Wetting Zisman plots

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. 

Zisman Plot See Critical Surface Tension of Wetting. 

FIGURE 2.4 The Zisman plot for n-alkanes on Teflon (Fox and Zisman, 1950). The liquids with cos X= 1 are wetting liquids. The error bar is shown in the inset. 

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). 

FIGURE 8.7 Zisman plots for a Teflon surface from which critical surface tensions of wetting are derived. T = 20°C. t, alkyl benzenes x, -alkanes , dialkyl esters , siloxanes A, polar liquids. 

Zisman Plot. A plot of the cosine of contact angle, between a solid of interest and a series of liquids, versus the surface tensions of those fiquids. The surface tension extapolated to zero contact angle is the critical surface tension of wetting of the solid. 

FIG. 24 Zisman plot for estimating the cellulose liber surface tension (the cosines of the contact angles were extracted from the measured normalized wetting rates) using the averaged constant C determined from Fig. 23. (From Ref. 118.)... 

Surface tension of solids Yes (Zisman plot extrapolation from liquid data, solubility parameters, parachor) Wetting and adhesion... 

Wetting and adhesion via the Zisman plot and theories for interfacial tensions... 

The Zisman plot is very useful in wetting studies. Polymers with low critical surface tensions, e.g. PE and especially Teflon (PTFE), are wetted by very few liquids. These surfaces need, thus, to be modified for improving wetting or surfactants should be used. In general, it is more difficult to wet plastics compared to clean metals and ceramics (materials which, when clean, have surface tensions of the ohIct of 500 mN m or more and are called high-enCTgy solids). 

William Zisman was the recipient of numerous awards for his great scientific achievements. The Zisman plot is still widely used in practical applications related to wetting and adhesion phenomena. An account of his research achievements is summarized by Shafrin (1987). 

Estimate the critical surface tension of PET using the Zisman plot. Is it easier to wet a PET or a polystyrene (33.0 mN m ) or a Teflon (18.0 mN m ) surface Which of the three polymers is easiest to wet and which is the most difficult to wet Explain briefly your answer. The values in parenthesis are the critical surface tension at 20 °C. 

Explain briefly the Zisman plot and how it can be used for estimating the wetting of solid surfaces. 

Fig. 17 Critical surface tension (Zisman) plots for advancing and receding contact angles. Liquid A wets the surface very well, B does not wet as well, but will not dewet. Liquids C, D, and E dewet. (From Ref. 5, used with permission.)...

The wetting angle can be measured using simple techniques such as a projector, as shown schematically in Fig. 2.54. This technique, originally developed by Zisman [73], can be used in the ASTM D2578 standard test. Here, droplets of known surface tension, at are applied to a film. The measured values of cos are plotted as a function of surface tension, at, as shown in Fig. 2.55, and extrapolated to find the critical surface tension, ac, required for wetting. 

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. 

Pioneering work on the evaluation of solid surface tensions was carried out by Zisman and co-workers. The principle was to measure the Contact angles 0q of a series of liquids of decreasing surface tension y on the polymer surface (see Critical surface tension). As the value of y decreases, so does that of 6q, whereas cos 0q increases. By plotting a graph of cos 0q versus y, extrapolation can be made to cos 0q = 1 (even if a liquid in this neighbourhood is only hypothetical). The value of y for cos 0o = 1 is known as the critical surface tension for wetting of the solid yc and corresponds to the value of the surface tension of a liquid that will just spread spontaneously. It does not, in fact, correspond... 

Our studies showed that the inner surface of the cardiovascular System was hydrophobic surface with Yc(Zis.)=29 dyne/cm. We could easily select polytetrafluoroethylene as the material with a smaller critical surface tension than 29 dyne/cm to make test materials. Figure-3 shows the surface properties of the inner surface of the cardiovascular system and polytetrafluoroethylene in relation to wetting properties viewed from Zisman s plots. How should we treat polytetrafluoroethylene to minimize the difference in wetting properties between the surface of polytetrafluoroethylene and the inner surface of the cardiovascular system. We tried to improve the surface properties of polytetrafluoroethylene by using the graft copolymerization method and expansion method. 

---