Probing the internal structure of nuclepore with hysteretic capillary condensation

We report filling (adsorption) and draining (desorption) measurements of superfluid ⁴He in the porous material nuclepore. These low-temperature measurements explore the classical hysteretic properties of the capillary condensation of the liquid, while utilizing the propagation of third sound in the superfluid helium as an in situ probe of the chemical potential. We present measurements of global hysteresis loops, subloops, and reversal curves. With this data, we determine that the interconnected pore structure of the material is critical to the draining process. In addition, we present measurements of the connectivity and pore size distributions for nuclepore, and compare these results to calculations and earlier measurements. This work establishes the utility of the novel working fluid superfluid ⁴He and the applicability of the techniques used here for such studies of porous materials.