation behavior of MXene thin films?

How do authors make sure that the films are completely dried?

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

This manuscript reported some information about the synthesis of the MXene film and MXene-polymer coatings toward effective protection of MXene against oxidation. However, the data in this paper is not rich enough. The ultimate purpose of materials preparation is application that is missing. Moreover, this paper is insufficient from the view point of novelty. Therefore, it is not recommended to be published in this journal. The main concerns are as follows:

>1. In the Introduction, the novelty of paper should be strengthened.

>2. The abbreviations have been given in the text, so the abbreviations should be used throughout the rest of the text, such as polyisobutylene (PIB), polystyrene (PSt), et al.

>3. The experiments about the application of MXene-polymer coatings should be done.

>4. Some important data should be added, such as the low magnification TEM image of Ti₃C₂Т_х, SEM image of Ti₃AlC₂ MAX, and Raman spectra of Ti₃AlC₂ MAX and MXene-polymer.

>5. On the line 194, the ‘Ti₂AlC₂ MAX’ should be changed to ‘Ti₃AlC₂ MAX’.

>6. The authors said that ‘Successful synthesis of Ti₃C₂T_x MXene was proved by the absence of characteristic reflexes of the Ti₂AlC₂ MAX phase and an increase in the interlayer distance, as evidenced by the shift of the 00l reflexes toward a lower 2θ value’. What does the absence of characteristic reflexes of the Ti₃AlC₂ MAX phase ? From Figure 2, the (002) characteristic peak shifts toward smaller angle instead of (001) peak.

>7. Why does the peak located at 124 cm^-1 occur at 784 nm excitation wavelength compared with 532 nm ? A detailed discussion should be added.

>8. The English language of the present manuscript needs to be further improved.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 4 Report

The manuscript is interesting and well organized. Before acceptance, some revisions are needed. 

1. please use unit of wt%;

2. please supply the facility for measuring electrical conductivity and testing method.

3. please give the molar ratio of Ti, Al, and TiC for synthesizing Ti3AlC2.

4. since the polymer coating is very thick, what is the reason inducing the decrease of electrical conductivity of Mxene film? water or oxygen? please explain more about the mechanisms.

5. please supply the XRD patterns of Mxene after long term exposion for comparison. 

6. please polish the manuscript again. 

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 5 Report

In this manuscript, Maltanava et. al studied the effect of the presence of 3 different polymeric coatings on the protection of MXene films. MXene films were prepared by drop casting of colloidal solutions in glass substrates, and drying. On top of the obtained films, 10 wt% PSt, PIB and SIBS solutions in toluene were added by drop casting to form the protective layer. Characterization of Mxene films was performed with SEM, Raman, and XRD analyses. Characterization of polymer coated samples were only performed by SEM. The degree of protection of Mxene coatings by different polymeric coatings was only studied by resistivity studies. In its current form, the results section is mainly composed of characterization of MXene film (Figures 1,2,3,4) which has zero novelty. And only Figure which is related to the main idea of the article which is protection of the MXene films are Figure 4 and 5. Even though the obtained result is very interesting, the study is very weak in terms of material characterization. Therefore, I cannot accept the article in its current form. In below you can find my suggestions to improve the quality of the manuscript.

 

Comment 1:

In the introduction it was mentioned that protection of MXene films by coating of polymers have not been described. Is there similar studies in the literature where this approach was used for the protection of other 2D materials such as graphene, etc. ? If so please cite relevant literature.

Comment 2:

Since the synthesis of SIBS was performed, its sufficient characterization should be provided in the supplementary section including FTIR, 1H-NMR, GPC data. For the other two polymers it was said that molecular-weight but is it number average or weight average ? Also you used mw/mn without defining what these abbreviations are ! Please first define the abbreviation whenever it is used for the first time.

Comment 3:

Please perform EDX characterization of the MXene and MXene-polymer coatings, and provide an elemental analysis by surface mapping. Was the thickness of the MXene film was uniform throughout the sample ? I know that in drop casting method there can be some curvature ? Why you did not chose other casting methods such as spin coating and doctor blade coating which provides more uniform thickness, as can be seen in the following citation: Progress in Organic Coatings, Volume 125, Pages 249-256. In the Figure 5, the thickness of the MXene films looks like 2-4 microns ? but it was mentioned that the thickness was 500 nm in Figure 3 ? The SEM images in Figure 5 have different scales and do not align well. Please re-make those images in the same scale and size. Those SEM images seem to be taken with secondary electron detector, please indicate which detector was used in the materials section. And please include images with BSE detector too, since it provides better contrast in the interface. In Figure 5b, The interface looks straight but the top part is curly, if the polymer was coated on top of the MXene it should be the other way, it looks here like as if MXene was coated on polymer ?

Comment 4:

What is the roughness of the coatings ? You can perform profilometry studies to determine roughness. Please see the following articles: Superhydrophobicity and Durability in Recyclable Polymers Coating, Spontaneous formation of microporous poly (lactic acid) coatings.

Comment 5:

Please provide a schematic to show the experimental design used to measure conductivity and resistivity of the MXene and MXene-polymer coatings.

Comment 6:

In the literature which methods is used to characterize protection of coatings ? Why you only studied the resistivity ? Please elaborate this part of the study more. With just one resistivity experiment, this work cannot be a full article.

Comment 7:

How stable is the MXene-polymer interface, due to the lack of intermolecular interactions I am expecting that MXene cannot bond well with those hydrophobic polymers ? Please provide EDX mapping of the MXene-polymer interface.

Comment 8:

Please improve the English language of the manuscript.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

• This paper is acceptable in present form.

Reviewer 5 Report

My points were addressed by the authors.