Nano-donuts from pH-dependent block restructuring in amphiphilic ABA triblock copolymer vesicles at the air-water interface

To understand the nature of polymers capable of forming multiply bound polymer chains (MBPCs) on surfaces, the Langmuir-Blodgett (LB) technique and Scanning Probe Microscopy (SPM) have been utilized to investigate surface morphology of the amphiphilic triblock copolymer (P2VP-b-dPS-b-P2VP, M _n = 125,000, dPS:P2VP = 1:1) at the air-water interface. The LB monolayer studies were carried out via π-A isotherms, compression-expansion cycles, kinetic stability, and nanoscopic surface morphological behavior. A strong pH effect was observed on the surface limiting area, stability, and morphology forming various 2-D aggregates. In particular, well-ordered interesting nanostructures (nano-donut formation) of the triblock copolymer aggregates depend on the effect of pH on the hydrophilic P2VP blocks, acting as a "cushion" at the air-water interface. In addition, equilibrium factors between the adsorption of the hydrophilic outer blocks (related to its solubility) and the entanglement of the hydrophobic dPS blocks during the evaporation of the spreading solution may play a critical role.