Water adhesion tension

Surface analysis is a big challenge for the modihed polymers. It is well known that hydrophilicity and hydrophobicity can be measured in terms of water adhesion tension (x°). x° greater than 30 dyne cm are designated as hydrophilic and x° less than 30 dyne cm are designated as hydrophobic (Ma et al., 2007). Attenuated total reflec-tance-Fourier transformed infrared spectroscopy (ATR-FTIR) and XPS are two widely used techniques for the analysis of surfaces of modihed polymers. ATR-FTIR is not very specihc to the polymer surfaces as the signals are a combination of surfaces and underneath. Therefore, XPS can be used for the surface analysis because this technique has much smaller sampling depth (typically, <10 nm) (Ma et al., 2007). 

Bartell and Flu [19] were able to determine the adhesion tension, that is, ysv -7SL. for the water-silica interface to be 82.8 ergs/cm at 20°C and its temperature change to be -0.173 erg cm K . The heat of immersion of the silica sample in water was 15.9 cal/g. Calculate the surface area of the sample in square centimeters per gram. 

Fig. 10 relates the composite extraction index (see above) obtained in the low-shear aqueous test system for these Tween surfactants, and adhesion tensions measured against various solids. Adhesion tensions against platinum and bitumen saturated pyrophyllite are irregularly related to tar sand extraction, while the adhesion tension against a fresh pyrophyllite surface is linearly (inversely) related to tar sand extraction. This is the first linear correlation between a measurable property of a surfactant solution and tar sand extraction which we have been able to obtain, and there appears to be no such finding in the literature. Fig. 11 gives the relations between extraction of bitumen with the paddle mill, solvent-aqueous-surfactant extraction and adhesion tensions measured against platinum, bitumen saturated pyrophyllite and hydrated (48 hours in water) pyrophyllite. 

A linear correlation is obtained between bitumen extraction with the paddle mill and the adhesion tension against water saturated pyrophyllite. That the degree of water saturation of the pyrophyllite is important in explaining the difference between the 2 extraction processes indicates that it will be necessary to study each process in terms of the relevant adhesion tensions. These results demonstrate that adhesion tension is the most important parameter found to date in determining the degree of separation in the presence of surfactants. Measurements of adhesion tension between surfactant solutions and minerals similar to those found in tar sand may be of considerable value in studies of surfactant utility in both aqueous-surfactant, solvent-aqueous-surfactant and in situ extraction processes. In addition, if appropriate model situations can be developed, measurements of adhesion tension may be useful in upgrading bitumen-water-clay emulsions obtained by a variety of in situ and heavy oil recovery processes. 

Among other things, a suspension of particles will be most stable in a liquid having the highest adhesion tension for the solid. Referring to Table 40 we see that the adhesion tension for silica in water and in ani-... 

Suppose that the solid is originally not in contact with water but is immersed completely (i.e., immersional wetting). In this case, the water penetrates the capillaries in the solid. The energy change for immersional wetting, called the adhesion tension, is given by ... 

When 9 < 90°, the adhesion tension is positive, and the penetration of water into the capillaries under no applied pressure becomes spontaneous. However, if 9 > 90°, work would be needed in order to immerse the solid in water. 

Figure 26.10, and (d e) in Figure 26.11] until the force in the direction of the wet surface exceeds the adhesive tension of emersion, Te, at the polymer surface/water interface. After exceeding the adhesive tension, the three-phase contact line starts to move toward the prewetted surface, seen as (D E) in Figure 26.9 and (C D) in Figure 26.12. The adhesive tension in the receding process is usually less than that in the advancing process unless the surface was completely wetted by the first immersion (i.e., zero contact angle). When the complete wetting occurs on the first immersion, the first emersion line retraces the first immersion line, such is the case with O2 plasma-cleaned glass.

Fluorinated surfactants (or fluorosurfactants, i.e., surfactants with hydrophobic tails comprising a fluorocarbon moiety) provide an alternative means of achieving extremely stable PFC emulsions, as they can provide very low PFC/water interfacial tensions [cr , another factor in Eq. (2)]. d s yet, this option has not been developed, in part because of the added cost involved in the evaluation for approval of a novel active excipient. A further means of effectively increasing the stability of EYP-based PFC emulsion consists of supplementing standard phospholipids with mixed fluorocarbon-hydrocarbon diblock compounds, such as 14 or 15. Such diblocks, which have fluorophilic-lipophilic amphiphilic properties, are expected to improve the adhesion of the phospholipid film onto the PFC droplet. 

