Confinement and cross-linking of 1,2-polybutadiene in 2D at the air-water interface

Langmuir monolayers of 1,2-polybutadiene (PB) were investigated by coupling thermodynamical measurements, Brewster Angle Microscopy (BAM) observations and Sum-Frequency Generation (SFG) spectroscopy. A homogeneous and stable monolayer is formed 1.5 hours after PB spreading provided that both light and oxygen are present. This was attributed to a slight oxidation of the PB at the air-water interface. The cross-linking of PB under UV photoirradiation was then studied. SFG spectroscopy demonstrates the in-situ formation of a 2D network. From surface pressure-area characterizations and BAM experiments, the cross-linked PB monolayer appears significantly denser and more rigid than the non-irradiated monolayer. Atomic Force Microscopy images reveal an increase by a factor of three in the root mean square roughness of the irradiated monolayers compared with the non-irradiated ones.