Density and compressibility measurements of a highly viscous polyelectrolyte solution: a study on aqueous solutions of sodium hyaluronate

The density of a highly viscous polyelectrolyte solution was measured using both pycnometers and oscillating-tube densimeters in parallel to elucidate the difficulties inevitably involved when an oscillating tube is employed for density measurements of viscous liquids. It was confirmed that the osci llating-tube densimeter gives too high values for viscous liquids, and the deviation increases with the increase in the viscosity of liquids. The anal ysis of adiabatic compressibilities of sodium hyaluronate (NaHy) solutions, as estimated from density and ultrasound velocity data of the same solutio n, suggests that the disaccharide unit of the NaHy chain is less hydrated t han the sum of its component monosaccharide residues.