Rheological oscillation experiments

Rheological measurements, 21 702-758 techniques in, 21 739-747 viscometers, 21 725-739 Rheological oscillation experiments,... 

Emulsion properties and stability can be measured by rheological studies and dielectric spectroscopy. Rheological studies include forced oscillation experi ments. The formation of stable emulsions is marked by a sharp increase in the elastic modulus. Water con tent is not a good indicator of emulsion characteristics other than that low water contents (<50%) indicate that an emulsion has not been formed and that the product is entrained water-in-oil. Interfacial measure ments are useful for measuring the film strength of... 

The drop and bubble shape tensiometer allows one to perform oscillation experiments. However, in contrast to similar studies with small spherical drops it is limited to slow oscillations. Depending on the hydrodynamic conditions, mainly the rheological behaviour of the bulk phases, oscillation from a certain frequency onwards do not provide drops or bubbles with a Laplacian shape, so that the data analysis will fail and yield unrealistic data. Even for liquids of high grade of purity interfacial tension changes are simulated and hence misinterpretations can be the consequence. Thus, the use of high speed video technique is not really relevant for shape analysis tensiometry (although provided by several companies), as the hydrodynamic relaxation can take much time to yield Laplacian menisci. 

Kovalchuk VI, Miller R, Fainerman VB and Logho G (2005). Oscillating bubble pressure experiments for dilational rheology studies. Adv Colloid Interface Sci 114-115 303-313... 

The software of the PAT1 allows the programming of a complete sequence of experiments, such as transient and harmonic relaxations after the equilibrium of adsorption has been established. The oscillations were usually performed at various frequencies, so that sufficient data for the dilational rheology were available. A typical result, as an example, is shown for / -LG in Figure 5, where... 

We want to give only two examples of interfacial relaxation methods. The whole field of interfacial relaxations and rheology is so broad and of strong practical relevance that this topic deserves a whole book. At first, two examples, a harmonic and a transient experiment will be shown as example for slow relaxation experiments, while as second we will present results of experiments performed under ground and microgravity conditions, respectively, based on the principle of oscillating bubbles. 

Additional information on interfacial layers can be gained from rheological and ellipsometry experiments. There is quite a number of different experimental setups used to determine surface rheological parameters (27). New possibilities to determine surface dilational parameters arise from oscillating-drop experiments. Using axisymmetric drop shape analysis (ADSA) the change in interfacial ten-... 

In Sect. 3.2.2, we mentioned the particular time-dependent rheological behavior of an equimolar solution of CPCl/NaSal (c = 2.1 wt. %). The shear-thickening transition was characterized by strong oscillations as a function of time in the shear and normal stresses at fixed shear rate (or vice versa). Using direct visualizations and SALS experiments, the authors showed that these oscillations were correlated... 

Although no direct comparison with other commercial products are given we can state that the instrument PATl discussed here has the best features in respect to interfacial rheology studies. It provides a comfortable function generator for any type of transient and harmonic relaxation studies and also the theoretical tools to analyse trapezoidal and sinusoidal relaxation experiments. The on-line control of the interfacial area changes is very accurate and the oscillations performed in the range between 0.01 and 0.2 Hz are ideally smooth sinusoidal functions in contrast to experiments performed with other instruments. 

Dynamic Oscillatory Experiments The dynamic rheological properties of a polymeric solution can be determined by small-amplitude oscillation tests [2]. In small amplitude oscillatory measurements, a sinusoidally varying shear stress field is imposed on a fluid and the amplitude of the resulting shear strain and phase angle between the imposed stress and the strain is measured. The test is... 

Dilatational rheology experiments were conducted with the contact angle meter mentioned earlier additionally equipped with an oscillating drop generator (ODG 20, same manufacturer). Experiments were performed at minimum drop age of 14 h and a drop volume of 28 0.3 pL. 

A number of small strain experiments are used in rheology. Some of the more common techniques are stress relaxation, creep, and sinusoidal oscillations. In the linear viscoelastic region all small strain experiments must be related to one another through G(t), as indicated by the basic constitutive equation, eq. 3.2.7, or through M(t), eq. 3.2.4. Different experimental methods are used because they may be more convenient or better suited for a particular material or because they provide data over a particular time range. Furthermore, it is often not easy to transform results from one type of linear viscoelastic experiment to another. For example, transformation from the creep compliance J t) to the stress relaxation modulus G(t) is generally difficult. Thus both functions are often measured. 

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