Synthesis of smart temperature responsive silicon quantum dots to stabilize Pickering emulsion for enhancing oil recovery

The silicon quantum dots (SiQDs) exhibited application potential in enhancing oil recovery (EOR) owing to their ultrasmall size and extremely large specific surface area. In the present study, the temperature responsive silicon quantum dots (SiQDsP8400) were synthesized by grafting poly (ethylene glycol)-block-poly (propylene glycol)-block-poly (ethylene glycol) (PEG-PPG-PEG, average molecular weight was 8400) via facile and mild one-pot method, which were characterized by Fourier transform infrared spectrometer, X-ray photoelectron spectroscopy, dynamic light scattering and transmission electron microscopy. Their interfacial activity was systematically evaluated by interfacial tension, interfacial expansion modulus and water contact angle measurements. The SiQDsP8400 more effectively reduced the n-octane/water interfacial tension to 5.12 mN/m at 70 ℃, while that at 30 ℃ was 16.67 mN/m. The higher temperature weakened the hydrogen-bond interaction between grafted PEG-PPG-PEG and water molecule to promote the spontaneous migration of SiQDsP8400 to the interface. Then the stability and temperature response of SiQDsP8400 stabilized Pickering emulsion were evaluated. The EI value of emulsions was 86.58% at 70 ℃ after standing for 120 h, and then its sharp decrease in cooling process suggested their smart demulsification. Subsequently, the molecular dynamics (MD) was employed to confirmed the amphiphilicity changing of the PEG-PPG-PEG groups with increasing temperatures. Finally, the SiQDsP8400 stabilized emulsions enhanced oil recovery by 14.93% at 70 ℃ in core flooding experiment, and the produced emulsion conduct demulsification/re-emulsification cycles for 3 times by changing temperature. The study raised a novel design method for temperature responsive silicon quantum dots in EOR application.