Novel Janus Fibrous Membranes with Enhanced Directional Water Vapor Transmission

Round 1

Reviewer 1 Report

This manuscript introduces a method to fabricate Janus Fibrous Membranes by a layer-by-layer electrospinning technique. The significance of such design has been well illustrated but more are suggested to be added to link to human life's benefit. Also, diverse characterizations have been performed to demonstrate an enhanced directional water vapor transmission. Finally the mechanism of water content on both sides have been well analyzed, which is really impressive. I would like to recommend this study to be published after authors address all my concerns. 

1. There are not many English grammar mistakes, which is convenient for reviewers to review. Thanks for your good work! However, there are still some minor drawbacks. For example, authors need to consider when you should use past tense or present tense of all the verbs. Please check through the whole manuscript and revise carefully. 

2. English style has to be improved a bit. For example, you don't have to repeat the unit like "0.6 mm, 0.8 mm, 1.0 mm, and 1.2 mm". You only need to leave the last one and delete all others like "0.6, 0.8, 1.0, and 1.2 mm". It happens frequently. Please revise throughout the whole manuscript. 

3. In line 23, usefully and helpful are synonym. 

4. In line 42, "et al" should be "et al.". And the reference should be put in the end of the sentence. 

5. In line 49, "enhance" should be "enhancing".

6. In line 82, stirring for 8h? 

7. "For measured" appeared many times. It is incorrect. You can change it to "to measure". 

8. "When peeling off" has been used a lot. And it is incorrect if the subject is different from the second half sentence. 

9. In line 131, what does "it" indicate? 

10. Line 135-137 has to be rewritten "Different concentrations of electrospun solutions and inner diameters of electrospun needle nozzles which are regarded as the main influential factors to the obtained morphology in electrospinning process are selected". 

11. In line 141 and 162, "increasing" should be "increase". 

12. In line 143, "of which" is used incorrectly. It should be on which. 

13. There are many typos. For example, tpye in line 163, dissolv in line 176, verifiy in line 201, capbility in line 260, transimssion in line 282, adsorpt in line 289. 

14. In line 177, analysis should be analyze. 

15. In line 185, what solvent do you specify? 

16. In line 188-189, "Since the -C=O stretching vibration of the ester and the
polyurethane overlap" need to be rewritten. 

17. In line 193, compared should be comparing. 

18. In line 195, you mentioned "CA characteristic peak was not shown in the
Janus membrane spectrum" but have you recorded the FTIR spectrum of CA side? 

19. In line 206, hydrophobicity should be hydrophobic. 

20. In line 211, to should be on. 

21. In line 295, resulted should be resulting. 

22. In the end, can you give a little idea about the future application regarding such property of the material? 

Author Response

Dear Editor,

 

Thanks very much for your E-mail on July. 17, 2019 and the comments of two referees for our manuscript (applsci-560080) entitled “Novel Janus Fibrous Membranes with Enhanced Directional Water Vapor Transmission”. We appreciate the constructive and positive comments provided by the reviewers and acknowledge the improvements that these comments have made to the manuscript. The following is a summary of the responses to the comments on this manuscript. Meanwhile, all changes have been highlighted with Blue Font in the revised manuscript. Thanks for your consideration of the manuscript.

 

Reviewer #1:

Comment (1) There are not many English grammar mistakes, which is convenient for reviewers to review. Thanks for your good work! However, there are still some minor drawbacks. For example, authors need to consider when you should use past tense or present tense of all the verbs. Please check through the whole manuscript and revise carefully.

Response: Thanks a lot for the kind suggestion of the reviewer. Under the suggestions, we have double checked the manuscript to ensure no similar issues in the manuscript.

 

Comment (2) English style has to be improved a bit. For example, you don't have to repeat the unit like "0.6 mm, 0.8 mm, 1.0 mm, and 1.2 mm". You only need to leave the last one and delete all others like "0.6, 0.8, 1.0, and 1.2 mm". It happens frequently. Please revise throughout the whole manuscript.

Response: Thanks for the reviewer’s important suggestion. We have double checked the whole manuscript to avoid the inappropriate English expression.

 

Comment (3) In line 23, usefully and helpful are synonym.

