Applications of Densiometry, Ultrasonic Speed Measurements, and Ultralow Shear Viscosimetry to Aqueous Fluids

Precision measurements of density and sound velocity can be used to follow changes in fluids such as micellization or phase separation. Both techniques have been implemented in the oscillating tube density meters in different sample cells for several years. However, to get better results for the density of viscous samples, a correction for viscosity effects is necessary. Therefore, a viscosity-dependent signal must be measured, which can be achieved by determining the damping of the oscillating tube. This is done routinely in the latest generation of such density meters. We present a method to convert this measured signal into actual viscosity data up to about 300 mPa·s and show some applications of all three measured signals to different problems in the field of the study of complex fluids: Density and sound velocity can be used to establish water or any other pure fluid as a secondary standard for small angle scattering experiments. Viscosity shows temperature-dependent structural changes and the critical temperature of diblock copolymers of the C i E j type. Finally, all three parameters density, sound velocity, and viscosity are used to establish a phase diagram of the PEO−PPO−PEO triblock copolymer P94 in aqueous solution.