Critical surface tension of wetting

The surface properties are of particular interest for composites and coatings. The n = 6 monomer will wet Teflon, and PTFE filled composites can be prepared. The critical surface tension of wetting for the fluoromethylene cyanate ester resin series has been determined from contact-angle measurements on cured resin surfaces. As indicated in Table 2.2, it parallels the fluorine composition and begins to approach the PTFE value of 18 dyn/cm. 

The viscosity or resistance to flow increases as the number of repeat units increases, but physical properties, such as surface tension and density, remain about the same after a DP of about 25. The liquid surface tension is lower than the critical surface tension of wetting, resulting in the polymer spreading over its own absorbed films. The forces of attraction between polysiloxane films are low resulting in the formation of porous films that allow oxygen and nitrogen to readily pass though, but not water. Thus, semipermeable membranes, films, have been developed that allow divers to breath air under water for short periods. 

C Critical surface tension of wetting, mixed series of test liquids. 

Critical Oxygen Index (COI), 853 Critical size, 704-705 Critical spherical nucleus, 710, 711 Critical strain, 867, 868 Critical stress energy factor, 474 Critical surface tension of wetting, 232 Critical temperature, 655 Cross-linked polymers, 29 Cross-linking, 148 Cross model, 731 Cross polarisation, 376, 377 Crystallinity, 728, 732, 815 Crystallites/Crystallisation, 690, 725 of rigid macromolecules, 739 Cyclical chain length, 782... 

Our own investigations have concerned (a) liquid spreading on solids and the laws relating the equilibrium contact angle and the critical surface tension of wetting to solid and liquid constitution (26, 27, 28, 53, 54,62), (b) liquid/liquid displacement from solid surfaces (1,5), (c) the properties of adsorbed monolayers on solids and their relation to the monolayer retraction method (28, 54, 62), (d) the surface electrostatic potentials of adsorbed organic monolayers on metals (9, 10, 11, 58, 59), (e) the effects of surface constitution on adhesion and abhesion (60),... 

Wettability. A description of the contact angle goniometer and the scheme used in determining the critical surface tension of wetting (yc) are described elsewhere (15, 18). 

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. 

To separate the roles of the pendant group and the backbone is a gross but useful simplification in explaining why PDMS has a critical surface tension of wetting similar to those of hydrocarbons with surfaces consisting of... 

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

Note (Tc is the critical surface tension of wetting, and a is the solid surface tension obtained in a manner similar to that of Owens and Wendt (7) but with a series of hydroxy-containing liquids rather than just water and methylene iodide. 

Surface tension studies of the most common fluorosilicone, poly(3,3,3-trifluoropropylmethylsiloxane) (PTFPMS), give unexpected results. Compared with (PDMS), PTFPMS has a higher liquid surface tension, a similar critical surface tension of wetting, and a considerably lower solid surface tension, as determined by water and methylene iodide contact angles and the method of Owens and Wendt (67). These results are summarized in Table X (7, 67, 72-74, 76, 77), in which PTFPMS is compared with two other fluorocarbon polymers, poly(tetrafluoroethylene) (PTFE) and poly(chlorotrifluoroethylene) (PCTFE). PTFE behaves like PTFPMS, whereas PCTFE behaves like PDMS. 

Polymer Equilibrium Liquid Surface Tension Ref. Critical Surface Tension of Wetting Solid Surface Tension"" Ref... 

TgS for polymers with architectures similar to PDMS are given in Table XII 21, 81). The TgS of poly(dimethylsilazane) and poly(dimethyl-silmethylene) lie between those of PDMS and poly(isobutylene) (critical surface tensions of wetting of 24 and 27 mN/m, respectively [70]). These values suggest that poly(dimethylsilazane) and poly(dimethylsilmethylene) will have critical surface tensions of wetting in the 25-26-mN/m range. 

Attenuated total reflection infrared critical micelle concentration electron spectroscopy for chemical analysis hydrophilic-lipophilic balance poly(chlorotrifluoroethylene) poly(dimethylsiloxane) poly(tetrafluoroethylene) poly(trifluoropropylmethylsiloxane) glass transition temperature critical surface tension of wetting Owens-Wendt solid surface tension surface tension of aqueous solution surface tension of liquid... 

Kelebek, S. et al.. Critical surface tension of wetting and filtration separation of hydrophobic solids, Sep. Sci. I echnol., 22, 1527, 1987. 

Extrapolation of the straight Hne to cos9 = 1 (9 = 0) gives the critical surface tension of wetting y. Any Hquid with y v Tc vvill give 9 = 0, that is, it wets the surface completely y,. is the surface tension of a liquid that just spreads on the substrate to give complete wetting. 

Table III. Critical Surface Tension of Wetting (Yj,) for some Photoresists (from Ref. 27, reprinted by permission of the publisher.

Measurement of the "critical surface tension of wetting" ycr. A liquid with a surface tension of less than ycr will spread on the surface of the solid. It is assumed that y=ycr to estimate the surface tension of the solid. 

Critical Wetting Surface Tension See Critical Surface Tension of Wetting. 

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