In-situ non-invasive imaging of liquid-immersed thin film composite membranes

We present a non-invasive method to directly image liquid-immersed thin film composite membranes. The approach allows accessing information not only on the lateral distribution of the coating thickness, including variations in its swelling and density, but also on the distribution of substrate porosity, roughness, accessibility of pores to liquid, and even the degree of pore intrusion related to the thin layer deposition process. The method can be particularly helpful in the fields of functional coatings or membranes to allow laterally-resolved studies under realistic application conditions thereby opening completely new research avenues. The approach is demonstrated in a study of two polymers of intrinsic microporosity, PIM-1 and PIM-6FDA-OH, coated on polyacrylonitrile support and immersed in water. Variations of the skin morphology using different coating methods (floating, spin-coating and dip-coating) are evaluated with the help of the presented method. Surfaces of at least tens of cm2 can be potentially analyzed.