The Effect of Electrolytes and Urea on the Ethyl Lauroyl Arginate and Cellulose Nanocrystals Foam Stability

Round 1

Reviewer 1 Report

There are a lot of publications devoted to the production and using of CNC. This work perfectly complements them.

On the one hand, it has been shown that the addition of сCNC contributes to a significant foam stabilization in a wide range of LAE concentrations, in comparison with sCNC. On the other hand, the action of various electrolytes is analyzed and it is shown that urea is an extremely strong defoamer in such systems.

1) Lines 41-54 I recommend adding a link to an extensive overview of CNC properties .https://iopscience.iop.org/article/10.1070/RCR4745 ( doi.org/10.1070/RCR4745 )

2) Line 66, 69 what is the sCNC ? Is it a typo or unnamed abbreviation of sulfated cellulose nanocrystals?

3) Line 163 Write in more detail how the dispersions were made. Ultrasonic power and treatment time are needed here. Was there a mechanical mixing before?

4) Line 314-342 Fig 7. The difference in the frequency dependence of the imaginary part of different modulus is described superficially.

 

Minor flaws:

5) Fig. 7. I propose to make the trend lines multi-colored for clarity. On axes, use a dot instead of a comma to separate the decimal part.

6) Line 201 I recommend making vertical axes at figures a and b with the same maximum (325 min) for a more visual comparison.

7) 234 The diameters data should be rounded.

Author Response

We appreciated the constructive criticism of the reviewer.  We have addressed each of concerns and questions below.  New or changed parts of the text in the manuscript was marked yellow.  We hope that our additional analysis and revisions in the manuscript help to improve its merit.

We also have to inform that following the Reviewer #3 recommendation, we shortened and changed the title of the manuscript and abandoned the title "Towards the interfacial action of urea in liquid foams with ethyl lauroyl arginate and carboxylated cellulose nanocrystals.  The effect of electrolytes and urea on the foam stability".  We made it shorter and more meaningful “The effect of electrolytes and urea on the ethyl lauroyl arginate and cellulose nanocrystals foam stability”.

 

Answers for 1# reviewer:

• Most of the literature concerning cellulose nanocrystals was cited in the introduction, for each application separately. The additional review of Surov et al. was also introduced as suggested by the Reviewer.
• The sCNC abbreviation was explained as sulphated cellulose nanocrystals – in Abstract, line 15 of the text
• The explanation of dispersion preparation was added, including ultrasonic power.
• The difference in the frequency dependence of the imaginary part might be linked to the increase of the dissipative losses in the system. Full explanation of the frequency dependence of imaginary part of the dilational modulus is very complicated for a multi-component system LAE-cCNC and deserves further investigations.  Analysis of the imaginary part of dilatational modulus in complex systems is hardly found in the literature for such systems. We modified the manuscript as follows:

“Upon addition of GauHCL, NaSal or urea its (i.e., the imaginary part of the dilational modulus values) were increased comparing to ones for LAE-cCNC, while 5 mM NaCl caused their decrease. Thus, addition of the simple salt (NaCl) renders the interfacial layer more elastic, presumably due to closer packing of nanocrystals.The presence of hydrotropic  NaSal or urea can induce forming of some dissipative structures at the interface, however that aspect needs further investigation.”

• The dot was used instead of a comma to separate the decimal part.
• Vertical axes were redrawn with the same maximum.
• The diameters data were corrected.

The misprints and minor errors found were also corrected.  

 

Reviewer 2 Report

This manuscript describes about enhanced foamabilty and foam stability of carboxylated cellulose nanocrystals (cCNC) with cationic surfactant ethyl lauroyl arginate (LAE).  Influences of some electrolytes and urea on the foam stability were examined.  It was found that urea has special effect to decrease the foam stability.  These findings are interesting and will be useful for future applications, although the detailed mechanism has not yet been elucidated.  The experimental data, discussion, and conclusions seem to be rational in general.  However, the introduction is too long and should be described more concisely.  The reviewer considers that it may be acceptable to be published in applied sciences after the revision of more concise introduction. 

