Epoxy Resin/Ionic Liquid Composite as a New Promising Coating Material with Improved Toughness and Antibiofilm Activity^†

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this paper, a new type of modified additive for hydrophobic ionic liquids, namely 1-dodecyl-3-methylimidazole dodecylbenzene sulfonate (C₁₂C₁IM-DBS), was first synthesized. Then, C₁₂C₁IM-DBS was dissolved in epoxy resin DER331 for curing to prepare a modified epoxy coating. After infrared treatment, Tests such as spectrophotometer and differential scanning thermal analysis were conducted, and comparisons were made with pure resin. The results showed that it had excellent mechanical properties and anti-film effects. The research in this paper is somewhat innovative and worthy of being recommended for publication, but some problems need to be revised.
1. The title of this article is not in line with the research content of this article and fails to reflect the research characteristics of this article. It needs to be rewritten.
2. The abstract contains unquantifiable data, which is inappropriate for research papers. These are mostly qualitative conclusions and thus need to be revised.
3. In the introduction section, the author has referred to a large number of literature. Please describe the differences between this article and the references, and what the prominent innovativeness is. Which blanks have been filled?
The first paragraph of the introduction is too long. It seems to merely list the literature without any comparative analysis. Therefore, a more in-depth comparative analysis should be conducted to point out the existing deficiencies.
Line 126 on page 3, "In this study,..." A new paragraph should be started to highlight the research content of this article.
6. The amount of wording duplication in the manuscript shows 38%, therefore, it needs to be revised to reduce it to less than 20%.
7. Please explain how the ability test for biofilm attachment is conducted and how to evaluate the anti-film effect of DER 331/C₁₂C₁IM-DBS composites.
8. Why is the cellular biomass of epoxy composites containing 20% ionic liquid significantly reduced, and what is the mechanism?
9. Two Figures 10 appear in the text, and the first Figure 10 should be provided with a ruler, while the second figure 10 should be provided with a color picture; otherwise, it will be difficult to distinguish the four different materials.
10. The conclusion part of this article is overly detailed. Therefore, it is suggested that the author be concise and describe it point by point. It should not be summarized in one or two paragraphs, respectively, which is not convenient for readers to review. Please make revisions.

Author Response

In this paper, a new type of modified additive for hydrophobic ionic liquids, namely 1-dodecyl-3-methylimidazole dodecylbenzene sulfonate (C₁₂C₁IM-DBS), was first synthesized. Then, C₁₂C₁IM-DBS was dissolved in epoxy resin DER331 for curing to prepare a modified epoxy coating. After infrared treatment, Tests such as spectrophotometer and differential scanning thermal analysis were conducted, and comparisons were made with pure resin. The results showed that it had excellent mechanical properties and anti-film effects. The research in this paper is somewhat innovative and worthy of being recommended for publication, but some problems need to be revised.

Comment 1. The title of this article is not in line with the research content of this article and fails to reflect the research characteristics of this article. It needs to be rewritten.

Response 1. Following alternative title could be suggested: “Epoxy resin/hydrophobic ionic liquid composite as promising coating material with improved toughness and antibiofilm activity”.

Comment 2. The abstract contains unquantifiable data, which is inappropriate for research papers. These are mostly qualitative conclusions and thus need to be revised.

Response 2. Thank you. The abstract has been corrected.

Comment 3. In the introduction section, the author has referred to a large number of literature. Please describe the differences between this article and the references, and what the prominent innovativeness is. Which blanks have been filled?

Response 3. In the introduction section, the problem of biofouling of epoxy-based protective coatings has been briefly analyzed, as well as approaches to impart antibiofilm activity in epoxy coatings. We also noted the lack of information in the literature regarding the use of cationic biocides based on long-chain ionic liquids for the protection of epoxy coatings from biofouling. This is precisely the novelty of this article.

Comment 4. The first paragraph of the introduction is too long. It seems to merely list the literature without any comparative analysis. Therefore, a more in-depth comparative analysis should be conducted to point out the existing deficiencies.

Response 4. The introduction also briefly describes multifunctional modifying additives to epoxy resins, which can act as biocides, plasticizers, fire retardants, corrosion inhibitors etc. Analysis of this information helps to better understand the current problems of modifying epoxy coatings and ways to solve them. However, we slightly shortened the introduction part in accordance with the reviewer’s remarks.

