Temperature and Pressure Effects on Wetting Behavior in Water + Polyoxyethylene Alcohol Binary Mixtures

• Main Authors: Chih-Kang Wu, 吳志剛
• Other Authors: 陳立仁
• Format: Others
• Language: en_US
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/60352884158259196757

博士 === 國立臺灣大學 === 化學工程學研究所 === 93 === A new integrated apparatus was assembled to obtain the experimental data of thermodynamic properties: equilibrium phase densities, compositions, and surface/interfacial tensions over a wide temperature and pressure range. The experimental results are important for understanding the phase behavior and wetting behavior of the phase equilibrium system. Consider three fluid phases, a, b, and r, in equilibrium under gravity and the densities of these three phases are in the order ρr > ρb > ρa. A small amount of the middle b phase at the a-r interface exhibits the wetting behavior, such as nonwetting, partial wetting, and complete wetting. A transition from a partial wetting regime to a complete wetting (or nonwetting) regime, or vice versa, is called a wetting transition. In this work, the effects of molecular structure, temperature, and pressure on wetting behavior were investigated by a series of the binary aqueous systems including the homologues of non-ionic polyoxyethylene alcohols. The wetting behavior and the location of a wetting transition could be deduced by the wetting coefficient derived from the surface/interfacial tensions. It was found that for the water + isomeric butanol systems, a wetting transition from partial wetting to complete wetting occurs with increasing temperature and the changes of molecular structure from a primary linear butanol to a secondary one. For the two water + isomeric 2-butoxy-ethanol systems, a wetting transition from partial wetting to nonwetting takes place with decreasing temperature and the changes of molecular structure from a branched alcohol to a linear one. Additional results were codified from this work and our previous study. Otherwise, the influence of temperature on wetting behavior was observed completely in the two water + isomeric 2-butoxy-ethanol systems. It was found that the alcohol-rich phase exhibits a sequence of wetting transitions, nonwetting->partial wetting->complete wetting, at the gas-aqueous interface along with increasing temperature over the temperature range of its closed-loop miscibility gap. Furthermore, the equilibrium phase densities and compositions were obtained to study the phase behavior of the systems simultaneously. The equilibrium phase compositions were then correlated with universal quasi-chemical (UNIQUAC) model by fitting the UNIQUAC interaction parameters as a function of temperature. Finally, the effect of pressure on wetting behavior was first observed experimentally in the simple water + 2-isobutoxy-ehtanol system. A wetting transition from partial wetting to nonwetting happens with increasing pressure at a fixed temperature near its LCST. However, the closed-loop miscibility gap of the system shrinks slightly with a pressure increase up to 100 bar. The wetting transition induced by a pressure change was successfully obtained.