Author Response

We appreciate the constructive criticism of the reviewer.  We have addressed each of concerns and questions below.  New or changed parts of the text in the manuscript was marked yellow.  We hope that our additional analysis and revisions in the manuscript help to improve its merit.

We also have to inform that following the Reviewer #3 recommendation, we shortened and changed the title of the manuscript and abandoned the title "Towards the interfacial action of urea in liquid foams with ethyl lauroyl arginate and carboxylated cellulose nanocrystals.  The effect of electrolytes and urea on the foam stability".  We made it shorter and more meaningful “The effect of electrolytes and urea on the ethyl lauroyl arginate and cellulose nanocrystals foam stability”.

Answers for 2# reviewer:

 

The introduction of the paper was shortened according to Reviewer’s suggestions.  We decided to omit the paragraphs concerning urea and guanidine hydrochloride effect on interfacial properties of proteins.  Most of the introduction concerning properties of cellulose nanocrystals is retained as it is consistent with applicability of our system.  Additionally, ee received other reviewers suggestions to introduce some applications of our system.

The misprints and minor errors found were also corrected. The list of references was modified accordingly.  

Reviewer 3 Report

The authors explored the foaming properties of mixtures of LAE and carboxylated and sulfated CNC and then studied the effect of the addition of electrolytes on ethyl lauroyl arginate – carboxylated CNC dispersions bulk and interfacial properties. The topic seems interesting, but there are still some issues to be resolved before publication.

1. The title of the manuscript is not suitable and needs to be revised.
2. After define those short names first, then we should use them, for instance, Carboxylated cellulose nanocrystals (cCNC).
3. Recheck 1 part-line 38-42 need citation and Page 2 part-line 66-72 need citation and more clear explanation.
4. Table 3 and Figure 3 need to be analysed in the manuscript.
5. The figures are mentioned as figure X or Fig. X. The format should be consistent.
6. No clear comparison between different test results. It is hard to find which finding is better.
7. The resolution of the most figures should be improved.
8. In Discussions section, it is necessary to add more explains.
9. The Conclusions need to be rewritten, and the future impact and consideration are not clear enough.
10. The whole manuscript need to be polished, which is lack of academic and format standardization. It is difficult to understand the meaning due to some grammar and spelling mistake and no using "of" in right place.

Author Response

We appreciate the constructive criticism of the reviewer. We have addressed each of concerns and questions below. New or changed parts of the text in the manuscript was marked yellow. We hope that our additional analysis and revisions in the manuscript help to improve its merit.

Answers for 3# reviewer:

• The title of the manuscript was revised. We made it shorter and more meaningful “The effect of electrolytes and urea on the ethyl lauroyl arginate and cellulose nanocrystals foam stability”.
• Carboxylated cellulose nanocrystals (cCNC) were defined in the first line of the abstract. The case with sCNC was corrected – defined.
• Line 38-42 contain the information included in Ref. 13. For clarity, the reference was shifted to the end of a paragraph. There are 3 citations in lines 66-72. The introduction contains only the hypothesis part without further references. The reference on that matter was added to conclusions,
• Data from figure 3 are analysed in lines 265-271. The figure (Fig.3) was mentioned in the revised version of the manuscript. Similarly, Table 3 was introduced before the description of relevant data from lines 273-291.
• The reference for figures is presented in abbreviated form in the text (Fig.1, Fig.2) but according to MDPI template names Figure 1, Figure 2, … are presented under figures.
• See explained for 8).
• Data from figures are now clear to read.
• Each experiment result is explained as well as cross-correlated. As an example, surface tension data and dilational elasticity were correlated with foaming experiments; dilatational experiments are correlated with aggregate size, elasticity in the presence of simple electrolyte is explained by electrostatic repulsion. The hypothesis for the specific effect of chaotropic and hydrotropic ions was formulated in the revised version. The more detailed explanation requires further experiments specific for that purpose and will be the subject for the next publication. Urea effect was hypothesized from the point of view of interfacial water orientation and increased solubility of larger aggregates. Careful analysis of the data presented might suggest that the second explanation is favorable.
• Conclusions were much extended with reference to further experiments introducing new measurement methods.
• The text is written following the template for the journal. We tried our best to correct grammar and spelling mistakes. References are also added and modified.

