Rheologica Acta

Techniques for evaluating the micromechanical properties of materials are crucial in engineering fields. In previous studies, many researchers have utilized atomic force microscopy (AFM) to address these subjects. However, there are few data on dispersion systems, such as slurries and creams, due to the AFM tip having a nanoscale length. These materials are essential in industrial and engineering settings, requiring an accurate evaluation in a manner similar to AFM. Hence, we focus on ultrahigh accuracy and sensitive spherical nanoindentation (SNI), allowing the measurement of tissue-level features at the surface layer to characterize this soft matter. In this study, we show that SNI potentially measures the local spatial properties of concentrated dispersion fluids, especially oil-in-water (O/W) emulsions with various multilamellar structures. We set the parameter te for considering the organization of an equilibrium state consisting of the energy release rate and the work of adhesion on the Johnson–Kendall–Roberts (JKR) predictions. An important consequence of introducing te is that the results obtained by SNI match the theoretical JKR values for large te, suggesting that we can evaluate the microscopic properties more accurately using the classical JKR model. We find that the local features are affected by the lamellar bilayers and the work of adhesion Δγ grows monotonically with increases in space occupied by lamellar structures. Since viscosity effects, such as mechanical energy dissipation and interpenetration, appear as a part of Δγ, the behavior of Δγ clearly shows the microscopic characteristics of the O/W emulsions.

The copolymer of ethylene and propylene possesses a sufficiently high thermo-oxidative resistance, making it possible to study its viscous properties, determine the appearance of elastic turbulence and wall slippage and to measure the rate of the latter over a wide interval of temperatures ranging from room temperature to 260 °C. At low shear stresses and rates the copolymer behaves like aNewtonian liquid with a viscosity of about 108 poise at room temperatures. Elastic turbulence and wall slippage are displayed in sharp form when the viscosity of the copolymer is lowered to its critical value, which depends very little on the temperature and may be accepted as averaging 2.2×104 poise. The corresponding critical shear stress values vary about 10-fold. The criteria of appearance of elastic turbulence suggested in (12, 14) do not agree with experimental data. The entrance losses during the flow of the copolymer through capillaries are low right until elastic turbulence sets in, after which it becomes practically impossible to measure them by the method of capillaries of different length. The average wall slippage rate values of the copolymer at shear stresses above 106 dyne/cm2 amount to tens of cm/sec. They increase very abruptly with rising temperature. The temperature dependence of the viscosity and the dynamic characteristics of the copolymer indicate that it has a phase transition at temperatures of about 100–120 °C, which must be related to melting of blocks contained in the copolymer macromolecules, having a structure close to that of high-pressure polyethylene. This shows that the rheological method of studying block-type polymer and grafted polymers is promising.

Lösungen von Polyacrylnitril (PAN) in Dimethylformamid (DMF) mit Konzentrationen von 0,05 bis 0,175 kg/l wurden in zwei Zylinder-Viskosimetern bei 22°C untersucht. Die Anlaufmessungen im Elastoviskosimeter nachLederer undSchurz, das durch einen Neubau betriebssicher gemacht wurde, ergaben eine Zunahme des Ruheschermoduls mit der vierten Potenz der Konzentration oberhalb 0,08 kg/l. Die Rückfederungsmessungen am Rotovisko mit Elastizitätsmeßzusatz der Firma Haake (wofür konstruktive Verbesserungen vorgeschlagen werden, um auch Vorgänge, die in weniger als 0,1 s ablaufen, erfassen zu können) zeigen gespeicherte Scherungen bei Deformationsgeschwindigkeiten über 10s−1 und Konzentrationen ab 0,1 kg/l. Für Lösungen von PAN in DMF kann der Übergang vom nicht vollständig ausgeprägten Partikeltyp zum Netzwerktyp im Konzentrationsbereich um 0,08 kg/l angenommen werden.

Es wird gezeigt, daß zwischen der Platzwechseltheorie und der linearen phänomenologischen Relaxationstheorie für das plastisch-elastische Verhalten keine Widersprüche bestehen. Die Platzwechseltheorie führt zu nichtlinearen Beziehungen, und die bekannten Gleichungen ergeben sich, indem statt der hyperbolischen Beziehungen jeweils die ersten Näherungen verwendet werden. Fließvorgänge, die durch verminderte Entropie (Änderung der Verteilung auf die vorgegebenen möglichen Lagen) und durch molekulare Haftstellen gekennzeichnet sind und die nach Aufhören einer äußeren Beeinflussung wieder rückläufig verlaufen, sind von solchen, bei denen eine Änderung der molekularen Verteilung auf die im Mittel unverändert bleibenden möglichen Plätze nicht erfolgt, zu unterscheiden. Es empfiehlt sich, neben den Ortskurven den Verlauf von tanϕ in Abhängigkeit von der Frequenz zu zeichnen, um nähere Auskunft über den zugrundeliegenden Fließmechanismus zu erhalten.

A mathematical model was developed to describe the behavior of Herschel-Bulkley fluids in a back extrusion (annular pumping) device. A technique was also developed to determine the rheological properties (yield stress, flow behavior index, and consistency coefficient) of these fluids. Mathematical terms were expressed in four dimensionless terms, and graphical aids and tables were prepared to facilitate the handling of the expressions.

The in situ study of the linear viscoelastic behaviour of complex biological materials with changing volume, such as fermenting dough, poses great challenges to the rheologist. The aim of this study is to develop a new methodology involving a parallel-plate setup with an adjustable gap, to enable time-tracking of the dynamic moduli and density of fermenting dough. Frequency sweep snapshots at specific points in time were obtained in multiwave mode to reduce measurement times, and overfilling effects were taken into account by establishing a calibration curve with unfermented dough. The new test protocol allowed to distinguish the rheological impact of the CO2 gas from that of the other metabolites produced during fermentation. A further validation of the test protocol was achieved by studying the impact of sugar and salt on the fermentation kinetics, for which the results of the oscillatory tests were combined with gas production data obtained with a rheofermentometer.