The Anti-Snow Behaviour of Icephobic Coatings: Laboratory and In-Field Testing

Round 1

Reviewer 1 Report

This paper describes the snow and ice resistance performance of SH, HP and SLs samples in laboratory environment and outside natural environment, which provides a method to solve some disasters caused by snow on metal surface in low temperature environment. In particular, two quantitative parameters are provided to reflect the anti-snow and ice behavior. After more than ten years of development, anti-snow and ice materials have become a worldwide research hotspot in recent years. The whole paper has a clear idea, and makes a constructive research on the application of anti-snow and ice materials in real environment.   Therefore, it is recommended to publish it in coating journal. However, there are still some issues to be resolved before the manuscript can be accepted.

1.    In line 126, please explain the role of SL-2 and write down the differences between SL-1 and SL-2 in subsequent experiments.

2. In line 238, the SEM image of oxide layer thickness should be added to prove the author's statement.

3. Please supplement the pictures of the contact angle and sliding angle of the sample in section 3.2.

4. In line 299, the SEM image of HP should be added to prove the author's statement.

5. In line 429, the author describes that contact angle is not a key parameter for predicting snow protection. However, it is observed in tables 5 and 6 that contact angles are associated with snow protection and snow thinning (in dry and wet environments). Please further analysis.

6. In line 423, the format is incorrect.

7. In Fig. 11, please explain why in the time range of 1700 to 2050, the performance of the bare substrate is better than that of the coated sample.

Author Response

Dear Revisor,

please see the attachment for the answers to your comment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Overall, the paper is interesting, but there are significant issues with the paper and I cannot recommend it for publications.

·       Most of the figures are not clear and are not informative. There are lots of single figures that can be easily combined like figures 3-5. However, my major issue is that there is nothing in these figures. The chemistry and materials are all presented and tested in prior research related to ice and anti-icing surfaces.

·       Ice adhesion could vary between different temperatures. At what temperature did you conduct the ice adhesion measurements?

·       They evaluate the ice adhesion of the different samples by comparing their ARF. Is it possible to also mention the actual ice adhesion (in Pascal) on these surfaces?

·       They classified snow as dry, wet, and dry-wet, and mentioned that the type of snow depends on the outdoor temperature. Is this the only parameter you used to classify the type of snow? How can you be sure about the wetness level of snow?

·       They show the effectiveness of these surfaces against snow removal using MLI which depends on the snow weight. Can you also mention the minimum snow weight required for snow removal from the top performing surfaces for at least one experiment? This is just to visualize the minimum weight required for snow to fall from the surface.

·       In section 3.6, they show that SH-1 has a better performance than SL-1. But earlier, you showed that SH-1 works very well for dry snow, while SL-1 is the better coating for wet snow. How do you explain that SH-1 was better than SL-1 for all snow events (A, B, C, and D) in section 3.6? and what was the type of snow for these events (dry, wet)?

Some minor comments:

·       For figure 9, can you be consistent with the colors used (black and grey)? For example, “ERL” is written in grey and in black.

·       For figure 11, the x-axis title is “Time interval (15 min)”, and the numbers on the x-axis range from 0 to 2400. What do these numbers mean? How do they relate to the “15 min”?

·       The same comment applies for figure 12, where the numbers range from 0 to 900.

·       They have not properly referred to snow literature. Some of the papers recently published in this journal could be cited easily…

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript claims coatings with hydrophobic, superhydrophobic and slippery surfaces have an effective anti-snow performances. The author exhibits the delay in snow accretion on the surface and/or the early shedding of the snow-sleeve based on the original anti-snow technology, which have a certain significance. Meanwhile, this study is therefore of both fundamental and practical value, but of limited novelty. The authors are suggested to explain the following concerns:

1. The equation MLI = max ERL_sample/max ERL_reference  (1) should be (4)，Please correct it.

The equation number was corrected.

2. Can the author explain in detail about the adhesion reduction factor (ARF)?  How is it calculated?

ARF is the ratio between the average shear stress measured on the bare Al alloy and the average of shear stress measure on samples. Text was modified from row 336 and an equation was also added.

3. The experimental temperature in table 1 is 25 ^oC?

The temperature was added in the manuscript (23°C ± 2 °C) at row 153

4. The length unit in Figure 6 is wrong, please correct it.

The length unit was corrected (m instead of mt)

5. Data graph with Figure 5,9,11 and 12 is a little rough, please revise it.

Higher quality graphs were included in the manuscript

6. Please give the scale bar in fig. 2.

The scale bar in the fig. 2a is reported. We added the sizes of the AFM image in the caption.

