Contact angle Zisman plots

Fig. 10. A schemalic Zisman plot for a given solid specimen. When the cosine of the static advancing contact angle is plotted against the surface tension for a series of apolar liquids against a test solid, a straight line results. Its extrapolation to cost = 1 yields the critical surface tension of the solid.

Fig. X-9. Zisman plots of the contact angles of various homologous series on Teflon O, RX , alkylbenzenes (f), n-alkanes , dialkyl ethers , siloxanes A, miscellaneous polar liquids. (Data from Ref. 78.)...

What is the critical surface tension for human skin Look up any necessary data and make a Zisman plot of contact angle on skin versus surface tension of water-alcohol mixtures. (Note Ref. 136.)... 

A requirement underlying the validity of Zisman plots is that there be no specific interactions, such as acid-base interactions, between the solid surface and the probe liquids. Such interactions, however, can, in principle, be taken into account by Young s equation, provided the contact angle remains finite. Their... 

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

There is a hysteresis effect associated with the wetting process which arises, at least in part, from the presence of defects and impurities in the surface under study. Thus advancing and retracting contact angles are slightly different. It is conventional to use the advancing contact angle in the Zisman plot. 

To determine yc for a solid, the advancing contact angles made by several non-polar or weakly polar liquids are measured and the value of Tlg which corresponds to 0 = 0 (i.e. cos 6=1) is found by graphical extrapolation. Zisman has determined yc for many solid surfaces by way of empirical plots of cos 0 versus -yLG (see Figure 6.2). According to equation (6.6), however, plots of cos 0 versus (Tlg)-1/2 should be approximately linear and permit more reliable extrapolation to cos 0=1. 

Although it is known that the surface tension increases with increasing HLB (all other things being equal), the dependence of contact angle on this quantity has not been studied previously. On the other hand, if one assumes that the linear relation between surface tension and contact angle found by Zisman and co-workers for both pure liquids and for solutions of surface-active agents (3) as a function of concentration holds for our herbicidal systems, it appears that the quantity, n, will exhibit at least one maximum when plotted as a function of HLB. 

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. 

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. 

Linear extrapolation of the data in a plot of cosine contact angle versus liquid surface tension to zero contact angle yields a quantity Zisman has called the critical surface tension. He proposed critical surface tension to be a characteristic quantity of a given solid. 

From the contact angles in Table III, cos 6 vs. Vly was plotted in Figure 2 for clean PMMA. From the intercept it is seen that 7c is approximately 39 dynes per cm., well within the range of 33 to 44 dynes per cm. recently reported by Wolfram [24]. Ellison and Zisman [9] also obtained a critical surface tension of between 39 and 40 dynes per cm. for poly (ethylene ter ephthalate), another polymer containing a large number of carboxylic ester groups. 

In many studies of wettability Zisman and coworkers have used the contact angles of a series of n-alkanes as a convenient means for determining for low energy solid surfaces [5,6,13,20]. In Figure 2 are plotted the cos 9 vs. 7lv° curves for the n-aUtanes on PMMA surfaces containing 0.5% additive I and 1.0% additive II. The critical surface tensions with additives I and n were 19 and 20 dynes per cm., respectively, representing a decrease of about 20 dynes per cm. from the value of obtained with the additive-free surface. Since the y values of 19 and 20 dynes per cm. are very close to that of 18 dynes per cm. reported by Fox and Zisman [l3] for the n-alkanes on poly-tetrafluoroethylene surfaces, it is apparent that a number of perfluoro-alkane groups are present in the outermost part of the surface phase with the principal axis of each carbon-carbon chain parallel to the surface. 

Surface tension Interfacial free energy mNm erg cm erg cm Contact angle (microscopy) Zisman plots Contact angle (degradation after prolonged UV irradiation) From isothermal crystallization studies At (2-D to 3-D) interface 16 16.5 16.5-14.4 30 10 (estimate) (53) (53) (54) (39)... 

Figure 2.10. A Zisman plot for polyethylene the contact angles of a variety of liquids on polyethylene are plotted against the surface tension of each liquid.

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