Vertically Heterogeneous 2D Semi-Interpenetrating Networks Based on Cellulose Acetate and Cross-Linked Polybutadiene

Area of Science:

• Polymer Science
• Materials Science
• Surface Chemistry

Background:

• Semi-interpenetrating polymer networks (IPNs) offer tunable properties.
• Controlling polymer blend morphology at interfaces is crucial for advanced materials.
• Polybutadiene (PB) and cellulose acetate (CA) are common polymers with distinct properties.

Purpose of the Study:

• To investigate the feasibility of forming 2D CA/PB semi-IPNs at the air-water interface via UV-induced PB cross-linking.
• To characterize the thermodynamic properties and morphology of these 2D blends.
• To understand the influence of polymer-polymer and polymer-environment interactions on the resulting network structure.

Main Methods:

• Langmuir film formation and compression.
• UV irradiation for polybutadiene cross-linking.
• Brewster angle microscopy (BAM) for mesoscopic morphology.
• In situ sum-frequency generation (SFG) spectroscopy for network formation.
• In situ neutron reflectometry (NR) for vertical structure analysis.

Main Results:

• CA/PB films exhibited contraction upon PB cross-linking, independent of composition.
• PB network formation was confirmed by SFG.
• Mesoscopic morphology remained laterally homogeneous, with no significant changes observed by BAM.
• NR revealed film thickening and partial expulsion of hydrophobic PB towards the air interface, especially in PB-rich films.
• PB-rich films transitioned from vertically homogeneous to inhomogeneous structures.

Conclusions:

• Feasible synthesis of 2D CA/PB semi-IPNs at the air-water interface using UV-initiated PB cross-linking.
• The morphology of these 2D networks is significantly influenced by polymer-polymer and polymer-environment interactions.
• Controlled vertical structuring, including phase separation at the air interface, can be achieved.