Effective Harmful Organism Management I: Fabrication of Facile and Robust Superhydrophobic Coating on Fabric
Round 1
Reviewer 1 Report
The manuscript is dedicated to the preparation and characterization of superhydrophobic fabric coated with the layer of TiO2-epoxy resin composite and fluorinated-SiO2 nanoparticles. This coating was possessed as antifouling material. Hence antifouling properties are observed in materials with slide angle less than 10°, still it is necessary to conduct antifouling experiments to state its properties.
Lines 67-68 Co-presence of TiO2 and silica NPs may serve as the constitution of micro-nano dual structure while the epoxy resin improves the robustness of the coating. This should be proved.
Slide angle and morphology of material with TiO2-epoxy layer only as well as the materials with fluorinated SiO2 particles only and proposed material should be compared to prove the statement that "the superhydrophobicity is attributed to the nanoparticles constituting the micro/nano hierarchical structure". The effect of each layer would be nice to evaluate.
Why TiO2-epoxy layer was used but not any other particles? One should prove the effect of this specific composition.
"Excellent robustness" of material could not be concluded using the only test in salty water for 13 days, as presented in the manuscript. What about, for example, mechanical stability, UV-durability?
Authors should provide values of contact angle and water slide angle for pristine substrate and modified fabric with experimental details and illustrations.
Lines 114-121 should be moved to introduction.
Author Response
Reviwer#1
The manuscript is dedicated to the preparation and characterization of superhydrophobic fabric coated with the layer of TiO2-epoxy resin composite and fluorinated-SiO2 nanoparticles. This coating was possessed as antifouling material. Hence antifouling properties are observed in materials with slide angle less than 10°, still it is necessary to conduct antifouling experiments to state its properties.
Response to the comment: Thank you for the comment. The purpose of this work is actually to show preliminary results for harmful organism management. For the practical harmful organism management, the superhydrophobic coating material and coating method should be first developed, along with the robustness acquisition of the coating material. That is why we evaluated the robustness of the coating in the salty water for 13 days at 500rpm, which may be close to an environment for the harmful organism management in the laboratory scale. The results of this study clearly prove that the coating surface ensures its hydrophobicity and robustness. The following task is then to evaluate the antifouling ability of the coating surface by actually performing the harmful organism management in a real environment. We believe that the facile preparation as well as the robustness of the coating material, itself, is worthy to be published as a separate work, and the subsequent task relevant the practical harmful organism management will be also reported separately in the near future. In this regard, stating “antifouling” in the title and manuscript text seems to be out of the scope of the current work. Therefore, we have re-named the title and modified abstract and manuscript text accordingly in line of 61-72.
Lines 67-68 Co-presence of TiO2 and silica NPs may serve as the constitution of micro-nano dual structure while the epoxy resin improves the robustness of the coating. This should be proved.
Response to the comment: Thank you for the comment. We prepared samples including TiO2-epoxy nanocomposite on the fabric, fluorinated-SiO2 NPs/ epoxy resin on the fabric, and fluorinated-SiO2 NPs/ TiO2 NPs on the fabric. We examined the morphology of each layer and measured slide angle to clarify the role of each layer. The role of epoxy resin was also investigated. We have addressed this issue in the manuscript of line 144-164.
Slide angle and morphology of material with TiO2-epoxy layer only as well as the materials with fluorinated SiO2 particles only and proposed material should be compared to prove the statement that "the superhydrophobicity is attributed to the nanoparticles constituting the micro/nano hierarchical structure". The effect of each layer would be nice to evaluate.
Response to the comment: Thank you for the comment. This comment is very similar to the second one. We believe that the response to the second comment could also address this one as well. Please refer to the discussion addressed above.
Why TiO2-epoxy layer was used but not any other particles? One should prove the effect of this specific composition.
Response to the comment: Thank you for the comment. This work is inspired by a work reported by Parkin et el. in 2015. [Science, 347, 1132 (2015)] In this report, the authors utilized TiO2 NPs to build micro/nano hierarchical structure. As you commented, however, other particles could be also applied to prepare the superhydrophobic coating, including Mg(OH)2 nanosheet, MgO particles, Al2O3 NPs, and Fe3O4 NPs according to the references. [ACS appl. Mater. Interfaces, 8, 16511 (2016), J. Colloid Interface. Sci. 498, 182 (2017), J. Colloid Interface. Sci. 555, 323 (2019)] It is presumed that the particles should be selected by considering the cost, structural robustness, and easy processibility.
