Mutual diffusivity in n-Heptane + n-Hexane isomers

A preliminary study of the effect of branching in the binary diffusion of hexane isomer + n-heptane systems is presented. Measurements have been performed with an instrument modeled for the Taylor dispersion technique, at several compositions, at 297 K, for the n-hexane + n-heptane and 2,2-dimethylbutane + n-heptane binary mixtures. The accuracy is estimated to be 1%. The influence of branching is discussed. It was found that the rough hard sphere model for binary diffusion can reproduce the experimental data within 6%. This model was used to predict the binary diffusion coefficients in the 2-methylpentane + n-heptane and 3-methylpentane + n-heptane mixtures, with an estimated accuracy of 5%

Mutual diffusivity in binary mixtures of n-heptane with n-hexane isomers

This paper presents a study of the influence of branching in the binary diffusion coefficients of n-heptane+n-hexane isomers, in the liquid state. The measurements have been made with the Taylor dispersion technique, at several compositions, at 283 and 298 K, for the X+n-heptane mixtures, where X=n-hexane, 3-methylpentane, 2, 3-dimethylbutane, and 2, 2-dimethylbutane. The results show a very interesting behavior of the composition dependence of the binary diffusion coefficients, presenting a maximum, for compositions about a molar fraction of n-heptane of 0.5, which increases with the increase in the degree of branching, suggesting the possibility of order~tisorder effects caused by stereochemically favored packing in the liquid phase and energetically favored segment interaction in the liquid mixtures. An attempt to apply the van der Waals model to these data could not predict the experimental binary diffusion coefficients of these systems within the experimental accuracy

Diisodecylphthalate (DIDP) — a potential standard of moderate viscosity: surface tension measurements and water content effect on viscosity

Our laboratory, along with several others, has been engaged in a project to determine the suitability of diisodecylphthalate (DIDP) as a standard reference material of viscosity for industrial purposes. As a part of that project, we have undertaken a study of the effects of surface tension and of impurities, of that liquid on viscosity measurements with routine, suspended level capillary instruments. For the former purpose, a set of surface tension measurements is reported here for DIDP and two reference standard mineral oils. In particular, surface tension data for DIDP, obtained using a pendant-drop shape-analysis method, at temperatures from 288K to 308K are presented. The present study suggests that surface tension effects upon viscosity measurements with routine capillary viscometers can be important enough to demand that the surface tension of the reference fluid(s) used for their calibration be specified. It is also evident that the surface tension of materials used for calibration may be relevant to their selection if errors arising from surface tension are to be avoided. In order to fulfil these requirements, the surface tension of the reference material should be included in the definition of the standard. The effect of the water content on the viscosity of a sample of DIDP is assessed as a part of the process of determining its suitability as a standard reference material