Comment 5. Line 126 on page 3, "In this study,..." A new paragraph should be started to highlight the research content of this article.

Response 5. Corrected

Comment 6. The amount of wording duplication in the manuscript shows 38%, therefore, it needs to be revised to reduce it to less than 20%.

Response 6. Corrected

Comment 7. Please explain how the ability test for biofilm attachment is conducted and how to evaluate the anti-film effect of DER 331/C₁₂C₁IM-DBS composites.

Response 7. The biofilm formation has been performed as before and as it was described in Materials and Methods. We apologise for not separating a specific subsection for this analysis so do it now as "2.5. Evaluation of antibiofilm effect" which can be found in Materials and Methods.

Comment 8. Why is the cellular biomass of epoxy composites containing 20% ionic liquid significantly reduced, and what is the mechanism?

Response 8. We hypothesize that the total surface charge provided by C12C1IM-DBS added to the surface might be critically changed for initial bacterial cell attachment when 20% of C12C1IM-DBS was added.

Comment 9. Two Figures 10 appear in the text, and the first Figure 10 should be provided with a ruler, while the second figure 10 should be provided with a color picture; otherwise, it will be difficult to distinguish the four different materials.

Response 9. We apologize for any inaccuracies in the numbering of the figures. One Figure is mistakenly numbered as 10.

Comment 10. The conclusion part of this article is overly detailed. Therefore, it is suggested that the author be concise and describe it point by point. It should not be summarized in one or two paragraphs, respectively, which is not convenient for readers to review. Please make revisions.

Response 10. The conclusion section has been corrected and shortened.

Reviewer 2 Report

Comments and Suggestions for Authors

The paper entitled “New promising coating material based on epoxy resin and hydrophobic ionic liquid” presents the effect of a new synthesized hydrophobic ionic liquid (1-dodecyl-3-methylimidazolium dodecylbenzenesulfonate (C12C1IM-DBS)) on modified composites coated with epoxy resin. The results showed excellent resistance to leaching from the epoxy coating in water; DER 25 331/C12C1IM-DBS composites demonstrated significantly improved impact resistance compared to pure resin; in the presence of Staphylococcus aureus and Pseudomonas aeruginosa a significant decrease in biofilm metabolic activity as well as cell biomass was observed.

