Volume 24, Issue 4

Electrorheological measurements represent a key approach in characterizing the efficiency of electrorheological fluids. The rotational rheometers, the Physica MCR 501 (Anton Paar) equipped with an electrorheological cell and the Bohlin Gemini CVOR 150 (Malvern Instruments) modified for electrorheological experiments generate an electric field in two completely different ways. Each of the two generations has a specific influence on electrorheological measurements. The experimental data were obtained and compared for a suspension of polyaniline powders mixed (10 wt%) in silicone oil. For a concentric-cylinders arrangement, it was shown that the data are fully comparable for both rheometers. However, for a parallel-plate arrangement, the data using the Physica MCR 501 provide higher values in comparison with both the corresponding plate-plate data obtained with the Bohlin Gemini CVOR 150 and with the mutually comparable concentric cylinders data.

A novel shear thickening suspoemulsion is formulated and studied with a new rheo-microscope instrument. The experimental fluid system is comprised of a immiscible blend of Newtonian, low molecular weight poly(dimethylsiloxane) and a shear thickening suspension of colloidal silica in poly(ethylene glycol). The blend is studied as a function of composition where phase inversion is evident at low shear rates and is found to be shear rate dependent. A shear thickening viscosity curve is observed when blends comprised of shear thickening fluid dispersed as droplets are subjected to high shear rates. Dispersing a continuously shear thickening fluid, Ø silica = 0.42, results in continuously shear thickening response from the blend. Dispersing a discontinuously shear thickening fluid, Ø silica = 0.51, results in bulk shear thickening that can also be discontinuous. Shear thickening in the final suspoemulsion is consistently first detected at Ø STF = 0.2, with the magnitude of shear thickening being dependent on the particle concentration in the STF phase. The onset of shear thickening also corresponds with the formation of extended droplet structures in the fluid. The complex properties of these suspoemulsions and the ability to formulate dispersed droplet morphologies in this mixture are shown to result from the underlying shear thickening rheology of the dispersed phase.

This work presents a technique based on optical tracking of the free fall in a Newtonian fluid used in falling ball viscometers. Classical techniques have shown, on one hand a limit in the ball falling height measurement, on the other hand a limit in the accuracy estimation of velocity and therefore a weak precision on the viscosity calculation of the fluids. Our method consist to measure the fall height by taking video scenes of the ball during its fall and thus to estimate its terminal velocity which is a preponderant parameter in the kinematic velocity computing, using both the Stokes or Hoppler formalisms. The precision reached in this approach adjoins encouraging values for future works in the purpose to improve this method further.

The influence of pH of walnut oil emulsions on droplet morphology, droplet size distribution, time and temperature stability, and rheological properties has been studied. It has been found that walnut oil based emulsions form a metastable gel-like microstructure at steady conditions revealed by a linear viscoelastic response at low deformations. Flow curves of investigated emulsions demonstrated shear thinning behavior at moderate shear rates with a tendency to a limiting viscosity at higher loads. The most stable emulsion was formed at weakly acidic conditions (pH = 6), which favors the formation of fine uniform droplets with no visible tendency to coagulation at ambient conditions.

Starch-based adhesives play a relevant role in paperboard production and are becoming more and more interesting, for different uses, because they are based on renewable biopolymers. Starch modifications or additive addition are becoming frequent to obtain the macroscopic properties desired for specific uses. In this paper the effects of the addition of four different tannins on a typical adhesive, adopted for corrugated paperboard production, were investigated by using fundamental rheological techniques, both in dynamic and steady conditions. It was found that tannins increase the onset of starch gelatinisation, estimated as the knee point of the storage modulus in a dynamic temperature ramp test, and decrease the steady shear viscosity. This is due to the interactions between tannin and starch that affect the gelatinisation and retrogradation reactions weakening the starch network. Even though a partial reinforcement effect was also observed, owing to the polymeric nature of tannin components, a lower consistency, with respect to the neat adhesive, was found for all modified samples. Tannin has shown itself able to modify technological properties such as gelatinization temperature and viscosity, since the specific results are determined by the nature and amount of tannin; therefore it could be used to adapt adhesive characteristics to specific applications, potentially improving starch-based adhesive competitiveness with respect to different adhesives.