Volume 21, Issue 1

This paper presents an experimental study of the rheological behaviour of water-in-oil mixtures without any additive, up to 10 % of mass water concentration, where the mixture is considered to be a Newtonian fluid. The selected oil is a classical turbine mineral oil. Viscosity was measured for five temperatures, ranging from 10 to 80°C, for droplet size below 30 mm. A light decrease of viscosity was detected for water concentrations below 0.1 %. For concentrations greater than 0.2 %, viscosity increases with water concentration. Moreover, the variation of viscosity with temperature shows good correlation with both Walther model and Mac Coull & Walther model. Finally, a new model of water-in-oil mixtures viscosity as a function of temperature and concentration was defined.

The effects of particle concentration, particle size and temperature on the shear rheology of suspensions of silica nanoparticles are studied. Sterically or electrostatically stabilized silica nanoparticle dispersions with sizes ranging from 5-75 nm and particle volume fractions ranging from 0.22-25 % exhibited a constant viscosity within the shear rate range of 1-200 s -1 . There is a non-linear relationship between the concentration and the viscosity of these dispersions that depends on the radii and surface energy of these nanoparticles. We propose an effective maximum packing fraction model based on the concept of an effective particle radius, which takes into account the thickness of the electrical double layer and the surface coating material. The viscosities of all the dispersions collapse onto a universal curve as a function of the volume fraction normalized by the effective maximum packing fraction.

This paper evaluates the use of lightweight aggregates (LWA), namely perlite (PER) and vermiculite (VER) in cement mortars. The workability of mortars was defined in rheometer and flow table tests. Three distinct LWA levels were added (0 - 3, 4.5 - 7, and 9- 10.5 wt%) requiring the use of distinct water/solids (W/S) ratios (0.18, 0.265 and 0.35, respectively). In order to evaluate the performance of such formulations in the hardened state, the flexural and compressive strength after 28 days curing was also measured. In general, LWA caused a high variation on the yield stress and spread on table, being the yield stress the best rheological parameter to be related with the flow table. PER exerts a strong impact on initial yield stress, while the effect of VER is stronger for longer rheology testing periods. The compressive strength ranged from 12.3 MPa (0 % LWA) to 2.77 MPa (PER) and 2.39 MPa (VER).

The effect of shear viscosity on taste and mouthfeel perception has been extensively studied; however, the effect of extensional viscosity on sensory perception has been mostly neglected. This may be important as in-mouth processing is complex and probably best described as a superposition of shear and extensional flow characteristics. Fluid mechanics researchers interested in separating elastic effects from viscous effects use Boger fluids and this approach was adopted here to investigate the effect of fluid elasticity on sensory perception. For the first time, two food grade Boger fluids based on glucose syrup and aqueous solutions of maltodextrin as solvents and xanthan gum as high molecular weight polymer were formulated. The elasticity of the Boger fluids was characterised in rotational shear rheometry, in a filament break-up device and in micro-contraction flow. Saltiness perception and mouthfeel of the Boger fluids and samples corresponding to the respective solvent were analysed. Surprisingly, there were no significant differences. Hypotheses attributing this finding to the intrinsic properties of the samples are discussed. A major study would be required to gain in-depth understanding of the sensory properties of these fluids as their flow properties are very different from typical liquid foods.