A Device and Method to Study the Ionic Permeation Properties of Membranes Under Continuously Tuneable, Uniform Pressure*

A well-known material test applied to thin films and membranes, bulge test is limited to measuring only mechanical properties. Further, two different experimental setups are needed to apply pressure and make a measurement. In this work, we describe a modified bulge test, where, one single experimental setup is used to apply a pressure as well as make measurements in-situ. A membrane is clamped at its periphery, with a circular window for measurement, and sandwiched between two liquids. By controlling the extent of immersion of membrane in the liquid below the membrane, differential pressure on the membrane may be controlled. The setup was tested and validated with Nafion, a proton conducting membrane, in a 2-electrode configuration by sandwiching H₂SO₄-saturated Nafion between liquid gallium. Electro-impedance spectroscopy was used to quantify permeation and frequency dependent response was modelled using equivalent circuits. The resistance of Nafion increased with depth of immersion, indicating decreasing proton permeation. Conductivity was calculated to be ∼6.4 × 10⁻³ S/cm at equilibrium position, where stress on the membrane is zero. This value matches well with existing literature value for partially hydrated Nafion.