Usual and Unusual Surface Tensions of Perfluorocarbon-Containing Binary Liquid Mixtures near a Critical Endpoint

✍ Scribed by Ian A. McLure; Richard Whitfield; James Bowers

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 150 KB
• Volume: 203
• Category: Article
• ISSN: 0021-9797
• DOI: 10.1006/jcis.1998.5497

✦ Synopsis

on established simple molecular models, e.g. the quasicrys-The surface tension of binary mixtures near critical endpoints talline model (1), with well-understood pathways for acis discussed with detailed focus on the composition dependence. counting for deviations from ideality. These deviations can The similarity with the corresponding composition dependence of often, although always with care, be interpreted in terms the vapor pressure is explored. The differences between mixtures primarily of the relative strength of the interaction between in which the more volatile component is of lower surface tension, the unlike molecules in the mixture and, when that primitive i.e. is less tense-known as usual mixtures-and those in which line of reasoning fails, of secondary molecular factors such the more volatile component is more tense-known as unusual as size, chain length, flexibility, shape, or local correlation mixtures-are analyzed. As a basis of discussion, a limited review of molecular orientation. However, although there is no simiof the related literature is presented along with some fresh results for two usual mixtures (octamethylcyclotetrasiloxane / perfluor-larly rigorous route to surface tension ideality, the nearopentane and heptane / perfluorohexane) and two unusual mixlinearity in mole fraction x of the surface tension s of argon tures (pentane / perfluoroheptane and 2-methylpentane / per-/ krypton (2), the archetypal real but effectively ideal liquid fluorotributylamine). These mixtures display a variety of horimixture, reminds us that a linear s(x) dependence relationzontal inflections characteristic of the behavior of the noncritical ship offers an equally useful operational benchmark for surinterface near a critical endpoint. The form of the horizontal inface ideality-and a simpler one than those previously sugflection is uniformly related to the sign of the difference between gested (3) -from which deviations can be as readily underthe surface tensions of the pure components, i.e. with the overall stood in terms of intermolecular forces as those from negative slope towards the less tense component. A number of the Raoult's law. The use of alternative definitions of surface mixtures also exhibit aneotropy or surface azeotropy. All these ideality, such as that suggested by Rusanov (4) in which results are shown to be well described by the Surface Regular the surface tension is necessarily concave, would little alter Solution theory.