Morphology of Anisotropic Banded Structures in an Emulsion under Simple Shear
, Marco Antonio Reyes Huesca 1, Federico Méndez Lavielle 1 and Enrique Geffroy Aguilar 2Round 1
Reviewer 1 Report
In their manuscript, Leiva-Mateus et al study banded structures in a water-in-oil emulsion under constant shear. Specifically, they use a commercial device to study the impact of varying shear rate on the banded structures and their dynamics. Their main conclusions are that the local viscosity of the emulsion varies in space according to the local density of drops, which leads to non-vanishing radial component of velocities and the formation of banded structures.
The main text is well-written. However, the figures and, especially, their captions, need to be substantially improved if they are to be published. Right now, most captions are in the state of those in a draft, and are not to the standards of a manuscript ready for scientific publication. Additionally, I raise some important concerns about the accuracy of the data analysis and some of the plotted data. Finally, I am concerned that Supplementary Figure S6 might be an instance of plagiarism.
I will possibly recommend this manuscript for publication if the authors carefully address my questions and concerns, as detailed below.
All figures
- The authors should *revise all figure captions* and make sure to (1) reduce to a minimum their extensive use of colons, semicolons, and em-dashes and (2) formulate more complete, grammatically sound sentences. In their current state, the captions are often quite confusing, even for a fluent English speaker.
Figure 1
- What is the numerical aperture of the microscope objective used? This will determine the imaging resolution. I could not find it, even in Ref. [30].
- Specify in the caption that “gradient” is a velocity gradient, and that “flow” refers to a mean flow
- Several elements of the figure are neither labeled nor explained in the caption: the green band, the cyan bands, the group of arrows that likely represent a linear velocity profile. They should be labeled and/or detailed in the caption.
- Why does the drawing represent velocity arrows for a purely linear flow accurate, when flow might in fact not be linear? As the authors themselves point out at l.279, the vertical velocity profile might be nonlinear. I would strongly suggest to add to the caption, as written in l.295, that this is only “the initial assumption of a linear, unidirectional velocity profile.“
- Shouldn’t the thickness of the imaged fluid on the right hand side match the thickness of the sheared fluid (i.e., gap) on the left hand side? Where are the cyan layers on the left hand side illustration?
- Does H equal 100 um? H should be added to the figure as an annotation.
- Does v_max equal the speed of the bottom disk?
- How is \dot{\gamma} calculated?
Table 1
- “Standard Deviation” of which observable? Probably add “of Velocity”
- “Relative Deviation” of which observable? Probably add “of Velocity”
- The number of significant digits are inconsistent in a given column; Keep them consistent.
Figure 2
- Given the circular geometry of the device, wouldn’t it be more relevant to use velocities in rad/s instead of um/s?
- Include \bar{v} in the legend, since it already includes \bar{v}/v_max.
- Indicate what quantities the error bars represent, e.g., standard deviation, standard error, etc
- Slopes m_1 and m_2: Are these linear regressions? If yes, what is the R value of those fits and the uncertainty on m_1 and m_2?
- Use the same values of m_1 and m_2 in both the caption and the annotations in the figure.
- Can the authors prove that the decrease of \bar{v}/v_max for the three highest shear rates is statistically significant? If yes, they may keep their statement l.238-239; If not, there is no basis for this statement.
- It would be very helpful to show on the plot the value of shear from which “the banded structure of the emulsion occurs” for instance by adding a vertical line that shows, and is labelled as, the shear rate for which the banded structure appears.
Figure 3
- According to which criteria are the “valley or peak” regions defined? Add the explanation for this criteria to the caption.
- It would be helpful to increase the contrast and/or change the color map of the micrograph inserted at the bottom of the plot to make the density changes more obvious.
- Detail how many drops are “few drops” and how many drops are “many drops”
- I am skeptical that the “mean velocities” represented as red markers would correspond to the mean of the corresponding velocity data point shown in this plot (especially the 1st, 3rd, and 7th data points). Are the authors confident that their data points are accurate? If yes, can they comment on my remark?
- “Higher velocities coincide with regions of lower concentration of drops“ I am skeptical of this statement, and will need confirmation that the plotted “mean velocities” are accurate before reassessing. But at the very least, currently, the first mean velocity data point invalidates this statement. Can the authors comment on that as well?
- I would strongly recommend adding error bars or box plots to the “mean velocity” averages
- What is the red line supposed to represent? What kind of fit is it? This is not explained neither in the legend nor in the caption.
Figure 4
- Why is this figure useful? It is for the very most part redundant with Figure 1.
- What is the “3d projection”? Is it actual data or only an illustration? This should be specified.
- What does “about the center” mean? The framed region (light blue dashed lines) is not at all near the center of the image.
- What does “Zone of a band” mean? What defines the boundaries of such a “zone”?
- Based on what evidence or principles do the author think that the “zone of a band” has a circular cross-section?
- Here as well, it should be added to the caption, as written in l.295, that the red arrows represent only “the initial assumption of a linear, unidirectional velocity profile.“
Figure 5
- What is the uncertainty on v/v_max values? Consider adding error bars.
