Pickering Emulsions and Viscoelastic Solutions Constructed by a Rosin-Based CO₂-Responsive Surfactant

Designing stimulus-switch viscoelastic solutions and Pickering emulsions with reversible CO₂-responsive behavior remains a challenge. A rosin-based CO₂-responsive surfactant, N-cetyl-maleimidepimaric acid N,N-dimethylenediamide (C₁₆MPAN), was synthesized and used to prepare CO₂-triggered viscoelastic solutions and Pickering emulsions. This surfactant exhibited excellent CO₂-responsive performance in water and formed a viscoelastic solution. This viscoelastic system was investigated by dynamic light scattering (DLS), rheology, and cryogenic transmission electron microscopy (Cory-TEM). The shear viscosity of the system increased by 3-4 orders of magnitude after bubbling with CO₂ and a large number of elongated, flexible, tubular wormlike micelles were observed. Further, Pickering emulsions were prepared by C₁₆MPAN⁺ synergistically with cellulose nanocrystals (CNCs), whose stability and switchability were investigated via adsorption isotherm, droplet size, contact angle, and macroscopic photographs. C₁₆MPAN⁺ was adsorbed with CNCs to form mechanical barriers at the oil-water interface, making the emulsion stable for at least three months, and desorption from CNCs enabled emulsion breaking. The cycle could be switched reversibly multiple times and the particle size distribution of emulsion was basically the same. This work enriches the application of biomass resources in intelligent responsive materials.