7. For the influence of anti- snow materials, the author shall give some recent progresses, e.g., Proc Natl Acad Sci U S A, 114(43), 11285-11290, [2] CCS Chemistry, 3 (2021), pp. 473-480, [3] Nature, 576(7787), 437-441, so that the readers could have an updated picture of the field.

References to suggested papers were added in the introduction paragraph (line 80)

Reviewer 4 Report

The manuscript “The anti-snow behaviour of icephobic coatings: laboratory and in-field testing” is devoted to the testing of different coatings on alumina wires for anti-snow protection 

in laboratory experiments and during real snow events. The set of studied coatings contained superhydrophobic, hydrophobic and two solid coatings with the slippery behavior.

The work is original and reports on novel results which are of great interest and importance for a wide society of researchers working in the field. In essence, this is the first study, presenting the climatic testing of snow-phobic coatings on long wires (80m.) in real climatic conditions of the Italian Alps. The manuscript is well organized and well written and therefore deserves acceptance as a good contribution to the field. The major part of discussion and conclusions is adequately supported by the experimental data. However, several experiments were inappropriately designed, which did not allow authors correctly correlating the samples wettability and the snow-phobic behaviour. Thus, the acceptance of this manuscript  is recommended upon its revision. The Reviewer believes that such a revision will strongly enhance the attractiveness of this manuscripts to the readers. Below are just a few comments/suggestions that might help improving the manuscript.

1. Please explain in the text, what was the reason of the different heat treatment temperature (70° versus 120°) for the superhydrophobic and the hydrophobic samples .

2. The main flaw of this experiment is related to erroneous measurement of the sample’s wettability at low temperatures.

The authors have detected strong deterioration of the contact angle and increase in roll-off angle for SH1. Evidently, this results from the supersaturation conditions arising due to inappropriate experimental design. The room air, even being undersaturated at room temperature, appears to be supersaturated with respect to the substrate temperature (-4°C). For the porous coatings like SH-1, the supersaturation may cause condensation inside the pores and the resistance to such condensation is defined by the capillary pressure inside the pores, hence by the pore sizes. The contact angle measured in such conditions has nothing to deal with the characteristic wettability of the sample at considered temperatures. The accurate measurements of the contact angles of superhydrophobic samples at humidity close to 100% were performed in the papers DOI: 10.1021/la403796g , 10.1063/1.3680567 and a weak deterioration of the contact angle was demonstrated there.

Thus, to compare the wettability of samples at different temperatures, the authors should ensure the similar humidities and avoid the supersaturation. The Reviewer believes that in such conditions, the authors will get very different result. Also, please note that the supersaturated conditions will influence the wettability of not only SH1 sample, but others as well. The newly measured contact and RA/SA angles will allow more accurate characterizing of the correlation between the wettability and snow-phobicity.

3. The authors write “as SH-1 at low temperature evidences high water adhesion, the liquid water in the snowflake sticks to its surface, and this effect is also magnified, with respect to HP, by the high surface area of SH-1 due to the micro-nano roughness.” However, this effect may be related to inappropriate way of the surface texturing to get the superhydrophobic state. It was well documented in the literature that mechanically weak coatings do not resist the mechanical loads arising during water freezing/melting or being subjected to damage in cyclic temperature variation conditions. The texture, used in this study, was shown to be not resistant in above conditions and under abrasion loads accompanying the snow shedding (DOI: 10.1016/j.ceramint.2021.01.009, 10.1021/acsnano.8b09549, 10.1016/j.jcis.2011.02.036). Thus, the phenomena observed in this manuscript may be related to the peculiarities of the prepared sample. It would be interesting to get (this is not obligatory, but might be very useful) the information on the prolonged exposure and performance of SH1 in exploitation conditions.

4. The interpretation of the vibration bonds, given in the manuscript, is not accurate enough.

The bond 2871 cm-1 is associated to the stretching vibration of C-H bond in methylene group, the broad band around 3400 cm-1 is related to the O-H stretching vibration in water molecules interacting via hydrogen bonds.

Author Response

Please see the attached file 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have revised the manuscript and answered all the questions. After check and read the revised manuscript and the responses. I have no other questions. This manuscript can be accepted in current form now

Author Response

Reviewer 4 Report

The required experiments were successfully performed. The manuscript is recommended for publication in present form.