"Excellent robustness" of material could not be concluded using the only test in salty water for 13 days, as presented in the manuscript. What about, for example, mechanical stability, UV-durability?
Response to the comment: The reason to adopt such a robustness test condition was already described in the response to the first comment. As you commented, the use of “Excellent robustness” seems to be overestimated. However, we believe that the robustness of the coating material would be sufficient for the practical harmful organism management evaluation in which the surface coating will be gently immersed in the sea water. We have replaced the “Excellent robustness” with “sufficient robustness for harmful organism management” in the manuscript of line 80-81, 234.
Authors should provide values of contact angle and water slide angle for pristine substrate and modified fabric with experimental details and illustrations.
Response to the comment: Thank you for the comment. We actually attempted to measure the static contact angle. However, the fabric substrate we applied for this study is too rough and not flat, and thus the accurate measurement of the static contact angle was very challenging with our apparatus. Nevertheless, the slide angle below 10° and the air entrapment were clearly demonstrated in this study, indicating that the coated surface possesses the superhydrophobic property as supported by some references.[Colloid Surface A, 448, 93 (2014), Langmuir, 33, 7181 (2017), Chem. Soc. Rev. 43, 2784 (2014)] As you commented, on the one hand, we missed to provide the slide angle of the pristine substrate. We have added a water slide angle of the pristine fabric substrate in the manuscript of line 205-207.
Lines 114-121 should be moved to introduction.
Response to the comment: Thank you for the comment. We have moved the sentences to introduction (line 65-72)
Reviewer 2 Report
This is a well presented, interesting article concerning a new approach to generate superhydrophobic surfaces on fabric. Although this is not a particularly new area, the simplicity of the approach and the extensive testing of the modified surfaces with respect to prolonged immersion in brine or deionised water could make this suitable for publication in Sustainability.
I would characterise this paper as an excellent technical paper that makes a useful technological advance, but note that the science could be more thoroughly developed. My areas of concern, which I think that the authors should consider in their revisions are as follows:
Much of the introduction and some of the discussion concerns applications of antifouling surfaces in marine environments. This article demonstrates a highly repellent surface in air, but superhydrophobicity in air does not guarantee low adhesion in water. There have been many reports on this effect and the limited duration of effectiveness for marine antifouling surfaces (e.g. https://0-www-tandfonline-com.brum.beds.ac.uk/doi/abs/10.1016/j.stam.2005.03.003 0 ) from 2005. I would recommend that the authors remove reference to marine antifouling from this work and focus on antifouling in a dry environment, for which they have shown significant results.
A small point, but some of the materials are not well defined and the experimental needs a little more detail in order for this work to be replicated. There is no mention of the type of fabric onto which the coatings were placed (cotton, polyester, nylon?), and there is no mention of the amount of each component deposited onto the fabric surface. (An approximate value e.g. g/m2 for each would help. Is it so much that the fabric becomes rigid? Figure 3 suggests that this might be the case as the aerated sample is not bouyant.) Does all of the formulation adhere to the surface?
I'm not an expert on environmental matters but but was wondering if fluorooctyl materials used (or toluene solvent) are compatibly with the aims of this journal. Maybe alternatives can be suggested?
The role of the TiO2 in the process is not explained either. It would be good to know more about the curing requirement for the first layer. What fraction of the epoxy has cured after 3h at 70C?
Overall, I think that this is a nice addition to the literature, but would be better if some of these minor questions can be addressed.
Author Response
Reviwer#2
This is a well presented, interesting article concerning a new approach to generate superhydrophobic surfaces on fabric. Although this is not a particularly new area, the simplicity of the approach and the extensive testing of the modified surfaces with respect to prolonged immersion in brine or deionised water could make this suitable for publication in Sustainability.
I would characterise this paper as an excellent technical paper that makes a useful technological advance, but note that the science could be more thoroughly developed. My areas of concern, which I think that the authors should consider in their revisions are as follows:
Much of the introduction and some of the discussion concerns applications of antifouling surfaces in marine environments. This article demonstrates a highly repellent surface in air, but superhydrophobicity in air does not guarantee low adhesion in water. There have been many reports on this effect and the limited duration of effectiveness for marine antifouling surfaces (e.g. https://0-www-tandfonline-com.brum.beds.ac.uk/doi/abs/10.1016/j.stam.2005.03.003 0) from 2005. I would recommend that the authors remove reference to marine antifouling from this work and focus on antifouling in a dry environment, for which they have shown significant results.
