The pH and Temperature Dual-Switchable Polymer Emulsion via Acid-Based Ionic Liquid with Ultrasensitive Releasing for Drag Reducer

One of the challenges in hydraulic fracturing of shale oil and gas is increasing the dissolution rate of the polyacrylamide drag reducer. The injection process of field application is extremely rapid for the drag reducer, which puts forward high requirements for the dissolution rate. This study synthesizes ionic liquids (ILs) from fatty acids and alcohol amines as a switchable emulsifier. Herein, two pH-responsive and pH- and temperature-responsive emulsions based on an interface switch are respectively proposed. The inverse emulsion polymerization is carried out using a W/O switch monomer emulsion of acrylamide (AM), acrylic acid (AA), and 2-acrylamide-2-methylpropanesulfonic acid (AMPS) as a template, which is used as a drag reducer. Taking the interface response characteristics as the entry point, the electrostatic interaction between carboxylic acid anions and amine cations is rapidly destroyed upon pH stimulation, resulting in emulsion instability and swift dissolution of the polymer. Furthermore, an ethoxy (EO) chain with multiple repeating units is introduced into the headgroup of the emulsifier to further endow the polymer emulsion with temperature responsiveness. Finally, the switchable polymer emulsion drag reducer is rapidly released and dissolved in water at pH 9, boasting an impressive dissolution rate of only 20 s. The drag-reduction rate of 0.05 wt % drag reducer in clear water could reach 74.93%, and in standard brine could reach 73.78%. Molecular dynamics simulations reveal the interaction of the polymer emulsion, and the release mechanism is analyzed.