Contact angles oxidized surfaces

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. 

Values of Fse range from 0.009 for a smooth metal surface with small perforations, to 0.029 for a pierced metal surface. The contact angle is a key parameter for wettability and was related to the surface tension by Shi and Mersmann. This accounts for the differences in wettabihty found by Yoshida and Koyanagi (Fig. 14-69). In general, aqueous systems will wet ceramic surfaces better than metal surfaces, unless the latter are oxidized. 

To inspect for contaminants, a water break test is frequently employed. Water, being a polar molecule, will wet a high-energy surface (contact angle near 180 ), such as a clean metal oxide, but will bead-up on a low-energy surface characteristic of most organic materials. If the water flows uniformly over the entire surface, the surface can be assumed to clean, but if it beads-up or does not wet an area, that area probably has an organic contaminant that will require the part be re-processed. 

Table 1 Contact Angles (0) and Surface Energies of LDPEs Oxidized Using Purple Hydrocarbon as Oxidant...

The most obvious change in an oxidation of the PP surface results in an increase in the wettability of the polymer. The PP shows a great decrease in contact angle with water or water/alcohol (3 1) after treatment with ozone or ozone-UV irradiation or atomic oxygen (Table 1). 

Alternate explanations for the loss of hydrophilicity upon aging include the blooming of hydrophobic impurities in the polymer to the surface (30), or the deposition of ubiquitous airborne contaminants onto the surface. However, since the (TD)2DPM surfaces can remain relatively hydrophilic for up to 1 year, these are probably not significant factors in the loss of hydrophilicity. It should be noted that oxidized polydiene films (exposed to air 1 year) can display contact angles as low as 65°. 

Films of purified PVCa were cast from methylene chloride solution on quartz plates. The solvent was allowed to slowly evaporate to give smooth, clear films with a thickness of ca. 5.0 nm. Contact angle measurements using water droplets were measured with a standard contact angle goniometer. Samples were photo-lysed in air with polychromatic light from a 150 watt xenon arc. Contact angles were measured after various times of irradiation to monitor the formation of oxidation products at the surface of the polymer films. 

The data in Figure 5 indicates that the presence of the naphthalene chromophore does not prevent the decrease in contact angle observed upon the irradiation of PVCa. Thus, naphathalene may rot be an effective quencher of the surface oxidation of PVCa film as it appears to be for the yellowing of PVCa in solution. 

The surface oxidation products dete ted by the decrease in contact angle upon photolysis of PVCa films may dominate the photoconductivity of t. is polymer. Work is underway to confirm this relatio. ship and measure surface conductivity simultaneously with bulk conductivity as a function of photodegradation. 

Note that a native oxide film also forms under dry conditions in ambient air the oxidation rate of this process can be enhanced by ultraviolet (UV)-ozone photooxidation (Tal, Vil]. Oxide-covered Si surfaces exhibit low contact angles. Only if the oxide surface is contaminated, for example by a monolayer of absorbed hydrocarbons, may larger contact angles be observed. 

Interlaminar shear strength (ILSS), AES atomic percent, contact angle, 0, and surface energy, y, data for untreated and electrochemically oxidized pitch-based carbon hber"... 

The adsorption of alkyl and aryl isocyanides on Au film [26, 32, 33], powder [36, 37] and nanoparticles [39, 41, 42] has been studied using several different techniques IR methods (RAIR, ATR-IR, DRIFT), Raman methods (SERS), X-ray methods (NEXAFS), ellipsometry (OE, SWE) and contact angle measurements (ACA). The gold surface is not oxidized under normal conditions consequently, the experiments were performed in air at room temperature. The gold film was obtained by physical vapor deposition of 100-200 nm of gold on different substrates glass [28, 33], mica [33], silicon [25, 27, 31, 32], ZnSe crystal [26]. A... 

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... 

Figure 2 Antifogging effect of titanium oxide thin-film-coated surface. The glass mirror, whose right side was coated with titanium oxide thin film, exhibits a clear image even in a high-water-moisture room like in a batluoom. Decrease in the contact angle of a water droplet under UV irradiation of the titanium oxide thin film surface, leading to a photoin-duced superhydrophUic property of tlie minor. (Supplied by TOTO.)...

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