Response to the comment: Thank you for the comment. The purpose of this work is to show preliminary results for harmful organism management. For the practical harmful organism management, the superhydrophobic coating material and coating method should be first developed, along with the robustness acquisition of the coating material. The results of this study clearly prove that the coating surface ensures its superhydrophobicity and robustness. The following task is then to evaluate the antifouling ability of the coating material by actually performing the harmful organism management. As you mentioned, the coating material may not be suitable for antifouling in aqueous system. Although the promising results are not guaranteed at this point, it would be worthy to give it a try. It will help realize limitations of our coating material and would eventually lead to the development of the coating material suitable for the practical harmful organism management. We appreciate for your advice though.
A small point, but some of the materials are not well defined and the experimental needs a little more detail in order for this work to be replicated. There is no mention of the type of fabric onto which the coatings were placed (cotton, polyester, nylon?), and there is no mention of the amount of each component deposited onto the fabric surface. (An approximate value e.g. g/m2 for each would help. Is it so much that the fabric becomes rigid? Figure 3 suggests that this might be the case as the aerated sample is not bouyant.) Does all of the formulation adhere to the surface?
Response to the comment: Thank you for the comment. The fabric substrate is made of thick cotton. The first coating material with TiO2-epoxy composite was sprayed on the fabric substrate with around 140 g/m2 and for the second coating material with fluorinated-SiO2 was sprayed with 7.84 g/m2. The coated fabric became a little rigid after the coating, but as described in the manuscript the rigidness is not severe. It recovered its flexibility after bending several times, and the coating materials were also well secured on the fabric during the bending process and robustness test as well. We have added the information on substrate type and coating material amount in Materials and Methods (line 90, 105-106).
I'm not an expert on environmental matters but was wondering if fluorooctyl materials used (or toluene solvent) are compatible with the aims of this journal. Maybe alternatives can be suggested?
Response to the comment: Thank you for the comment. A toluene solvent was thoroughly washed off several times after the fluorination process, and the fluorinated-SiO2 was dried at a thermal oven. Therefore, the remains of the solvent could be negligible. On the other hand, fluorocarbon on fluorinated-SiO2 may be hazardous to human health in particular as fluorocarbon molecules freely drift in aqueous medium. [Environ. Sci. Technol. Lett. 3, 344 (2016)] In our coating material, however, its robustness was secured, indicating that the environmental impact may be minimized. Despite of the potential threat, fluorocarbon based coating materials are still employed for marine antifouling. [ J. Mater. Chem. B, 8, 3701 (2020)] Recently, alternatives to the conventional fluorocarbon coating material have been developed. A representative work is associated with hexamethyldisilazane (HMDS) functionalized SiO2 combined with polymer matrix. [J. Mater. Chem. A, 6, 357 (2018)]. Other strategies to yield non-fluorinated superhydrophobicity include the utilization of Polydimethylsiloxane (PDMS) and dimethyldichlorosilane (DDS). [New J. Chem.43, 7471 (2019), ACS Omega. 4, 6947 (2019)]
The role of the TiO2 in the process is not explained either. It would be good to know more about the curing requirement for the first layer. What fraction of the epoxy has cured after 3h at 70C?
Response to the comment: Thank you for the comment. The role of each coating layer was investigated and discussed in the manuscript of line 153-162. Since the epoxy is mixed with TiO2 NPs, it would be difficult to give the exact curing fraction of the epoxy. Based on our experiment, after 4h curing time, the epoxy was almost completely cured, implying that the curing proceeded around 80%.
Overall, I think that this is a nice addition to the literature, but would be better if some of these minor questions can be addressed.
Reviewer 3 Report
Dear authors,
Thank you very much for the submission of your obtained results.
The research topic about the achievement of superhydrophobic coatings made of fluorocarbon-coated silica nanoparticles is not the latest one. Different approaches were reported before, even the use of a polymeric matrix for embedding the particles and the application of layers by spray coating using an airbrush. I miss completely the citation of papers like:
Huang et al., New J. Chem., 2020, 44, 1194. – Combination of FOTS-SiO2/TiO2 applied by spray coating using an inorganic matrix.