- What does “better-defined bands” mean in quantitative terms?
- “It is an expanded view of the densest band's selected region” is a confusing statement. I recommend replacing it by something like “(b) shows the densest band region”.
- Right panel is missing a horizontal axis label; vertical axis label can be omitted.
Figure 6
- Figures 4, 5, and 6 share a lot of redundant information. I strongly recommend merging Figures 4, 5, and 6 into a single figure, and removing all redundant information.
- The only new information in Figure 6, as compared to Figure 5, are the red bands and the “GAP” vertical axis in panel a). Do these justify keeping Figure 6 as it is?
- If the authors chose not to merge those figures, then they need to keep consistent between them the orientation of the vertical axes of v/v_max.
- In the caption, “Left axis” and “right axis” are mistakenly switched.
Figure 7
- Is the colorbar “counts” or “frequency”? If it is count, it makes no sense to use anything else than integers on the axis. Note that Counts are probably irrelevant. A more relevant quantity that can be actually compared to the model is the fraction of droplets of a certain size for a given shear rate, not their absolute numbers (i.e., counts).
- Is “2.R_cr” (legend) the same as “C a_cr” (caption)? If yes, choose either, or write their equality explicitly in the caption or legend.
- What boundaries does each of the black dashed lines represent?
Figure 8
- Indicate the shear rate for all panels
- Based on my understanding on the plots, I would expect the sum of the histograms in c’) and d’) to equal the histogram in b’). Why is it not the case?
- Again, how are “valleys” defined? How are “flow regions” defined? Is a “flow region” identical to what the authors called a “peak” in Figure 3?
- What is the fraction of non-spherical drops?
- What is the fraction of drops larger than 40 um in diameter, that is, those excluded from the histogram plots?
- “Size diameter”: choose between "size" and "diameter"
- The following sentence does not make any grammatical sense, and I do not understand it: “processed image selecting spherical drops only: the sum of all-spherical drops, color-coded by size: total number of drops counted ??????=1460, with volume ??????=6×107 μm3”
- Adding “(top)”, “(middle)”, and “(bottom)” when panel letters are already used, is confusing
- What does “high” mean, in quantitative terms, in “flow region of high concentration”
Figure 9
- What is D_4,3? Add reference to main text
- Where is D_cr defined?
- What do regions “I”, “II”, “III”, “IV”, and “V” refer to? They should to be defined in the caption, or at the very least, unambiguous references to “Regime I”, “Regime II”, etc, should be added to the relevant sentences of the main text.
- Why are there 2 red lines labelled identically “D_cr/H”?
References
- The format of the references is inconsistent (e.g., ref. [1] vs ref. [2]) and need to be fixed.
Supplementary Figure S6
- The graphics that the authors use in this figure is copied from the webpage https://www.originlab.com/doc/en/Origin-Help/GaussAmp-FitFunc. It would appear that the authors use this graphics without permission (the webpage specifies “all rights reserved”) and without citing the source of the graphics. This seems to me quite inacceptable.
- Furthermore, the first sentence of the caption is clearly incorrect, since the figure does not show any experimental data.
Supplementary Figure S7
- There is no label to the left axis of panel a)
- I do not see how +/- 2 standard deviation is not twice as far from the average intensity as +/- 1 standard deviation. Can the authors comment on this?
Supplementary Figure S8
- What does “[…], for to peaks” mean?
The quality of the language is good in the main text, however, surprisingly, the figure captions are barely intelligible and need substantial improvements.
Author Response
We appreciate you for your precious time in reviewing our paper and providing valuable comments. It was your valuable and insightful comments that led to possible improvements in the current version. The authors have carefully considered the comments and tried our best to address every one of them. We hope the manuscript after careful revisions meet your high standards. The authors welcome further constructive comments if any.
Below we provide the point-by-point responses. All modifications in the manuscript have
been highlighted in red.
Sincerely,
Eduardo Leiva
eleiva@iim.unam.mx
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The paper under review deals with the research on morphology of banded structures in an emulsion (water in oil) under simple shear. The authors showed results and in my opinion very good their detailed description. The results in this paper are achieved via experimental and computational study. A structure of the paper is in accordance with principles of scientific reports. The article contains adequate and appropriately selected 42 literature items. However, single items were published within five years, which proves the novelty of the issue taken up by the authors. The article tackles an issue in the formation of flow-induced, oriented structures in two-phase systems is suitable for Fluids - Special Issue: Waves in Viscoelastic Fluids.
The authors focused on the effects of confinement factor, viscosity ratio and the applied shear rate. Furthermore the authors showed that a detailed analysis of the dynamics of the bands structures is possible, as well as the measurement of the flow field anomalies that are simultaneously observed. The authors carried out observations of the induced structure under different simple shear rates, as well as statistical and morphological analysis of these bands. The authors noticed that the emulsion changes macroscopically with time. These changes are attributed to the effects of coalescence and rupture of drops. However, I have doubts to improve the conduct of the experiment.
