Liquids contact angle measurements

The first observation suggests that the results derived from the infinite dilution state are related to the most active adsorption sites which leads to a high surface free energy value. It is then not evident that a relationship exists between the results at infinite dilution and those of the classical liquid contact angle measurement as one of the wetting methods or the results at finite concentration. 

The surface tension is calculated by using the Young-Dupre equation (Equation 2.10). In this equation, Ylv is the surface tension between the liquid and its vapour, and 0e is the solid/liquid contact angle measured at equilibrium . The critical surface tension, which is characteristic of a material surface, corresponds to 0e = 0 (or cos 0e = 1). As zero angles cannot be... 

The effects of surface modification may be studied by X-ray photoelectron spectroscopy (XPS), also known as electron spectroscopy for chemical analysis (ESCA) [51-53], liquid contact angle measurement [54,55], and chemical deri-vatization (whereby chemical species are specifically labeled with a molecular tag that confirms the presence of the target species) [56,57]. 

Discuss the paradox in the wettability of a fractal surface (Eq. X-33). A true fractal surface is infinite in extent and a liquid of a finite contact angle will trap air at some length scale. How will this influence the contact angle measured for a fractal surface ... 

The surface energy of the solid can be obtained from equilibrium contact angle measurements of a series of test liquids on the solid surface, providing the relationship between ysi and the solid yg (in vacuo) and liquid yiv surface energies is known. The exact relationship is given by the Good and Girifalco equation [13,14] ... 

Induction period measurements can also be used to determine interfacial tensions. To validate the values inferred, however, it is necessary to compare the results with an independent source. Hurley etal. (1995) achieved this for Cyanazine using a dynamic contact angle analyser (Calm DCA312). Solid-liquid interfacial tensions estimated from contact angle measurements were in the range 5-12 mJ/m which showed closest agreement with values (4—20mJ/m ) obtained from the log-log plots of induction time versus supersaturation based on the assumption of — tg. 

For the DMFC, Zhang et al. [127] used the sessile drop method to study the wettabilities of liquid methanol solutions on the surface of the anode DLs and MPLs. They were able to observe that the contact angles of the materials were the smallest with low PTFE content. In addition, the effect of Nafion ionomer content on the MPL (to increase hydrophilicity see Section 4.3.2) was also shown through the contact angle measurements (i.e., smaller contact angles compared to MPLs with PTFE). 

The above equation can be used to determine the total surface tension of a low energy solid from a single contact angle measurement (Neumann et al., 1974). If the liquid is chemically inert with respect to the solid... 

A simple and direct method of contact angle measurement has also been proposed (Yamaki and Katayama, 1975 Carroll, 1976) by observing the shape of the liquid droplet attached to a single fiber, the so-called droplet aspect ratio method . The liquid is assumed to form a symmetrical droplet about the fiber axis as shown schematically in Fig. 2.21. Neglecting the effect of gravity, the droplet shape can be defined by the following expression ... 

The critical surface tension has been evaluated by means of advancing contact angle measurements for water, various hydrocarbon liquids and for plasma polymerized fluorocarbon films " " . The most comprehensive, however, is that of Yasuda... 

In order to calculate polymer/filler interaction, or more exactly the reversible work of adhesion characterizing it, the surface tension of the polymer must also be known. This quantity is usually determined by contact angle measurements or occasionally the pendant drop method is used. The former method is based on the Young, Dupre and Eowkes equations (Eqs. 21,8, and 10), but the result is influenced by the surface quality of the substrate. Moreover, the surface (structure, orientation, density) of polymers usually differs from the bulk, which might bias the results. Accuracy of the technique maybe increased by using two or more liquids for the measurements. The use of the pendant drop method is limited due to technical problems (long time to reach equilibrium, stability of the polymer, evaluation problems etc.). Occasionally IGC is also used for the characterization of polymers [30]. 

The dispersive and polar parts of the surface energies were calculated from contact angle measurements with test liquids of different surface tension and polarity, using a modified Wihelmy technique [79] Organoclay filler yF = + = 24.3 mJ m + 1.0 mJ m 2 EPDM = I = 24.2 mj... 

Contact angle measured through the liquid, f Dielectric constant, dimensionless. 

As we see in Chapter 6, surface tension and contact angle measurements provide information on liquid-liquid and solid-liquid adhesion energies (Fig. 1.26c). Contact angles measured under different atmospheric environments or as a function of time provide valuable insights into the states of surfaces and adsorbed films and of molecular reorientation times at interfaces. 

Gas permeabilities for 02, N2 and CO2 were realised with Lyssy GPM 20 apparatus. Surface tensions of modified and unmodified polymers films were derived from contact angle measurements which were evaluated with six liquids (H20, HCONH2, Hg, CH2I2, tricresyl-phosphate and 1 -bromonaphtalene). 

The wettability of a polymer film normally is determined by static contact angle measurements. The surface free energy (SE) of a polymer can be determined by wettability measurements with two different liquids. The dispersion force and polar contributions to SE, 7 d and 7 p respectively, are also calculated normally by using the Owens and Wendt, and Kaelble methods [146,147], The measurements of contact angles (CA) on a given solid surface is one of the most practical ways to obtain surface free energies. 

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