Critical Zisman surface tension

The purpose of this chapter is to present the LAD performance experiments carried out in room temperature liquids. Bubble point and reseal pressure tests for a 325x2300, 450 X 2750, and 510 x 3600 Dutch Twill screen are conducted in storable liquids, methanol, acetone, IPA, water, and binary methanol/water mixtures of various methanol concentrations. First screen pore diameters are estimated based on analysis from scanning electron microscopy and historical data. Experimental results are used to compare methods for determining effective pore diameter. Next, contact angles are measured for both pure and binary mixture fluids using a modified version of the Sessile Drop technique. Then, the equation of state analysis from Neumann and Good (1979) is used to determine the critical Zisman surface tension for stainless steel LAD screens, which... 

The critical Zisman surface tension is anticipated to be only slightly dependent on temperature between room and LH2 temperatures. Tbe temperature dependent coefficient for the surface tension of the liquid and solid materials is negative so that the surface tension increases as the temperature is cooled below the critical temperature (Adamson and Cast, 1997). This property is difficult to measure in solids but is most probable tbat tbe S/V surface tension of SS is at most somewhat larger at LH2 temperatures than at room temperatures. 

Equation (3.16) clearly predicts that bubble point pressure should scale linearly with the surface tension of the liquid when corrected for the contact angle between liquid and screen pore. Binary mixture bubble point test results from Chapter 4 showed that the critical Zisman surface tension value for liquids with these SS304 LAD screens was... 

It is not permissible to adopt data acquired from changes of the liquid resin s surface tension for solid state polymer. Zisman [72] does it supposing that the reversible adhesion work of the solid polymer must be close to that estimated for the liquid state. The conclusion follows from the assumption that the forces that act on the phase separation boundary spread out to a depth that does not exceed the size of some molecules. As a result, the interaction on the bound y cannot depend on the change of state of the substance. One must accept this because the determined v dues of the surface tension of solid polymers significantly exceed those for the liquid oligomers. If we deal with undercured products the v dues usually exceed those for the polymer surface tension acquired by wetting agent critic d surface tension methods. 

In film floatation, which was developed by Fuerste-nau and co-workers (59, 60), particles of similar size are sprinkled on the surface of a liquid with a known surface tension and the fraction of particles that sink into the liquid is measured. From this, the critical wetting surface tension, (of Zisman), of solid particles (i.e. the liquid surface tension at which the solid surface is completely wetted by the test liquid) can be determined. 

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... 

Figure X-9 shows plots of cos 6 versus 7l for various series of liquids on Teflon (polytetrafluoroethylene) [78]. Each line extrapolates to zero at a certain 7l value, which Zisman has called the critical surface tension 7 since various series extrapolated to about the same value, he proposed that 7 was a quantity characteristic of a given solid. For Teflon, the representative 7 was taken to be about 18 and was regarded as characteristic of a surface consisting of —CF2 — groups.

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.)... 

Take the data from Fig. X-12 on the propyl monolayers and make a Zisman plot to determine the critical surface tension for the surface. 

The interesting implication of Eq. XII-24 is that for a given solid, the work of adhesion goes through a maximum as 7b(a) is varied [69]. For the low-energy surfaces Zisman and co-workers studied, )3 is about 0.04, and Wmax is approximately equal to the critical surface tension yc itself the liquid for this optimum adhesion has a fairly high contact angle. 

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.

Critical surface tension data for low-energy surfaces of varying surface chemistry obtained from Zisman plots... 

Zisman s plot cos 6 varies linearly with yi,. Zzisman = Predicts critical surface tension linearity does not hold universally y depends on probe liquids. [73-76]... 

The ability of a liquid to "wet" the membrane material is an indication of that liquids ability to establish and maintain such an interfacial layer. Liquids of surface tension values less than the critical surface tension iy ) of the membrane material are capable of completely "wetting" the polymer. It may be possible therefore, to select membrane materials capable of accomplishing specific separations by their ability to be wet by one solution component but not by the other. For this reason Yc membrane materials is important. By employing the standard techniques of Zisman (43), the critical surface tension for PSF and CA were determined to be 43.0 and 36.5 dynes/cm, respectively. This data indicates that PSF is more readily wet by a larger number of liquids than is CA. Similar measurements for the various sulfonated polysulfones are underway. 

Zisman discovered that there is a critical surface tension characteristic of low-energy solids, such as plastics and waxes. Liquids ihat have a lower surface tension than the solid will spread on that solid, while liquids with a higher surface tension will not spread. Examples of critical surface tension values for plastic solids in dynes per cm are "Teflon/ 18 polyethylene, 31 polyethylene terephthalate, 43 and nylon, 42-46. As one indication of the way this information can be used in practical applications, one can consider the bonding of nylon to polyethylene. If nylon were applied as a melt to polyethylene, it would not wet the lower-energy polyethylene surface and adhesion would be poor. However, molten polyethylene would spread readily over solid nylon to provide a strong bond. 

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. 

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. 

Critical Surface Tensions. The data in Table II may be plotted (Figure 5) as cos 6 vs. yLV, according to the approach of Zisman (37). Then one may estimate the critical surface tension, yc of the undissociated polycation+-Cl surface of this particular nylon film in equilibrium with saturated water vapor by extrapolating the last four data points (which... 

Despite the approximation, Zisman s critical surface tension (39, 40) still provides the most convenient means of expressing the surface tension of a solid. Later Gardon (6) suggested a possible linear relationship between the critical surface tension yc and the solubility parameter for liquid-like polymers. He also proposed the following relation between solid surface tension and critical surface tension ... 

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. 

Zisman critical surface tension of wetting of solid (aj,... 

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