In this example we will use the five liquids in the Table 2 (Liquid Data) to find the critical wetting surface tension needed to effectively wet PC (polycarbonate) using the Zisman Plot.
The data of the liquids given from the table above is then graphed on the Zisman Plot (Figure 2) with the independent variable as the surface tension of the liquid in dynes/cm and the dependent variable as 1-cos(θ). There also are different variations of the Zisman plot since the Y-axis is unitless as seen in Table 1 and as mentioned above.
Liquids 1 and 2 fully wet the surface as shown by their low contact angles, so they should be neglected when first drawing the line of best fit to find the critical liquid surface tension needed to effectively wet the PC surface, γ, which is simply the x-intercept of the best fit line for the Zisman Plot. To find the best fit line a least squares regression is recommended by using a computer program such as Microsoft Excel, Minitab, Matlab, or it can also be done using a modern graphing calculator such as a TI-84. This was done with the data from Table 1 and the fit data for liquids 3,4, and 5 can be seen on Figure 3.
The x-intercept lands at 39.5 dynes per centimeter (This can be calculated by setting y equal to zero and solving for x) which is less than that of liquid 2, 42.9 dynes per centimeter; therefore, a more accurate measurement of the critical liquid surface tension needed to effectively wet the surface of PC can be obtained by including liquid 2 when making the line of best fit, as seen in Figure 4.
The x-intercept here lands at 42.1 dynes per centimeter (This can be calculated by setting y equal to zero and solving for x), indicating the critical liquid surface tension for PC.