Intense interest has been shown in the development of “smart nanofluids” because they can dramatically change their flow properties in complex fluid systems. We introduce a robust and straightforward approach to develop a smart nanofluid system, in which associative silica nanoparticles (ASNPs) were incorporated to regulate their flow properties in rock pores. ASNPs were synthesized by covalently coating a hydrophobically associative hygroscopic zwitterionic poly­[2-methacryloyloxyethyl phosphorylcholine (MPC)-co-divinylbenzene (DVB)] shell layer on 20 nm sized silica nanoparticles (NPs) by surface-mediated living radical polymerization. The essence of our approach is to copolymerize DVB, which endows the polymer shell of ASNPs with a weak long-range hydrophobic attraction. This leads to the favorable formation of a wedge film as a result of structural disjoining pressure. This wedge film made the oil adsorbed on the rock surface more dewettable, thus enhancing the efficiency of oil recovery. As a result of this unique behavior, the ASNP nanofluid developed in this study remarkably improved the fluidity of complex oil fluids; ∼5 vol % oil recovery enhancement and ∼0.3 psi pressure reduction were also achieved in comparison to neat nanofluid controls.

This study reports a Pickering emulsion flooding system, in which the oil–water interface is structurally stabilized by a complex colloidal layer consisting of silica nanoparticles, dodecyltrimethylammonium bromide (DTAB), and poly­(4-styrenesulfonic acid-co-maleic acid) sodium salt (PSS-co-MA). The colloidal layer was generated by adsorption of PSS-co-MA on the silica nanoparticles as a result of the van der Waals attraction and by adsorption of DTAB onto the PSS-co-MA layer as a result of the electrostatic attraction, thus providing the mechanically robust, stable interface. To demonstrate a practical applicability to the enhanced oil recovery, the complex colloidal dispersion fluid was injected into the Berea sandstone for a core flooding experiment. The result revealed that the colloidal dispersion significantly increased the oil recovery by ∼4% compared to the case of flooding water. This means that the emulsion drops in situ produced in the core could readily flow through the rock pores. We attribute this to the fact that the oil–water interface made with the complex colloidal phase not only increased the structural stability of the emulsion drops but also provided them deformability without any drop breakup or coalescence.

No abstract

No abstract

Cellulose fibrils, unique plant-derived semicrystalline nanomaterials with exceptional mechanical properties, have significant potential for rheology modification of complex fluids due to their ability to form a physically associated semiflexible fibrillary network. Here, we report new associative cellulose nanocrystals (ACNCs) with stress-responsive rheological behaviors in an aqueous solution. The surface-mediated living radical polymerization was employed to graft poly(stearyl methacrylate-co-2-methacryloxyethyl phosphorylcholine) brushes onto the nanofibrils, and then 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation was conducted to produce nanoscale ACNCs in the aqueous solution. The ACNCs displayed interfibril association driven by the hydrophobic interaction that resulted in the formation of a nanofibrillar crystalline gel phase. We observed that the viscosity of the ACNC fluid showed reversible shear thinning and temperature-induced thickening in response to applied shear stress and thermal shock. Moreover, thanks to generation of a mechanically robust nanofibrillar crystalline gel network, the ACNC suspension showed extraordinary stability to changes in salinity and pH. These results highlighted that the interfibril hydrophobic association of ACNCs was vital and played an essential role in regulation of stimuli-responsive sol-gel transitions.