A Study of Interfacial Behavior Near the Tricritical Point of the System‘Water + Oil + Surfactant’

• Main Authors: Ping-Chang Lin, 林炳昌
• Other Authors: Li-Jen Chen
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/30950437655244467961

碩士 === 國立臺灣大學 === 化學工程學研究所 === 92 === In a three-phase coexisting equilibrium system, the middle phase may exist in the form of nonwetting, partial wetting, or complete wetting. The transition from a partial wetting regime to a nonwetting (or a complete wetting) regime, or vice versa, is called a wetting transition. What we are concerned about is the wetting behavior near the tricritical point and if the wetting transition exists. By adjusting the system parameters, such as temperature, pressure, salt concentration and compositions, we can make the system come close to its tricritical point. In a multicomponent liquid mixture, a tricritical point (tcp) is defined as a point at which three coexisting liquid phases become simultaneously identical single phase. In this study, we try to search the tricritical point by changing the oil of the system “water +oil +surfactant”. With the decrease of the oil chain length, we can successfully approach the tricritical point. There are two main systems: “H2O +Alkane( k=7,8 ) +C4E1” and “H2O +Alkylbenzene( k=11,12,13 ) +C6E2” carefully examined in this study. Pendant drop/bubble tensiometry was applied to measure interfacial tensions to judge the wetting behavior of the systems. When rising temperature from the lower critical point to upper critical point, we can find both the two systems exist two wetting transitions: complete wetting→partial wetting→complete wetting. Besides, we also performed an experiment on the system “H2O +Octylbenzene +C4E1”. It is found that complete wetting behavior is observed over the whole three-phase region, consistent with Kahlweit’s finding: only complete wetting would be observed near the tricritical point. Cahn’s theory addresses that for a three-phase coexisting system, complete wetting should be observed near the critical temperature. All the systems examined in this study always exhibit complete wetting behavior near the critical temperature, in accord with Cahn’s theory.