Superhydrophilic Coating of Pine Wood by Plasma Functionalization of Self-Assembled Polystyrene Spheres

Round 1

Reviewer 1 Report

The work is original and reports on novel results which are of interest and importance for a wide society of researchers working in the field. It is well organized and well written and therefore deserves acceptance as a good contribution to the field. The discussion and conclusions are adequately supported by the experimental data. Thus, the acceptance is recommended upon its (minor) revision. Below are just a comments/suggestion that might help improving the manuscript
The contact angle scattering across the samples, both on pine wood and on wood, covered with PS is highly desirable.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

In this contribution by Dahle and co-workers, the authors investigated how plasma functionalization of a composite material based on polystyrene spheres may affect the wettability of the surface. The results are interesting and potentially attractive to the readership of Coatings. However, some issues must be handled first before the paper can be recommended for publication.
1) Please change the referencing format to match the MDPI requirements
2) The introduction section is too short as it lacks two critical components. Firstly, "in this work [...]" part is generally absent and it is very important for the readers to know what the article is about in this place. I, therefore, invite the authors to summarize the main findings of this work in this place. Secondly, since the above-mentioned section is missing, the novelty factor has not been defined. Please specify exactly what is in this paper that was not discovered by others in the field already.
3) What was used as a reference to position the peaks obtained by XPS correctly?
4) One of the most important factors for a scientific article is that it should be reproducible by others. Although many experimental details have been provided, certain information should also be included. For instance, since PS spheres play a central role in this study, the authors should provide the trade name or product number. It would also be good to provide a schematic of the plasma treatment setup. Please carefully go through the experimental section to find out if there are any other details that should be supplemented.
5) The headlines should not be separated from text e.g. Line 146.
6) Scale bar markers are too small to read in Fig. 2 and 3. Additionally, redundant ribbons with unnecessary parameters should be removed.
7) XPS plots should have legends and the deconvoluted peaks should be labeled.
8) It is not enough to write down the contact angles, but the images should also be provided.
9) Contact angle values are strongly affected by the roughness of the surface. Thus, it would be vital to find out how plasma treatment affects the values of roughness and, in turn, how these findings can be correlated with the observed wettability of the surface.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Authors demonstrate a method to hydrophilize the pine wood using dip coating of polystyrene spheres and oxygen plasma treatment. And the surfaces were well characterized by XPS, AFM, CLSM, and SEM. It could be publishable in due course but these points below must be addressed prior to publication in Coatings.

1. Please provide the full form before providing the abbreviated form. Ex: ‘FCC’ in the abstract.
2. In the Introduction, the authors should make more efforts to explain why having a superhydrophilic coating on pine wood is important or necessary.
3. In the Materials and Methods, the process of dip coating should be described in details. Such what’s concentration of PS spheres solution? how long the pine wood was immersed in the PS spheres solution before pulling it out? what’s the speed of pulling out the pine wood from the PS spheres solution? Was the surface rinsed by any solvent after being pulled out?
4. In Figure 3 caption, ‘top…middle…bottom…’ should be corrected to ‘left…middle…right’.
5. What’s the driving force of forming multilayers of PS spheres on the pine wood?
6. The spheres are densely packed prior to the plasma treatment, but there are gaps between the spheres after plasma treatment, due to the repulsion (electrostatic and hydration forces) formed between the hydrophilic spheres. A recent review (Curr. Opin. Colloid Interface Sci. 44, 95-106 (2019)) related to this issue should be cited.
7. It is better to add the contact angle images of the surfaces with different treatments.

Author Response

Please see attached response.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Thank you. The article can be accepted in principle. There are three further issues, which can be handled at the proofing stage:
1) Lots of empty space on Page 9.
2) Contrary to the response of the authors (no. 1 in the rebuttal letter), the MDPI reference format was not fully reproduced. The references should be indicated in the text with Arabic numerals.
3) At the end of the article, just before the references, there is a Figure with three SEM micrographs numbered Fig. 1. Firstly, it should rather be Fig. S1. Secondly, it should be moved to a dedicated SI file.