The versatility of tailored polymers in investigating reactive transport in porous media

Subsurface transport takes place in a heterogenous and dynamic network of pores, solids, interfaces, and biota that share a complex topology and create a multitude of migration pathways for fluids and their constituents, i.e., the total mobile inventory (TMI). Owing to the highly variable reactivity of different fractions of the TMI towards biogeochemical interfaces provided by associations of minerals, organic matter and biota, characteristics of the transport regime mainly express in response to the availability and exposition of reactive interfaces. We exploit the rich possibilities of polymer synthesis to design a library of reactive, organic polymers that can represent specific fractions of the TMI regarding their size or reactivity and serve as non-conventional tracers. We show the strong and nearly irreversible adsorption of specific polymers towards unoccupied clay mineral surfaces in column experiments. With that, tailored polymers not only presented as tracers for the transport of organic colloids, but also as sensitive interfacial tracers for the assessment of clay surface exposition that enable the quantification of available reactive surface area accessible to fluids and constituents transported therein. We also use polymers to label potentially mobile clay mineral colloids and follow their mobility in porous media by tracking polymers being co-transported along with the colloids. We further use polymers to introduce a fluorescent label to reactive mineral sites and localize their relative distribution on rock surfaces using fluorescence microscopy. As polymers can also be subjected to other spectroscopic techniques such as infrared spectroscopy, a tailored synthesis of polymers towards adsorption to specific sites might open a novel perspective on the characterization and mapping of (mineral) surfaces and their functional role in general.