Humic acids (HA) are ubiquitous in surface waters, leading to significant fouling challenges. While zwitterion-like and zwitterionic surfaces have emerged as promising candidates for antifouling, a quantitative understanding of molecular interaction mechanism, particularly at the nanoscale, still remains elusive. In this work, the intermolecular forces between HA and charged, zwitterion-like or zwitterionic monolayers in aqueous environments were quantified using atomic force microscope. Compared to cationic MTAC ([2-(methacryloyloxy)ethyl]trimethylammonium chloride), which exhibited an adhesion energy of ∼1.342 mJ/m with HA due to the synergistic effect of electrostatic attraction and possible cation-π interaction, anionic SPMA (3-sulfopropyl methacrylate) showed a weaker adhesion energy (∼0.258 mJ/m) attributed to the electrostatic repulsion. Zwitterion-like MTAC/SPMA mixture, driven by electrostatic attraction between opposite charges, formed a hydration layer that prevented the interaction with HA, thereby considerably reducing adhesion energy to ∼0.123 mJ/m. In contrast, zwitterionic MPC (2-methacryloyloxyethyl phosphorylcholine) and DMAPS ([2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide) displayed ultralow adhesion energy (0.06–0.07 mJ/m) with HA, arising from their strong dipole moments which could induce a tight hydration layer that effectively inhibited HA fouling. The pH-mediated electrostatic interaction resulted in the increased adhesion energy for MTAC but decreased adhesion energy for SPMA with elevated pH, while the adhesion energy for zwitterion-like and zwitterionic surfaces was independent of environmental pH. Density functional theory (DFT) simulation confirmed the strong binding capability of MPC and DMAPS with water molecules (∼–12 kcal mol). This work provides valuable insights into the molecular interaction mechanisms underlying humic-substance-fouling resistance of charged, zwitterion-like and zwitterionic materials at the nanoscale, shedding light on developing more effective strategy for HA antifouling in water treatment.

中文翻译：

---

带电、类两性离子和两性离子表面腐殖酸抗污染性的分子相互作用机制

腐植酸 (HA) 在地表水中普遍存在，导致严重的污垢挑战。虽然类两性离子和两性离子表面已成为防污的有希望的候选者，但对分子相互作用机制的定量理解，特别是在纳米尺度上，仍然难以捉摸。在这项工作中，使用原子力显微镜量化了水性环境中HA与带电、类两性离子或两性离子单层之间的分子间力。与阳离子 MTAC（[2-（甲基丙烯酰氧基）乙基]三甲基氯化铵）相比，由于静电引力和可能的阳离子 - π 相互作用的协同作用，其与 HA 的粘附能约为 1.342 mJ/m，阴离子 SPMA（3-由于静电斥力，甲基丙烯酸磺丙酯）表现出较弱的粘附能（~0.258 mJ/m）。类似两性离子的 MTAC/SPMA 混合物在相反电荷之间的静电引力的驱动下，形成了一个水化层，阻止了与 HA 的相互作用，从而大大降低了粘附能至 ∼0.123 mJ/m。相比之下，两性离子MPC（2-甲基丙烯酰氧基乙基磷酰胆碱）和DMAPS（[2-（甲基丙烯酰氧基）乙基]二甲基-（3-磺丙基）氢氧化铵）与HA表现出超低的粘附能（0.06-0.07 mJ/m），这是由于它们的强大的偶极矩可以诱导紧密的水化层，有效抑制HA结垢。 pH 介导的静电相互作用导致 MTAC 的粘附能增加，但随着 pH 值升高，SPMA 的粘附能降低，而类两性离子和两性离子表面的粘附能与环境 pH 无关。密度泛函理论（DFT）模拟证实了MPC和DMAPS与水分子（∼12 kcal mol）的强结合能力。这项工作为纳米尺度带电、类两性离子和两性离子材料的腐殖质抗污性的分子相互作用机制提供了有价值的见解，为开发更有效的水处理中HA防污策略提供了线索。