Solvent-Engineered Conformational Ordering of Phosphonic Acid SAMs on ZnO for Thermally Robust Biomimetic Interfaces

Self-assembled monolayers (SAMs) have emerged as versatile platforms for tailoring nanomaterial surfaces while emulating the ordered architectures and interfacial properties of biological systems. However, the solvent-mediated pathways governing molecular ordering and interfacial stability during SAM formation remain poorly understood, hindering the fabrication of robust biomimetic surfaces for sustained performance. Here, we fabricated octylphosphonic acid (OPA) SAMs on ZnO using solvent systems with varied polarity and molecular size and characterized their molecular ordering and surface coverage by FT-IR spectroscopy, then assessed their thermal stability by both FT-IR spectroscopy and water contact angle measurements after thermal treatment. Complemented by molecular dynamics simulations using a fine-tuned machine-learning interatomic potential (MLIP) and time-averaged mean square displacement (TAMSD) analysis, we elucidated OPA diffusion behavior in different solvents and found that the observed trends are consistent with a combined influence of diffusion and solubility on the quality, density, and thermal stability of the SAMs, providing experimental insights into solvent-engineered self-assembly, with the simulations offering complementary bulk-phase information. This solvent-engineered strategy offers a versatile platform for durable biointerfaces and advances the understanding of solvent-regulated self-assembly for engineering robust biomimetic interfaces.