Flow-MRI Platform Design

The capillary flow-MRI platform is schematically shown in Figure ​Figure11. The components of the platform were purchased from commercial suppliers, namely: (1) the pressure controller (Elveflow) for controlling the applied pressure, P_app in the range 0–8 bar with an operational error of ±1 mbar; (2) the PTFE connecting tubing with w = 0.9 mm (BGB Analytik); (3) the hydrophilic and hydrophobic glass capillaries with diameters in the range 100–540 μm (BGB Analytik); and (4) the PEEK connectors with w = 0.5 mm (BGB Analytik). Since velocities in cylindrical capillaries scale according to (w/2)², we have measured the radius of all capillaries with μCT (see Figure S2 in the SI). The 1.2 mm saddle coil was supplied by Bruker BioSpin and was adapted in-house. For all experiments, the length of the capillary L = 14.7 ± 0.2 cm. The fluid of interest is placed in the reservoir, and the target pressure is applied. The sample flows in the tubing and through the connected glass capillary positioned inside the saddle coil. If the sample exhibits spatial heterogeneities, e.g., due to sedimentation or aging, it is possible to place the reservoir on a stirrer plate and to apply continuous stirring with a magnetic bar during the course of the measurement. Such an approach was followed here for the FCD. The flow measurements were carried out at a constant temperature of 20 °C, which is set by the temperature of the cooling water of the triple axis MRI gradients.

(a) Scheme of the capillary flow-MRI platform in a WB 600 MHz NMR spectrometer. (b) μCT images of the glass capillaries, used for quantification of the capillary inner diameters.