Response: Thanks very much for the reviewer pointing out many errors in our manuscript patiently and meticulously. We delete the word “helpful”.

 

Comment (4) In line 42, "et al" should be "et al.". And the reference should be put in the end of the sentence.

Response: We have revised the English abbreviation and the location of the cited reference in line 41 of the revised manuscript under the reviewer’s suggestion.

 

Comment (5) In line 49, "enhance" should be "enhancing".

Response: We are apologized for such mistake and our carelessness. We have corrected it in line 51 on the revised manuscript.

 

Comment (6) In line 82, stirring for 8h?

Response: In this work, the PU pellets were dissolved in mixture of DMF and THF solvent at 40 °C, forming PU/(DMF/THF) electrospun solution. In order to make PU pellets dissolve completely in the mixed solvent, PU/(DMF/THF) solution was magnetically stirring for 8 hours.

 

Comment (7) "For measured" appeared many times. It is incorrect. You can change it to "to measure".

Response: Thanks for the suggestion. We corrected “For measured” to “To measure” in line 98-99 and line 102 in the revised manuscript.

 

Comment (8) "When peeling off" has been used a lot. And it is incorrect if the subject is different from the second half sentence.

Response: We revised the expressions in line 127-128, line 133-134 and line 168-170 on the revised manuscript.

 

Comment (9) In line 131, what does "it" indicate?

Response: Indeed, “it” is ambiguous. We corrected the sentence as “When the composited two layers were peeled off form the Al foil substrate, the Janus membrane with wettability contrast was formed.” (in line 133-134).

 

Comment (10) Line 135-137 has to be rewritten "Different concentrations of electrospun solutions and inner diameters of electrospun needle nozzles which are regarded as the main influential factors to the obtained morphology in electrospinning process are selected".

Response: It has been rewritten as “Among them, the electrospun solutions and electrospun needle nozzles are regarded as the main factors affecting the morphology of the electrospun materials. Therefore, we explored the effects of different concentrations of electrospun solutions and inner diameters of electrospun needle nozzles on the morphology of nanofibrous materials”, and highlighted in line 138-141 on the revised manuscript.

 

Comment (11) In line 141 and 162, "increasing" should be "increase".

Response: Thanks for the reviewer’s suggestion. We have corrected in the revised manuscript.

 

Comment (12) In line 143, "of which" is used incorrectly. It should be on which.

Response: Thanks a lot for the reviewer to point out our mistake. We revised it in line 147 on revised manuscript.

 

Comment (13) There are many typos. For example, tpye in line 163, dissolv in line 176, verifiy in line 201, capbility in line 260, transimssion in line 282, adsorpt in line 289.

Response: We corrected corresponding typos in Line 167, 181, 210, 269, 308, and 315, respectively, on the revised manuscript. Meanwhile, the whole manuscript has been double checked to avoid similar mistakes.

 

Comment (14) In line 177, analysis should be analyzed.

Response: We revised it in line 182 on revised manuscript.

 

Comment (15) In line 185, what solvent do you specify?

Response: The solvents were the DMF and acetone which were used to dissolve the CA. Meanwhile, we explain it in line 190-191 on the revised manuscript.

 

Comment (16) In line 188-189, "Since the -C=O stretching vibration of the ester and the polyurethane overlap" need to be rewritten.

Response: Under the reviewer’s suggestion, we rewrite the related FTIR analysis. The details were in line 193-198 on the revised manuscript.

 

Comment (17) In line 193, compared should be comparing.

Response: We changed “compared” to “comparing”, and highlighted it in line 201 on the revised manuscript.

 

Comment (18) In line 195, you mentioned "CA characteristic peak was not shown in the Janus membrane spectrum" but have you recorded the FTIR spectrum of CA side?

Response: To make FTIR analysis clearer and more rigorous, we supplemented FTIR spectrum recorded from the CA side and re-constructed the corelated Figure 4(a). The detailed analysis was added in line 201-209 on the revised manuscript.

 

Comment (19) In line 206, hydrophobicity should be hydrophobic.

Comment (20) In line 211, to should be on.

Comment (21) In line 295, resulted should be resulting.

