Surface versus bulk CaCO3 crystals with ethylene vinyl alcohol co-polymers and polyamide thin-film composite membranes

Abstract

We conducted experiments to study the influence of material surface chemistry and morphology on the crystallization of calcium carbonate from supersaturated solution containing mixed electrolytes. The study evaluated ethylene vinyl alcohol (EVOH) co-polymers and fluorinated and non-fluorinated polyamide thin film composite membranes to evaluate how surface functional groups impact partitioning of salt crystals between the surface and the bulk fluid. Our methodology and results can aid in developing scaling-resistant thin film composite membranes and in selecting materials for engineered structures exposed to supersaturated solutions. We analyzed turbidity, surface scale deposition, bulk crystal yield, and overall Ca balance to quantify salt crystal adhesion (aka scaling) during exposure to the supersaturated stream and subsequent desupersaturation. Through our studies, we found polyethylene was much more prone to scaling as compared to EVOH. We also show that EVOH containing 56% vinyl alcohol monomer appears to have higher scaling resistance as compared to an EVOH containing 68% vinyl alcohol monomer. These two grades of EVOH were analyzed using atomic force microscopy to elucidate if differences in co-polymer morphology existed; it appears so and this may underlie the measured differences in the salt crystal's surface adhesion. Also, the studies found that the incorporation of fluorine in the polyamide thin film composite membrane surface by means of a novel mono-fluorinated trimesoyl chloride derivative does not impact salt scaling or the total solution de-supersaturation. Our studies provide new insight that not only -OH functional group quantity but also polymer chain configuration and conformation need to be optimized for surfaces that are resistant to calcium carbonate scale buildup.