Generally, the manuscript is clearly written and succinct, likely appealing to a more specialized audience. Figures and tables effectively present the data, making it easy to interpret and understand. Overall, the conclusions are well presented, and the references cited are predominantly from recent publications.
Due to its methodology, significance and attitude, this research can be accepted for publication after major revisions. 
Detailed comments are as follows:
1.    What is the main objective of the study? The corrosion resistance of the new composite or the resistance to microbiological corrosion or both? It is not specifically clear what the general objective is.
2.    What is the novelty element of the obtained composite? What is new about this study compared to previous studies in the field?
3.    The bibliographic references need to be updated with new ones. Approximately 50% of the references given in the study are older than 10 years. Please use new bibliographic references, mostly from the last 5 years, that are eloquent to your field of study.
4.    Authors can discuss deep learning for the other field and expand the readership. Therefore, corrosion studies that were done using exodidic resin could be cited in the introduction: DOI10.3390/polym17030378,  DOI10.3390/ma14081991 and so on.
5.    Lines 108-110: “The composite material based on commercial epoxy resin and C12C1IM-DBS has been prepared and characterized in terms of their physicochemical properties and antibiofilm activity.” Initially, the authors discussed corrosion properties, not microbiological corrosion (they are forms of corrosion that are studied separately). The authors mentioned in the introduction comparisons with other works and studies on the mechanical properties of new composites with epoxy resin. There is a contradiction regarding the intention of the study and the introduction. The study should focus on certain properties that emerge from the experimental part.
6.    Line 120-127. Mass as substances is in 1 L, 500 mL. The same for 0.12mol, 0.15 mol. The authors gave the mass and the number of moles, without specifying in what quantity the dissolution, the mixture, the molar concentration of the reactants was made. These data are necessary for the process of obtaining the new composites. The data presented are incomplete in this form. 
7.    Lines 145: Why the authors used this concentration (10, 20 and 30% wt%)? Are there previous studies by the authors or in the literature that use these concentrations? Why didn't the authors try using lower concentrations or use 10, 15, 20, 25 and so on?
8.    Line 168: Why the authors conducted studies on Vicker's hardness. Polymers, epoxy resins are not hard materials. The load on the indenter was 100 g. The load is very small, it does not highlight the mechanical properties, if a comparison of the mechanical properties for the new composite material obtained was considered.
9.    For accuracy, please use the value 20.0 in table 1 for the oxygen concentration of the DER 331/C12C1IM-DBS composite (20%)
10.    Figure 4 is legible. Please use a clearer image obtained with SEM.
11.    In figure 7, the authors present UV-spectra only for the DER 331/C12C1IM-DBS composite (30%). Why did the authors not perform UV spectra for 10% and 20% in order to make a relevant comparison between the properties of the new composites obtained?
12.    The values obtained for Vicker's hardness for the types of composites obtained with 10, 20, 30 wt% of C12C1IM-DBS are very close (0.16 GPa, 0.158 GPa and 0.157 GPa). The results obtained can be used to highlight the properties of the new composites compared to epoxy resin type DER 331, but the effect of the concentration of the synthesized hydrophobic ionic liquid on the mechanical properties of the composite cannot be concluded.
13.    Figure 11 is difficult to interpret. Please use contrasting colors so that the attachment of bacteria to the surface, the formation of EPS and biofilm in the presence of attached bacteria can be correctly interpreted.
14.    CLSM imaging of S. aureus is missing. Why didn't the authors perform these studies for Staphylococcus aureus as well?
15.     The study conclusions should be presented much more succinctly.
16.    Please add the shortcomings of this study and the direction of further research in the "Conclusions" part of the review.

Author Response

The paper entitled “New promising coating material based on epoxy resin and hydrophobic ionic liquid” presents the effect of a new synthesized hydrophobic ionic liquid (1-dodecyl-3-methylimidazolium dodecylbenzenesulfonate (C12C1IM-DBS)) on modified composites coated with epoxy resin. The results showed excellent resistance to leaching from the epoxy coating in water; DER 25 331/C12C1IM-DBS composites demonstrated significantly improved impact resistance compared to pure resin; in the presence of Staphylococcus aureus and Pseudomonas aeruginosa a significant decrease in biofilm metabolic activity as well as cell biomass was observed.

Generally, the manuscript is clearly written and succinct, likely appealing to a more specialized audience. Figures and tables effectively present the data, making it easy to interpret and understand. Overall, the conclusions are well presented, and the references cited are predominantly from recent publications.
Due to its methodology, significance and attitude, this research can be accepted for publication after major revisions. 

Detailed comments are as follows:
Comment 1.    What is the main objective of the study? The corrosion resistance of the new composite or the resistance to microbiological corrosion or both? It is not specifically clear what the general objective is.

Response 1. At the end of the introductory part, we noted that the main goal of this work was to synthesize a new promising antimicrobial additive for epoxy resin based on a hydrophobic ionic liquid. It is known from the literature that such compounds can also be effective corrosion inhibitors, but we have not conducted these studies.

Comment 2. What is the novelty element of the obtained composite? What is new about this study compared to previous studies in the field?

Response 2. The novelty of this research lies in the use of a newly synthesized hydrophobic ionic liquid, C₁₂C₁IM-DBS, as an antifouling additive for protective epoxy coatings. As noted in the introduction, there is no literature data on the use of ionic liquids as biocidal additives for epoxy resins. Several studies reported the use of ILs as modifying additives for epoxy resins, which can play the of curing agents, plasticizers, and flame retardants. [Ref. 25, 26].

Comment 3. The bibliographic references need to be updated with new ones. Approximately 50% of the references given in the study are older than 10 years. Please use new bibliographic references, mostly from the last 5 years, that are eloquent to your field of study.

Response 3. We have replaced some older references with more modern ones. However, some references are difficult to replace due to their specificity.