T. Iacono and A. R. Jennings, Nanomaterials, 2019, 9, 684. – Review about fluorocarbon-coated silica nanoparticles.
J.-D. Brassard et al., Appl. Sci., 2012, 2, 453. – “Fluorine Based Superhydrophobic Coatings”
C.-H. Xue et al., J. Mater. Chem. A, 2012, 2, 15001. – Polystyrene/SiO2 core/shell nanoparticles as a coating skeleton and polydimethylsiloxane as hydrphobic interconnection.
Li et al., Matter, 2019, 1, 661-673. – Superhydrophobic interfaces were obtained by a “glue + powder” approach via the surface-embedding of functional micro-/nanoparticles.
Furthermore please describe why your approach is different from the state of the art.
What is the aim of the TiO2-layer embedded in resin in your approach? Photocatalytical effect in bulk material? Please explain.
Which type of epoxy resin and hardener was purchased from Dasol? (page 2, line 79)
Why did you selected for a soft and flexible surface a stiff epoxy resin and not a flexible one like rubber or a poly(urethane) or silicone based one? Please reply?
You use very often the term “fluorination” or “fluorination process”. In a strict interpretation the fluorination is a reaction with a carbon and a source of fluorine to obtain organofluorine compounds. Please change to fluorocarbon-silane modified particles or FC-silane modified particles.
Which fluorinated silane was used in your experiments? You mention Trichloro(1H,1H,2H,2H-pefluorooctyl)silane and used the abbreviation FDTS. But FDTS is Trichloro(1H,1H,2H,2H-pefluordecylyl)silane. Do you mean FOCTS?
Page 3, line 109: You use the unit PSU for describing the salinity of the salt water. Here a comment from a paper regarding the unit PSU. “It is important to emphasize that Practical Salinities do not have units. This fact, confusing to non-specialists, is related to technical issues that prevented an absolute definition when PSS-78 was constructed. Sometimes this lack of units is awkwardly handled by appending the acronym PSU (Practical Salinity Units) to the numerical value, although doing so is formally incorrect and strongly discouraged. Practical Salinities are numerically smaller by about 0.5% than the mass fraction of dissolved matter when this mass fraction is expressed as grams of solute per kilogram of seawater. Practical Salinities were, however, defined to be reasonably comparable with numerical values of chlorinity-based salinities, to maintain a historical continuity.”
Please describe how you obtained the salted water (preparation).
Page 4, line 149: The element of fluorine is not alone responsible for lowering the surface energy. Fluorcarbon compounds can be in charge for this effect.
Page 4, Figure 1 (g): The elements beside Titanium are hardly to be recognized in this size and contrast. Why didn’t you use XPS for the detection of the desired elements by scanning after the application of each layer? The O, F, Si signals seems to be like noise in comparison to the Ti-signals. Light elements are under standard EDS conditions not suitable for a proper detection. Make the evaluation by XPS, please
Why didn’t you measure the simple water contact angle of a drop on a) the fabric, b) after the application of the matrix embedded TiO2-layer and at least on the final system? Please explain and provide this information.
Which type of fabric was used for the experiments? Please explain?
At least, you mentioned your coating is an antifouling. Where is the proof of this statement? From a logical point of view is superhydrophobic = antifouling, unfortunately not from a scientific point of view. Why didn’t you immerse the samples in sea water to show a significant growth reduction or better no growth of bacteria films or macrofoulers? Please explain?
When you will perform the water contact angle tests use a control for the demonstration of the impact of the new coating. Use the fabric, the TiO2-coated fabric and the final system. I miss this controls in the slide angle determination.
Despite a lot of critics I hope you can clarify the described topics and do more measurements.
With kind regards,
The reviewer
Author Response
Reviwer#3
Dear authors,
Thank you very much for the submission of your obtained results.
The research topic about the achievement of superhydrophobic coatings made of fluorocarbon-coated silica nanoparticles is not the latest one. Different approaches were reported before, even the use of a polymeric matrix for embedding the particles and the application of layers by spray coating using an airbrush. I miss completely the citation of papers like:
Huang et al., New J. Chem., 2020, 44, 1194. – Combination of FOTS-SiO2/TiO2 applied by spray coating using an inorganic matrix.
- Iacono and A. R. Jennings, Nanomaterials, 2019, 9, 684. – Review about fluorocarbon-coated silica nanoparticles.
