First Studies on the Rheological Behavior of Suspensions in Ionic Liquids

Abstract

The suspension rheology of hematite in the ionic liquid Ecoeng TM. 212 was studied in detail and compared to the pure ionic liquid. This is the first report on the rheological behavior of suspensions in ionic liquids, and it is postulated that colloidal stability and rheology must be considered to understand these results, and to overcome limitations on the production of nanosized particles in industrial applications. Concentrated suspensions of particles in the nanometer range show non-Newtonian flow behavior including shear thinning and shear thickening. These phenomena are mainly caused by particle-particle interactions in the suspension, and control of these interactions is critical. The influences of temperature and solid concentration on flow behavior were shown for the pure liquid and the suspensions. It is seen that the ionic liquid follows the Arrhenius equation for non-associating electrolytes. It is possible to shift all hematite suspension curves to a master curve according to the model of Gleißle and Baloch. Furthermore, the flow behavior of the suspensions can be modeled with the well-known Herschel-Bulkley plot. A 10 wt % suspension of Fe 2 O 3 follows Newtonian behavior over the entire range, similar to the pure ionic liquid. It is believed that the ionic liquid has an influence on the stability of the particles, leading to a decrease of attractive particle-particle forces.

Rheological behavior of multiwalled carbon nanotube-imidazolium tosylate ionic liquid dispersions

“…[21,29,36,37] and has also been predicted by Molecular Dynamics simulations [38]. After this value is reached, at medium and high velocity rates, a Newtonian behavior is found and the viscosity is constant with a value 10 times lower than the one found at low shear rate.…”

Magnetorheological Fluids Based on Ionic Liquids

“…For example, it is though that for suspensions containing a high concentration of hematite nanoparticles in an IL, the particle-particle interactions are much stronger than in the low-concentration cases, which may be responsible for the non-Newtonian behavior observed in such systems. [26] For instance, MRF9 (25 wt % of dispersed micrometer-sized magnetic particles in IL 8) showed a considerably lower sedimentation rate than MRF11 (2 wt % of dispersed micrometer-sized magnetic particles in the same IL); an intermediate case, MRF10 (8.5 wt % of dispersed micrometer-sized magnetic particles in IL 8), is also displayed in Figure 1B. Summarizing, Figure 1A shows that the use of ILs as carriers in dispersions of micrometer-sized magnetic particles allows the preparation of MRFs with improved stability against sedimentation in the absence of antisettling additives (at least under the investigated experimental conditions).…”

“…[26] On the one hand, it was found that concentrated suspensions of nanoparticles show non-Newtonian characteristics, including shear thinning and shear thickening, which probably originate from particle-particle interactions and, on the other hand, it is addressed that suspensions with a low content of nanoparticles follow a Newtonian behavior similar to the one shown by pure ILs. However, this study does not provide any information about the magnetorheological behavior of the suspensions and/or the influence of the structure of the ILs on the stability of the suspensions against sedimentation.…”

“…On the one hand, it is known that most of the ILs are typically more viscous than common organic solvents, that small amounts of impurities can have an important effect on their viscosity, and that, in general, most ILs show Newtonian behavior (a few examples are known where ILs form a liquidcrystalline phase, which show a thixotropic behavior). [26,42,43] On the other hand, it has been reported in the literature that the viscosity of suspensions, in both ILs [26] and conventional solvents [31] will differ from that of the carrier liquid due to the presence of the suspended particles. Thus, the viscosity of the investigated MFRs in the absence of a magnetic field is deter- mined by the viscosity of the carrier liquid (ILs) and the volume fraction of suspended magnetic material (f) according to established theories of the viscosity of suspensions.…”

Magnetorheological Elastomers Containing Ionic Liquids

“…The sedimentation problem in MRFs is of such importance that it has even been investigated (together with other properties) under microgravity conditions in outer space 24 . A very recent study reports on the rheological behaviour of suspensions of hematite nanoparticles in an IL 25 . On one hand, it was found that concentrated suspensions of nanoparticles show non-Newtonian characteristics, including shear thinning and shear thickening, which probably originate from particle-particle interactions.…”