Interfacial Tension and Wettability in Water鈥揅arbon Dioxide Systems: Experiments and Self-consistent Field Modeling

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• 作者：Soumi Banerjee ; Eveline Hassenkl枚ver ; J. Mieke Kleijn ; Martien A. Cohen Stuart ; Frans A. M. Leermakers
• 刊名：The Journal of Physical Chemistry B
• 出版年：2013
• 出版时间：July 18, 2013
• 年：2013
• 卷：117
• 期：28
• 页码：8524-8535
• 全文大小：473K
• 年卷期：v.117,no.28(July 18, 2013)
• ISSN：1520-5207

文摘

This paper presents experimental and modeling results on water鈥揅O₂ interfacial tension (IFT) together with wettability studies of water on both hydrophilic and hydrophobic surfaces immersed in CO₂. CO₂鈥搘ater interfacial tension (IFT) measurements showed that the IFT decreased with increasing pressure and the negative slopes of IFT鈥損ressure isotherms decreased with increasing temperature. Water contact angle on a cellulose surface (hydrophilic) immersed in CO₂ increased with pressure, whereas the water contact angle on a hydrophobic surface such as hexamethyl disilazane (HMDS) coated silicon surface was almost independent of pressure. These experimental findings were augmented by modeling using the self-consistent field theory. The theory applies the lattice discretization scheme of Scheutjens and Fleer, with a discretization length close to the size of the molecules. In line with this we have implemented a primitive molecular model, with just small variations in the molar volume. The theory makes use of the Bragg-Williams approximation and has binary Flory鈥揌uggins interaction parameters (FH) between CO₂, water, and free volume. Using this model, we generated the complete IFT鈥損ressure isotherms at various temperatures, which coincided well with the trends reported in literature, that is, the water鈥揅O₂ interfacial tension decreased with increasing pressure for pressures 鈮?00 bar and became independent of pressure >100 bar. The transition point occurred at higher pressures with increasing temperature. At three-phase coexistence (water鈥揅O₂鈥揻ree volume) and at the water鈥搗apor interface (water鈥揻ree volume), we always found the CO₂ phase in between the water-rich and free volume-rich phases. This means that for the conditions studied, the water鈥搗apor interface is always wet by CO₂ and there are no signs of a nearby wetting transition. Calculation of the water contact angle on a solid surface was based on the computed adsorption isotherms of water from a vapor or from a pressurized CO₂-rich phase and analysis of surface pressures at water鈥搗apor or water鈥揅O₂ coexistence. The results matched reasonably well with the experimental contact angle data. Besides, we also computed the volume fraction profiles of the CO₂, H₂O, and the V phase, from which the preferential adsorption of CO₂ near the hydrophilic surface was deduced.