(158g) Copolymer-Coated Stabililization of Superparamagnetic Iron Oxide Nanoclusters At High Ionic Strength and High Temperature Designed by Combinatorial Materials Chemistry

Electrosteric stabilization of copolymer-coated nanoparticles is uncommon for high monovalent salinity (upto 5 M NaCl), and rarely reported for concentrated divalent cations. However, high mono and divalent concentrations are routinely encountered in subsurface applications including electromagnetic imaging and oil recovery.  Stabilization of nanoparticles at high calcium salinity, especially at high temperatures (up to 100 °C), is challenging because of the high counterion association of calcium with anionic polymer stabilizers.   With the goal of identifying a suitable polymer for NP stabilization in such high calcium high temperature conditions, we conducted a combinatorial study by coating various compositions of acrylic/sulfonic acid copolymers on platform citrate-coated iron oxide (IO) nanoclusters. Hundreds of experiments were conducted by judicious choice of coating parameters - pH, concentration and type of electrolytes, temperature and polymer concentration. Based on these results, a select class of sulfonic acid copolymers was found to provide nanoparticle stability in API brine (8% NaCl + 2% CaCl2 w/v) for at least 3 weeks at 90 °C. A fundamental explanation is provided to describe electrosteric stabilization at these unusually harsh conditions. This enhanced stability will enable the study of NPs for various applications including oil and gas exploration and production.