DESCRIPTION OF AN INTERFACE LIGHT-SCATTERING SPECTROMETER WITH A CYLINDRICAL HIGH-PRESSURE SCATTERING CELL INCLUDING PERFORMANCE-TEST ON A MODEL GAS CONDENSATE SYSTEM

A versatile interface light-scattering (ILS) spectrometer for the dete ction of light scattered by thermally excited capillary waves at fluid interfaces has been developed. The instrument permits observation ove r a wide range of capillary mode wave numbers, using scattering cells with cylindrical geometry. Owing to the cylindrical geometry, it is po ssible with this spectrometer to perform combined interface and bulk l ight scattering experiments using the same cell. The performance of th e experimental set-up, including a sapphire-tube high-pressure piston cell, has been assessed through measurement of the interfacial tension in a system of coexistent, mutually saturated phases of water and 2-b utanol. The results obtained at ambient pressure were shown to be in e xcellent agreement with those previously obtained with the use of an e xperimental set-up including a planar optical geometry scattering cell . The light scattering measurements demonstrate one particularly attra ctive feature of this method: Not only is it a nonperturbative and abs olute method for determining interfacial tension, but it also provides a way to check the reliability of the results. Consistency of results over a wide range of capillary mode wave numbers provides assurance t hat no biases exist either in the experimental system or in the data a nalysis. A preliminary study of a six-component hydrocarbon model gas- condensate system, which in certain respects resembles real gas-conden sate systems, demonstrates that reliable information can be obtained o n the interfacial tension and the sum of the gas and liquid shear visc osities. The prospects of using the ILS method for more systematic stu dies of such systems appear very good. (C) 1994 Academic Press, Inc.