Interplay of Interfacial and Rheological Properties on Drainage Reduction in CO2 Foam Stabilised by Surfactant/Nanoparticle Mixtures in Brine
, Bruno Giordano Alvarenga 1, Ana Maria Percebom 2 and Aurora Pérez-Gramatges 1,2,*Round 1
Reviewer 1 Report
Title: Interplay of interfacial and rheological properties on drainage reduction…
Manuscript ID: colloids-2039087
Authors: Azevedo et al.
Dear Authors,
Thank you for the opportunity to read your article. I found the topic is interesting and fundamental. Generally speaking, the methods and results need to be clearly presented, and the results need to be described and discussed with fair point of view. I suggest that this article will be revised extensively before its re-submission for another review process if applicable. As a conclusion, I recommend its major revision at this state.
I hope my comments are helpful.
Good luck,
A reviewer
Major concerns:
“Keywords”
->Please consider providing keywords that are not used in the article title.
“1. Introduction”
-Lines 34-37: “…the presence of salt in the aqueous phase…reduces the electric double layer…decreasing the repulsive forces and increasing the coalescence rate.”->Please consider citing relevant references.
DOI: 10.1039/C8SM01949E
doi.org/10.3390/ma14071808
-Lines 42-44: “Solid NPs have a higher detachment energy from the interfaces…”->In this statement, please consider revising this phrase since it is not complete and against the common sense. (a) NPs have a higher detachment energy than what? (b) NPs usually have higher attraction with other objects due to higher specific surface leading to higher van der Waals forces.
-Based on your literature review, please consider clearly mentioning the research gap(s) and unique contribution of this work.
“2. Materials and Methods”
“2.1. Materials”
-“…to evaluate the influence of charges on foam stabilization.”-In this section, please consider stating the difference in charges of the surfactants studied.
“2.2. Experimental procedures”
“2.2.4. Dynamic light scattering”
-“The dispersion of NPs…were evaluated in…in brine…”->In this section and other relevant sections, please consider stating the type and concentration of electrolytes/salts in your brine since they would significantly affect your results.
doi.org/10.1021/la9808768
DOI 10.1002/elps.201700314
“3. Results”
“3.1. CO2-foam behavior of cationic…”
-Figure 1 (and elsewhere): In the figure title, please consider providing the details of your brine (e.g., type and concentration of electrolytes/salts in your brine).
“3.2. Effect of SiO2 and Al2O3 NPs on foam stability”
-Figure 2 (and elsewhere): In the main text, please consider justifying why you measured NPs in wt.% (not in vol.%). Since alumina and silica have different specific gravities, they have different particle numbers and total surface areas at the same wt.% even their sizes are similar. In other words, 0.5 and 1.0 wt.% Al2O3 cannot be simply comparable with 0.5 and 1.0 wt.% SiO2.
-“…CO2-foam stability in oppositely charged systems…”->Please consider showing and discussing your zeta potential measurement results.
“3.3. Interfacial, colloidal and rheological properties…”
-Figure 3(b): In the main text, please consider mentioning your justification why you selected 10 s-1 out of many other shear rates you applied during rheological measurements. In other words, how comparing the viscosities at 10 s-1 is useful for your study?
-“This increase in the viscosity was more pronounced in systems containing oppositely charged surfactant/NP pairs than in those with the same charge.”->Please consider explaining more in this aspect in relation to the foam behavior.
-“The zeta potential of SiO2 and Al2O3 NPs showed significant variations…However, in the systems bearing the same type of charged, the changes in the zeta potential were negligible.”->Please consider citing your results in order to support your statements.
Minor concerns:
-Please consider polishing English more. You may use some of my comments above for this purpose.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript entitled “Interplay of interfacial and rheological properties on drainage reduction in CO2-foam stabilised by surfactant/nanoparticle mixtures in brine” is devoted to the study and determination of the stability of CO2-foams containing surfactants and nanoparticles mixtures with different nature at the low pH and high-salinity brine. Several surfactants and nanoparticles with different types of interaction were used to study interfacial and bulk properties. The optimal surfactant and nanoparticles combination was revealed on the basis of received results.
The topic it highly relevant due to high potential application of CO2-foam for EOR and for the utilization of CO2 in the technology of Carbon capture, utilization and storage (CCUS).
The article is clearly and concisely written, the illustrations are in high level, understandable. I believe that this manuscript will be interesting for all scientists involved in such studies and I suggest publication after minor revision.
1. The topic is related to fundamental studies in this direction and covers bulk and interfacial properties, foam stability experiments. The potential practical application is high but not showing and proved in the manuscript. At least some simulation study would increase the value of the article.
2. The main part of the manuscript is devoted to foam stability experiments. Only few data is shown for the surface tension experiment (mainly static surface tension and CMC of surfactants determined by Wilhelmy method). Did you study the dynamical surface tension?
3. The surfactants CMC play important role in the interfacial properties, including surface tension, foam stability and etc. And it is different for studied surfactants. As it is shown in Table 2, CMC of CAPB is 25 times less than DTAB, 5 times less than SDS. But in Figure 2 all surfactants in one concentration 0,1wt%, which much higher than CMC of abovementioned surfactants. Do you think it is worth to compare these surfactants?
Author Response
Please see the attachment.
Author Response File: 
Author Response.docx
Round 2
Reviewer 1 Report
Dear Authors,
As all the comments were addressed, I would suggest the journal accept this article for its publication.
Best regards,
A reviewer
