Polar component of surface tension

Note All data are from references 88 and 89 except where indicated, is the nonpolar component of surface tension, is the polar component of surface tension, and o sv is the Owens-Wendt solid surface tension. All values are in units of millinewtons per meter. 

Wu has proposed to separate the surface energy into non-polar (dispersion) and polar components (Eq. (2.12)). The subscripts d and p designate non-polar (dispersion) and polar components, respectively. The concept of the additive nature of surface energy components has been accepted by a number of researchers such as Fowkes ° and Meyer et al. The polar component of surface tension includes various dipole interactions and hydrogen bonding. The various components have been lumped together to simplify the discussions. The dispersion component includes the nonpolar fraction of surface energy. Fractional polarity is defined by Eq. (2.13) and non-polarity by Eq. (2.14). 

Although it was assumed that Eq. (13) is valid also when an apolar material enters into interaction with a polar one, in practice polar surfaces interact with each other more often. Several attempts were made to generalize the correlation of Fowkes for such cases and the geometric mean approximation gained the widest acceptance. This considers only the dispersion and polar components of surface tension, but the latter includes all polar interactions [63]. Thus interfacial tension can be calculated as... 

The harmonic mean equation is generally considered to be applicable to low surface tension materials such as organic polymers and liquids. If y and y are known for two liquids, and the contact angles of those liquids on the solid of interest are measured, equation 36 produces two simultaneous equations that can be solved to find the surface tension and polarity of a solid polymer surface. Numerous assumptions have been made in developing the theory of fi actional polarity. For example, it ignores the possibility of induced polarity at the interface between polar and nonpolar materials (82). These assumptions limit the application of equation 36 to systems where at least one and preferably both of the components are relatively nonpolar. The theory breaks down when interfacial interactions lead to molecular rearrangements at the interface between solid and liquid. In addition, it was foimd that pairs of liquids with similar dispersive and polar components of surface tension gave umeasonable results for the substrate surface tension calculated by the harmonic mean method (83). 

The surface tension of two thermoplastics and three fillers are listed in Table 2. Large differences can be observed both in the dispersion, but especially in the polar component. The surface tension of the majority of polymers is in the same range, in fact between that of PP and PMMA. Those listed in Table 2 represent the most important particulate fillers, and also reinforcements used in practice, since clean glass fibers possess similar surface tensions to Si02. Surface treatment lowers the surface tension of fillers significantly (see Sect. 6.1). 

The three EME coupling agents in Table 1 were analyzed using contact angle measurements to determine their polar and dispersion components of surface tension. From the surface tension data, wettability envelopes were constructed and compared with the surface tension properties of the epoxy coating [4], These data predicted that EME 47 would be wet by the epoxy, but not EME 23. This is believed to be the reason for the very low peel strength when EME 23 was employed [4],... 

For non-polar liquids, the dispersion component is essentially the total surface tension (see Eqn. 3). For polar liquids, the dispersion component of surface tension can be obtained using Eqn. 4 after measuring both surface tensions and interfacial tension, provided that... 

Latex (emulsion) adhesives. In contact with water, adhesive bonds with latex adhesives may release surfactants, which will have the effect of lowering surface tension and changing the thermodynamic work of adhesion. Some latices based on copolymers of vinyl acetate were dried to give films which were then immersed in small quantities of water. The surface tensions (/w) fell from 72.8 mN m to values in the range 39-53 mN m in the first hour and then remained fairly static [76]. Measurements of interfacial tensions against n-hexadecane showed the dispersion components of surface tension remained essentially constant but polar components were reduced into the range 6-20 mN m ... 

The adsorption of dicarboxyhc acids is more comphcated than that of their monocarboxylic counterparts. They are more polar and the acidic groups situated at both ends of the aliphatic chain offer a variety of possibilities for adsorption. The two groups might be attached to different filler particles, they may be oriented vertically or paraUel to the surface or can also form loops. The changes in the dispersion component of surface tension are plotted against the amount of surfactant used for the treatment for fillers coated with the two dicarboxyhc acids in Fig. 8. The surface tension of the fiber treated with stearic acid is also presented for comparison. Several conclusions can be drawn from the results shown in the figure. A much smaher decrease can be achieved in... 

The Ys values are obtained by the Owens and Wendt approach [10] (Equation 9.3) using water and diiodomethane, where y is the sum of the dispersion force component of surface tension, y, and the polar component, and the subscripts LV and SV refer to the liquid/vapor and solid/vapor interfaces, respectively. 

DF is F gain for the CB content increase in the substratum (PP) from 0 to 42 vol. % calculated from the ratio of polar and dispersion components of surface tension [17]. 

Two test liquids, such as deionized water and formamide of known polar and dispersion components of surface tension were used to evaluate the polar and dispersion components of surface energies of FBI through measurement of their contact angle by the sessile drop method. 