Response: Thanks very much for the reviewer’s careful revision. We apologize for our carelessness and corrected these as-mentioned mistakes in line 215(Comment 19), 220(Comment 20), and line 327(Comment 21), respectively. Meanwhile, the whole manuscript had been double checked.

 

Comment (22) In the end, can you give a little idea about the future application regarding such property of the material?

Response: The hydrophobic/hydrophilic Janus fibrous membranes exhibits higher water vapor transmission capacity when tiny water droplets pass from the hydrophobic side to the hydrophilic side than that from the reverse direction. These novel insights may be useful in efficient moisture permeable fabric design and fabrication which provide a cooler and drier micro climate to satisfy the personal comfort, and for designing high efficiency water or fog harvesters. The corresponding revisions have been made in “Conclusions” part on the manuscript.

 

All changes have been highlighted with Blue Font in the revised manuscript. Thanks for your consideration of the manuscript.

 

 

Sincerely,

Jing Wu

Author Response File: Author Response.docx

Reviewer 2 Report

This manuscript reports the development of PU/CA Janus membranes via the layer-by-layer electrospinning technique. An array of characterization techniques were employed in this study with some convincing evidences provided to support the formation mechanisms and experimental observations.New insights into the design and fabrication of efficient moisture permeable fabrics and clothing were provided. For these reasons, I recommend the publication of this manuscript with the following revisions:

 

1. This manuscript is not English-ready for publication. It needs to be thoroughly revised by a native English speaker for proper English language, grammar, punctuation, spelling, and overall style. 

 

2. The authors should read through the manuscript thoroughly to make sure that abbreviations are used correctly and consistently.

 

3. In the first sentence of the Introduction Section, the authors should consider citing review and research articles on Janus membranes for other applications to provide a broader perspective and attract a broader audience, which will greatly improve the visibility of this manuscript. The following articles are recommended. A short introduction on what Janus membranes are would be helpful to potential readers who may not be familiar with Janus membranes.

 

H.-C. Yang, J. Hou, V. Chen, Z.-K. Xu, Janus membranes: Exploring duality for advanced separation, Angew. Chem. - Int. Ed. 55 (43) (2016)13398-13407.

 

G. Zuo, R. Wang, Novel membrane surface modification to enhance anti-oil fouling property for membrane distillation application, J. Membr. Sci. 447 (2013) 26-35

H. Zhou, Z. Guo, Superwetting Janus membranes: Focusing on unidirectional transport behaviors and multiple applications, J. Mater. Chem. A 7 (21) (2019)12921-12950

 

N.G.P. Chew, S. Zhao, C. Malde, R. Wang, Polyvinylidene fluoride membrane modification via oxidant-induced dopamine polymerization for sustainable direct-contact membrane distillation,J. Membr. Sci. 563 (2018) 31-42.

 

H.-C. Yang, Y. Xie, J. Hou, A.K. Cheetham, V. Chen, S.B. Darling, Janus membranes: Creating asymmetry for energy efficiency, Adv. Mater. 30 (43) (2018) 1801495.

 

N.G.P. Chew, Y. Zhang, K. Goh, J.S. Ho, R. Xu, R. Wang, Hierarchically structured Janus membrane surfaces for enhanced membrane distillation performance, ACS Appl. Mater. Interfaces (2019).

 

4. In line 53 of the Introduction Section, the authors claimed that the ‘layer-by-layer’ electrospinning technique is novel. However, there are articles in the literature that have reported on this technique albeit for other applications. The authors need to elaborate on the novelty of this study. The authors should also justify their reasons for choosing electrospinning and not other techniques.

 

5. In the Introduction Section, the authors should justify their reasons for selecting PU and CA as materials for their membrane (i.e., benefits).

 

6. The authors should label each significant peak in the FTIR figure to provide better clarity and cite articles where information on the characteristic peaks of the CA and PU membranes were obtained.

 

7. In line 209 of the manuscript, the authors claimed that “…high surface roughness are the main reasons for their hydrophobicity and hydrophilicity.” The authors should provide measurements on surface roughness.

 

8. In Figure 4(c), the plotted point and reported water contact angle value of CA-8G are not consistent. Please correct the typo error.

