Nanoscale Correlations of Ice Adhesion Strength and Water Contact Angle

Round 1

Reviewer 1 Report

In this manuscript the Authors consider the correlation between ice adhesion and water contact angle. This is done by carrying out molecular dynamic simulations for the liquid water/graphene and ice Ih/graphene systems. The general conclusion is that there is indeed a relationship between the two quantities. Since experimental results show that this is not always the case, a discussion is provided as to the origin of the discrepancies.

I find the manuscript to be very interesting. The topic is of great practical interest and this work brings some molecular-level insight to the table. Below are several issues that should be considered prior to eventual publication:

1) While discussing the difference between the water contact angle from simulation vs. experiment. The issue is even more complicated. One has to ask the question how many graphene layers should be used in simulation (and how many were used in experiment). The contact angle will depend on that, cf. Mabudi et al., Colloids and Surfaces A 569 (2019) 43-51. Another important problem is that the single or double graphene layer cannot be realized in experiment as sheet(s) floating in the air. They have to be supported on some substrate, it can be silicon, it can be nickel, glass etc. The contact angle may depend on that as well. Only for sheets thick enough the onset of the supporting substrate becomes negligible. Yet another issue is the possibility of contamination by the air-borne alkane molecules, cf. Terzyk et al. Langmuir 35 (2019) 420-427.

2) The theoretical relations are of somewhat limited use as they compare quantities evaluated at different temperatures, and of course depending on the temperature these quantities will vary a bit. It is fair to say that full microscopic understanding of this problem has not been achieved yet.

3) What was the cut-off distance used for Lennard-Jones interactions? What was the distance for switching from real space to k-space calculations for PME method? What was the time used for calculating the averages (the water contact angle) in the case of liquid water? I mean, the instanteneous value of the contact angle may well differ from the equilibrium one, one has to perform the time average in order to get a meaningfull quantity.

4) One has to bear in mind that TIP4P ice was designed to describe the solid phase and the solid-fluid melting temperature as best as possible, but the description of the liquid water phase, particularly at room temperature, is worse than that in other TIP4P models.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The paper presents a molecular dynamic study on ice adhesion on graphene substrate. The goal is to investigate the correlation between wetting properties (i.e. contact angle) and ice adhesion.

The paper is overall well written, and the claims are supported by the data shown. Before I can recommend publication, however, I have a few comments that the authors should address to improve the paper.

1. The correlation from Eq. 6 works well when γ_w ≈ γ_i and γ_w,s  ≈ γ_i,s. As such, it may not be too surprising that Eq. 6 holds well even at the nanoscale, if the water/ice model that has been used  (TIP4P/ICE) provides similar interfacial tension for ice and water. The authors should thus explicitly provide the values γ_w, γ_i, γ_w,s  and γ_i,s and comment on the validity of Eq. 6 on the basis of such values.
2. The authors say only on page 13, line 295-296, that “Furthermore, in contrast to most experimental ice adhesion tests which utilises shear force [16], the ice adhesion strength in this study was determined through tensile ice detachment.”. This should be clearly stated upfront, since other works have clearly highlighted the difference of applying normal vs. tangential stress (https://doi.org/10.1002/admi.201500330).
3. It is not clear to me why systems A, B, C and D give statistically different results. I understand the difference is only the dimension. Is there anything else? If not, please explain why differences are observed.
4. Simulated adhesion tests have been performed at 180 K. It should be clearly stated that ice adhesion can change at different temperatures.
5. 8 does not really have any physical meaning. It can be removed.

Author Response

Please see attachment.

Author Response File: Author Response.docx