Designing polyurethane-based microcapsules with tailored swelling behaviours for enhanced oil recovery†

Polyurethane (PU) materials have been widely used for developing microcapsules due to their excellent polymerization, encapsulation, and controlled release properties. These unique properties endow PU-based microcapsules with desired functions for enhanced oil recovery (EOR). However, there are some special requirements for PU-based microcapsules in their application of the EOR process, such as they are expected to exhibit good stability at room temperature but thermo-responsive swelling-release properties in the oil reservoir. To enhance the functionality of PU-based microcapsules for EOR, after validating the swelling-release behaviors of PU-based microcapsules, we employed all-atom molecular dynamics (MD) simulations to study the effects of molecular structure of PU-based polymers on thermo-responsivity of microcapsules. The simulation results demonstrate that the diisocyanate segments have significant influence on swelling behaviors of PUs. The different diisocyanate segments, including isophorone diisocyanate (IPDI), toluene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI), and hexamethylene diisocyanate (HDI), have different impacts on the flexibility of the polymer, which further influence the network structure of the polymer matrix. The different swelling behaviors of PU-based polymers were further analyzed from energetic and kinetic perspectives, and it is demonstrated that TDI–PU can combine stability and thermo-responsivity together. In addition, the introduction of anionic functional groups can further facilitate the swelling process. The findings in this study serve as a foundation for future studies toward the development of polymer flooding technology and provide valuable molecular insights into the swelling mechanism of PU-based polymers.