Abstract :
Shear viscosity η is a basic parameter of the liquid state strongly correlated to the dielectric relaxation time of polar compounds. Thermal variations η(T) are often explained by the “old” free-volume model which implies a critical temperature T0 at which the free volume is vanishing and the viscosity infinite. This point of view was recently criticized (1, 2). The case of supercooled water is still more complex since the viscosity seems to diverge for another singular temperature TS ≅ -45°C far from the glass transition temperature Tg. To clear up this paradoxal situation in relation with other water anomalous properties, we have measured the shear viscosity of binary aqueous solutions (C3 H8 O3)x (H2O)1-x. The range 10-3-1012 Pl (1P1 = 1 Pa.s = 10P) has been investigated by means of three methods: capillary, rotational and penetroviscosimetry. In the highly viscous range (104-1012 Pl) we have designed a cylindric penetrometer described elsewhere (3). The penetration depth h(t) is measured with an electromagnetic displacement device and recorded and treated by a desktop computer. According to the Navier Stokes equation describing the laminar flow of a newtonian liquid, h2(t) is a linear function versus time the slope giving η.