 

9. In Figure 5(b), the water content from the hydrophilic side to the hydrophobic side was higher for electrospinning times of 25 and 30 min. The authors should provide an explanation on this phenomenon. 

 

10. In Figure 5(c), the authors should consider reporting the one-way transport capability of individual CA layer and PU layer as controls.

 

11. The authors explained that when the thickness of the hydrophilic layer increased, there were fewer pores between the fibers, which made it difficult for water vapor to pass through. The authors should also explain why a very short CA electrospinning time does not guarantee the best one-way transport capability.

 

12. It is highly recommended that the authors compare the water vapor transmission capability of their membrane to those of other previously reported/traditional membranes in the form of a table to highlight the performance of their membrane.

 

 

 

Author Response

Dear Editor,

Thanks very much for your E-mail on July. 17, 2019 and the comments of two referees for our manuscript (applsci-560080) entitled “Novel Janus Fibrous Membranes with Enhanced Directional Water Vapor Transmission”. We appreciate the constructive and positive comments provided by the reviewers and acknowledge the improvements that these comments have made to the manuscript. The following is a summary of the responses to the comments on this manuscript. Meanwhile, all changes have been highlighted with Orange Font in the revised manuscript.

Thanks for your consideration of the manuscript.

Reviewer #2:

Comment (1) This manuscript is not English-ready for publication. It needs to be thoroughly revised by a native English speaker for proper English language, grammar, punctuation, spelling, and overall style.

Response: Thanks very much for the reviewer’s suggestion. We will try our best to improve our English in the future. We double checked the manuscript to avoid English language, punctuation, grammar, spelling mistakes.

Comment (2) The authors should read through the manuscript thoroughly to make sure that abbreviations are used correctly and consistently.

Response: Thanks for the reviewer’s suggestion. Indeed, there were some abbreviation mistakes in the manuscript. We have carefully checked the whole manuscript and corrected some mistakes in the revised manuscript.

Comment (3) In the first sentence of the Introduction Section, the authors should consider citing review and research articles on Janus membranes for other applications to provide a broader perspective and attract a broader audience, which will greatly improve the visibility of this manuscript. The following articles are recommended. A short introduction on what Janus membranes are would be helpful to potential readers who may not be familiar with Janus membranes. H.-C. Yang, J. Hou, V. Chen, Z.-K. Xu, Janus membranes: Exploring duality for advanced separation, Angew. Chem. - Int. Ed. 55 (43) (2016)13398-13407. G. Zuo, R. Wang, Novel membrane surface modification to enhance anti-oil fouling property for membrane distillation application, J. Membr. Sci. 447 (2013) 26-35. H. Zhou, Z. Guo, Superwetting Janus membranes: Focusing on unidirectional transport behaviors and multiple applications, J. Mater. Chem. A 7 (21) (2019)12921-12950 N.G.P. Chew, S. Zhao, C. Malde, R. Wang, Polyvinylidene fluoride membrane modification via oxidant-induced dopamine polymerization for sustainable direct-contact membrane distillation,J. Membr. Sci. 563 (2018) 31-42.     H.-C. Yang, Y. Xie, J. Hou, A.K. Cheetham, V. Chen, S.B. Darling, Janus membranes: Creating asymmetry for energy efficiency, Adv. Mater. 30 (43) (2018) 1801495.     N.G.P. Chew, Y. Zhang, K. Goh, J.S. Ho, R. Xu, R. Wang, Hierarchically structured Janus membrane surfaces for enhanced membrane distillation performance, ACS Appl. Mater. Interfaces (2019).

Response: Thanks for the suggestion. The brief introduction of Janus membrane were given in line 47-50 and some related reviews and research articles were cited as reference [24]-[29] in the revised manuscript.

Comment (4) In line 53 of the Introduction Section, the authors claimed that the ‘layer-by-layer’ electrospinning technique is novel. However, there are articles in the literature that have reported on this technique albeit for other applications. The authors need to elaborate on the novelty of this study. The authors should also justify their reasons for choosing electrospinning and not other techniques.

