Zisman method

In 1950, Fox and Zisman [8] reported their study of the wettability of poly(tetrafluoroethylene) (PTFE) with n-alkanes, di( -alkyl)ethers, n-alkylbenzenes, and many other liquids. A linear relationship between the cosine of the contact angle (cos0) and the surface tension of the liquid (7lv) for the n-alkane solvents was obtained (Fig. 7.2). Similar plots were also obtained for di(n-alkyl)ethers and 

7 Determination of Solid Surface Tension by Contact Angle 

7 mN/m, determined by Nishino et al. using the dynamic contact angles of water and diiodomethane [11]. The results demonstrate that the Zisman plot can be used to determine the surface tension of different chemical constituents on the solid surface. Indeed, the critical surface tensions of different chemical constituents from surfaces of fluorocarbon, hydrocarbon, chlorocarbon, and nitrated hydrocarbon polymers have been determined [12], 

It is important to point out that the Zisman critical surface tension analysis is only limited to low surface energy surfaces and alkane solvents, where van de Waals force is the prime interaction. Many exceptions were found with polar andH-bonding solvents. Despite this limitation, the Zisman analysis remains as one of the useful tools to estimate the surface tension of low surface energy material to date [13]. 

The value of may be compared with that of y by applying Equation 8.5 

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. 

Combining Young and Duprd s law (Equation 8.3) with Girifalco and Good s approximation (Equation 5.29), allows for a further analysis of y.. Thus, 

When using pure liquids and for 0 15 may be neglected. Then, based on the definition of 

Because, as a rule 1 1 (see Table 5.3), it follows again that y. Substitution of f according to Equation 8.17 in 8.16 results in 

---

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. 

In practice, hydrophilic surfaces are often covered by hydrophobing adsorbates. The Zisman method cem then also be applied, provided wetting does not lead to desorption. 

The vibrating capacitor method known as the Kelvin-Zisman method was developed by Zisman based on the previous method. Instead of simply distancing the electrodes from each other, Zisman periodically vibrates an electrode, thus creating an alternating current that is easier to detect. 

The vibrating capacitor method, or Kelvin-Zisman method, is a non-destructive method that does not disturb the surface using photon or electron beams. It can be used for a large number of materials, and in a wide temperatnre and pressure range. It is therefore highly appropriate for the stndy of snrface properties of polyciystalline metal oxides. 

The Kelvin-Zisman method makes it possible to monitor the variations in a sample s work function, provided the reference electrode s work function is stable under the chosen experimental conditions. It is therefore important to choose the right reference electrode depending on the gas atmosphere and the temperature. The materials most commonly employed as a reference are metals, metal oxides, glass-coated metals and graphite. 

Further refinement of the above concepts was made by Kitazaki and Hata, who showed that the value of yc, obtained by the Zisman method. 

Fig. 6 Surface energy (by the Zisman method) and sessdle-drop contact-angie slopes for various fresh and durability-tested cloth GDLs. CARBEL CL GDL data represent before and after values from a 26,300-h test operated under stationary conditions by W.L. Gore Associates (Cleghom et al. 2006, Wood 2007)...

Table 15.3 shows components of surface tension for some solid polymers estimated by the Owens-Wendt methods the Zisman critical surface tensions values are also given. There is rather good agreement between the predicted polymer surface tensions from the Owens-Wendt and Zisman methods. 

Fig. 3-14 Determination of the critical surface energy yc of polymer films using the Zisman method (0 is the contact angle).

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... 

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... 

In the dynamic condenser, or the vibrating plate or vibrating condenser method (Fig. 5), also called Kelvin, Zisman, or Kelvin-Zisman probe, the capacity of the condenser created by the investigated surface and the plate (vib. plate) is continuously modulated by periodical vibration (GEN.) of the plate. The ac output is then amplified and fed back to the condenser to obtain null-balance operation (E,V). " " ... 

Shafrin, E.G. and Zisman, W.A. "Constitutive Relations in the Wetting of Low-Energy Surfaces and the Theory of the Retraction Method of Preparing Monolayers," Naval Research Labs Report 5394, Surface Chemistry Branch, Chemistry Division, October 21, 1959. 

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

Thomson s method has been used for the investigation of adsorption layers, especially in the arrangement described by Zisman (42) [c/. also Potter (43), Frost and Hurka (44), and Rosenfeld and Hoskins (45)]. In Zisman s method the mobile electrode vibrates mechanically, causing periodic variations of the above-mentioned electrometer charge. If the electrometer is replaced by an amplifier, a signal is heard in a telephone at the output of the amplifier, which vanishes if the difference of the contact potential is compensated. 

Shafrin, E.G. and Zisman, W.A. (1960) Constitutive relations in the wetting of low-energy surfaces and the theory of the retraction method of preparing monolayers. /. Phys. Chem., 64, 519-24. 

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. 

A very sensitive modification of this method has been described by Zisman 1 one of the plates is made to vibrate rapidly parallel to itself, thus periodically altering the distance between the plates. The oscillating current thus caused to flow to and from the plate is amplified and operates a loud speaker. A potentiometer is used to vary the potential applied to the plates, until the sound vanishes, and the value of the applied potential is then the contact potential. 

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). 

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. 

---