Contact angles of water

Fowkes and Harkins reported that the contact angle of water on paraffin is 111° at 25°C. For a O.lAf solution of butylamine of surface tension 56.3 mJ/m, the contact angle was 92°. Calculate the film pressure of the butylamine absorbed at the paraffin-water interface. State any assumptions that are made. 

Detergents may be produced by the chemical reaction of fats and fatty acids with polar materials such as sulfuric or phosphoric acid or ethylene oxide. Detergents emulsify oil and grease because of their abiUty to reduce the surface tension and contact angle of water as well as the interfacial tension between water and oil. Recent trends in detergents have been to lower phosphate content to prevent eutrification of lakes when detergents are disposed of in municipal waste. 

Early waterproofing treatments consisted of coatings of a continuous layer impenetrable by water. Later water-repellent fabrics permitted air and moisture passage to improve the comfort of the wearer. Aluminum and zirconium salts of fatty acids, siUcone polymers, and perfluoro compounds are apphed to synthetic as well as natural fibers. An increase in the contact angle of water on the surface of the fiber results in an increase in water repeUency. Hydrophobic fibers exhibit higher contact angles than ceUulosics but may stiU require a finish (142). 

The contact angles of water and adhesive resin on wood are higher in the case of freshly harvested wood compared to stored chips. This means that the surface of particles from this fresh wood is more hydrophobic. This influences the wetting and the penetration negatively and with this the gluability. Reason for this lower wettability of freshly harvested wood is a higher content of some wood chemical components, or wood extractives, as has been determined by water extraction. This result, however, must not be confused with the better wettability of a freshly cut surface, independently if it is freshly harvested or stored wood. 

Table 7 reveals that the grafting of TAC onto PE decreases the equilibrium contact angles of water and formamide from 92° to 65° and from 75° to 53°, respectively. This decrease is a function of the monomer level and the irradiation dose. At a fixed irradiation dose of 15 Mrad, variation of the TAC level from 0.5 to 3 parts causes a reduction in the contact angles of water by 13° (from 88° to 75°) and of formamide by 11° (from 72° to 61°). This is due to the fact that the concentration of... 

The effect of irradiation of samples in the absence of TAC on the contact angles is also reported in Table 7. Modification of the surface takes place, as is evident from the decrease in the contact angles of water and formamide. The change, which is maximum at an irradiation dose of 10 Mrad, is due to the generation of polar functionalities on the surface. This is also corroborated from the IR/XPS studies described later. The contact angles are lowered further when TAC is incorporated in the system (compare TO/5 with Tl/5, TO/15 with Tl/15, etc.)... 

Table 9 Contact Angle of Water and Surface Energies of EPDM, Silicone and Their 50 50 Blend...

The FTE SAMs have a good hydrophobic property. Ohio et al. [36] have compared the variation of contact angles with immersing time in a neat FTE and a 100 mM FTE solution. The contact angles of water and hexadecane increased to about 110° and 73° from the initial value 76° and 36°, respectively, after 24 h immersion. Their works also indicate that the adsorption rate in 100 mM FTE solution is slightly faster than that in neat FTE. 

FIG. 9 Silver nanoparticles capped by 4-carboxythiophenol electrostatically adsorbed to positively charged octadecylamine monolayers, (a) Mass uptake versus number of layers at subphase pH 12 and pH 9 the inset shows the contact angle of water versus the number of layers, (b) Absorbance spectra as a function of the number of layers transferred (left), with the inset showing the plasmon absorbance at 460 nm versus the number of layers. Thickness versus number of layers as determined by optical interferometry is shown on the right. (Reprinted with permission from Ref. 103. Copyright 1996 American Chemical Society.)... 

A very different behavior is observed when condensation occurs on a mica surface that has been exposed to air for a few hours (we will refer to it as contaminated mica ). In this case glycerol forms droplets in the shape of spherical caps, indicating that it does not completely wet the surface. This behavior is similar to that of water, which we present in detail later. The contact angle of water on mica surfaces increased from 0° on the freshly cleaved surface to a small value between 2 and 3° on the contaminated mica [51]. 

Wettability measurements show that most soil constituents are water wettable or hydrophilic,28 although calcium carbonates [calcite, CaC03, and dolomite, CaMg(C03)2] are slightly hydrophobic for example, the contact angle of water and heptane is 100 to 105°. Therefore, carbonaceous reservoirs are usually oil-wet. 

Figure 5. Contact angle of water with films of polyfti-vinylcarbazole) (---------),...

Contact angles of water on the top (Interfaced with air during film preparation) and the bottom (interfaced with the glass plate) surfaces of both the SPSF-Na and SPSF-K membranes are listed in Table IV along with the value for cellulose acetate (CA). The reported values are the average of ten separate measurements made immediately after introduction of the water droplet onto the membrane. Contact angles on the top side of the SPSF-Na series... 

Young s equation at liquid —solid l iq uid2 has been investigated in various systems where it has been found that the liquid-solid-liquidi surface tensions meet at a given contact angle. For example, the contact angle of water drop on Teflon is 50° in octane (Chattoraj and Birdi, 1984 see Figure 5.3). 

Furthermore, titanium oxide thin films have been found to exhibit a unique and useful function (i.e., a superhydrophilic property). Usually, the contact angle of a water droplet on a surface is 50 -70° therefore, metal oxide surfaces become cloudy when water is dropped on them or if there is moisture in the atmosphere. However, under UV light irradiation of the titanium oxide surfaces, this contact angle of water droplets becomes smaller, even reaching zero (superhydrophil-icity), its extent depending on the UV irradiation time and irradiation intensity. Thus, under UV light irradiation, titanium oxide thin-film surfaces never become... 

The vertical rod method of the preceding problem was used to study the contact angle of water at the gold-water-air junction at 25°C. The following data show how the value of 0a depends on the prior history of the metal surface. For a gold surface polished, washed, and heat treated for 1 hr at T°C, then allowed to stand in air for t hr we obtain... 

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