Response: The novelty of this work is that the hydrophobic/hydrophilic Janus fibrous membranes were facile fabricated by electrospinning. And the work uncovers the asymmetric wettability-related-property of fibrous membrane, i.e., water vapor transmission capacity is enhanced when tiny water droplets pass from the hydrophobic side to the hydrophilic side than that from the reverse direction. Indeed, apart from constructing Janus membrane, “layer-by-layer” electrospinning technique have been reported for other applications. The main advantage of using “layer-by-layer” electrospinning to fabricate Janus membrane is that it’s facile to control the composited layers with different/contrast wettability in thickness direction. That is, for one thing, original materials with different natural wettability (hydrophobic/hydrophilic) can be chosen and electrospun to form fibrous membrane directly. For another thing, the thickness of each layer which plays important role in the property can be easily controlled by adjusting the electrospinning time.

Comment (5) In the Introduction Section, the authors should justify their reasons for selecting PU and CA as materials for their membrane (i.e., benefits).

Response: The main target of the work is constructing the Janus fibrous membrane with contrast wettability. For one thing, the natural wettable properties of PU and CA are hydrophobic and hydrophilic which make them good candidates for Janus membrane fabrication. For the other thing, both the PU and CA have been used as fabric and textile. Selecting PU and CA as materials to construct the Janus membrane provides possibility for its application in efficient moisture permeable fabric design and fabrication. The details were also added in the Introduction Section (line 53-59) on the revised manuscript.

Comment (6) The authors should label each significant peak in the FTIR figure to provide better clarity and cite articles where information on the characteristic peaks of the CA and PU membranes were obtained.

Response: Under the reviewer’s suggestion, to make FTIR figure clearer, we re-constructed and revised the Figure 4(a). The detailed analysis has been added and highlighted in line 186-209. Meanwhile, some related literatures have been cited and marked as reference [36]-[39].

Comment (7) In line 209 of the manuscript, the authors claimed that “…high surface roughness are the main reasons for their hydrophobicity and hydrophilicity.” The authors should provide measurements on surface roughness.

Response: Wetting at solid and liquid interfaces, one of the most common phenomena, is governed by surface chemistry and surface roughness. Surface roughness will enhance surface wettability. That is surface roughness makes hydrophobic surface more hydrophobic and hydrophilic surface more hydrophilic [Shutao Wang, Lei Jiang, et al., Chem. Rev. 2015, 115, 8230-8293.; Jie Ju, Lei Jiang, et al., Acc. Chem. Res., 2014, 47, 2342-2352.; Hua Zhou, Tong Lin, et al., Adv. Mater. Interfaces, 2016, 3, 1600402-1600421.]. Unfortunately, we cannot provide the measurement on surface roughness (e.g. by using AFM) in short response time. Because we don’t have the measurement equipment in our college. If the samples are sent to other testing center, the time to get the results are uncertain. Thanks very much for the reviewer’s important suggestion. More rigorous planning and experiments will be carried out in our future research work. In order to make up the deficiency and explain the influence of surface roughness on wettability, water contact angles of PU and CA membranes prepared by spin-coating (relative smooth surface) and electrospinning (rough surface) were measured respectively (Figure R1). It can be seen the wettability improve to some extent, viz., PU membrane become more hydrophobic and CA membrane becomes more hydrophilic. Figure R1. Water contact angles of PU and CA. (a) PU membrane prepared by spin-coating; (b) Electrospun PU membrane; (c) CA membrane prepared by spin-coating; (d) Electrospun CA membrane

Comment (8) In Figure 4(c), the plotted point and reported water contact angle value of CA-8G are not consistent. Please correct the typo error.

Response: We apologized for our carelessness to make incorrect labels in insertions of Figure 4(b) and Figure 4(c). Both Figure 4(b) and 4(c) were reconstructed and revised in the manuscript.

Comment (9) In Figure 5(b), the water content from the hydrophilic side to the hydrophobic side was higher for electrospinning times of 25 and 30 min. The authors should provide an explanation on this phenomenon.

Response: We are apologized that the data has made a mistake in figure 5(b). Thanks for the reviewer's suggestions. After measurement, we have explained and added the reason in line 279-299 on the revised manuscript.

Comment (10) In Figure 5(c), the authors should consider reporting the one-way transport capability of individual CA layer and PU layer as controls.

