Review Reports - Monitorization of Cleaning Processes from Digital Video Spatiotemporal Analysis: Cleaning Kinetics from Characteristic Times

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors report a digital video based tool that monitors color changes during cleaning processes to determine the efficacy and kinetics of the cleaning process. The process employed is very basic and does not take into account variabilities with respect to cleaning agents, and substrates. For example, would this technology work if the cleaning agent is not colorless or if the metal substrate is colored? Some of these uncertainties are visible for the case of peanut butter cleaning process which could not be accurately quantified given the low variance in color changes. Additionally, how does the authors determine the surface is actually clean, given there is no pre- and post-characterization of surface organic residues on the steel surface. As such, I would not recommend publication of the manuscript in its current state.

Comments on the Quality of English Language

The quality of English needs to be improved throughout the manuscript, particularly in the introduction.

Author Response

Answer to Referee 1

The process employed is very basic and does not take into account variabilities with respect to cleaning agents, and substrates. For example, would this technology work if the cleaning agent is not colorless or if the metal substrate is colored? Some of these uncertainties are visible for the case of peanut butter cleaning process which could not be accurately quantified given the low variance in color changes.

We agree with some of what has been said. We know that this is a basic methodology, and we do not intend to universalize this way of working. This work proposes the use of this methodology to kinetically optimize standardized cleaning processes. We have modified the text in the introduction and conclusion sections to clear the real aim of this work. The interest of this methodology is in situ monitoring of the process, which does not mean that it cannot be used in conjunction with other techniques, preferably also in situ.

Regarding the possibility of following the process when the detergent is not transparent or the electrode is not bright, we have previous results of copper electrodeposition from copper sulfate solutions (bluish) on composite materials with high graphite content (black) where it was possible to follow the growth of the copper layer[1]. It must be considered that with this technique we measure color changes and not the absolute color and in the three coordinates (RGB). Therefore, although no changes can be seen in blue (if it is saturated in blue), they are detectable in red and green.

Finally, the reviewer comments of low variance in color changes in the case of peanut butter. The experimental results show significant relative color changes during the cleaning process. It is true that sometimes the color change is not clearly visible to the naked eye, but the technique does allow these changes to be quantified. We have added this consideration into the introduction section.

Additionally, how does the authors determine the surface is actually clean, given there is no pre- and post-characterization of surface organic residues on the steel surface. As such, I would not recommend publication of the manuscript in its current state.

The aim of the work is not to evaluate the usefulness of the cleaning product since this has already been tested and proved. We propose the use of our methodology to characterize the kinetics of cleaning process. We have amended the text to make it clearer.

We have revised and corrected the grammar of the text and changed some parts of the manuscript for better understanding.

We hope that after these corrections we have been able to better define the real purpose, interest and applicability of the work.

Thank you very much for your criticism and comments. We sincerely believe that they have helped to improve the work considerably.

References

Agrisuelas, J.; García-Jareño, J.J.; Guillén, E.; Vicente, F. RGB Video Electrochemistry of Copper Electrodeposition/Electrodissolution in Acid Media on a Ternary Graphite:Copper:Polypropylene Composite Electrode. Electrochimica Acta 2019, 305, 72–80, doi:10.1016/j.electacta.2019.03.016.

Reviewer 2 Report

Comments and Suggestions for Authors

Authors present a very interesting study on the monitorization of cleaning processes for specific cases that could be applied to more general cases. The manuscript is well writen and data analysis and interpretation of results are in general good.

Before possible acceptance some issues need to be attended:

In lines 192-193 please add information on how do kinetic orders are defined.
From figure 2 caption, please explain in detail in the main text of the manuscript what does n order reaction mean in the context of their study?
Please revise the phrase: "are not very large size" in line 221
From discussion in line 228, if chemical reactions occur when dissolving dirt, do you have an estimate of solution degradation with accumulated use?
Please deepen discussion on the behavior of time evolution of variance presented in lines 245-251, speciffically, commenting on why the lack of thickness homogeneity is related to the appearance of a shoulder at 9 h in fig 4B.
in line 320 write times longer, instead of timeas greater.

Author Response

Answer to Referee 2

Before possible acceptance some issues need to be attended:

In lines 192-193 please add information on how do kinetic orders are defined.

We have added more information and 2 equations about the kinetic parameters and their relationship with the mean color intensity.

From figure 2 caption, please explain in detail in the main text of the manuscript what does n order reaction mean in the context of their study?

The new equation 3 introduces the kinetic order parameter of the cleaning process. The added paragraph corresponding to point 1 also explains this point.

Please revise the phrase: "are not very large size" in line 221

We correct it in the new version of the manuscript. Thanks

From discussion in line 228, if chemical reactions occur when dissolving dirt, do you have an estimate of solution degradation with accumulated use?

Thanks to the reviewer for the observation. We do not have an estimate of the actual degradation of the cleaning solution and we cannot be sure that after filtering and removal of product residues, the solution will still be effective. We therefore prefer to delete this paragraph in the new version of the manuscript to avoid any misunderstanding.

Please deepen discussion on the behavior of time evolution of variance presented in lines 245-251, speciffically, commenting on why the lack of thickness homogeneity is related to the appearance of a shoulder at 9 h in fig 4B.