In my opinion, this article can be accepted for publication in Fluids after major revision.
Comments:
1. References must be corrected in accordance with the rules of Fluids.
2. I have doubts about improving the conduct of the experiment. Has the sample been protected against evaporation during its storage and during the tests on the rheometer? The obtained results may be caused by a change in the composition of the sample by evaporation. Please comment on this.
3. Where can the obtained mixture be used? Please, add additional comment about practical aspects.
4. Page 3 (114,115) - please correct sentence. (…them. Ca >> Cacr, Droplets…)
5. Page 3 (130) - O/W is an oil in water emulsion, and according to your description it is a W/O - water in oil emulsion. Please specify correctly.
6. Page 3 (140,141) - please write the viscosity units correctly
7. Page 3 (142) - please write the shear rate unit correctly
8. All Figures should be shifted to the right or be re-scaled
9. Table 1 should be shifted to the right or be re-scaled
10. Page 10 - What other perturbations? Can you explain more?
Author Response
We appreciate you for your precious time in reviewing our paper and providing valuable comments. It was your valuable and insightful comments that led to possible improvements in the current version. The authors have carefully considered the comments and tried our best to address every one of them. We hope the manuscript after careful revisions meet your high standards. The authors welcome further constructive comments if any.
Below we provide the point-by-point responses. All modifications in the manuscript have
been highlighted in red.
Sincerely,
Eduardo Leiva
eleiva@iim.unam.mx
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
I thank the authors for carefully addressing my first report and I do appreciate their thorough reply. I am satisfied with all the replies that I do not address below. Note that page numbers below refer to the author’s reply PDF.
The manuscript seems nearly ready for publication to me, provided that my comments below are addressed, especially those on Figure 2.
p.3-4 - Figure 1
I appreciate the details provided my the authors on how to obtain NA of their system. However, as a note, NA = lambda / (1.22 * Resolution) = 0.55/(1.22*4.921), which means NA = 0.09 (and not NA = 0.06, as written in the reply).
p.5 - Figure 2
- Figure 2 has apparently not been updated, and the caption still needs to be improved.
- Caption: At the very least, the sentence between l.250-253 needs to be re-written, so that it makes sense.
2 - Not done. Figure has apparently not been updated.
3 - Not done. Should be specified in the caption.
4 - Add to caption (or main text) that m1 and m2 were obtained by fitting linear functions, and add the R-Squares values either as annotations in the figure, or in the caption.
Additionally, note that m1 = 49.76571 rounds up to 49.77, not 49.76.
6 - The two statements “6- The dimensionless velocity values for 2.25 and 3.00 are 0.51 and 0.45 respectively. The decrease is 12.1 %” (reply) and ”12.1 % for the three highest shear rates. ” (caption) seem incompatible, i.e., the statement in the caption is inaccurate.
6- Furthermore, importantly, I inquired in my first report whether “the decrease of \bar{v}/v_max for the three highest shear rates is statistically significant ”. This concern has not been addressed in the authors’ reply. I would suggest running a Student’s T test, between each of the 3 largest shear rates and 2.25 s^-1, and reporting the obtained p-values in the caption to demonstrate whether, despite the large error bars, there is a statistically significant change of \bar{v}/v_max.
p.7-8 - Figure 3
3 - I would recommend adding the table you included in your reply to the SI, as I find it useful.
4 - I had indeed missed that the scales on the left and right axes were not the same. I do think that that the new version of the figure, i.e., using the same scales, is an improvement as it makes it easier for the reader to understand the data. (Also note that it is unusual to add an extra axis for the mean of the data which is already plotted and labeled on the left axis.)
p.9 - Figure 4
I do think that the manuscript gain in clarity with this new Figure 4.
- Note that “(left axis)” and “(right axis)” are still incorrectly assigned (they should be the opposite).
p.12 - Figure 6
The updated caption makes much more sense.
- Still, “contained in the green area ” and ”contained in the blue area” seem inaccurate (the areas are contained in the plots, not the opposite), thus I would suggest removing them.
p.13 - Figure 7
The updated caption is very satisfying.
p.14 - Figure S7
- “2- For a normal distribution (Gaussian curve) […]” Your reply makes sense. My misunderstanding came from the legend in Figure S7: I would suggest replacing “+/- X standard deviation” by “”data within +/- X standard deviation”, which seems more accurate to me.
The language in the caption of Figure 2 can still be substantially improved. The language in the other updated captions is now good.
Author Response
Dear Reviewer,
Thanks so much for sharing your experience with us. Especially with the corresponding author who is in a continuous learning process.
Best regards.
Author Response File: Author Response.pdf
Reviewer 2 Report
I accept this article for publication in the Fluids.
Author Response
Dear reviewer
Thank you for sharing your experience with us.
Best regards
Round 3
Reviewer 1 Report
I thank the authors for their second reply. I believe that the review process was quite constructive and the manuscript was improved. I am satisfied with the author's reply and the latest version of their manuscript and supplementary files. I recommend this manuscript for publication.
