On the supramacromolecular structure of core–shell amphiphilic macromolecules derived from hyperbranched polyethyleneimine

Abstract

The supramacromolecular structure of core–shell amphiphilic macromolecules (CAMs) with hyperbranched polyethyleneimine (HPEI) cores and fatty acid chain shells (HPEI-Cn) for different chain lengths was investigated both, in colloidal suspension, solid phase and at the air–water interface using Small Angle X-ray Scattering (SAXS), Wide Angle X-ray Scattering (WAXS), X-ray Reflectometry (XRR) and Langmuir isotherms. At low temperatures colloidal toluene suspensions of the HPEI-Cn polymers form, as evidenced by peaks arising in the structure factor of the system showing mean particle-to-particle distances correlated with the length of the aliphatic chains forming the shells of HPEI-Cn unimicelles. The CAM sizes as found from the SAXS experiments also display a clear dependence on shell thickness suggesting that the aliphatic chains adopt a brush-like configuration. After solvent extraction, HPEI-Cn adopts ordered structures with hexagonal packing of the aliphatic chains. Submitted to lateral pressure Π at the air–water interface, HPEI-Cn undergoes a disorder–order transition with increasing transition pressure for increasing chain lengths. The CAMs show different behaviors in-plane and out-of-plane. While out-of-plane the aliphatic chains behave as a brush remaining almost fully unfolded, whereas parallel to the air–water interface the chains fold down in a mushroom way with increasing lateral pressure Π.