Self-Assembly Mechanism of pH-Responsive Wormlike Micelles and Their Structure-Property Correlation with Macroscopic...

Stimuli-responsive wormlike micelles (WLMs) are pivotal intelligent soft materials with tunable macroscopic rheology, yet the cross-scale correlation between molecular interactions and micellar assembly remains elusive. Herein, we investigate a pH-responsive ternary system of N,N,N',N'-tetramethyl-1,3-propanediamine (TMPDA), sodium dodecyl sulfate (SDS), and 3-sulfopropyl tetradecyldimethyl betaine (TDAPS). A synergistic approach combining rheological measurements, Cryo-TEM/Cryo-SEM/AFM imaging, density functional theory (DFT) calculations, and dissipative particle dynamics (DPD) simulations was employed to decipher its self-assembly mechanism and structure-property relationship. At alkaline pH (11.39), unprotonated TMPDA stabilizes spherical micelles by localization in the hydrophobic core. Acidification triggers sequential protonation of TMPDA (TMPDA-1H⁺/2H⁺), which migrates to the micelle-water interface and neutralizes anionic headgroup repulsion via electrostatic interactions (>70% of total interaction energy), reducing interfacial curvature and driving a spherical-to-wormlike micellar transition. The system exhibits exceptional viscoelasticity with a maximum zero-shear viscosity of 6.99 × 10⁵ mPa·s over pH 6.07-9.83, accompanied by shear-thinning and quasi-Maxwellian relaxation behavior. This multiscale study establishes quantitative correlations between protonation state, intermolecular forces, micellar architecture, and bulk rheology, providing fundamental insights for the rational design of high-performance responsive soft materials.