Physicochemical properties and potential applications of silica-based amphiphilic Janus nanosheets for enhanced oil recovery

Nanofluid flooding has recently garnered significant attention as a novel enhanced oil recovery (EOR) technology; however, there are limitations to the current simple nanofluid flooding. Compared with the commonly used homogeneous spherical nanoparticles, amphiphilic Janus nanosheets have a higher interfacial activity and greater application potential for EOR. In this paper, a carboxyl/alkyl composite silica-based amphiphilic Janus nanosheets (CSAJN) were prepared by a bottom-up synthesis strategy, and the physicochemical properties and EOR potential were systematically investigated. The results showed that the CSAJN displayed a distinct ultrathin flake-like morphology and a lateral size in the range of hundreds of nanometres. More specifically, the CSAJN had two different sides, one side containing a carboxyl group that was hydrophilic, and the other side containing an alkyl group that was hydrophobic. Because of the amphiphilic and Janus nature, the CSAJN could be dispersed in different polar solvents, reduce the oil-water interfacial tension and enhance the oil-water interfacial film strength. Core displacement experiments showed that the CSAJN nanofluid could significantly increase the efficiency of oil recovery to ∼18.31% even at an ultralow concentration of 0.005 wt% and cause minimal impairment to the permeability. By observing and analysing the interfacial behaviour of CSAJN in a toluene/brine system, it was found that the formation of a climbing film and high-strength elastic oil-water interfacial film by CSAJN may play an important role in EOR mechanism. This work reveals the physicochemical properties of silica-based amphiphilic Janus nanosheets and provides a novel efficient nanofluid system for EOR.