Preparation of Janus Polymer Nanosheets and Corresponding Oil Displacement Properties at Ultralow Concentration.

Conventional methods for preparing Janus nanosheets, including graphene oxide-based nanosheets, molybdenum disulfide-based nanosheets, and silicon dioxide-based nanosheets, as well as polymer-based nanosheets, involve complicated procedures, poor repeatability, and difficulty in imparting Janus properties, which hinder further application. Here, the present authors develop a facile modified suspension polymerization method for preparing Janus polymer nanosheets, in which deep eutectic solvents completely replace water as the continuous phase. Janus polymer nanosheets can be fabricated using common hydrophobic and hydrophilic monomers, such as styrene (St), butyl acrylate (BA), acrylamide (AM), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), acryloyloxyethyl trimethylammonium chloride (DAC), and maleic anhydride (MAH). Additionally, the thickness of the Janus polymer nanosheets can be precisely controlled in a range from 40 to 100 nm by adjusting the volume ratio of higher alkanes to the hydrophobic monomer. Subsequently, the emulsification properties of polystyrene-based nanosheets were evaluated, showing better performance at concentrations ranging from 1 to 50 mg/L compared with higher concentrations. This observation aligns with the corresponding reduction in interfacial tension and changes in the moduli of the interfacial film. Moreover, the adsorption of the nanosheets onto the core alters its wettability, changing it from a water-wettable state to an oil-wettable state. Consequently, a series of core flooding tests reveal that the poly(St--AM), poly(St--MAH), and poly(St--AMPS) nanosheets enhance oil recovery and reduce injection pressure at ultralow concentrations (50 mg/L).