J.-D. Brassard et al., Appl. Sci., 2012, 2, 453. – “Fluorine Based Superhydrophobic Coatings”
C.-H. Xue et al., J. Mater. Chem. A, 2012, 2, 15001. – Polystyrene/SiO2 core/shell nanoparticles as a coating skeleton and polydimethylsiloxane as hydrphobic interconnection.
Li et al., Matter, 2019, 1, 661-673. – Superhydrophobic interfaces were obtained by a “glue + powder” approach via the surface-embedding of functional micro-/nanoparticles.
Furthermore, please describe why your approach is different from the state of the art.
Response to the comment: Thank you for the comment. Before addressing your comment, the main purpose of this study should be aware. The purpose of this work is actually to show preliminary results for harmful organism management. For the practical harmful organism management, the superhydrophobic coating material and coating method should be first developed, along with the robustness acquisition of the coating material. That is why we evaluated the robustness of the coating in the salty water for 13 days at 500rpm, which may be close to an environment for the harmful organism management in the laboratory scale. The results of this study clearly prove that the coating surface ensures its superhydrophobicity and robustness. The following task is then to evaluate the antifouling ability of the coating material by actually performing the harmful organism management. We believe that the facile preparation as well as the robustness of the coating material, itself, is worthy to be published as a separate work, and the subsequent task relevant the practical harmful organism management will be also reported separately in the near future.
We agree with your opinion that using fluorocarbon-coated silica NPs to achieve superhydrophobicity is not novel. As described above, however, our approach is specifically designed as a preliminary work to eventually endow real harmful organism management which will be performed in the near future. We used the fabric as a substrate to render versatile processibility. For example, the superhydrophobic fabric could be readily secured on a buoy and harbor wall. The superhydrophobic fabric also provides a structural flexibility that objects with any shaep could be covered by the fabric. The easy replacement and low cost are other advantages of the fabric substrate. In addition, the robustness test condition in our work is directly related to the harmful organism management, which differs from the refereed works mostly conducting an ablation test with sand paper, scotch tape, and knife for the robustness test. We have cited the referred publications and added this discussion in the manuscript of line 68-72, 151-152, 156-161.
What is the aim of the TiO2-layer embedded in resin in your approach? Photocatalytical effect in bulk material? Please explain.
Response to the comment: Thank you for the comment. We have added the discussion about the role of TiO2 layer in the manuscript of line 153-157. It has nothing to do with photocatalysis.
Which type of epoxy resin and hardener was purchased from Dasol? (page 2, line 79)
Response to the comment: Thank you for the comment. The main component of the epoxy resin and hardeners is 2,2-bis(4´-glycidiyloxyphenyl) propane (diglycidyl ether of bisphenol A) and trimethylolpropane poly(oxypropylene)triamine, respectively. We have added this information in Materials and Methods (line 88-89).
Why did you selected for a soft and flexible surface a stiff epoxy resin and not a flexible one like rubber or a poly(urethane) or silicone based one? Please reply?
Response to the comment: Thank you for the comment. We think that the answer to this comment was already made in the response to your first comment.
You use very often the term “fluorination” or “fluorination process”. In a strict interpretation the fluorination is a reaction with a carbon and a source of fluorine to obtain organofluorine compounds. Please change to fluorocarbon-silane modified particles or FC-silane modified particles.
Response to the comment: Thank you for the correction. We have changed the term as you requested in the manuscript line of 18, 75, 96, 97, 103, 107, 112, 139, 146, 147, 151, 152, 154, 164, 174, 245.
Which fluorinated silane was used in your experiments? You mention Trichloro(1H,1H,2H,2H-pefluorooctyl)silane and used the abbreviation FDTS. But FDTS is Trichloro(1H,1H,2H,2H-pefluordecylyl)silane. Do you mean FOCTS?
Response to the comment: Thank you for the correction. We have used Trichloro(1H,1H,2H,2H-pefluorooctyl)silane that can be abbreviated with PFOCTS. We have replaced FDTS with PFOCTS (line 85, 95, 197).
Page 3, line 109: You use the unit PSU for describing the salinity of the salt water. Here a comment from a paper regarding the unit PSU. “It is important to emphasize that Practical Salinities do not have units. This fact, confusing to non-specialists, is related to technical issues that prevented an absolute definition when PSS-78 was constructed. Sometimes this lack of units is awkwardly handled by appending the acronym PSU (Practical Salinity Units) to the numerical value, although doing so is formally incorrect and strongly discouraged. Practical Salinities are numerically smaller by about 0.5% than the mass fraction of dissolved matter when this mass fraction is expressed as grams of solute per kilogram of seawater. Practical Salinities were, however, defined to be reasonably comparable with numerical values of chlorinity-based salinities, to maintain a historical continuity.”
