Regioisomeric Effect on the Stereoscopic Conformational Transition of Polymer Monolayers at the Aqueous Interface

Amphiphilic polymers form molecular monolayers at aqueous interfaces, stabilizing the discontinuity between two phases and acting as macromolecular surfactants. These polymer monolayers exhibit superior mechanical stability compared to traditional surfactants, making them useful in various applications, including structured liquids, drug delivery, lung surfactant therapy, protein encapsulation, extraction separation, and templates for synthesis. Despite their significance, the molecular-level understanding of the structure of polymer monolayers and their relationship to their physical properties remain obscure. Thus, understanding their structural behavior is crucial for controlling interfaces and tailoring system properties. At the air–water interface, polymer chains adopt two-dimensional (2D) Gaussian coil conformations, scalable by 2D-conformational polymer scaling theory and a few parameters such as temperature, surface concentration, and surface pressure (Π). Beyond a critical Π, polymer chains transition to 3D conformations, a critical but understudied phenomenon. This study investigated regioisomeric effects on these stereoscopic transitions using the poly(vinylpyridine) (PVP) polymer family. Despite sharing solubility parameters, steric differences in nitrogen positioning within the pyridine ring significantly influence solvation and stereoscopic conformational transitions. Alloying these regioisomeric polymers further enables fine-tuning of monolayer transitions and mechanical properties, providing deeper insights into the design and control of interfacial polymer systems.