Reviewer 4 Report

The authors deal with the problem of preparing foams with sCNC and its properties.

The paper presents the method of foam preparation from sCNC and cationic surfactant LAE. The authors have only measured the surface tension and zeta potential of obtained foams. The paper can be accepted, but after some correction:

1. Line 39-40. The authors should highlight the possible application of sCNC foams. The authors have suggested the applications of their work in just one sentence. CNC has many exciting properties, and using them in foams for cosmetics seems very interesting.
2. The authors should add some experiments.
3. The authors should change the order of described methods in the method section. First, the Particle characterization section should be the following surface tension. In this order, the results are discussed section 3.
4. The authors should highlight the novelty of this work.
5. The authors should use the template provided by mdpi.

Author Response

We appreciate the constructive criticism of the reviewer.  We have addressed each of concerns and questions below.  New or changed parts of the text in the manuscript was marked yellow.  We hope that our additional analysis and revisions in the manuscript help to improve its merit.

We also have to inform that following the Reviewer #3 recommendation, we shortened and changed the title of the manuscript and abandoned the title "Towards the interfacial action of urea in liquid foams with ethyl lauroyl arginate and carboxylated cellulose nanocrystals.  The effect of electrolytes and urea on the foam stability".  We made it shorter and more meaningful “The effect of electrolytes and urea on the ethyl lauroyl arginate and cellulose nanocrystals foam stability”.

 

Reviewer #4:

 

The authors deal with the problem of preparing foams with sCNC and its properties.

The paper presents the method of foam preparation from sCNC and cationic surfactant LAE. The authors have only measured the surface tension and zeta potential of obtained foams. The paper can be accepted, but after some correction:

1. Line 39-40. The authors should highlight the possible application of sCNC foams. The authors have suggested the applications of their work in just one sentence. CNC has many exciting properties, and using them in foams for cosmetics seems very interesting.
2. The authors should add some experiments.
3. The authors should change the order of described methods in the method section. First, the Particle characterization section should be the following surface tension. In this order, the results are discussed section 3.
4. The authors should highlight the novelty of this work.
5. The authors should use the template provided by mdpi.

 

Answers for 3# reviewer:

 

• The we described some potential applications of of LAE-cCNC foams were added at the end of the “Introduction”.
• We performed the set of experiments first to characterize cCNC (size, zeta potential) which together with the earlier experiments concerning the interfacial properties of Mirena LAE [ref 21] allowed determination of basic features of the components. Then results of measurements of dynamic surface tension and elasticity could be correlated with foaming properties in presence of various additional componets in LAE-cCNC mixtures. Additional experiments could be applied in future with the application of advanced technique as neuron reflectivity or sum-frequency generation spectroscopy that will be the subject of the subsequent publications. However, in our opinion the results optaned at that stage could be interestesting for scientific community.
• The order of described methods was changed: first particle characterization, than the surface tension, the same order as for results.
• The novelty of the work was underlined in the last paragraph. Urea effect is very spectacular and it has not been decribed before as defoaming agent in the system stabilized by surfactant/nanoparticles mixtures..
• The manuscript is presented in the MDPI Applied Sciences 2022 template. The correct form of the References was applied.

 

The misprints and small errors found in the manuscript were also corrected. References were also added and their numbering modified.

Round 2

Reviewer 3 Report

Agree to publish.

Reviewer 4 Report

The paper can be accepted as it is. The authors have improved their work.