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Woven and nonwoven fabrics and the corresponding fibers have been analyzed using a Wilhelmy microbalance. A self-developed analysis software (written using Labview flow-data language) has been used to extract the advancing and receding angles and also other informations commonly neglected by the standard data analysis of Wilhelmy technique, such as the immersion cross-sectional area, the effective wet perimeter, the liquid absorption, the parallelism of the straight lines describing the immersion and the withdrawal of the sample in a typical force vs immersion graph. This approach has previously been proposed for rigid porous materials such as stones and wood with some success. In the present cases some modifications of the approach have been introduced to take into account the specificity of the materials. The results appear promising for the more rigid nonwoven fabric, but suffer from a greater uncertainty and from even unacceptable inconsistencies in the case of the softer and traditional fabric. Throu...

The acid-base theory as developed by van Oss, Chaudury and Good is a powerful tool to analyze the surface free energy of polymeric materials; however, some problems are encountered in its application and some authors have shown that these problems can be theoretically solved considering this theory as an example of the so-called LFER theories. From this point of view, the definition of a well-defined scale of acid-base strength and the use of a wide and well-equilibrated, appropriate set of liquids is very important. In the present paper some recent results are presented which are based on the mathematical approach discussed by Della Volpe and Siboni in previous papers. The treatment is developed as a list of questions, Frequently Asked Questions (FAQs), whose theoretical implications are discussed using numerical examples chosen from the literature. Some literature data, collected by the opponents of the acid-base theory and recently published, are re-analysed using these methods, showing that they const...

—According to the general guidelines presented in the accompanying paper, some relevant examples of common polymer surfaces are analysed and discussed; a number of polymers commercially available or laboratory synthesized have been analysed. In particular, the case of poly(vinyl chloride) (PVC), often considered as peculiar in the literature, is fully analysed on the basis of a new set of well-prepared samples, whose compositions were checked by high-vacuum spectroscopies. 'Equilibrium' contact angles, obtained by a new experimental technique, are presented. The results are, however, preliminary, because the final set of liquids used is not so 'well equilibrated' as possible, from the point of view of acid–base properties. The contact angle data obtained are analysed in a non-linear way to calculate the acid–base components of all the liquids and solids. The results are discussed and compared with those obtained from liquid–liquid interfaces presented in the accompanying paper. The physico-chemical featur...

The individual effects of heterogeneity and roughness on contact angles have been repeatedly analysed in the literature, but the application of the accepted models to practical situations is often not correctly performed. In the present paper the combined effects of roughness and heterogeneity on the contact angles of water on stone surfaces protected by a hydrophobic polymer coating are considered. Two different kinds of calcareous stone with different surface roughnesses and porosities were protected against the effect of water absorption by two different polymer coatings. The contact angles of water on the protected stone surfaces were measured by the Wilhelmy and the sessile drop techniques. A comparison of the results obtained shows not only the limits of the static sessile drop technique, but also the combined effect of roughness and heterogeneity. Some considerations are developed on the application of commonly accepted models to surfaces with a combination of roughness and heterogeneity. Some othe...

The overwhelming basicity of all analysed surfaces strongly dependent on the choice of liquid triplet used for contact angle measurements and the negative values sometimes obtained for the square roots of the acid-base parameters can be summarized as the main problems arising from the application of the Good-van Oss-Chaudhury (GvOC) theory to the calculation of Lewis acid-base properties of polymer surfaces from contact angle data. This paper tries to account for these problems, namely: (1) the Lewis base, or electron donor component, is much greater than the Lewis acid or electron-acceptor component because of the reference values for water chosen in the original GvOC theory. A direct comparison of the acidic component with the basic one of the same materials has no meaning. A new reference scale for water which is able to overcome this problem is suggested. For the calculation of acid-base components, a best-fit approach is proposed which does not require any starting information about the liquids or po...

Contact angle measurements have been performed using the Wilhelmy microbalance on disc-shaped samples of different thicknesses and these are compared with the theoretical analysis proposed by Dryden and Andrade (D-A). In disagreement with the original D-A results, our conclusion is that not only are the force values well reproducible, but also the determination of the contact angles, by inverting the force equations, provides acceptable estimates. This conclusion is supported by the analysis of error propagation for the various physical and geometrical parameters of the model. By taking into account the thickness of the samples a correction is introduced, the significance of which is analysed with respect to some of the experimental parameters. Moreover, a second method of analysis based on an iterative procedure is proposed; it uses only the force data collected during the immersion of the diameter zone of the disc samples and can be applied to both discoidal (e.g. lenses) and plane disc-shaped samples. Finally, an accurate analysis of the meniscus shape during the immersion leads to a third method for the estimation of contact angles on discs. It requires the detection of the immersion level at which the lateral meniscus becomes perfectly planar. Its use is restricted to the case of thick discs and the precision achieved is not high.