Electrical Impedance Spectroscopy
Membranes possess energy storage and dissipation properties.
In EIS, alternating current (AC) of known amplitude and angular frequency is injected through the membrane and the potential difference response measured to allow the calculation of the electrical impedance.
A filtration membrane is a non-homogenous system composed of distinct layers with different properties. The calculation of impedance across a range of frequencies allows EIS to identify the electrical properties of each individual sub-structural layer.
Of particular interest in RO filtration are the properties of the boundary layer at the membrane surface where ‘concentration polarisation’ of solutes occurs when a flux is present. Agglomeration and other changes of this accumulated material are a prelude to what is usually referred to as “fouling”. CMS’s EIS technology can detect these changes as they occur.