Please describe how you obtained the salted water (preparation).
Response to the comment: Thank you for the comment. We have prepared the salty water by dissolving 35 g of sodium chloride in 1000 mL D.I. water, which correspond to 35 PSU to the best of our knowledge. If the use of “PSU” is confusing, it would be better to use “ppt” instead. We have replaced “PSU” with “ppt” and added the preparation procedure of the salty water in Materials and Methods (line 121-122).
Page 4, line 149: The element of fluorine is not alone responsible for lowering the surface energy. Fluorcarbon compounds can be in charge for this effect.
Response to the comment: Thank you for the correction. We have modified the manuscript as corrected in Line 187, 189, 196, 246.
Page 4, Figure 1 (g): The elements beside Titanium are hardly to be recognized in this size and contrast. Why didn’t you use XPS for the detection of the desired elements by scanning after the application of each layer? The O, F, Si signals seems to be like noise in comparison to the Ti-signals. Light elements are under standard EDS conditions not suitable for a proper detection. Make the evaluation by XPS, please
Response to the comment: Thank you for the comment. As you commented, EDS is not the best instrument to analyze the chemical composition. The high recognition of titanium could be associated with the size and amount of TiO2 NPs. Actually, the amount of TiO2-epoxy composite and fluorinated-SiO2 is 140 g/m2 and 7.84 g/m2, respectively. I agree with that the XPS is much more powerful instrument to quantify the chemical composition of the coating. However, the preparation of our superhydrophobic fabric is not based on a new chemistry, and as you mentioned in the first comment, the synthesis of FC-silane modified NPs is well known. If we propose a new synthetic methodology, we have to elucidate the chemical composition of the coating by using XPS. The elemental mapping image is simply to show the presence of the coating materials applied, not for the quantification of the coating materials. We hope that this answer sounds reasonable to you.
Why didn’t you measure the simple water contact angle of a drop on a) the fabric, b) after the application of the matrix embedded TiO2-layer and at least on the final system? Please explain and provide this information.
Response to the comment: Thank you for the comment. We actually attempted to measure the static contact angle. However, the fabric substrate we applied for this study is too rough and not flat, and thus the accurate measurement of the static contact angle was very challenging with our apparatus. Nevertheless, the slide angle below 10° and the air entrapment were clearly demonstrated in this study, indicating that the coated surface possesses the superhydrophobic property as supported by references. [Colloid Surface A, 448, 93 (2014), Langmuir, 33, 7181 (2017), Chem. Soc. Rev. 43, 2784 (2014)] If using the term of “superhydrophobic” still seems unreasonable without giving contact angle values, please let us know, and then we will use “high water repellency” instead.
Which type of fabric was used for the experiments? Please explain?
Response to the comment: Thank you for the comment. The fabric substrate is made of thick cotton. We have added this information in Materials and Methods (line 90).
At least, you mentioned your coating is an antifouling. Where is the proof of this statement? From a logical point of view is superhydrophobic = antifouling, unfortunately not from a scientific point of view. Why didn’t you immerse the samples in sea water to show a significant growth reduction or better no growth of bacteria films or macrofoulers? Please explain?
Response to the comment: Thank you for the comment. We believe that this comment was already addressed in the response to your first comment. Briefly, this study is to focus on the fabrication of superhydrophobic coating and its robustness as a preliminary work for the real harmful organism management which will be performed in the near future. . In this regard, stating “antifouling” in the title and manuscript text seems to be out of the scope of the current work. Therefore, we have re-named the title and modified abstract and manuscript text accordingly in line of 61-72.
When you will perform the water contact angle tests use a control for the demonstration of the impact of the new coating. Use the fabric, the TiO2-coated fabric and the final system. I miss this controls in the slide angle determination.
Response to the comment: Thank you for the comment. As mentioned in the previous comment, the accurate contact angle value is not obtainable in our system. Instead, we have added slide angle and optical images of water droplet on control samples including pristine fabric and TiO2-epoxy nanocomposite coating in the manuscript of line 147-151, 206-208.
