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This article reviews the various theoretical approaches that have been developed for determination of the surface tension of solids, and the applications to food industrial products. The surface tension of a solid is a characteristic of surface properties and interfacial interactions such as adsorption, wetting or adhesion. The knowledge of surface tension is thus of great interest for every domain involved in understanding these mechanisms, which recover a lot of industrial investigations. Indeed, it is the case for the packaging industry, the food materials science, the biomedical applications and the pharmaceutical products, cleaning, adhesive technology, painting, coating and more generally all fields in relation with wettability of their systems. There is however no direct method for measurements of surface tension of solids, except the contact angle measurements combined with an appropriate theoretical approach are indirect methods for estimation of surface tension of solids. Moreover, since the publication by Young (1805) who developed the basis of the theory of contact angle some two hundred years ago, measurements and interpretations are still discussed in scientific literature, pointing out the need to better understand the fundamental mechanisms of solid-liquid interfacial interactions. Applications of surface tension characterization in the field of food materials science are detailed, especially for packaging and coating applications, which recover different actual orientations in order to improve process and quality.
Keywords surface tension, contact angle, wettability, packaging, food, polymer, coating
INTRODUCTION
The understanding of phenomena that occur at interfaces still remains an actual subject of interest for a lot of industrial products. The phenomenon of wetting or non-wetting of a solid by a liquid has been widely studied by contact angle measurement. Contact angle methods have been developed since the 60s and a lot of data has been collected in scientific literature for various domains on contact angle and surface properties.34,35,41,43,81,101,111,115 Whilst surface tension of liquids can easily be determined via semi-empirical equations84 or direct measurements, it is much more complicated for solids. A good way to access this information is by choosing indirect methods such as the contact angle technique which can be applied in different models, the main ones will be reviewed in this paper. The knowledge of surface tension of solids has great technological importance for all interfacial phenomena, as it...