Nanocellulose-g-poly(2-dimethylamino)ethyl methacrylate foam stabilizer with temperature and pH responsiveness

Abstract

Stimulus-responsive foam stabilizers are highly desirable for enhanced oil recovery (EOR) applications, yet the development of renewable, dual-responsive systems with controllable performance remains challenging. Herein, we report a series of cellulose nanocrystal-g-poly(2-(dimethylamino)ethyl methacrylate) (CNC- g -PDMAEMA) copolymers synthesized via a “grafting-from” free radical polymerization. This copolymer exhibits intrinsic dual responsiveness to pH and temperature; reversible CO₂-triggered foam regulation is an indirect effect originating from CO₂-mediated pH shift instead of an independent stimulus. The grafting density and molecular weight of PDMAEMA side chains increase monotonically with the feeding ratio, as confirmed by GPC, XPS, and TGA. The copolymers exhibit tunable surface activity, with the lowest surface tension achieved at pH = 5 due to full protonation of tertiary amine groups. The lower critical solution temperature decreases with increasing pH and PDMAEMA content, enabling precise thermal switching. Foam stability tests demonstrate that higher grafting density ( f w ≥ 8.0 wt%) and polymer concentration yield finer droplet sizes (200–300 nm), lower creaming index (only 30–40% for high density after 80 h), far lower than pristine CNC (80%), and excellent high-temperature performance (up to 90 °C). The CNC- g -PDMAEMA/SDS hybrid system maintains outstanding foaming height (≈ 160 mm) across a wide pH range (5 ~ 9) and shows reversible CO 2 /N 2 adjustable ability in ζ-potential (≈ 30 mV amplitude). This work provides a green, renewable, and intelligent foam stabilizer platform with dual stimuli responsiveness, broad operational windows, and on-demand foam control for EOR foam flooding.