Fluorinated liquids, contact angles

In addition to providing a direct visualization of ionic clusters, the discovery of the thin fluorine-rich layer may have important implications with regard to the liquid/vapor sorption of these materials. To be sure, the nature of this layer would depend on the specific liquid or vapor environment contacting the membrane surface. In particular, the molecular polarity of the environment and its influence on surface tension would be involved. The difference between the liquid water versus saturated water vapor sorption was mentioned in this report. Also, the contact angle experiments of Zawodzinski et al. 

The hydrophobic nature of F-treated graphite can be evaluated from contact-angles of liquid droplets. The surface free-energy can be reduced from 50 mJ m-2 to as low as 7 mJ m-2 after exposure to NF3 or SF6 rf plasmas. A significant coverage of surface fluorination is achieved for exposure times of 10-15 min under an NF3 plasma, yielding water contact angle of 115° [91], In some case this value has been found to exceed that of PTFE [92]. 

A porous medium is sometimes modeled as a bundle of capillary tubes of circular cross section. Suppose that an air-filled porous medium is contacted with a liquid at atmospheric pressure. For what range of contact angles will liquid spontaneously enter the porons medinm When entry is not spontaneous, develop an expression for the liqnid pressnre required for entry in terms of the surface tension of the liqnid, the contact angle, and tube diameter. In view of yonr answers, why do yon think that fluorinated compounds are often nsed for waterproofing fabrics ... 

In the present work, we aimed to examine how the structure of a nanosphere array affected the contact angle between a liquid droplet and fluorinated surfaces. Four types of silica nanospheres with various diameters were stacked to form different organized arrays using a self-assembly technique. To clarify the superhydrophobicity, we proposed a modified parameter into the conventional Cassie-Baxter equation. This mathematical model presented in this study can probably shed some light on how the variation of particle size would induce the superhydrophobicity of nanosphere surfaces. 

Fox and Zisman [62,63] characterised some polymer surfaces by measuring the contact angles for a series of liquids, and plotting the data in the form of cos 0 against the surface tension of the liquids. When 9 = 0 (cos9= 1), the liquid spreads on the surface and the surface tension of the liquid is then equal to the critical surface tension of the polymer. A plot is shown in Fig. 15 for liquids on some fluorinated copolymers the values of 7. are obtained from the intercept with the upper abscissa. The values of critical surface tension for some polymers are given in Table 10. 

FIGURE 11.10 Single fiber contact angles of Toray TGP-H materials (hydrophobized to 17 wt% fluorinated ethylene propylene, FEP) aged in accelerated fashion in different liquid-water environments. (With kind permission from Springer Science+Business Media Polymer Electrolyte Fuel Cell Durability, Durability aspects of gas-diffusion and microporous layers, 2009, pp. 159-195, Wood, D.L. and Borup R.L.)... 

As the liquid for filling all pores in LEPP we have used the fluorinated hydrocarbon Porofil 3 (Beckman-Coulter, USA). According to the manufacturer creos 0= 0.16 bar m (where cr is the surface tension, and 6 the contact angle). From comparison of capillary outflow-time for water and Porofil its viscosity was estimated as // = 1.25 mPa s. 

---