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Wpływ surfaktantów na zwilżalność ciał stałych ze szczególnym uwzględnieniem skóry ludzkiej

Harkot J., Jańczuk B.

Wiadomości Chemiczne

2007

[Z] 61, 9-10

707-731

This paper reviews wetting phenomena in relation to different types of solids and human skin in the presence of surfactants. Wettability of solids by surfactants is important for many technological applications. The addition of surfactants is necessary to achieve a better wettability of a given solid. In the first part of this article the definition of a contact angle and an interfacial tension along with methods of their determination is presented. Next, a relationship between a liquid--air, a solid-air and a solid-liquid interfacial tensions and wettability of solids is shown. Three types of wetting are discussed in this work: a spreading wetting, an adhesional wetting, and an immersional wetting. Wettability forces of hard surface and powders are also described in this part of the article. In the third part of the article main aspects related to the solids critical surface tension of wetting are presented. Different problems of solids' wetting critical surface tension are described, since there is still no unambiguous method to determine this value. Later, based on the Lucassen-Reynolds equation we described the dependence between the adsorption of surfactants at the interfaces, mainly in a solid-water-air systems and wetting of solids, because they are both strongly related. From this equation the slope of a plot of ?LVcos? (adhesion tension) versus ?LV (surface tension) gives us the information about the surface concentration of the surfactant at water-air and a solid-water interfaces in a solid--water-air system including both non-polar (low-energy) and polar (high-energy) solids. We have also shown that in the case of hydrophobic solids, for several types of surfactants, there is a constant negative slope of ?LV cos?-?LV curve. However, for high-energy polar solids the positive slope of this curve is observed and there is no linear dependence between adhesional and surface tension. Thus, for a high energy solid-aqueous surfactant solution-air systems it is difficult to establish synonymous mutual relationships between the adsorption of surfactant at a solid-air, a solid-liquid and a liquid-air interfaces and wettability of high-energy hydrophilic solids. At the end we presented main problems dealing with wettability of human skin surface, which is the most important factor of the skin protective function. It minimizes water loose, prevents entry of a foreign matter and chemicals, and defines smoothness and elasticity of the skin. Surprisingly, this subject has received a little attention in the literature. The human skin surface, after the extraction of sebum (skin surface lipids) belongs to hydrophobic surfaces (low-energy) in terms of critical surface tension and polar and dispersion components of a free surface energy. El-Shimi and Goddard compared the skin surface with polymer surfaces such as polyvinylchloride, polytetrafluoroethylene and polyethylene, but we have to remember that the human skin is a living matter and in the presence of sebum becomes hydrophilic. In order to remove this fatty film from the skin surface cleansing products, which contain many various surfactants, are used. Good wetting and cleansing effects of such products depend on surfactants ability to adsorb on the skin surface and reduce an interfacial tension at water-skin interface in skin-water-air system.

Wpływ substancji powierzchniowo czynnych na zwilżalność niskoenergetycznych hydrofobowych ciał stałych

Jańczuk B., Szymczyk K., Wójcik W.

Wiadomości Chemiczne

2005

[Z] 59, 5-6

489--508

The paper reviews the thermodynamic of the most important problems of wettability of a solid and correlation between adsorption of surface active agents at water-air, and solid-water interfaces and wettability of hydrophobic low-energy solids. Three types of wetting have been considered; spreading wetting, adhesional wetting and immersional wetting. The usefulness of the Good and Girifalco, Fowkes, Owens and Wendt, and van Oss et al. approaches to interfacial free energy of liquid- -liquid and solid-liquid for determination of work of spreading, immersion and adhesion is presented. The correlation between the work of spreading, immersion and adhesion and contact angle is also shown. On the basis of the contact angle the relationship between wettability of the solids and its surface free energy and surface tension of liquid is discussed. Zisman found for low-energy solids a straight linear relationship between cos<θ((θ is the contact angle) and surface tension of liquids or aqueous surfactant solutions. The extrapolation of this relationship to cosθ = 1 allows estimation of the liquid surface tension required to give a contact angle of zero degree, which Zisman described as the critical surface tension. However, in contrary to Zisman, Bergeman and van Voorst Vader, stated that there is straight linear relationship between the adhesional tension (γ1γ,cosθ) and surface tension, γ1γ, of aqueous solutions of several types of surface active agents (surfactants). Such relationship was also confirmed by other investigators, however, the different equations describing the wettability of the same solids than Bergeman and van Voorst Vader by aqueous solutions of surfactants has been suggested. A direct method to investigate relative adsorption at interfaces is described. The usefulness of Lucassen-Reynders equation derived from Young and Gibbs equations for the studies of the correlation between adsorption of the surface active agents at water-air and solid-water interfaces and wettability of low-energy hydrophobic solids is discussed. We proved that on the basis of the surface tension of low-energy hydrophobic solids, surface tension of aqueous solution of surfactants or their mixtures, and Fowkes approach to interfacial tension the wettability of low-energy hydrophobic solids can be predicted.