Comment 4. Authors can discuss deep learning for the other field and expand the readership. Therefore, corrosion studies that were done using exodidic resin could be cited in the introduction: DOI 10.3390/polym17030378, DOI 10.3390/ma14081991 and so on.

Response 4. Thanks for these useful references. They have been added to the introduction section (Ref. 1, 5).

Comment 5. Lines 108-110: “The composite material based on commercial epoxy resin and C12C1IM-DBS has been prepared and characterized in terms of their physicochemical properties and antibiofilm activity.” Initially, the authors discussed corrosion properties, not microbiological corrosion (they are forms of corrosion that are studied separately). The authors mentioned in the introduction comparisons with other works and studies on the mechanical properties of new composites with epoxy resin. There is a contradiction regarding the intention of the study and the introduction. The study should focus on certain properties that emerge from the experimental part.

Response 5. In the introduction section, the problem of biofouling of epoxy-based protective coatings has been briefly analyzed, as well as approaches to impart antibiofilm activity in epoxy resins. We have hardly discussed the problem of anti-corrosion properties of epoxy coatings. The analysis of literature data indicates that both inorganic (TiO₂, ZnO, Ag) and organic (DCOIT, polyaminophenol, oregano essential oil etc.) antimicrobial agents can be used to prevent biofouling on the surface of epoxy resins. We also noted that antimicrobial additives can perform additional functions (such as corrosion inhibitors, impact modifiers etc.) in epoxy coatings. From this point of view, hydrophobic long-chain ionic liquids seem especially promising multifunctional modifying additive for epoxy resins, since they are known to combine broad-spectrum biological activity and plasticizing efficacy towards different polymer binders. Thus, the main objective of our work was to develop a new biocidal additive for epoxy resin based on a hydrophobic ionic liquid and study its effect on the main physicochemical properties of protective coatings.

Comment 6. Line 120-127. Mass as substances is in 1 L, 500 mL. The same for 0.12mol, 0.15 mol. The authors gave the mass and the number of moles, without specifying in what quantity the dissolution, the mixture, the molar concentration of the reactants was made. These data are necessary for the process of obtaining the new composites. The data presented are incomplete in this form.

Response 6. This reaction was carried out without a solvent. The mixture of reagents in the indicated ratio was heated and stirred. So, the term "molar concentration of reagents" is not applicable here.

Comment 7. Lines 145: Why the authors used this concentration (10, 20 and 30% wt%)? Are there previous studies by the authors or in the literature that use these concentrations? Why didn't the authors try using lower concentrations or use 10, 15, 20, 25 and so on?

Responce 7. This selection of ionic liquid concentrations in the polymer matrix is ​​based on the results of previous studies. It was found that hydrophibic ionic liquids impart antibiofilm and antifouling activity to protective coatings at a sufficiently high content [Ref. 25, 26]. This is probably due to the contact mechanism of antimicrobial activity of the modified epoxy coating, which requires a high content of biocide in the surface layer of the polymer matrix. Changing the concentration in 5% increments has little effect on the anti-biofilm activity of the polymer coatings. The step with a change in concentration by 10% is also optimal for studying the plasticizing effect of the additive on epoxy resin.

Comment 8. Line 168: Why the authors conducted studies on Vicker's hardness. Polymers, epoxy resins are not hard materials. The load on the indenter was 100 g. The load is very small, it does not highlight the mechanical properties, if a comparison of the mechanical properties for the new composite material obtained was considered.

Response 8. The Vickers method was chosen to study the microhardness of the structure using the stationary HV-1000 hardness tester, since this device is equipped with a diamond pyramidal indenter with an angle of 136°, with automatic loading and unloading (measurement accuracy ± 0.031 μm), which allows obtaining a symmetrical imprint, convenient for accurate measurement of the microhardness of not only metals, ceramics and hard alloys, but also polymers such as epoxy resins. For example, in the Knoop method, unlike the Vickers method, an elongated rhombic pyramid with asymmetric angles of 172.5° for the long diagonal and 130° for the short one is used. This shape of the indenter makes it especially effective for measuring the hardness of brittle or polycrystalline composite materials that have large grain sizes in the bundle, and not very effective for polymers. A load of 100 g is standard and quite acceptable for assessing the microhardness of epoxy resins. Although these materials do not belong to the category of classically hard, the Vickers method with this load allows you to reliably determine their hardness, providing sufficient sensitivity to changes in the structure. Higher loads lead to an increase in the size of the indenter impression, which significantly complicates the accurate determination of hardness on the hardness tester.

