Dropwise Condensation Mechanism on Smooth Hydrophilic Surfaces

Round 1

Reviewer 1 Report

This work utilises surface plasmon resonance and is a prime example of where the technique can find more widespread acceptance. The technique is ideally suited to examining water and surfaces such as this. It would be nice to se it replicated with hydrophobic surfaces and developed as a measure of the wetting/properties f experimental hydrophobicity.

The paper is well written and very clear, without making too many claims.

Author Response

Thanks for your support. The manuscript was professionally proofread again to fix errors. 

Reviewer 2 Report

Compared to the filmwise condensation, the dropwise condensation has not been fully understood yet. The authors attempted to contribute to this difficult problem by using the Surface Plasmon Resonance Imaging (SPRi) for two kind of experimental setup of the Stable Dropwise Condensation (SDC) and the Unstable Dropwise Condensation (USDC). The visualized figures seem quite nice and have high resolution especially in thickness direction, which is owing to the use of SPRi. In this study, the authors concluded that neither the nucleation theory nor the film rupture theory can individually explain the physics of dropwise condensation. In my opinion, the paper seems valuable enough to be published in the journal but the following points should be reconsidered by the authors to further improve the quality of this paper. 

1. In the title, the word 'smooth' is included. I wonder how flat the surface of the gold layer is. The surface roughness could affect the dropwise condensation.
2. In the title, the word 'Hydrophilic' is also included. The value of the contact angle between the water droplet and the gold thin layer should be informed if it has been known or it can be measured. 
3. In the introduction, experimental studies are introduced, but the numerical ones are not appeared. Are there any studies using the molecular dynamics simulation for this kind of dropwise condensation? If there are some such studies, I would suggest the authors try to introduce some of such numerical attempts in the introduction. 

Minor items:

1. A figure caption number must be modified. Figure 1 in page 8 should be Figure 8.
2. The instantaneous time (a) and (b) in Fig. 5 should be in page 6. 

In conclusion, minor revision would be necessary before recommendation for publication in the journal.

Author Response

Thanks. See the attached, our response to your comments.

Best,

CK

Author Response File: Author Response.docx