RHEOLOGICAL PROPERTIES OF HUMAN SALIVA

Summary-From measurements with a Couette-type viscometer provided with a guard ring it was shown that at the saliva-air interface a protein layer is adsorbed. Measurements of the surface shear modulus of this layer on saliva of 7 healthy subjects were performed at a frequency of about 70Hz and a temperature of 25°C. For a surface age of about 1.5 h the surface shear modulus and the surface viscosity were in the order of 1 Nm- ’ and IO- ’ Nm- ’ s, respectively. From ellipsometric measurements it was found that the thickness of the protein layer was approx. 100 nm and, using this value, it could be concluded that the shear modulus and the dynamic viscosity were in the order of 10 ’ Pa and lo4 Pa s, respectively. The layer appeared to be fragile. Even shear deformation amplitudes of 4 x IO- ’ are too high to assure linearity. The c.omplex viscosity (q = ‘1 ’- iv”) of the bulk liquid of human submandibular saliva below the absorbed layer was measured in the frequency range 70 Hz-200 kHz with 3 torsional resonators, each for a different frequency, and a Ni-tube resonator. It was concluded, that the real part of the complex viscosity (n’) decreases from 1.1 mPa s at 70 Hz to a value of 0.95 mPa s at high frequencies. Except at the lowest frequency (70 Hz), the value of n ” was too small to be detected