Viscosity of diisodecyl phthalate by surface light scattering (SLS)

Surface light scattering (SLS) has been used for the measurement of the viscosity of diisodecyl phthalate (DIDP), a potential candidate for an industrial reference material in the moderate- to high-viscosity region from (0.01 to 1) Pa center dot s. The investigations reported here were stimulated by recent research activities of the International Association for Transport Properties (IATP), which aim at evaluating a recommendation concerning standard reference values for DIDP at moderately high viscosity at room temperature. For this purpose, the measurement of the viscosity of DIDP using viscometers of different types and operating principles was encouraged. Even though in the case of high-viscosity fluids reference data for the interfacial tension are needed for data evaluation, the integration of the SLS method within this project is particularly interesting. In contrast to conventional viscometers, SLS allows the determination of viscosity in macroscopic thermodynamic equilibrium. Furthermore, whereas almost all conventional methods determine the viscosity in a relative manner, for the SLS technique no calibration procedure using a fluid of known viscosity is needed. In the present work, for temperatures between (283.15 and 313.15) K, corresponding to a viscosity range of about (250 to 50) mPa center dot s, an expanded uncertainty (k = 2) of less than +/- 1.4% could be achieved for the viscosity of DIDP by carrying out a data evaluation procedure based on an exact description of the hydrodynamic capillary wave problem for a free liquid surface.