Solid surface tension, contact angle Zisman method

Owens and Wendt (1969) report for PTFE (Teflon) contact angle measurements for water (108°) and for methylene iodide (88° and 77°, the latter with their own mcasiu-ements). Similarly, they report for PE contact angle measurements for water (94° and 104°, the latter with their own measrrrcments) and for methylene iodide (52°). Calculate the dispersion and specific contribution of the strrface tension of the two polymers using the OW method and compare the obtained solid surface tensions with the Zisman values of the critical surface tension which are 18.5 (PTFE) and 31 (PE). AU measurements arc at room temperature and all strrface tensions are in mN m. Provide a discussion of the results. 

They believe that these deviations are not due to experimental error or problems of the theory but aU have a clear explanation. In most cases, they attribute the problems to either interaction between the solid and the liquid and/or the presence of a non-zero spreading pressure due to vapour adsorption from the liquid. They improve the smoothness of their plots, in these cases, by eliminating several (in some cases many of the) liquids, sometimes even alkanes, used in the analysis in order to maintain the maximum possible inertness of the test liquids used to estimate the solid surface tension using the Neumann method. They mention that with this approach, i.e. careful selection of test liquids (bulky molecules are often useful), some of the experimental contact angle data, even with the goniometer method used in the extensive studies of Zisman, can be used in the context of the Neumann method (Kwok and Nemnann, 2000b). 

Keywords Solid surface tension Solid surface energy Contact angle Work of adhesion Zisman method Surface tension component mefliod Fowkes method Owais-Wendt-Rabel-Kaelble mefliod Extended Fowkes mefliod Equation of state... 

An empirical method to estimate the surface tension of a solid is Zisman s plot (cos 9 as a function of yl), which obtains the critical surface tension of wetting. In the absence of specific interaction between the surface and the liquids used for the measurement of contact angles, the critical contact angle of wetting can be accurately estimated and its value used as the surface tension of the surface. However, if a surface interacts with liquids used as the sessile droplet for the contact angle measurement, to the extent that the surface tension is altered, Zisman s plots deviate from the ideal linear relationship. In a strict sense, the plot is applicable only to imperturbable surfaces with which liquid contact does not alter surface configuration, i.e., no surface dynamics applies. 

In summary, there are three basic approaches to use contact angle data to determine the surface tensions of solid surfaces. These approaches are the Zisman method, the surface tension component methods, and the equation of state. Within these three approaches, there are many variants. It is reasonable to wonder the merit, accuracy, and limitation of some of the methods. The Zisman method is an empirical approach based on the correlation between the cosines of the contact angles on a solid surface versus the surface tensions of the test liquids. With alkanes, linear plots are usually obtained, and the critical solid surface tension (yc) is determined by extrapolating... 

Contact Angle Goniometry as a Tool for Surface Tension Measurements of Solids, Using Zisman Plot Method 221... 

The surface energy (critical surface tension) of solids is measured by a method developed by Zisman.9 In this method a series of contact angle measurements are made with various liquids with known surface tensions on the solid to be tested. The contact angle 9 is plotted as a function of the yLV of the test liquid. The critical surface tension is defined as the intercept of the horizontal line cos 9=1 (i.e., when the contact angle is 0°) with the extrapolated straight-line plot of cos 9 against yLV of the liquids. The yLV at this intersection point (i.e., where a hypothetical test liquid would just spread over the substrate) is defined as the critical surface tension of the solid. 

Three ways are available for the estimation of ys, the surface tension of the solid. The first is the method measuring the contact angle between the solid and different liquids and applying Eq. (8.9). The second is the determination of ycr according to Zisman (1964), with the assumption that ys ycr. The third way is the extrapolation of surface tension data of polymer melts to room temperature (Roe, 1965 Wu, 1969-1971). 

These properties are listed in order of usefulness for comparative review purposes. Liquid surface tension is the most fundamental property, because it pertains only to the material in question (provided the material is adequately pure) and the technique used for measurement. All the other properties listed are dependent also on solvents, contact-angle test liquids, and liquid or solid substrates selected. For solids, approaches such as the Owens-Wendt analysis (7) have supplanted the Zisman method (18) in recent years, but data from the Zisman method for organosilicon polymers are more available compared with data from the Owens-Wendt approach. Some useful data on aqueous surface tensions and Langmuir troughs are also available. Data for other listed properties are of less fundamental use and rather scanty. 

Fox and Zisman first proposed the concept of critical surface tension in the early 1950s. In Zisman s method, the relationship between the contact angle of various liquids on a solid and the surface tension of the liquids are investigated. Specifically, cos 9 is plotted against yLv (known as Zisman plot) in which a straight line is often obtained when a homologous series of liquids are used to wet the solid s surface (non-linear for non-homologous liquids). 

Several authors have tried to determine critical surface tensions for solid surfaces by determining the contact angles for a set of solutions of different concentrations. Zisman s method is, however, not applicable to solutions due to the large probability for specific and selective adsorption of the components constituting the solution. 

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