Unlike in the bulk, the hydrogen bond network of water is interrupted at water interfaces, and thus chemical reaction occurs at the water interface in a different manner than in the bulk, owning to, e.g., the possibility of templating molecules. On-water chemistry has generated highly crystalline, functional 2D materials through surfactant-monolayer-assisted interfacial synthesis (SMAIS). Yet, the details of the on-water reaction mechanism have remained unresolved. Here, by tracking the quasi-2D polyaniline film generation process using in situ surface-specific vibrational technique, we clarify how the polymerization reaction occurs at the water surfaces during SMAIS. We identify an aniline derivative with a positively charged terminal =NH₂ group as a key reaction intermediate species for highly crystalline film formation. A comparison of differently designed water interfaces reveals that intermediate species can be accumulated and ordered at the interface by the negatively charged surfactant headgroups, prompting highly crystalline, conductive polyaniline film formation. These results demonstrate the importance of interfacial electric fields and electrostatic interactions for controlled on-water chemistry.

与本体不同，水的氢键网络在水界面处中断，因此化学反应在水界面以与本体不同的方式发生，这归因于例如模板化分子的可能性。水上化学通过表面活性剂单层辅助界面合成 (SMAIS) 生成了高度结晶的功能性二维材料。然而，水上反应机理的细节仍未得到解决。在这里，通过使用原位表面特定振动技术跟踪准二维聚苯胺膜生成过程，我们阐明了 SMAIS 期间聚合反应如何在水表面发生。我们确定了一种带有正电荷末端的苯胺衍生物 =NH ₂基团作为高结晶膜形成的关键反应中间体。不同设计的水界面的比较表明，中间物质可以通过带负电荷的表面活性剂头基在界面处积累和排序，从而促进高度结晶的导电聚苯胺膜的形成。这些结果证明了界面电场和静电相互作用对于受控水上化学的重要性。