Review Reports

Round 1

Reviewer 1 Report

Manuscript identifier: cosmetics-859915

Title: How to use the normalized Hydrophilic-Lipophilic Deviation (HLDN) concept for the formulation of equilibrated and emulsified Surfactant-Oil-Water Sy(s)tems for Cosmetics and Pharmaceutical Products.
By
Jean-Louis Salager, Raquel Antón, Johnny Bullón, Ana Forgiarini and Ronald Marquez

Comments:
The article is an updated and exhaustive review on the important items relevant to the complex multi-phase multi-component systems constituted by oil, aqueous solutions and mixed surfactants, namely: a) emulsion types, b) emulsion stability, c) physical parameters and d) description of emulsion behavior by semi-empirical equations.

The review is divided in five distinct sections, specifically 1) observable phenomena and involved variables, 2) one-dimensional scan formulation variables, 3) multidimensional scans and optimum formulation events, 4) relation of HLD values with emulsion properties, 5) additional advantages and complications.

In the above-mentioned sections the authors clearly point out the major findings about the increasing concern of surfactant-oil-water applications, which are examined and discussed in the reviewed literature. Indeed the review of the present manuscript is helpful for the reader in order to understand the accomplished steps from the earlier stages (i.e., the HLB parameter) up to the present knowledge (in particular the HLD parameter).

The authors of the manuscript have a well-known international reputation since long time ago, due to their collaboration with the most important worldwide crude oil industries. The acquired expertise of the authors grants the overall trustworthy quality of the present manuscript.

Certainly, the subject of the manuscript is of large interest for the industrial and economic community working in in different emulsion application fields, with a particular hint to cosmetics and pharmaceutical products.

The text shows a satisfactory structure with paragraph subdivisions, following a logical sequence of concepts. All sections, and the overall manuscript as well, presents a logical completeness.. The style of the manuscript is detailed and careful. The scientific terminology is correct. The readability of the text is clear. The figures are useful for supporting the presented text. The quality of the figures is good. The references are updates. The title and abstract text  definitely indicate to the scientific community the research scope, the present state-of-the-art and the relevant concluding account.
I consider the paper as a significant new contribution on the emulsion formulations.

Then I suggest publication in the present form,  after a minor revision about a possible missing of a symbol (see line 615, 631, 639, 682, 687). Moreover, I also suggest a possible minor revision of the English language (see in particular “s” missing in the manuscript title.

Author Response

see attached file below

Author Response File: Author Response.docx

Reviewer 2 Report

The review article shows the development of concepts for the characterisation/classification of surfactants in various field of application, such in cosmetics and pharmaceuticals. Discussed are for example the hydrophilic-lipophilic deviation (HLD) and the hydrophilic-lipophilic balance (HLB) concepts as historical approaches. The authors show how results differ when the definitions of the concepts only slightly deviate from each other.

To avoid confusions a “normalized” HLDN equation is introduced and discussed for various examples..

 

I am quite impressed by the presented amount of knowledge, which is enormously important for people working in formulations. There are two things I would like the authors to do prior to publication:

 

1. The language deserves some improvement. As an example, in lines 115, 218, 232 the authors used of the word “limit” instead of “interface” which is not useful. With the help of a native speaker, it will be easy to polish the manuscript accordingly.
2. The reference list contains about 40% of self-citations. This seems far too high although the leading authors is famous in this field. Still a reduction of the self-citations dawn to half appears doable.

Else, this is a valuable manuscript and should be published in a good journal.

Author Response

see attached file below

Author Response File: Author Response.docx