Response: Under the reviewer’s suggestion, the one-way transport capability of individual PU (electrospun 5 mins) and CA (electrospun 15 mins) layer are -25.9% and 49.8%. When the value is negative, it means water vapor does not exhibit one-way transmission capacity. While, if the value is positive, it indicates water vapor shows one-way transmission. The details were added in line 306-307. Figure 5(c) was also reconstructed.

Comment (11) The authors explained that when the thickness of the hydrophilic layer increased, there were fewer pores between the fibers, which made it difficult for water vapor to pass through. The authors should also explain why a very short CA electrospinning time does not guarantee the best one-way transport capability.

Response: When the hydrophilic CA was electrospun in a very short time, the CA layer was thin. It can be understood the hydrophilic micro/nanopores form abundant capillaries that could rapidly absorb water and allow the directional transmission. If the hydrophilic CA layer was very thin, there was no enough CF to “drag” tinny water droplet from the hydrophobic PU layer efficiently and could not guarantee the best one-way transport capability. We explained and added the reason in line 319-324 on the revised manuscript.

Comment (12) It is highly recommended that the authors compare the water vapor transmission capability of their membrane to those of other previously reported/traditional membranes in the form of a table to highlight the performance of their membrane.

Response: Under the reviewer’s suggestion, we compared the water vapor transmission capability of other works. The details are shown in Table R1. According to Table R1, since different testing times were used in different reported works, it should be less rigorous to make a quantitative comparison. In general, Janus membrane reported in this work shows greater one-way transport capability. Table R1 Comparison of One-way transport capability of previously reported works and this work One-way transport capability (%) Testing time(s) Reference 861 120 [1] 1413 500 [2] 1021 500 [3] 1245 500 [4] 120 This work Reference: [1] C. Zeng, H. Wang, H. Zhou, et al. Directional Water Transport Fabrics with Durable Ultra-High One-Way Transport Capacity[J]. Advanced Materials Interfaces, 2016, 3(14):1600036-1600042. [2] A. Babar, X. Wang, N. Iqbal, et al. Tailoring Differential Moisture Transfer Performance of Nonwoven/Polyacrylonitrile-SiO2 Nanofiber Composite Membranes[J]. Advanced Materials Interfaces, 2017, 4(15):1700062-1700071. [3] D. Miao, Z. Huang, X. Wang, et al. Continuous, Spontaneous, and Directional Water Transport in the Trilayered Fibrous Membranes for Functional Moisture Wicking Textiles[J]. Small, 2018, 14(32):1801527-1801536. [4] X. Wang, Z. Huang, D. Miao, et al. Biomimetic Fibrous Murray Membranes with Ultrafast Water Transport and Evaporation for Smart Moisture-Wicking Fabrics[J]. ACS Nano, 2019, 13(2):1060-1070. All changes have been highlighted with Orange Font in the revised manuscript. Thanks for your consideration of the manuscript. Sincerely, Jing Wu

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The authors have addressed my concerns. 

Author Response

Dear Editor, Thanks very much for your E-mail on July. 28, 2019 and the comments of Academic Editor for our manuscript (applsci-560080) entitled “Novel Janus Fibrous Membranes with Enhanced Directional Water Vapor Transmission”. We appreciate the constructive and positive comments provided by the Academic Editor and acknowledge the improvements that these comments have made to the manuscript. The following is a summary of the responses to the comments on this manuscript. Meanwhile, all changes have been highlighted with Green Font in the revised manuscript. Thanks for your consideration of the manuscript. Academic Editor: Response: Thanks very much for the Academic Editor’s suggestion. The Figure R1 in the reviewer #2's response was given in line 277-280 as the Figure 5 in the revised manuscript. Meanwhile, the corresponding explanation has been added and highlighted in line 268-276. In addition, Table R1 and related content in Reviewer #2's response were highlighted in line 349-355 of the revised manuscript (Table 1) and some related reviews and research articles were cited as reference [40]-[43] in the revised manuscript. Correspondingly, other graphic content in the manuscript has been modified. All changes have been highlighted with Green Font in the revised manuscript. Thanks for your consideration of the manuscript. Sincerely, Jing Wu

Author Response File: Author Response.docx