Article

Polyelectrolyte-surfactant mixtures as model for understanding the performance of 2-in-1 shampoo formulations

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Abstract

Background 2-in-1 shampoos are very complex multi-component mixtures used for the cleansing of the hair fibers and the modulation of their tribological properties, contributing to the reduction of the negative charge of damaged hair fibers. This is the result of the combined action of the polyelectrolytes and surfactants that play a central role in the effectiveness of modern 2-in-1 shampoo formulations. Thus, surfactants contribute to the removal of the dust and fatty compounds during the washing process, whereas polyelectrolytes present a strong ability to be deposited on the surface of damaged fibers, and enhance their tribological properties. However, the lack of knowledge about the main forces driving the conditioning process has pushed the research and development strategy of the cosmetic industry towards the design of state-of-the-art experimental and theoretical methodologies for evaluating the behavior of mixtures formed by polyelectrolytes and surfactants in solution and adsorbed onto solid surfaces with negative charge and contact angle for water similar to those appearing in the surface of damaged hair fibers, which have become a very promising tool for obtaining important insights that can be exploited for the optimization of new formulations for hair cleaning and conditioning. Aims This work tries to provide an updated perspective of the current understanding of the behavior of mixtures containing polyelectrolytes and surfactants bearing opposite charges in relation to their performance in hair care and conditioning for providing a link between physico-chemical aspects and the performance of real 2-in-1 formulations. Conclusions Polyelectrolyte-surfactant are powerful tools for obtaining useful information for the optimization of cosmetic formulations for hair care and conditioning. However, the rational design of this type of cosmetic products must be considered a multi-disciplinary challenge, which requires the combined efforts of researchers with very different backgrounds.

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A shampoo is a cleaning aid for the hair and is counted among the foremost beauty products. Today's shampoo formulations are beyond the stage of pure cleaning of the hair. Additional benefits are expected, e.g, conditioning, smoothing of the hair surface, good health of hair, i.e, hair free of dandruff, dirt, grease and lice and, above all, its safety benefits are expected. As the scalp is one of the most absorbent part of the body, products applied to the scalp go directly to the blood, without being filtered in any way. So it is very important to know and understand the effects of ingredients used in shampoo formulations. In the present review the shampoos based on synthetic ingredients and herbal ingredients are compared for their effectiveness and safety.
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Hair cosmetics are an important tool that helps to increase patient's adhesion to alopecia and scalp treatments. This article reviews the formulations and the mode of action of hair cosmetics: Shampoos, conditioners, hair straightening products, hair dyes and henna; regarding their prescription and safetiness. The dermatologist's knowledge of hair care products, their use, and their possible side effects can extend to an understanding of cosmetic resources and help dermatologists to better treat hair and scalp conditions according to the diversity of hair types and ethnicity.
Article
A chemical mapping with high lateral resolution using an Atomic Force Microscope in the Pulsed Force Mode with chemically modified tips, introduced as "dynamic Chemical Force Microscopy" (dCFM), was carried out to investigate the chemical properties of the cuticle of human hair and its changes following an oxidative treatment. Chemically modified AFM-tips, CH3- and NH2-terminated, were applied to achieve a defined chemical contrast (hydrophobic and ionic) in aqueous medium. A comparative FTIR-ATR-spectroscopy identified the dominant chemical groups of surface vicinity of the hair fiber resulting from the bleaching process. The combined experimental results lead to the conclusion that the hydrophobic top layer is partially removed after bleaching, resulting mostly in hydrophilic SO3- end groups at the top of the surface of the hair, with a mean surface density "dmean" of negatively charged groups of approximately 2,2 molecules/nm² corresponding to ~600 µg/m² of cysteic acid. This indicates that thioester bonds are disrupted and fatty acids are removed due to cysteine oxidation. At the molecular level, our results indicate a clustered "Self Assembled Monolayer" alignment of cysteic acid with a crystal-like structuring, reminding of the "fluid mosaic model of cell membranes" with a surface energy of approx. 0.04N/m. In spite of previous extensive works of AFM on human hair, this is, to our knowledge, the first time that the hydrophobic and ionic sites at the top surface of hair have been imaged at the nano-scale with the dynamic Chemical Force Microscopy.
