Spherical Micelles with Nonspherical Cores: Effect of Chain Packing on the Micellar Shape.

ABSTRACT: Self-assembly of amphiphilic polymers into micelles is an archetypical example of a "self-confined" system due to the formation of micellar cores with dimensions of a few nanometers. In this work, we investigate the chain packing and resulting shape of C _n -PEOx micelles with semicrystalline cores using small/wide-angle X-ray scattering (SAXS/WAXS), contrast-variation small-angle neutron scattering (SANS), and nuclear magnetic resonance spectroscopy (NMR). Interestingly, the n-alkyl chains adopt a rotator-like conformation and pack into prolate ellipses (axial ratio ? ? 0.5) in the "crystalline" region and abruptly arrange into a more spheroidal shape (? ? 0.7) above the melting point. We attribute the distorted spherical shape above the melting point to thermal fluctuations and intrinsic rigidity of the n-alkyl blocks. We also find evidence for a thin dehydrated PEO layer (?1 nm) close to the micellar core. The results provide substantial insight into the interplay between crystallinity and molecular packing in confinement and the resulting overall micellar shape.

SUBMITTER: Konig N 

PROVIDER: S-EPMC7735752 | biostudies-literature | 2020 Dec

REPOSITORIES: biostudies-literature