On the other hand, in the earlier literature opinions to the contrary have been expressed. Both Bangham [5] and Cassel [18] have suggested that systems exist for which the FZ assumption cannot hold. Further, one may cite the adhesion tension data for water on graphite reported by Fowkes and Harkins [30] and the corresponding film pressures determined by Harkins, Jura, and Loeser [43]. 

For the adhesion tension data considered below, the liquid phase denoted by Subscript 1 will in all cases be water. Hence, for present purposes. Equation 13 can be written as... 

These authors, as noted above, adopted the FZ assumption regarding the magnitude of the film pressures. They did not choose to use the adhesion tension value for water, ( 13. The present approach, on the contrary, uses the value of < 13, since it is assumed that 1 can be neglected. Thus, eliminating 0 3 between Equations 16a and 19 yields... 

In the case of paraffin, no film pressures are available, since two-liquid adhesion tension data are lacking. Thus, it was necessary to assume a film pressure for one of the liquids in contact with paraffin. For this, a value of 1 dyne per cm. was taken as the film pressure of tert-butylnaphthalene. If a higher value had been chosen, the solid-vacuum and solid-liquid water tensions would have been correspondingly higher. Since the interfacial tension with water in this case seems already high, in comparison with liquid-liquid interfacial tensions for paraffin hydrocarbons [23], the quoted film pressure was adopted. 

The hysteresis of wetting (At) is low for the aqueous solutions (in distilled water), a. For the alkaline solutions, b, the hysteresis is larger but does not exceed 10 dynes. (This result was obtained for silica slides which had been soaked overnight in aqueous 4N HCl. Following this treatment the results of adhesion tension measuring became... 

Duriez [1] imderlines the necessity of considering the ternary system mineral-binder-water to explain the affinity for coating wet materials on the one hand and the stripping of coated materials by water on the other hand. He emphasizes the role played by dopes as modifiers of the absolute value of the adhesion tensions of water and binder on the minerals, which are the motivating factors behind the development of coating, the viscosity of the binder and the roughness of the stone acting as a brake. 

We have been able to define the difference in behavior of the mineral-hydrocarbon-water system according to whether the mineral is initially wetted by water or by hydrocarbon, by utilizing J. Guastalla s wetting balance which permits one to measure successively the immersion, and emersion, adhesion tensions. 

With amine hydrochlorate, the problem is still more paradoxical. The adhesion tensions are negative and their absolute values may, in a high dope concentration, be equal to the value of the interfacial tension, but of opposite sign. The solid is, therefore, perfectly wetted by water. 

Problem 1. A wetted stone is to be coated with a binder. This problem arises at the time the macadam is made. Water is to be displaced by the binder on the surface of the mineral. This process is equivalent to the immersion of the slide in thekerosine phase. We must consider, therefore, the immersion adhesion tension. 

When an amine is dissolved in the hydrocarbon phase, a threshold of concentration exists, beyond which the adhesion tension becomes positive. This threshold is characteristic of the efficacy of the dope employed on the mineral. It is equal to the concentration of the dope required for the binder to displace the water off the mineral surface. 

Problem 2. A different problem appears when the material is set in place on the road and we want to avoid displacement of the binder by water. It is a matter of protecting the structure, if, for example, the laying is followed by rain. This is equivalent to the emersion process and the force of displacement is then the emersion adhesion tension. 

However, although positive, the emersion adhesion tensions are very low (practically nil in the case of porphyry). Because of the hysteresis (difference between immersion and emersion adhesion tensions) imder the effect of outside energy—mechanical action, for example—the binder may be irreversibly replaced by water, and the stripping will continue, leading to the destruction of the structure. 

Measurements of adhesion tensions on polished mineral slides by the Guastalla wetting balance point out certain aspects of the physical mechanism of the wetting of aggregates with doped hydrocarbons in the presence of water. 

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