Structure-directed self-assembly of alkyl-aryl-ethylene oxide amphiphiles

Area of Science:

• Polymer Science
• Materials Science
• Nanotechnology

Background:

• Polyethylene/poly(ethylene oxide) diblock oligomers exhibit strong phase separation and lamellar crystallization.
• Controlling the nanoscale structure of block copolymers is crucial for advanced material properties.

Purpose of the Study:

• To synthesize and characterize novel polyethylene/poly(ethylene oxide) diblock oligomers with a benzene ring at the junction.
• To investigate the solid-state structures and self-assembly behavior of these modified block copolymers.

Main Methods:

• Synthesis of exact length polyethylene/poly(ethylene oxide) diblock oligomers with varying alkyl chain lengths (C14-C20) and poly(ethylene oxide) chain lengths (0-7 repeat units).
• Solid-state structure determination using Powder X-ray Diffraction (PXRD).
• Thermal analysis via Scanning Calorimetry (DSC) and vibrational spectroscopy.

Main Results:

• Phase separation into lamellar structures with benzene rings aligned at the interface between polyethylene and poly(ethylene oxide) blocks.
• Observation of a transformation from bilayer to interdigitated motifs upon annealing for certain compounds.
• Independent crystallization of both alkyl and poly(ethylene oxide) blocks, with alkyl chains crystallizing first upon cooling.

Conclusions:

• The incorporation of a benzene ring at the junction effectively directs the self-assembly into ordered lamellar structures.
• The crystallization of both blocks facilitates the alignment of the aromatic rings within the nanostructure.
• This approach provides a general strategy for aligning polar molecules in nanometre-scale materials.