Comment 9. For accuracy, please use the value 20.0 in table 1 for the oxygen concentration of the DER 331/C12C1IM-DBS composite (20%).

Response 9. Thank you, it is corrected.

Comment 10. Figure 4 is legible. Please use a clearer image obtained with SEM.

Response 10. We appreciate the reviewer’s comment. We would like to clarify that the SEM images were acquired directly from the instrument without any additional processing. The lower contrast and reduced clarity are due to the use of a 10 keV accelerating voltage, which was intentionally chosen to avoid deformation of the polymer films under the electron beam. This approach typically results in less distinct images, but it is essential for preserving the integrity of the samples. Nevertheless, we have made an effort to improve the image quality in the revised version of Fig. 4.

Comment 11. In figure 7, the authors present UV-spectra only for the DER 331/C12C1IM-DBS composite (30%). Why did the authors not perform UV spectra for 10% and 20% in order to make a relevant comparison between the properties of the new composites obtained?

Response 11. We studied the release of ionic liquid in water from epoxy coatings at a maximum additive content of 30%. Spectrophotometric analysis of aqueous solutions that were in contact with DER 331/C₁₂C₁IM-DBS (30%) coatings for 30 days showed no absorption of ionic liquid (imidazolium cation). Aqueous solutions contacted for 30 days with DER 331/C₁₂C₁IM-DBS (10%) and DER 331/C₁₂C₁IM-DBS (20%) coatings have a similar UV-Vis spectrum as in the case of DER 331/C₁₂C₁IM-DBS (30%). Therefore, we have shown in Figure 7 only one spectrum for the coating with 30% ionic liquid content.

Comment 12. The values obtained for Vicker's hardness for the types of composites obtained with 10, 20, 30 wt% of C12C1IM-DBS are very close (0.16 GPa, 0.158 GPa and 0.157 GPa). The results obtained can be used to highlight the properties of the new composites compared to epoxy resin type DER 331, but the effect of the concentration of the synthesized hydrophobic ionic liquid on the mechanical properties of the composite cannot be concluded.

Response 12. Here we can agree that the microhardness values ​​are very close, and indeed these results do not allow us to draw an unambiguous conclusion about a clear dependence of mechanical properties on concentration. However, we noted this in the text that “…the hardness decreased sharply from 0.215 GPa for pure DER 331 to 0.16 GPa for the epoxy composite…”, and then “…a further increase in the IL content to 20 and 30% had no noticeable effect on the hardness value, which was 0.158 and 0.157 GPa, respectively…”. In this study, microhardness was primarily used for comparison with the base epoxy resin DER 331. Overall, the obtained results indicate that the epoxy resin-ionic liquid composites retain sufficiently good hardness even at a high additive content of 30%.

Comment 13. Figure 11 is difficult to interpret. Please use contrasting colors so that the attachment of bacteria to the surface, the formation of EPS and biofilm in the presence of attached bacteria can be correctly interpreted.

Response 13. The colours shown in Fig.11 correspond to the emission spectra of the applied dyes. The overall contrasting is dependent on the object size and the structure of EPS of biofilms. To improve the quality of Fig.11 the dpi was changed from 150 to 300. We hope this will improve contrast perception, too.

Comment 14. CLSM imaging of S. aureus is missing. Why didn't the authors perform these studies for Staphylococcus aureus as well?

Response 14. We did but since there was no biofilm of SA observed (Fig.10) and the initial autofluorescence of the coating was observed we decided not to include the images of the tested surface as there is no story to tell behind them.

Comment 15. The study conclusions should be presented much more succinctly.

Response 15. Conclusions have been shortened.

Comment 16. Please add the shortcomings of this study and the direction of further research in the "Conclusions" part of the review.

Response 16. At the end of the conclusions, we briefly outlined the direction of further research that is necessary to assess the further prospects for using the developed material.

