The Influence of Mechanical Deformations on Surface Force Measurements

Round 1

Reviewer 1 Report

Accept.

Author Response

Thank you.

Author Response File: Author Response.pdf

Reviewer 2 Report

The author has made an interesting research on the measurement of surface force, and I think the results have a very good reference and guidance for the research in this field. The article is well written, and there is only one question for the author to answer

According to my understanding, I don't see the reason for choosing ionic liquids, and will the structural type of ionic liquids affect the test results?

Author Response

The choice of the ionic liquid is justified at line 92 of the manuscript: “… measurements are performed with an ionic liquid, because these liquids have proved to resist squeeze-out even under very large loads [21], a regime in which significant mechanical deformations of the surfaces are expected.” In other words, the results presented in this paper are not specific to ionic liquids, but thanks to their remarkable resistance to squeeze-out ionic they are systems of choice to investigate the influence of mechanical deformations on surface force measurements.

Many experimental studies have examined how the structural force varies when the ionic liquid or the confining substrates are changed (see for example references 62 to 72 of the manuscript). In particular, they showed that the period of the oscillation is given by the mean ion pair diameter, and that the composition of the first layer depends on the surface charge. For the [C4C1Pyrr][NTf2]/mica system used in this paper, the detailed shape of the structural force profile is shown to be strongly affected by the mechanical deformations of the surfaces, with a mica compression that is dominant compared to the ionic liquid compression. I do not expect this conclusion to depend on the structural type of ionic liquids, but rather on the compressibility of the liquid film compared to the compliance of the confining solids: this is the essence of the scaling criterion presented in the last part of the manuscript.

Author Response File: Author Response.pdf

Reviewer 3 Report

This papers presents experimental data of surface force apparatus operated in dry and ionic liquid conditions. The analysis shows that some work on modelling the contact conditions should be continued. The manuscript is very well written and the analysis is detailed. I am not an SFA expert, but I always thought that SFA had to be operated in a fluid medium to get the rings. Could the author please clarify this? Otherwise, I think that the manuscript should be accepted.

Author Response

The SFA can be used with any confined medium, providing it is transparent enough to perform in-situ optical interferometry. This can be vacuum, a gas or a liquid (including apolar liquids, electrolytes, polymer melts, liquid crystals, colloidal suspensions etc.). Most of the time publications report on experiments with a liquid, but this is not required, and actually the first SFA experiments were dedicated to the measurements of van der Waals interactions across a gaseous medium (see reference 38 of the manuscript).

Author Response File: Author Response.pdf