Validation of temperature‐controlled rheo‐MRI measurements in a submillimeter‐gap Couette geometry

Abstract

A temperature-controlled submillimeter-gap (500 μm) rheo-magnetic resonance imaging (MRI) Couette cell has been developed to measure confined flow of soft structured materials under controlled temperature. The proposed setup enables performing rheo-MRI measurements using (i) a spatially uniform temperature control over the range 15 C to 40 C and (ii) a high spatial resolution up to 10 μm, as a consequence of the improved mechanical stability of the in-house developed rotating elements. Here, we demonstrate the performance of the cell for the rheo-MRI velocimetry study of a thixotropic fat crystal dispersion, a complex fluid commonly used in food manufacturing. The submillimeter-gap geometry and variable temperature capability of the cell enable observing the effects of shear-and temperature-induced fat recrystallization on both wall slip and shear banding under strongly confined flow. Our improved rheo-MRI setup opens new perspectives for the fundamental study of strongly confined flow, cooperative effects, and the underlying interparticle interactions and for ultimately aiding optimization of products involved in spreading/extrusion, such as cosmetics and foods.

Quantifying cooperative flow of fat crystal dispersions

“…We study the global flow behavior in both wide-and narrow-gap CCs with classical rheology, and compare the results with spatially-resolved rheo-MRI velocimetry measurements using an in-house developed 500 μm gap CC. 22 We find that the presence and spatial extent of cooperative flow depends on the microstructural changes induced by varying crystallization rates. By fitting the data to a numerical fluidity-based model adapted for narrow-gap CC, we show that the flow cooperativity length depends not only on the sizes of the fat crystal aggregates, but also on the inter-particle interactions modulated via the colloidal network.…”

“…The magnet was equipped with the standard Bruker rheo-MRI accessory, consisting of a stepper motor and drive shaft, used in combination with a custom-made 500 μm CC ( = 8.5/9 mm) with 𝒓 𝒊 /𝒓 𝒐 smooth walls. 22 1D velocity profiles were measured using a Pulsed Gradient Spin Echo (PGSE) 25 sequence, within a slice 1 mm thick along two dimensions, echo time T E = 20 ms and repetition time T R = 2 s. The duration of the velocity-encoding gradient pulses, and their inter-pulse spacing, were δ = 1 ms and ∆ = 13 ms, respectively. To avoid chemical-shift artefacts, a CHEmical Shift Selective (CHESS) suppression module, as implemented by Serial et al, 26 was used in all measurements using three 90 o chemically selective pulses with bandwidth of 0.8 kHz and offset of 1.1 kHz.…”

“…This cell was designed to enable imposing confined flow while keeping stress inhomogeneity and off-axis wobbling negligible. 22 These conditions are essential for observing and quantifying confined flow behaviour, without distortions originating from the rotating geometry. The rheo-MRI velocity profiles of all FCDs, acquired at the same shear rates as the stress measurements by standard rheology (Fig.…”

Capillary Flow-MRI: Quantifying Micron-Scale Cooperativity in Complex Dispersions

“…Under such circumstances, magnetic resonance imaging (MRI) velocimetry can be beneficial, as it does not suffer from this limitation. In recent years, MRI velocimetry has been applied to unravel flow cooperativity in fluids with particle sizes ≳30 μm, like cellulose, fat crystal dispersions (FCDs), and milk microgels, or even granular materials. − These studies were performed using rotational rheo-MRI setups , equipped with commercially available or custom-made Couette cells (CC) with gap sizes down to 0.5 mm, or cone–plate (CP) geometries with angles down to 4°. Figure S1 in the Supporting Information (SI) shows the scheme of a rotational rheo-MRI setup with both CC and CP geometries.…”

Contact‐mediated nucleation in melt emulsions investigated by rheo‐nuclear magnetic resonance

“…[25] Furthermore, recrystallization and network formation of crystalline dispersions of a fat were successfully investigated. [26,27] Rheo-NMR also allowed the exploration of the influence of fluid dynamics on polymerization as a function of temperature. [28] In a preliminary study, [29] the crystallization of emulsions was inline measured by NMR at a laminar Couette flow.…”