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript presents a method for formulating a coating using a synthesized ionic liquid with functional properties. The work is of interest from both scientific and practical perspectives. The manuscript is informative and is recommended for publication following minor revisions.

1. In Section 2.2, lines 124–126, the reviewer suggests that a prior explanation may be needed, as indicated in lines 133–135. If this is the case, please revise the text accordingly to ensure logical flow.
2. For improved clarity, it is recommended to include the names of each compound as presented in the manuscript, which would aid reader comprehension.
3. It is suggested to correlate Scheme 1 with the FTIR results to strengthen the analysis. The authors are encouraged to present the corresponding IR characterisation of the compounds formed after the reactions.
4. In Figure 2, the spectral bands should be indexed correctly in alignment with the discussion in the text. Additionally, it is recommended to revise the figure caption for enhanced clarity and understanding.
5. In line 279, please clarify the structural context of the "-C-C-O-C-" moiety mentioned in the vibrational analysis. It is not clear whether this refers to an ether linkage (C–O–C), an ester group, or another functionality. The use of standard IUPAC or spectroscopic terminology (e.g., “C–O stretching in ethers”) would improve the clarity.
6. The same clarification is required for the "-O-C-C" moiety in line 282.
7. A more detailed description of Scheme 2 is recommended, and the names of each compound should be included as they appear in the manuscript to assist the reader.
8. In Section 3.2, the analysis of the IL distribution appears unclear, as Figure 3 displays very similar images. Therefore, the statement in lines 313–314 seems inadequate. This section should be revised to clarify the observed differences, or potentially omitted if they do not contribute significantly to the overall findings.
9. The quality of Figure 7 requires improvement for a more effective visual presentation.
10. In lines 198–205, XPS measurements are mentioned; however, no corresponding results are presented. Please include this information, as it would reinforce the manuscript and the interactions discussed therein.

Comments on the Quality of English Language

There are minor areas where the language can be refined for improved clarity and readability. Checking grammatical accuracy and refining sentence structure can enhance overall readability.

Author Response

The manuscript presents a method for formulating a coating using a synthesized ionic liquid with functional properties. The work is of interest from both scientific and practical perspectives. The manuscript is informative and is recommended for publication following minor revisions.

Comment 1. In Section 2.2, lines 124–126, the reviewer suggests that a prior explanation may be needed, as indicated in lines 133–135. If this is the case, please revise the text accordingly to ensure logical flow.

Response 1. If we understood correctly, it was necessary to provide a description of the product C₁₂C₁IM-Cl (a precursor for the synthesis of the ionic liquid C₁₂C₁IM-DBS). This description has been added.

Comment 2. For improved clarity, it is recommended to include the names of each compound as presented in the manuscript, which would aid reader comprehension.

Response 2. Thanks for this useful remark. In section 2.2 we provided the full names of the synthesized compounds and their abbreviations. Further in the text the corresponding abbreviation was used to designate the ionic liquid.

Comment 3. It is suggested to correlate Scheme 1 with the FTIR results to strengthen the analysis. The authors are encouraged to present the corresponding IR characterisation of the compounds formed after the reactions.

Response 3. Thank you for this insightful comment. Indeed, the reaction Scheme 1 depicts the synthesis of water-soluble ionic liquid C₁₂C₁IM-Cl (precursor), which was further converted into the final product, hydrophobic ionic liquid C₁₂C₁IM-DBS. The structure of both synthesized compounds was confirmed by nuclear magnetic resonance (¹H NMR) spectroscopy, which is more accurate method than IR-analysis. Infrared spectra were obtained only for the main product C₁₂C₁IM-DBS and its composites with epoxy resin, in order to study the physicochemical interactions between the coating components.

Comment 4. In Figure 2, the spectral bands should be indexed correctly in alignment with the discussion in the text. Additionally, it is recommended to revise the figure caption for enhanced clarity and understanding.

Response 4. Figure 2 has been corrected. It shows the wavelengths for the main absorption bands of the ionic liquid, epoxy resin, and their compositions, which are discussed in the text.

Comment 5. In line 279, please clarify the structural context of the "-C-C-O-C-" moiety mentioned in the vibrational analysis. It is not clear whether this refers to an ether linkage (C–O–C), an ester group, or another functionality. The use of standard IUPAC or spectroscopic terminology (e.g., “C–O stretching in ethers”) would improve the clarity.

