(439e) Stable Polymer Grafted Iron Oxide Nanoclusters in High Salinity Brine for Transport and Imaging in Subsurface Reservoirs

Magnetic nanoparticles with high mobility in subsurface reservoirs at high salinities and temperatures are expected to have a major impact on enhanced oil recovery, carbon dioxide sequestration, and electromagnetic imaging. Herein we present a rare example of elelctrosteric stabilization of iron oxide (IO) nanoparticles (NPs) grafted with poly(2-acrylamido-2-methylpropanesulfonate-co-acrylic acid) (poly(AMPS-co-AA)) that not only display colloidal stability in standard American Petroleum Institute (API) brine (8% NaCl + 2% CaCl2 by weight) at 90 °C for 1 month but also resist undesirable adsorption on silica surfaces (0.4% monolayer NPs). In this copolymer coating, the AMPS groups interact weakly with Ca2+, so that the poly(AMPS-co-AA) chains grafted onto IO NPs surface remain sufficiently well solvated and negatively charged to provide electrosteric stabilization. The AA groups, in addition, enable covalent grafting of the poly(AMPS-co-AA) chains to amine-functionalized IO NPs via formation of multiple amide bonds and prevent polymer desorption even after a 40 000-fold dilution. The remarkable stability and transport properties of poly(AMPS-co-AA) grafted IO NPs is attributed to the high stability of poly(AMPS-co-AA) chains as revealed by dynamic light scattering and electrokinetic measurements. The low equilibrium silica adsorption capacity of poly(AMPS-co-AA) grafted IO NPs correlates well with the low retention in 1D column flow experiments. The aforementioned methodology may be readily adapted to stabilize a variety of other functional inorganic and organic NPs at high salinities and temperatures.