Article
Hair-conditioning polymers are in most cases cationic. Their adsorption to the negatively charged hair surface is strongly affected by their interaction with the anionic surfactants, which are also present in modern "2-in-1" shampoos. Almost 20 years ago, Goddard proposed that the adsorption process takes place, when the shampoo is washed off the hair [1]. Upon dilution a phase boundary is crossed and the polymer-surfactant complex precipitates on the hair surface. Since then, no systematic investigations on the adsorption process of conditioning polymers have been published. We reinvestigated this model employing a variety of physicochemical methods: turbidity, surface tension and surface rheology, AFM were used to characterise the polymer/surfactant complex of two polymers (polyquaternium) and an anionic surfactant (Texapon® NSO).
Article
Sorption of Polymer JR, a cationic cellulose ether, by human hair is greatly decreased in the presence of added electrolytes. This reflects the competition between cations of the added salt and the quaternary ammonium groups of the polymer for sorption sites in the substrate. In this respect the hair can be regarded as a “strong-acid” ion-exchanger, and it displays a selectivity to ions similar to that observed for conventional resin exchangers. Cations can be ranked in order according to their ability to decrease the sorption of Polymer JR as follows: La ⁺⁺⁺ > Al ⁺⁺⁺ < Fe ⁺⁺⁺ < Ca ⁺⁺ < Fe ⁺⁺ < Cs ⁺ < Na ⁺ < Li ⁺ . Salts also promote desorption of Polymer JR that is already sorbed by hair. However, selectivity is less evident in desorption than in sorption and is only observed at relatively low concentrations of salt. About half of the sorbed polymer is readily removed by salt solutions; the rest appears to be tightly attached to the substrate.
Article
Oppositely charged polyelectrolyte-surfactant mixtures are ubiquitous in biology and the basis of numerous consumer healthcare products. Despite their broad use, however, a rational approach to formulation remains challenging because of the complicated association mechanisms. Through compilation and analysis of literature reports and our own research, we have developed a semi-empirical correlation between the binding strength of surfactants to polyelectrolytes in salt-free mixtures as a function of the polyion linear charge density and surfactant hydrophobicity. We find that the cooperative binding strength increases as the quadratic of the polyelectrolyte's linear charge density and in proportion to the surfactant's hydrophobicity, such that a quantitative relationship holds across a broad range of polyelectrolytes. Deviations from the correlation reveal the role of system-specific interactions not considered in the analysis. This engineering relationship aids in the rational design of oppositely charged polyelectrolyte-surfactant formulations for consumer products and biomedicines by enabling prediction of binding strengths in polyelectrolyte-surfactant mixtures based on mesoscale parameters determined from the chemical composition.
Article
What happens if polymers are added to a macroscopic foam or to foam films? This is an important question for many technical applications, but it is also important for materials and life science. This paper reviews the effect of the surface composition on the thickness and stability of aqueous foam films containing surfactants and polymers. The surfactant concentration is below the critical micellisation concentration (cmc) and the critical aggregation concentration (cac). The addition of polymers to foam films leads to the formation of surface active polymer/surfactant complexes or to depletion of polymers close to the interfaces, which has a strong effect on the film stability. The review mainly concentrates on the dilute polymer regime (below the overlap concentration c*), and results at the semi-dilute regime (above c*) are briefly reviewed. A principle concept for the relation between the surfactant/polymer combination and the film thickness and stability is developed. It allows the prediction, of whether an unstable Newton black film (NBF) or a stable common black film (CBF) will be formed.
Article
Some routes of preparation of water-soluble nonstoichiometric complexes (N-PEC) are considered. The structure of water-soluble N-PEC is examined and it is shown that in certain aspects they behave like individual macromolecular compounds and represent a new class of complex water-soluble polyelectrolytes. The behavior of N-PEC in aqueous salt solutions is considered and reasons and a mechanism of conformational transformations of the N-PEC macromolecules in these media are discussed. Disproportionation phenomena observed in N-PEC solutions are described in connection with the peculiarities of a phase separation in these systems. Data on the kinetics of the macromolecular exchange reactions in N-PEC solutions are presented.
