High-speed NMR imaging of capillary action in thin nontransparent porous media

An improved high-speed NMR profiling method is introduced that enables us to measure capillary action in thin, nontransparent porous media. Liquid profiles can be measured as fast as 10 ms with a spatial resolution of $14.5\mu \text{m}$. Capillary absorption of microliter-sized droplets into nontransparent nylon-6,6 porous membranes was studied. In nylon-6,6 sharp fronts obeying a one-dimensional Darcy model were observed. In paper the uptake did not follow this model: retardation in uptake, broader fluid fronts, and swelling was observed. These measurements nicely demonstrate the possibilities and versatility of the developed method.

Figure 1

Schematic representation of the measurement setup.

Figure 2

Liquid profiles measured by GARField ${}^1\mathrm{H}$ NMR of a 50-wt % glycerol mixture inside a $0.42\text{−}\mu \text{m}$ pore diameter nylon membrane. Profiles are measured every 25 ms and the top of the nylon membrane is set to the 0 position. The squares mark the fluid front positions. In blue, the signal acquired just before the droplet hits the sample surface is shown.

Figure 3

Imbibition experiments for different water-glycerol mixtures (0, 25, 50, and 75 wt % glycerol) in nylon membranes with different pore radius ($r=0.21\mu \text{m}$ and $r=0.27\mu \text{m}$). The legend gives the amount of glycerol in wt % and the pore radius of the nylon membranes in $\mu \text{m}$. The fluid front position is given as a function of $\sqrt{t}$.

Figure 4

The liquid penetration depth as function of the rescaled time for the different water-glycerol mixtures (0, 25, 50, and 75 wt % glycerol) in nylon membranes with different pore radii ($r=0.21\mu \text{m}$ and $r=0.27\mu \text{m}$) membranes.

Figure 5

Liquid profiles for a 0.25-M ${\mathrm{CuSO}}_4$ solution in Mondi Niveus Top printing paper. For clarity, the initial paper-liquid interface at position $0\mu \text{m}$ is marked with a dashed line. Shown in top right are the liquid front (black) and swelling front paper-liquid interface (red) indicated by arrows in the main figure. In blue, the signal acquired just before the droplet hits the sample surface is shown.