Response 5. We have specified the assignment of the IR bands of functional groups in the text.

Comment 6. The same clarification is required for the "-O-C-C" moiety in line 282.

Response 6. Corrected. We have indicated more precisely the functional groups of the epoxy resin to which the corresponding absorption bands in the IR spectrum belong.

Comment 7. A more detailed description of Scheme 2 is recommended, and the names of each compound should be included as they appear in the manuscript to assist the reader.

Response 7. The results of IR analysis of epoxy resin/ionic liquid composites indicate a significant decrease in the intensity of the absorption band of the hydroxyl groups C-OH of the resin. This may indicate the involvement of OH groups in the formation of hydrogen bonds with the polar groups of the ionic liquid. In Figure 2, we have designated the polar groups in the cation and anion of the ionic liquid that are capable of forming hydrogen bonds with the hydroxyl groups of the epoxy resin. Unfortunately, the band at 3151 cm^-1 which is assigned to the bending vibrations of C-H bonds of the imidazolium cation has very low intensity, and it is impossible to determine its position in the epoxy/ionic liquid composite. As for another polar group of the ionic liquid, SO₃^- anion, its bands at 1213 and 1033 cm^-1 overlap with the bands of C-O-C stretching vibrations of the epoxy resin. Therefore, we can only speculate on possible physicochemical interactions between the ionic liquid and the hydroxyl groups of the epoxy resin, as shown in Scheme 2.

Comment 8. In Section 3.2, the analysis of the IL distribution appears unclear, as Figure 3 displays very similar images. Therefore, the statement in lines 313–314 seems inadequate. This section should be revised to clarify the observed differences, or potentially omitted if they do not contribute significantly to the overall findings.

Response 8. We appreciate your valuable comment. In response, Figure 3 has been moved to the Supplementary Information section to improve the flow and clarity of the main text. The corresponding text in Section 3.2 has been revised to the following: "Complementary EDX mapping (Fig. S1) reveals the presence and uniform distribution of Nitrogen (N) and Sulfur (S) atoms throughout the bulk of all samples, indicating effective incorporation of the ionic liquid." It is worth noting that the purpose of the EDX mapping was to qualitatively, not quantitatively, assess the homogeneous distribution of the ionic liquid within the polymer matrix. It is also important to mention that the applied 3 nm thick platinum coating (used to prevent potential sample degradation during EDX mapping) combined with the extended acquisition time required for statistically reliable spectra, reduced the apparent intensity of the detectable elements. Nevertheless, quantitative insights into the elemental composition are provided in Table 1 and the EDX spectra (Fig. 3).

Comment 9. The quality of Figure 7 requires improvement for a more effective visual presentation.

Response 9. Figure 7 has been adjusted to improve its visual quality.

Comment 10. In lines 198–205, XPS measurements are mentioned; however, no corresponding results are presented. Please include this information, as it would reinforce the manuscript and the interactions discussed therein.

Response 10. Thank you for your observation. In response, we have included the relevant XPS results in the revised manuscript. The XPS survey spectra (Figure S2), along with the S 2p (Figure 5) and N 1s (Figure S3) core-level spectra, have been added to the Supplementary Information and main figures. The following text has also been included in the manuscript to reflect this addition: "Surface analysis by XPS (Figures 5, S2, and S3) further supports these findings. In particular, Figure 5 demonstrates an increase in sulfur content at the composite surface with increasing amounts of the ionic liquid. Notably, the sulfur content at the surface shows only a slight increase between 10 wt% and 20 wt% ionic liquid loading. However, at 30 wt%, a more pronounced increase of the sulfur peak is observed. This may suggest that at higher iolic liquid concentrations, the epoxy matrix becomes less capable of fully incorporating the additive, leading to partial migration of ionic liquid on the surface." These data provide additional confirmation of the successful incorporation of the ionic liquid and support the elemental distribution trends observed by EDX. Moreover, they indicate that at higher ionic liquid content, the concentration of the ionic liquid at the composite surface increases.

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript has been carefully revised and can be accepted