Article
Human hair is a nanocomposite biological fiber. Hair care products such as shampoos and conditioners, along with damaging processes such as chemical dyeing and permanent wave treatments, affect the maintenance and grooming process and are important to study because they alter many hair properties. Nanoscale characterization of the cellular structure, mechanical properties, and morphological, frictional, and adhesive properties (tribological properties) of hair are essential to evaluate and develop better cosmetic products, and to advance the understanding of biological and cosmetic science. The atomic/friction force microscope (AFM/FFM) and nanoindenter have become important tools for studying the micro/nanoscale properties of human hair. In this review article, we present a comprehensive review of structural, mechanical, and tribological properties of various hair and skin as a function of ethnicity, damage, conditioning treatment, and various environments.
Article
The adsorption of polyelectrolytes onto negatively charged substrates has been studied using dissipative quartz crystal microbalance (D-QCM) and ellipsometry. The polymers studied belong to two families of cationic polymers frequently used as hair conditioners. One of the families is formed by four polymers derived from the poly(diallyl-dimethylammonium chloride), and the other one is formed by two polysaccharide polymers. The control parameters in the study of both families of polymers were the charge density and the rigidity of the chains. The adsorption kinetics of the polymers showed a complex behavior with several processes involved. The total adsorbed amount depends on the nature of the polymer chains, on the ionic strength, and on polymer concentration of the solutions. The comparison of the mass of the adsorbed layers obtained from D-QCM and from ellipsometry allowed us to calculate the water content of the layers. This variable takes high values for all the polymers studied, which is related to the non-homogeneous character of the adsorbed layer, as confirmed by AFM. The analysis of D-QCM results also provides information about the shear modulus of the layers, whose values have been found to be in the MPa range as for rubber-like polymer system. The adsorptions of the polyelectrolytes are not driven exclusively by the electrostatic interactions. entropic contributions being of fundamental importance, and arise mainly from the release of counterions during the adsorption process, and/or the number of loops and tails of the adsorbed chains protruding into the solution. (C) 2010 Elsevier B.V. All rights reserved.
Article
Interactions between mica surfaces across aqueous solutions containing mixtures of a highly positively charged polyelectrolyte and an anionic surfactant were studied by use of a surface force apparatus. The investigation was carried out with a constant polyelectrolyte concentration (20 ppm) and a wide range of surfactant concentrations [0−1 times the critical micelle concentration (cmc)]. The chemical composition of the adsorbed polyelectrolyte-surfactant layers was analyzed by x-ray photoelectron spectroscopy (XPS). The properties of polyelectrolyte-surfactant aggregates formed in bulk were studied by measurements of turbidity and electrophoretic mobility. The aggregates formed at low surfactant concentrations (<0.04 times cmc) were positively charged, whereas at higher surfactant concentrations the aggregates carried a net negative charge. It was shown that polyelectrolyte−surfactant aggregates rapidly adsorb on negatively charged mica surfaces regardless of the sign of their charge. At surfactant concentrations up to 0.01 times cmc, the polyelectrolytes adsorb on mica surfaces with loops and tails stretching out into solution and repulsive steric forces are generated. The thickness of the layer decreases with time and we suggest that this conformational change is accompanied by some expulsion of surfactant from the adsorbed layers. Thick adsorbed layers were formed in the surfactant concentration range 0.02−0.1 times cmc. In this concentration regime the measurement of equilibrium forces was inaccessible due to a very slow layer relaxation. During compression the forces were repulsive and during separation an attraction developed. We attribute this to formation of interlayer surfactant bridges. Finally, at high surfactant concentrations (≥0.4 times cmc) highly negatively charged aggregates adsorb on the surfaces in rather thin layers, resulting in purely repulsive forces of mixed electrostatic and steric origin.