Bernhard Senge

Rheological properties of rice dough for making rice bread

The rheological properties of two varieties of rice with Hydroxy propyl methyl cellulose (HPMC) added as gluten substitute were studied using a farinograph and a rheometer and compared with wheat dough to find its suitability for making rice bread. The water absorption and dough development time data were obtained from the farinogram. The tests conducted in the rheometer were oscillation measurements (frequency sweep from 0.1 to 20 Hz at 1% strain), shear measurement (shearing from 0.1 to 5 s−1) and creep tests with an instant loading of 50 Pa for 60 S. Baking tests were conducted with all the dough samples and the loaf volume and moisture loss of bread were measured. The farinogram showed that rice flour supplemented with HPMC reached a consistency of 500 BU at a later time than that of standard wheat dough. The rheological measurements from the oscillation tests and creep tests showed that the rice dough with 1.5% and 3.0% HPMC had similar rheological properties to that of wheat flour dough and was suitable for making rice bread. The long grain rice sample produced a rice bread with better crumb texture.

Shear thickening in electrically stabilized non-aqueous colloidal suspensions

The authors previously introduced an activation model for the onset of shear thickening in electrically stabilized colloidal suspensions. It predicts that shear thickening occurs, when particles arranged along the compression axis in a sheared suspension do overcome the electrostatic repulsion at a critical shear stress, and are captured in the primary minimum of the DLVO interaction potential. A comparison with an experimental investigation on non-aqueous silica suspensions, carried out by Maranzano and Wagner, is performed. For particle systems that fall into the applicability range of the theory, a good coincidence between the experimental data and the model predictions can be found.

Rheologische Untersuchungen von zellstrukturierten Materialien

Rehydrated material with cellular structure and alcohol insoluble substance may be regarded as concentrated suspension with viscoelastic properties. The rheological properties of disperse systems are determined on the basis of the material properties of the disperse phase apart from its concentration. The material properties of the disperse phase depend on the macrostructural parameters of the particles including the interactions occuring and the chemical structure of the cell wall. The material properties of the rehydrated material with cellular structure may be detected by means of classical rheological examinations and specifically systemizing their evaluation. The description of material with cellular structure with the aid of CASSONs model and the further investigation of the yield stress τ0 as a function of its concentration and of the effektive viscosity ηeff as a function of its concentration and shear rateγ seem to be established. If comprehensivly applied this method allows to interpret the rheological properties of the material with cellular structure in specific respect. The dominant linear dependence of the influencing variables yield stress, CASSONs viscosity and effectiv viscosity on concentration is especially remarkable.

Shear Thickening in Concentrated Soft Sphere Colloidal Suspensions: A Shear Induced Phase Transition

A model of shear thickening in dense suspensions of Brownian soft sphere colloidal particles is established. It suggests that shear thickening in soft sphere suspensions can be interpreted as a shear induced phase transition. Based on a Landau model of the coagulation transition of stabilized colloidal particles, taking the coupling between order parameter fluctuations and the local strain-field into account, the model suggests the occurrence of clusters of coagulated particles (subcritical bubbles) by applying a continuous shear perturbation. The critical shear stress of shear thickening in soft sphere suspensions is derived while reversible shear thickening and irreversible shear thickening have the same origin. The comparison of the theory with an experimental investigation of electrically stabilized colloidal suspensions confirms the presented approach.

Structural transitions in sheared electrically stabilized colloidal crystals

A Landau theory is presented for the structural transition of electrically stabilized colloidal crystals under shear. The model suggests that a structural transition from an ordered layered colloidal crystal into a disordered structure occurs at a critical shear stress. The shear induced structural transition is related to a change of the rheological properties caused by the variation of the microstructure which can be verified by scattering experiments. The theory is used to establish the shape of the flow curves. A good qualitative agreement with experimental results can be achieved, while a scaling relation similar to the elastic scaling is established.