Liquid-Phase Components. It is usual to classify organic Hquids by the nature of the polar or hydrophilic functional group, ie, alcohol, acid, ester, phosphate, etc. Because lowering of surface tension is a key defoamer property and since this effect is a function of the nonpolar portion of the Hquid-phase component, it is preferable to classify by the hydrophobic, nonpolar portion. This approach identifies four Hquid phase component classes hydrocarbons, polyethers, siHcones, and duorocarbons. 

Geometric mean approximation Dispersive and polar components of solid surface energy are found by solving yiv(l +COS0) = 2(y,Xf + 2(y Yl S An extension of GGF equation ysa predicted is significantly higher than the critical surface tension. [84]... 

Equation 24 is derived from the Young (Eq. 21), the Dupre (Eq. 8) and the Eowkes (Eq. 10) equations by assuming complete wetting (cos 0 =0). Measurements with polar solvents give the polar component of the surface tension, but acid/base constants and the corresponding work of adhesion can also be calculated from them ... 

The extent to which surface tension can be controlled by fluoroalkyl-containing coupling agent type treatments is summarized in Table 1. Its purpose is to simply illustrate the range of control possible detailed comparisons are unwarranted because of differences in sample preparation and choice of substrate, data acquisition and treatment. Some of the critical surface tensions (crc) are obtained with -alkanes, some with other liquids. Some of the dispersion force components (of) and polar components (of) of solid surface tension are derived by use of different equations. The reader is referred to the key references in Table 1 for full details. 

The dispersive and polar components of the surface tensions of the liquids were estimated to be 7 = 21.8 mN/m and 7 = 51.0 mN/m for water and 7 = 49.5 mN/m and 7 = 1.3 mN/m for methylene iodide. This estimation was done by measuring contact angles with various hydrocarbons and assuming that there are only nonpolar interactions. What are the surface energies, 7s, of the polymers ... 

Turning now to the solid/water/oil measurements, we compare the predicted Ooic values according to Equations 14 and 15 with experimental values in Tables IV-VII for the substrates investigated. In the case of Teflon, where it is possible to test Equation 11, values are given for heptane and n-hexanol. The dispersion and polar components of the surface tension of water-n-hexanol, i.e. water saturated with n-hexanol, and hexanol-water were obtained by measuring the contact angle of liquid drops on paraflSn wax (ys = 25.5 dynes/cm), which served as a... 

Interesting features are observed in two-phase systems containing surfactants soluble in both water and oil, especially when they are present at high concentrations. The increased content of a component with intermediate polarity in both phases results in smaller differences in polarity of contacting phases and leads to a very significant lowering of surface tension on top of that caused by the adsorption. The surface tension may reach extremely low... 

The subscript d and p refer to dispersive and polar components of the surface tension coefficients. Eq 4.38 is called the harmonic-mean... 

Chen et al. [36] presented a conclusive comparistMi of the latex particle surface polarities (as determined by contact angle measuremoits) to the measured interfacial tensions of various polymer phases dissolved in the second-stage monomer against the aqueous phase. They prepared PS/PEMA composite particles using two different monodisperse PS seed latexes (produced by the Dow Chemical Co. as model colloids). The results of the interfacial tension measurements for each polymer phase, i.e. PS core particles and PEMA shell polymer dissolved in EMA monomer, showed that the interfacial tension first decreased and then remained constant as the polymer concentration was increased. This demonstrated that the polarity of the polymer-monomer solution interface with the aqueous phase increased until reaching a certain equilibrium point, which depended on the amount and nature of the polar components of the polymer. 

Equations (17) and (18) can be used to predict 6 if the various dispersion and polar components of the surface tensions are known. Some predictions and the corresponding experimental values are compared in Table V. The agreement is not especially good for either the HM or GM approximations. However, both theories correctly predict the expected trend in contact angle with surface tension. 

Surface energy is critically important to many processes (printing, multilayering, etc.) and it influences the interfacial tension. The surface energy of a PLA made up of 92 per cent L-lactide and 8 per cent meson-lactide was found to be 49mJm , with dispersive and polar components of 37 and llmJm, respectively [34], which suggests a relatively hydrophobic structure compared with that of other biopolyesters. 

Table 59.3 is based primarily on the Zisman critical surface tension of wetting and Owens and Wendt approaches because most of the polymer data available is in these forms. The inadequacies of equations such as Eq. (59.7) have been known for a decade, and newer, more refined approaches are becoming established, notably these of van Oss and coworkers [24]. A more limited number of polymers have been examined in this way and the data (at 20 °C) are summarized in Table 59.4. is the component of surface free energy due to the Lifshitz-van der Waals (LW) interactions that includes the London (dispersion, y ), Debye (induction), and Keesom (dipolar) forces. These are the forces that can correctly be treated by a simple geometric mean relationship such as Eq. (59.6). y is the component of surface free energy due to Lewis acid-base (AB) polar interactions. As with y and yP the sum of y and y is the total solid surface free energy, y is obtained from... 

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