Temperature- Triggered Release of Chromium Chloride from Nanocapsules for Controlled Burst Release and Gelation of Hydrolyzed Polyacrylamide to Plug High-Permeability Channels

Chromium(III) (Cr3+)-hydrolyzed polyacrylamide (HPAM) gels have been applied extensively as blocking agents for sweep efficiency improvement. Previous studies focused on delaying the gelation time and ignored the diffusion of the crosslinkers during the transportation process. The gelation time of Cr3+- HPAM was too long to be controlled. This study systematically describes a novel approach of using thermoresponsive nanocapsules to precisely control the release of Cr3+. The nanocapsules are successfully prepared by a controlled nanoprecipitation of hydrophobic polymers [poly (methyl methacrylate)] (PMMA) and Pluronic (R) P-123 onto stable aqueous Cr3+ solution nanodroplets. The stable aqueous nanodroplets are obtained by double inverse miniemulsions with oil-soluble surfactant Span (R) 80. The nanoprecipitation occurs when heating the mixture at 50celcius, which leads to the evaporation of solvent and precipitation of the PMMA into the interface of the aqueous droplets to form the shells. Pluronic P-123 is introduced to stabilize the double miniemulsion and enhance the precipitation efficiency of the shell polymer during the fabrication process. The fabricated nanocapsules show a size range from 211.9 to 297.2 nm depending on the feed contents of the Cr3+. The thermoresponsive function of Pluronic P-123 is studied and applied as a temperature-trigger on the shell. Gelation results show that the thermoresponsivity of Pluronic P-123 dominates the release rate rather than the diffusion rate through PMMA, which could be used to shorten the gelation interval time.