Zisman

The topic of spreading rates is of importance in the technology of the use of mono-layers for evaporation control (see Section IV-6) it is also important, in the opposite sense, in the lubrication of fine bearings, as in watches, where it is necessary that the small drop of oil remain in place and not be dissipated by spreading. Zisman and coworkers have found that spreading rates can be enhanced or reduced by the presence of small amounts of impurities in particular, strongly adsorbed surfactants can form a film over which the oil will not spread [48]. 

The detailed mathematical developments are difficult to penetrate, and a simple but useful approach is that outlined by Garrett and Zisman [130]. If gravity is not important, Eq. 11-36 reduces to... 

When a surface-active agent is present in a liquid droplet, it can adsorb to the surface, lower the surface energy, and cause the liquid contact angle to increase. This phenomenon, known as autophobicity, was postulated by Zisman many years ago [78, 79]. Autophobicity is quite striking in wetting films on clean... 

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.)...

A major contribution to the rational organization of contact angle data was made by Zisman and co-workers. They observed that cos 6 (advancing angle) is usually a monotonic function of 7l for a homologous series of liquids. The proposed function was... 

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.

An important and expensive problem in surface science occurs in the prevention of the attachment of marine animals such as barnacles to ship surfaces, a process known as biofouling. Baier and Meyer [159] have shown that the Zisman plot can be used to predict biofouling, thus avoiding costly field tests to find a successful coating to prevent biofouling. 

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. 

Levine and Zisman [46] confirmed and extended Hardy s results, using films on glass and on metal surfaces that were deposited by adsorption either from... 

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. 

Bigelow WC, Piokett D L and Zisman W A 1946 Oleophobio monolayers. 1. Films adsorbed from solution in non-polar liquids J. Colloid Interface Scl. 1 513-38... 

W. A. Zisman, in F. M. Fowkes, ed.. Contact single, Wettability andA.dhesions (Adv. Chem. Ser. No. 43), American Chemical Society, Washington,... 

W. A. Zisman, in K. J. Mysels and co-workers, eds., 20 Years of Suface and Colloid Chemistry, The Kendall Award Addresses, American Chemical Society, Washington, D.C., 1973, p. 109. 

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