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[Display omitted] Contact angle can be a key parameter in chemical engineering. However, the development and the optimization of numerous processes using supercritical CO 2 , considered as environmentally friendly, require new measurements under dense CO 2 atmosphere. Besides, the influence of the roughness or the wetting regime on the contact angle is known at ambient conditions but remains to be discussed for systems under high pressure. Contact angle measurements of ethanol, water, and their mixtures, with ethanol mass fractions ranging from 0.25 to 0.75, on two stainless steels in saturated CO 2 at pressures ranging from 0.1 MPa to 15.1 MPa, and at 313 K and 333 K were carried out in a set-up improving mass transfer between the studied liquid and the continuous fluid phase. Stainless steel surfaces have been characterized by atomic force and scanning electron microscopies allowing the application of the Wenzel equation. Ethanol wetted totally both stainless steels while contact angles of all other liquids were increased by the rise of pressure, with contact angles up to 128° for water at 15.1 MPa. Trapped bubbles were observed at the solid/liquid interface and the bubble formation is discussed. Furthermore, the potential influence of bubble presence on the wetting regime is prospected through the question: could the pressure rise modify the wetting regime? [ABSTRACT FROM AUTHOR]

Phase change heat transfer (e.g., boiling of water) on surfaces can be enhanced by tuning the surface wettability, which is often quantified by the contact angle and is expected to be influenced by temperature and pressure. However, the temperature (and pressure) dependence of contact angles of water on metallic surfaces remain unclear. In this study, an in situ characterization of the contact angles of water on 304 stainless steel surfaces at temperatures from room temperature to 250 °C and at pressures up to 15 MPa was performed using the sessile drop method. It was shown that three distinct regimes can be identified on the contact angle-temperature curves. A slightly-decreasing trend of the contact angles with temperature was observed below 120 °C, followed by a steeper linear decrease at higher temperatures. A further rise of the decreasing rate with temperature was observed above 210 °C. In contrast to temperature, the pressure was shown to have little effects on the contact angles. Based on the theory of surface thermodynamics, the effects of temperature (and pressure) on the contact angles were analyzed in terms of the interfacial tensions. An empirical correlation was developed to predict the contact angles as a function of temperature. [ABSTRACT FROM AUTHOR]

Abstract: The macroscopic flow geometry has long been assumed to have little impact on dynamic wetting behavior of liquids on solid surfaces. This study experimentally studied both spontaneous spreading and forced wetting of several kinds of Newtonian and non-Newtonian fluids to study the effect of the macroscopic flow geometry on dynamic wetting. The relationship between the dynamic contact angle, θD , and the velocity of the moving contact line, U, indicates that the macroscopic flow geometry does not influence the advancing dynamic wetting behavior of Newtonian fluids, but does influence the advancing dynamic wetting behavior of non-Newtonian fluids, which had not been discovered before. [Copyright &y& Elsevier]

Abstract: The surface tension of molten Sn–Bi (mole fraction ) alloy has been determined by the sessile drop method at oxygen partial pressure of and different temperatures. The experimental results have been analyzed and discussed, and the positive temperature coefficient of surface tension of molten Sn–Bi alloy has been elucidated. The surface tension of this molten alloy has also been obtained by calculation using STCBE based on Butler''s equation and thermodynamic data. The experimental results agree well with the calculation values. [Copyright &y& Elsevier]

The influence of boron concentration (CB/mass%) on the surface tension of molten silicon has been investigated with the sessile drop method under oxygen partial pressure PO2=1.62×10−25–2.63×10−22 MPa, and the results can be summarized as follows. The surface tension increases with CB in the range below 2.09 mass%, and the maximum increase rate of the surface tension is about 30 mN m−1 (mass% CB)−1. The temperature coefficient of the surface tension, (∂σ/∂T)CB, was found to increase with the boron concentration in molten silicon. At the interface between molten silicon and the BN substrate, a discontinuous Si3N4 layer was reckoned to form and the layer might prevent BN from dissolving into the molten silicon. Since dissolved boron from the BN substrate into the molten silicon is below 0.054 mass% and the associated increase in surface tension is below 1.5 mN m−1, the contamination from the BN substrate on the surface tension can be ignored. The relation between the surface tension and CB indicates negative adsorption of boron and can be well described by combining the Gibbs adsorption isotherm with the Langmuir isotherm. [Copyright &y& Elsevier]

The surface tension of molten tin has been determined by the sessile drop method at temperatures ranging from 523 to 1033 K and in the oxygen partial pressure (PO2) range from 2.85×10−19 to 8.56×10−6 MPa, and its dependence on temperature and oxygen partial pressure has been analyzed. At PO2=2.85×10−19 and 1.06×10−15 MPa, the surface tension decreases linearly with the increase of temperature and its temperature coefficients are −0.151 and −0.094 mN m−1 K−1, respectively. However, at high PO2 (3.17×10−10, 8.56×10−6 MPa), the surface tension increases with the temperature near the melting point (505 K) and decreases above 723 K. The surface tension decrease with increasing PO2 is much larger near the melting point than at temperatures above 823 K. The contact angle between the molten tin and the alumina substrate is 158–173°, and the wettability is poor. [Copyright &y& Elsevier]