CHANGES OF OSCILLATION FREQUENCY OF A QUARTZ RESONATOR IN CONTACT WITH A BINARY-LIQUID MIXTURE OF CRITICAL COMPOSITION AS FUNCTION OF TEMPERATURE

The temperature dependence of the oscillation frequency of a quartz resonator operated with one face of the quartz crystal in contact with air and the other in contact with a homogeneous n-butoxy-ethanol/water mixture of critical composition (lower critical point) exhibits an unexpected increase of the effective value of the parameter (eta-rho)T1/2 (eta, viscosity; rho, density) approaching the critical temperature. This phenomenon appears at temperatures at which the correlation length of local concentration fluctuations reaches values comparable to or larger than the decay length of the shear gradient produced by the oscillating crystal. The effect is interpreted by assuming that the large shear gradient S of the quartz oscillator (S = O(10(4)-10(5)) s-1) probes the viscosity of the mixture in the presence of long range correlations of local concentration fluctuations near the critical point in a manner different from that of the smaller shear gradient in a capillary viscometer (S = O(10(2) s-1).