Despite a lot of critics I hope you can clarify the described topics and do more measurements.
Reviewer 4 Report
This manuscript describes about Superhydrophobic coating of materials by TiO2-epoxy resin nanocomposite. The authors have to revise the manuscript with addition of some important data and discussion in accordance with following comments;
- To discuss hydrophobicity of surface, an information about contact angle is necessary. The authors must add the contact angle for all tested samples and discuss a relationship between hydrophobicity and data especially in Figure 3b and 4.
- How much shear stress was applied to surface in robustness test? If possible, please describe (can be calculated?) about the shear stress.
- The evaluation of surface morphology until/after robustness test is needed to understand about reason for change of slide angle. The sample after robustness test has to estimate by SEM and EDS and the authors have to discuss about relationship between surface morphology and slide angle.
- Despite of claim about antifouling, there is no result about antifouling nature of some materials on superhydrophobic coated surface. The authors have to show some evidence about the antifouling nature in accordance with the title of manuscript.
Author Response
Reviwer#4
This manuscript describes about Superhydrophobic coating of materials by TiO2-epoxy resin nanocomposite. The authors have to revise the manuscript with addition of some important data and discussion in accordance with following comments;
To discuss hydrophobicity of surface, an information about contact angle is necessary. The authors must add the contact angle for all tested samples and discuss a relationship between hydrophobicity and data especially in Figure 3b and 4.
Response to the comment: Thank you for the comment. We actually attempted to measure the static contact angle. However, the fabric substrate we applied for this study is too rough and not flat, and thus the accurate measurement of the static contact angle was very challenging with our apparatus. Nevertheless, the slide angle below 10° and the air entrapment were clearly demonstrated in this study, indicating that the coated surface possesses the superhydrophobic property as supported by references. [Colloid Surface A, 448, 93 (2014), Langmuir, 33, 7181 (2017), Chem. Soc. Rev. 43, 2784 (2014)] If using the term of “superhydrophobic” still seems unreasonable without giving contact angle values, please let us know, and then we will use “high water repellency” instead.
How much shear stress was applied to surface in robustness test? If possible, please describe (can be calculated?) about the shear stress.
Response to the comment: Thank you for the comment. The shear stress could be calculated with some assumptions: (1) the stir bar used to generate rotation frequency is cylindrical, (2) the salty water is pure water, and (3) the samples are equally distanced from the stir bar. The shear rate was calculated by the equation: , where , R, , and d is shear rate, radius of the stir bar, and rotation frequency, respectively. The shear rate calculated is around 37.4 s-1, and the resultant shear stress is around 8.9 10-4 Pa. The shear stress is not so high because of the low rotation frequency and long distance between the stir bar and the samples. We have added the calculated shear stress value in the manuscript of line 218-219 and calculation procedure in ESI (section1).
The evaluation of surface morphology until/after robustness test is needed to understand about reason for change of slide angle. The sample after robustness test has to estimate by SEM and EDS and the authors have to discuss about relationship between surface morphology and slide angle.
Response to the comment: Thank you for the comment. We examined the coated sample after the robustness test for 13 days by using SEM and EDS. The comparison results concerning morphology and composition effect on the slide angle change before and after the robustness test are discussed in the manuscript of line 228-231.
Despite of claim about antifouling, there is no result about antifouling nature of some materials on superhydrophobic coated surface. The authors have to show some evidence about the antifouling nature in accordance with the title of manuscript.
Response to the comment: Thank you for the comment. The purpose of this work is actually to show preliminary results for harmful organism management. For the practical harmful organism management, the superhydrophobic coating material and coating method should be first developed, along with the robustness acquisition of the coating material. That is why we evaluated the robustness of the coating in the salty water for 13 days at 500rpm, which may be close to an environment for the harmful organism management in the laboratory scale. The results of this study clearly prove that the coating surface ensures its hydrophobicity and robustness. The following task is then to evaluate the ability of the coating material as antifouling by actually performing the harmful organism management. In this regard, stating “antifouling” in the title and manuscript text seems to be out of the scope of the current work. Therefore, we have re-named the title and modified abstract and manuscript text accordingly in line of 61-72.
Round 2
Reviewer 3 Report
Dear authors,
Thank you very much for your response.
With kind regards
Author Response
I just resubmitted the final version.
Reviewer 4 Report
The manuscript was well revised in accordance with reviewer's comments.
Author Response
I just resubmitted the final version
