Review Reports - Surface Potentials of Mixtures Containing Oddly Charged Colloids

Round 1

Reviewer 1 Report

Comments from Reviewer

Manuscript ID: coatings-1910264-peer-review-v1.pdf

Title: Surface Potentials of Mixtures Containing Oddly Charged Colloids

The current form's presentation of methods and scientific results is satisfactory for publication in the Coatings journal. The minor and significant drawbacks to be addressed can be specified as follows:
1.    Line 9, equation. Problems with brackets ;) exp – exp = 0 <3. See also lines 32 and 33.
2.    Line 17. Surface potentials ---> Surface Potentials.
3.    Line 27. DLVO?
4.    KT or kT? k – the Boltzmann constant?
5.    Line 130. NP? Nanoparticle?
6.    Eq. 8. What is no?
7.    Why 4.1 has no title? See also 4.2 and 4.3.
8.    Figures. There were numerous typographical errors. - lack of attention to detail, consistent with the standard of a scientific presentation. For example, Fig. 1 (it isn't easy to distinguish colours), Fig. 5 (Lyso mmol ---> Lyso (mmol)).
9.    Literature should also be standardized: the size of letters in the titles of journals, initials of names, and the size of letters in the titles of articles.

Sincerely,
The reviewer.

Author Response

- Reviewer 1

Thank you for patience and useful suggestions. The following are our replies

The energy term KT has been rewritten everywhere as kT.

Lines 7-8 (so named after Derjaguin, Landau, Verwey and Overbeek, etc…)

Line 13 (exp^(zeψ/kT)- exp^-(zeψ/kT))

Line 17 Surface Potentials

Line 20 dramatic

Line 130 (nano-particle)

In Eq. 8 n° is the number of ions

In 4.1 we added the title Colloid Crystals and Hybrid Colloids

The minor changes you suggested have been corrected.

Thank you again.

Reviewer 2 Report

The paper represents an attempt to advance the theory of colloid electrostatics at significant dilution of charged particles and surrounding ions in solvent. In the present form the presentation requires a serious correction. Equation (5) and (6) in the paper can be derived from equation (2) only if we assume that surface potentials (or the surface charge) of the two kind of particles (namely "psi_A" and "psi_B") are of opposite sign, psi_A = (1 + alpha)* |psi_B| and the leading multiplier in equation (5) appears to have a half of its exponent argument written in the text. Anyway, the final equation (6) is written correctly. Only after such a correction of the "strightforward algebra" in equations (2) - (5) the following results can be presented.

Author Response

Reviewer 2

Thank for help in getting a better manuscript. The following are our replies

I believe the author considers the electrostatic interaction in the paper. Why does the author exclude the Van der Waals force, which should dominate the interaction of two colloidal when both are close?

I know how important are vdW forces in colloid stability. I did consider only the electrostatic terms because data from which I started writing the manuscript are based on electrophoretic mobility. And vdW forces are traceless on this regard.

2. In line 202, the author claim that: “Cells too interact with hosts and viruses by electrostatic effects, regulated by membrane charge and/or by that of viral capsids.” I kind of disagree with this claim. As far as know, most hosts or viruses are negatively charged. Their interactions are not dominated by the electrostatic effects, which is a nonspecific interaction but dominated by the ligand-receptor interaction, which is a specific interaction.

Your statement is generally true. However, cases are known where the double layer thickness may play a key role in electrostatic interactions of viruses. This fact holds true when the concentration in the membrane boundary layer differs from that in the bulk. Both pH and presence of salts (in the bulk) influence the double layer thickness. Increasing salt concentration, or valency, reduce the thickness of such layer and facilitates virus adsorption onto surfaces. In words, surface potentials do change. See, for instance, the paper Role of hydrophobic and electrostatic interactions for initial enteric virus retention by MF membranes. By E.M. van Voorthuizen, N.J. Ashbolt, A.I. Schäfer, in J. Membrane Sci., 2001,194, 69-79, indicated as Ref. [45].

3. For figure 4, can the author clarify the size and shape of the colloids? Why is there DNA/CNTs in the figure? I get misled by this figure.

The size of DNA/CNT adducts has been indicated in the caption to Figure 4. Roughly it is about 2-300 nm in length and nearly 40+15 in thickness.

Thank you.

Author Response File: Author Response.docx

Reviewer 3 Report

In this paper, the authors conduct the theoretical calculation on the interaction of the two colloidal using the reformulated model. I think this work is kind of complete. However, there are still some issues in this paper. Below are my comments.

1. I believe the author considers the electrostatic interaction in the paper. Why does the author exclude the Van der Waals force, which should dominate the interaction of two colloidal when both are close?

3. For figure 4, can the author clarify the size and shape of the colloids? Why is there DNA/CNTs in the figure? I get misled by this figure.

Author Response

Reviewer 3

The paper represents an attempt to advance the theory of colloid electrostatics at significant dilution of charged particles and surrounding ions in solvent. In the present form the presentation requires a serious correction. Equation (5) and (6) in the paper can be derived from equation (2) only if we assume that surface potentials (or the surface charge) of the two kind of particles (namely "psi_A" and "psi_B") are of opposite sign, psi_A = (1 + alpha)* |psi_B| and the leading multiplier in equation (5) appears to have a half of its exponent argument written in the text. Anyway, the final equation (6) is written correctly. Only after such a correction of the "straightforward algebra" in equations (2) - (5) the following results can be presented.

Thank you for indicating that point. We stated that

Implicit in Eq. [2] is the assumption that surface potentials (or surface charge densities) of the two kind of particles (i.e. ψ_Aand ψ_B) bear an opposite sign.

Thank you.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

My comments have been appropriately addressed in the revised manuscript.

Author Response

Thank you for collaboration.

Reviewer 3 Report

I‘d like to see author can make the revision directly on the manuscript based on my previous comments. For instance, the author claims that they only electrostatic terms because data from which I started writing the manuscript are based on electrophoretic mobility. And vdW forces are traceless on this regard. Why is the vdW forces are traceless? Is it because the distance between the colloidal particles is low? Shall we use model like DLVO theory to calculate colloidal interaction? I hope the author can make revision directly on the manuscript based these questions and other related question in the 1st revision.

Author Response

In the text I added the sentences

In colloidal dispersions the by far major inter-particle interaction forces are van der Waals (vdW) and electrical double layer ones. The former is usually attractive and favors the coagulation (often through untoward mechanisms). The second term can be attractive, repulsive, or change from one mode to another, depending on the separation distance among particles (i.e. on concentration) and ionic strength. The combined action of two such forces, eventually in combination with minor ones, is responsible for the onset of different colloidal aggregates, someway modulated by the medium ionic strength, I.

In the calculations I fixed the ionic strength to 5.0 mmol kg^-1 (the particle content was close to 0.10 % volume fraction), in such a way to get nearly the constancy of all forces but double layer ones. The latter arose from the net NP surface charge density. In this way terms due to vdW forces are practically constant.