Wetting coefficient

Equation (6.39) was first derived by Young, and is often referred to as the Young-Dupre equation. We usually distinguish between full (6< 90°) and partial wetting (0 > 90°) and an alternative measure of the same property is given by the wetting coefficient ... 

The form of Equation 22 for the overall gas-liquid-actively wetted coefficient ks is consistent with the expected Reynolds and Schmidt number dependence for flowing gases and liquid films in packed beds (12) Equation 23 for the stagnant liquid-to-solid coefficient kg s may be viewed as some measure of the ratio of diffusivity to mean film thickness (Dm/Hes/Dp). 

Wetting Coefficient In the equilibrium of a system of solid, gas, and liquid the wetting coefficient is given as k = (7sg — 7sl)/7jgJ where 7 is the interfacial tension, and the subscripts g, 1, and s refer to gas, liquid, and solid phases at the interfaces, respectively. Complete wetting occurs for k > 1 and nonwetting for k < 1. 

Crowding factor Permeability of porous medium Rate constant, I th-order homogeneous reaction Thermal conductivity or thermal conduction coefficient Wave number, Eqs. (10.4.2b), (10.4.28) Wetting coefficient, Eq. (10.1.9)... 

There are extreme cases when Eq. 3.72 does not define the equilibrium position of the line of contact. This happens under conditions of complete wetting, when > 7si + 7ig, or when the liquid does not wet the solid at all and the gas displaces the liquid completely along the solid surface (7 1 > y g + 7ig)- Therefore, it is more convenient to consider the wetting coefficient... 

Wetting Coefficient for Different Blends/Filler Combinations the Filler Localization Was Characterized by Electron Microscopy... 

As Table 2.1 shows, the concept of the wetting coefficient has been successfully applied in filled polymer blends containing various fillers, such as carbon black [36], silica [26,27,37], or nano-CaCOs particles [38,39]. Limitations of this criterion include strong discrepancies in interfacial tensions, due to the lack of data in the literature regarding polymer/filler interfaces and issues of extrapolation to the appropriate temperature. Also, this criterion assumes that thermodynamic equilibrium has been reached, which is not always the case experimentally due to the limited processing time. 

Alternatively, some papers have based their analysis on the values of the work of adhesion, W and the interfacial tensions rather than co [40,41] to predict the filler localization. Ma et al. [39] compared three different methods to predict the morphology of composites containing nano-CaCOs, based on interfacial tension data, estimation of the work of adhesion, and estimation of the wetting coefficient. They reported that the wetting coefficient is the most accurate tool to predict the phase structure, by comparing with the actual localization of the nano-CaCOg particles observed using SEM. 

Table 17.6 Estimate of the equilibrium localization of fillers in polymer blends by calculation of a wetting coefficient, coa, from Young s equation. Here, 1 and 2 are two polymer components in blend and p represents solid filler...

V2 Viscosity of phase 1 and 2 respectively Vd> Vm Viscosity of dispersed and matrix phase respectively A Time constant mm Micrometer To Melt yield stress T Relaxation time Volume fraction Xc Percent crystallinity (o Frequency tOa Wetting coefficient... 

The quantity = cos0 is called the wetting coefficient. Perfect wetting corresponds to = 1, the absence of wetting results in -1. 

In this study the concept of the triple-continuous structure is apphed to several polymer/polymer blends loaded with carbon nanotubes or graphite particles with an aim to obtain injection moldable carbon-fiUed polymer blends with high electrical conductivities and snfficient mechanical properties for the bipolar plate application of PEM fuel cells. The distribution of CNTs in the polymer blends is examined in terms of their wetting coefficients and minimization of the interfacial energy. The relationships among the microstructure, electrical conductivity, and mechanical properties are studied with an emphasis on achieving simultaneous improvement in both conductivity and tensile strength. 

In this equation, cOa is the wetting coefficient used for judging the location of filler in different polymer phase in the term of thermodynamics. The symbols represented in the numerator are the different interfacial tensions between filler and polymers 1 and 2 and in the denominator the interfacial tensions between the two blend phases. If > E fillers preferentially distribute in polymer 2 if co < 1, fillers preferentially distribute in polymer 1, and if -1 < co < 1, fillers distribute at... 

The driving force for localization is believed to be the thermodynamics of polymer/filler interaction, as described by Young s equation. Sumita et al. have calculated a carbon black wetting coefficient, Eq. (3), from Young s equa-... 

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