Capillary breakup extensional magnetorheometry

Magnetorheology: a review

“…205 A model for the MRF adhesion under nonhomogeneous magnetic fields was reported by the authors. Finally, Sadek et al 206 studied the uniaxial extensional flow of MRF using a CaBER device with a fixture that is capable to impose a controllable and homogeneous magnetic field over the sample volume, either parallel or perpendicular to the strain direction. Both magnets 207 and coils 206 have been implemented in the setup.…”

“…Finally, Sadek et al 206 studied the uniaxial extensional flow of MRF using a CaBER device with a fixture that is capable to impose a controllable and homogeneous magnetic field over the sample volume, either parallel or perpendicular to the strain direction. Both magnets 207 and coils 206 have been implemented in the setup. It is shown that the filament created during the extensional flow broke earlier when the sample underwent larger Hencky strains (what promoted the capillary forces in the filament) or later when the MRF yield stress was enhanced (either increasing the applied field or particle concentration).…”

Extensional Magnetorheology as a Tool for Optimizing the Formulation of Ferrofluids in Oil-Spill Clean-Up Processes

“…The coils are connected in series to a DC power supply (PS 5200-02A, power supply, Elektro-Automatik, Viersen, Germany), which allows a current of up to 2A to be applied. Samir et al [22] reported the correspondence between the current strength provided by the source and the field strength (H). Finally, for the case study of FFs without a magnetic field, the original configuration of CaBER is used (see Figure 3 (2b)).…”

“…The experimental setup consists of a Capillary Breakup Extensional Rheometer (CaBER-1 device, Thermo Fisher Scientific, Waltham, MA, USA) equipped with the magnetorheological cell (ExMRFx) developed by Sadek et al [22]. The CaBER device imposes a sudden extensional step strain (from h 0 to h f ) to a stable liquid bridge, reaching a state of unbalance in which capillary forces cause the filament thinning process until it breaks.…”

“…In 2015, Galindo et al [21] developed two magnetorheolgical cells consisting of permanent magnets that allowed to studying the effect of the magnetic field and its orientation on the filament thinning process of ferrofluids under extensional flow, but for a single value of the intensity of the magnetic field strength. More recently, Sadek et al [22] developed a new version of these magnetorheological cells consisting of solenoids that allowed to control the intensity of the magnetic field by controlling the intensity current; however they only focused on the rheological characterization of magnetorheological fluids. If we intend to improve the oil-spill clean-up processes by means of the magnetic separator proposed by Zahn et al [6], it is paramount to have a full rheological characterization of the ferrofluids, as it will allow for optimizing the formulation of the ferrofluids and modelling the fluid-flow in real configurations, where shear and extensional flow are coexisting, and the magnetic field may be oriented in any direction.…”