Relations between loss angles in isotropic linear viscoelastic materials

Starting from the relations between complex dynamic moduli simple diagrams are deduced connecting the locus of complex Poisson's ratiov* ≡v′ +iv″ in the complexv* plane with differences between various loss angles. From these diagrams the sequence of magnitudes of several loss angles appearing in linear viscoelastic theory is deduced. Although theoretically this sequence depends on the values ofv′ andv″, it is found experimentally that for polymeric materials, due to the fact that the values ofv′ andv″ are constrained to limited ranges, general rules can be given. The sequences deduced are compared with experimental data. Finally some relations are used to illustrate the phase relationships between stress and deformations in an uniaxial stress experiment. From these relations a new method for measuring the loss angle in compression is suggested

Inertia effects in rheometrical flow systems

The flow field of a linear viscoelastic material in the orthogonal rheometer, taking fluid inertia into account, has been studied theoretically and an exact solution is given. The flow field of a Newtonian liquid is included in this solution as a special case. The forces on the plates are readily deduced from this solution. The paper concludes with an energy consideration

Inertia effects in rheometrical flow systems Part 2: The balance rheometer

The flow field of a linear viscoelastic fluid in the balance rheometer, taking fluid inertia into account, has been studied theoretically and an exact solution is given. The flow field of a Newtonian fluid is included in this solution as a special case. The forces and couples on the hemispheres are readily deduced from this solution

Inertia effects in rheometrical flow systems Part 3: Some energy considerations with respect to the flow field in the balance rheometer

Following up a previous paper by one of the presents authors on the flow field in the balance rheometer, inertia effects being included, in this paper some energy considerations with respect to this flow field are presented. It is shown that in a frame rotating with the same angular velocity as the hemispheres the power supplied by these hemispheres equals the rate of energy dissipation in the sample, i.e. in this coordinate system there is no “stress power paradox”. Further it is shown that the “elastic” couple for a Newtonian liquid, appearing in the calculations, stems from the extra kinetic energy caused by the deviation of the actual flow field from the flow field that appears when inertia effects are ignored

On the use of a nickel-tube resonator for measuring the complex shear modulus of liquids in the kHz-range

An apparatus for the measurement of liquid-shear impedance in the frequency range 4–200 kHz with the aid of a thin-walled Ni-tube resonator is described. A magnetostrictive mechanism is used for setting the tube into torsional oscillation. Real and imaginary parts of the liquid-shear impedance are found from the change in the 3 dB band-width of the resonance curve and the shift of the resonance frequency, respectively, when the tube is immersed from the air into the liquid. The amount of liquid required is 20 ml. The necessary theory is given and some preliminary results are presented

An ellipsometric study of protein adsorption at the saliva-air interface

At the liquid-air interface of human saliva a protein layer is adsorbed. From ellipsometric measurements it was found that the thickness of the surface layer ranged from 400 to 3600 Å and the amount of protein material adsorbed was 9–340 mg/m2. Based on the concentration of protein in the layer the samples could be classified into two groups: a low concentration (ca. 0.15 g/ml) and a high concentration (0.7–1.1 g/ml). In the low concentration group the surface layers appeared to be thin (500–600 Å) while those in the high concentration group appeared to be much thicker (1000–3500 Å). A correlation between the bulk pH and the thickness of the surface layer could be established

Rheological properties of saliva substitutes containing mucin, carboxymethylcellulose or polyethylenoxide

Apparent viscosities at different shear rates were measured for 3 types of saliva substitutes: (a) mucin-containing saliva; (b) substitutes based upon carboxymethylcellulose (CMC), and (c) solution of polyethylenoxide (PEO). The apparent viscosities were compared with those of human whole saliva. Human whole saliva and mucin-containing saliva substitutes appeared to be similar in their rheological properties. Both types of solution are viscoelastic solutions and adjust their apparent viscosities to their biological functions. Preparations containing CMC or PEO are non-Newtonian liquids. From this study it is concluded that mucin-containing saliva substitutes appear to be the best substitutes for natural saliva, as far as rheological properties are concerned

Rheological properties of human saliva

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 70 Hz 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−1 and 10−3 Nm−1 s, respectively. From ellipsometric measurements it was found that the thickness of the protein layer was approx. 100nm and, using this value, it could be concluded that the shear modulus and the dynamic viscosity were in the order of 107 Pa and 104 Pa s, respectively. The layer appeared to be fragile. Even shear deformation amplitudes of 4 × 10−5 are too high to assure linearity. The complex viscosity (η = η′ − iη′′) 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 (η′) 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 η′′ was too small to be detected