We have added these lines at the end of the paragraph explaining why shoulders appear:

“The inhomogeneity of the dirt layer can mean that it takes longer for regions with a thicker dirt layer to remove it. Translating this into a change in variance, there will be a portion of the surface where 50% of the last layer has been removed and therefore the variance will be at its maximum, while other portions have not yet reached 50% and will have lower values. This means that the ideal predicted peak shape is partially deformed and shoulders can appear. When a small region is analyzed, the peak shape appears without a shoulder.”

This is better understood looking at Figure 6B: 3D plots of variance of color intensity of red color against the elapsed time and the distance in pixels. In this plot it is shown how the maximum in variance is reached at different times on different parts of the metal surface.

in line 320 write times longer, instead of timeas greater.

We have corrected it, thank you for the correction.

We would like to thank the referee for his constructive criticism, which undoubtedly helps us to improve the clarity of the presentation of our results and conclusions.

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors,

The manuscript presents an innovative approach to understanding cleaning kinetics through color-change analysis. The concept is concise, and the experiments are logically designed, making it a valuable contribution to publication. However, there are a few suggestions for improvement:

1. Please modify Table 4 regarding the term "Not observed," as its placement is unclear.

2. Since the cleaning process is divided into two stages—whitening and peeling—the combined dynamics may be challenging to analyze. In reality, these two processes might overlap, making it difficult to accurately identify the kinetics using the models presented in Table 2, especially for the peeling process in the manuscript. This issue could stem from relying solely on the average color intensity (Ī) as the standard. For instance, under zero-order kinetics, Ī is expected to be linear with time (t), yet the individual pixel intensities, I(j) (j = 1, 2, ..., n_p), may not necessarily follow a linear trend with time. Thus, accounting for changes in individual pixels appears crucial for a more accurate description of the cleaning kinetics.

Author Response

Answer to Referee 3

Dear Authors,

Please modify Table 4 regarding the term "Not observed," as its placement is unclear.

Thank you for this remark. Indeed, it was not clear what 'not observed' referred to. We have changed to grey shaded cells when the process is not observed.

Since the cleaning process is divided into two stages—whitening and peeling—the combined dynamics may be challenging to analyze. In reality, these two processes might overlap, making it difficult to accurately identify the kinetics using the models presented in Table 2, especially for the peeling process in the manuscript. This issue could stem from relying solely on the average color intensity (Ī) as the standard. For instance, under zero-order kinetics, Ī is expected to be linear with time (t), yet the individual pixel intensities, I(j) (j = 1, 2, ..., n_p), may not necessarily follow a linear trend with time. Thus, accounting for changes in individual pixels appears crucial for a more accurate description of the cleaning kinetics.

We agree with the reviewer that it is not always possible to separate superimposed processes. This is a simplified model, but it provides valuable information on the overall kinetics and in some cases has allowed the separation of superimposed processes [2,3].

We also agree that analysis only the average color intensity may not be a solution in many cases, but the idea of analyzing the evolution of all individual pixels turns into very complicated due to the large amount of information to process. For example, a 100x100 pixel image contains 10000 pixels, which multiplied by 3 coordinates to characterize each pixel makes 30000 points per image/photo. If we follow its evolution in time at 1 image per second for 1 hour, it makes 108x10⁶ data to be processed. This makes us work with statistical parameters such as average color intensity and color variance to summarize this information[4,5].

However, in this technique there is always the possibility to select a part of the image for more localized information, or even the 3D maps (Figures 6, 8 and 10), which are a very good approach to the temporal evolution of color in different parts of the metal surface.

We have added a short explanation of the need for statistical parameters in these analyses.

We sincerely appreciate the reviewer's ideas and suggestions. The inclusion of these ideas in the text helps the reader to better understand the work.

References

Agrisuelas, J.; García-Jareño, J.J.; Guillén, E.; Vicente, F. RGB Video Electrochemistry of Copper Electrodeposition/Electrodissolution in Acid Media on a Ternary Graphite:Copper:Polypropylene Composite Electrode. Electrochimica Acta 2019, 305, 72–80, doi:10.1016/j.electacta.2019.03.016.
García-Jareño, J.J.; Agrisuelas, J.; Vargas, Z.; Vicente, F. Electrogeneration and Characterization of Poly(Methylene Blue) Thin Films on Stainless Steel 316 Electrodes—Effect of pH. Molecules 2024, 29, 3752, doi:10.3390/molecules29163752.
García-Jareño, J.J.; Agrisuelas, J.; Vicente, F. Overview and Recent Advances in Hyphenated Electrochemical Techniques for the Characterization of Electroactive Materials. Materials 2023, 16, 4226, doi:10.3390/ma16124226.
Agrisuelas, J.; García-Jareño, J.J.; Vicente, F. Quantification of Electrochromic Kinetics by Analysis of RGB Digital Video Images. Electrochem. Commun. 2018, 93, 86–90, doi:10.1016/j.elecom.2018.06.011.
Agrisuelas, J.; García-Jareño, J.J.; Guillén, E.; Vicente, F. Kinetics of Surface Chemical Reactions from a Digital Video. J. Phys. Chem. C 2020, 124, 2050–2059, doi:10.1021/acs.jpcc.9b10689.