Stabilization mechanisms at oil–water interfaces in high internal phase emulsified asphalt: Effects of polymers on molecular arrangement and hydrogen bonding networks

High internal phase emulsified asphalt (HIPEA) offers energy-saving and environmental benefits for road engineering, but its adoption is hindered by poor storage stability due to dense droplet packing. This study integrates experimental characterization and molecular dynamics (MD) simulations to elucidate stabilization mechanisms of polyoxyethylene (EO) chain polymers with varying degrees of polymerization (DP = 22, 45, 55) in HIPEA systems. Fluorescence microscopy reveals that DP55 maintains uniform droplet distributions (10–40 μm) over 28-day storage, with average particle size increasing from 2.57 ± 0.12 to 5.42 ± 0.31 μm, markedly superior to DP22 (4.20 ± 0.18 to 6.70 ± 0.42 μm with phase separation). Centrifugal testing confirms exceptional stability (99.41±0.08%) for DP55 systems. MD simulations uncover synergistic stabilization mechanisms: (1) DP55 and STAC emulsifier construct a robust bilayer interfacial architecture (32.45 Å thickness, 162% enhancement versus STAC alone); (2) competitive water molecule attraction by EO segments reduces chloride ion hydrogen bonding by ∼45% while establishing stable polymer-water networks; (3) free volume fraction (FVF) decreases by 44.7%, disrupting interconnected water channels into isolated nanocavities that prevent droplet coalescence; (4) increasing DP elevates oil–water interfacial energy (47.3%), van der Waals interactions (38.6%), and electrostatic contributions (40.9%), creating dual reinforcement of interfacial barriers. These findings demonstrate that long-chain polymers achieve sustained storage stability through concurrent interfacial reconstruction, hydrogen bond network modulation, free volume optimization, and interfacial energy amplification. This work provides fundamental insights and practical strategies for developing advanced emulsified asphalt formulations with enhanced long-term performance.