QCM study of mineral surface crystallization on aromatic polyamide membrane surfaces

The mineral scaling propensity of aromatic polyamide membrane surfaces was evaluated for surfaces ranging in roughness from about 1 to 94 nm, surface feature heights ranging from a few nanometers to as high as 400–450 nm and average peak separation of ∼140 nm to 2 μm. The polyamide surfaces were interfacially polymerized onto quartz crystal microbalance (QCM) sensors and silicon wafer substrates which were previously structured with a polyelectrolyte film formed by a layer-by-layer self-assembly method. Mineral scaling was quantified via QCM measurements of the time evolution of surface crystallization along with SEM and AFM surface characterization. Crystal surface mass density and rate of surface crystallization increased with increasing surface roughness. However, surface scaling propensity was also significantly impacted by the details of surface topography revealing fewer but larger crystals on rough surfaces that possessed large features with large separation distances. It is hypothesized that the separation distance between features and feature heights (dictating the geometry of surface “valleys”), for a given surface roughness, could affect the availability of surface nucleation sites as well as constrain growth of crystals within surface valleys.

► Gypsum scaling of polyamide membranes of varying topography was evaluated via QCM.
► Polyamide surfaces were interfacially polymerized onto modified QCM sensors.
► Surface scaling increases nonlinearly with increased surface roughness.
► Crystal size and shape are affected by surface topography (micro- and nano-scale).
► Presence and separation of “hills” and “alleys” impacted surface crystallization.