Dilatancy, viscosity measurements, dispersed

They adapted an interfacial shear rheometer (plate/ rod) to measure the shear viscoelasticity of the system with and without dispersant. At an applied shear stress, creep curves for the system were monitored. There were no instantaneous elasticity and viscosity for the Kuwait and Tia Juana crudes with and wifliout dispersant. They attributed this to a network structure of flocculated asphaltenes in the films. They found that there was some dilatancy in their crude oil films, described as a stick/slip flow in their flow curves. However, fliis flow was attributed to thick films of asphaltene particles building up at the interface. Lfsing creep measurements, they examined a model system of as-phaltenes/n-heptane/toluene. They found a retarded elastic deformation, which was different from the response of the crade oils. This suggested to fliem that there was a different type of interfaeial slrueture formed with the model oil, and this may be attributed to die solveney of the medium and not to die lower asphaltenes eontent in the model system. 

The longitudinal-wave method was first described by Lucassen [498]. Since Lucassen s original work, propagation characteristics of longitudinal waves have been widely used for measuring dilatational elasticity and interfacial viscosity of adsorbed surfactant monolayers. The pure longitudinal waves motion obeys the dispersion relation... 

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