Surface energy critical

It is now opportune to consider the structure-property relationships of fluorochemical finishes in more detail [501,502]. Water repellency depends mainly on reducing the critical surface energy of the fabric surface. This parameter must be less than that of the wetting... 

Table 10.47 Critical surface energies for low energy surfaces [502]...

The fluorine content, density, critical surface energy, glass transitions, thermal expansion coefficient above and below the glass transition, and 300°C isothermal thermogravimetric stabilities of the fluoromethylene cyanate ester resin system with n = 3, 4, 6, 8, 10 are summarized Table 2.2. Also included for the purpose of comparison are the corresponding data for the aromatic cyanate ester resin based on the dicyanate of 6F bisphenol A (AroCy F, Ciba Geigy). 

Contact Angle Measurement and Critical Surface Energy... 

Figure I. Fepreseniaiive contact angle and critical surface energy data. Key a, untreated 52/48 butadiene/styrene block copolymer and x, butadiene exposed to ozone at 375 ppm for 150 min and crosslinked with 1% benzoyl peroxide.

Figure 2. Effects of ozone exposure on critical surface energy. Exposure curve units are ppm-min. Key , butadiene o, crosslinked butadiene and+, 75/25 butadiene/styrene random copolymer.

Figure 4. Effects of ozone exposure on critical surface energy of block copolymers and homopolymers as afunction ofbulk percent styrene content. Key to ozone treatment , untreated o, until chamber equilibrium +, 375 ppm for 75 min and , 375 ppm for 150 min.

Figure 8. Critical surface energy as a function of oxygen carbon ratio for butadiene styrene copolymers and homopolymers after ozone exposure at 375 ppm for 150 min. Key a, crosslinked butadiene o, random copolymers and 0, block copolymers.

Critical Surface Energy. The effect of sulfonation depth on the surface tension of sulfonated PS films is shown in Figure 6c. For comparison the result for an unconverted PS film is shown also. Increased sulfonation causes yc, in general, to increase to a sulfonation depth of approximately 10 monolayers and then decrease beyond this value. It is interesting to note that the untreated PS values for yc are slightly higher than those observed at very low sulfonation depths and at very high conversion ratios. The former data were taken for a PS film that had... 

Clearly it can be seen that the repulsion properties are derived from lowering the critical surface energy of the hydrophobic surface below that of the wetting liquid, thus creating a chemical barrier against the penetration by the liquid. 

Whilst with liquids the surface tensions can be directly measured, this is not posible with solid surfaces. Therefore, a corresponding quantity for solid surfaces was derived as so-called critical surface energy Yc, which can be extrapolated in several ways. 

The connection between repellency, contact angle 0 and the critical surface energy, Yc, is described with the empirical relationship (Zisman, 1964) ... 

The aim of a fluorocarbon finish is to produce a surface of closely packed trifluoromethyl groups which gives the lowest possible critical surface energy (Duschek, 2001). From a chemical point of view, the generation of such structures on the fabric can be achieved by using some chemical-physical phenomena. 

The detailed mathematical derivations of Eq. (10) are shown in the appendix. Eq. (10) implies that wetting a solid substrate with liquids will yield a linear relationship between the cos0 and nYj y. The intercept of this linear relationship at cos0=l defines the critical surface energy of wetting (Yq). The slope of this linear relationship... 

As has been discussed, the new equation of state implies that a plot of cos 0 versus will exhibit a linear relationship as shown in Fig. 3. The intercept at cos 0 =1 defines the critical surface energy (Tq), and the value of... 

Table 3, Yq is the critical surface energy of PS measured using the classical zisman plot. The difference between and is less than 12%.

The critical surface energy Yc of the CF3 and CT2 groups are much lower compared with the surface energy of the corresponding hydrocarbons (CH3 and CH2), which is described in Table 1. 

This has been demonstrated in the literature [2, 3] on fluorochemicals that there is a relationship of the chain length of the perfluorinated chains that is related to the critical surface energy of the surface as described in Fig. 3. 

With plasma treatment, surface wettability can be readily induced on a variety of normally non-wettable materials as shown in Table P. 5. Certain polymeric surfaces, such as the polyolefins, become crosslinked during plasma treatment. The surface skin of polyethylene, for example, will become crosslinked so that if the polymer were placed on a hot plate of sufficient heat, the interior would turn to a molten liquid while the crosslinked outer skin held a solid shape. Other polymers have their critical surface energy affected in different ways. Plasma-treated polymers usually form adhesive bonds that are two to four times the strength of nontreated polymers. Table P.5 presents bond strength of various plastic adherends pretreated with activated gas and bonded with an epoxy or urethane adhesives. 

This surface energy is a characteristic of the solid surface and called the critical surface energy/tension , Yc-... 

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