Annealing of single lamella nanoparticles of polyethylene

TL;DR

This study investigates how thermal annealing affects the size and structure of single lamella polyethylene nanoparticles, revealing lamella thickening and recrystallization behavior through advanced microscopy and scattering techniques.

Contribution

It demonstrates that annealing doubles the crystalline lamella thickness and establishes a linear relationship between lamella thickness and temperature in polyethylene nanoparticles.

Findings

Lamella thickness doubles after annealing at 125°C.

Inverse lamella thickness increases linearly with temperature.

Nanoparticles serve as ideal models for equilibrium polymer crystals.

Abstract

We study the change of the size and structure of freely suspended single lamella nanoparticles of polyethylene during thermal annealing in aqueous solutions. Using small-angle x-ray scattering and cryogenic transmission electron microscopy, it is shown that a doubling of the crystalline lamella sandwiched between two amorphous polymer layers is obtained by annealing the nanoparticles at 125 C. This thickening of the crystalline lamella can be understood in terms of an unlooping of polymer chains within a single nanoparticle. In addition a variation of the annealing temperature from 90 C to 115 C demonstrates that the inverse of the crystalline lamellar thickness increases linearly with the annealing temperatures leading to a recrystallization line in a Gibbs-Thomson graph. Since the nanoparticles consist of about only eight polymer chains, they can be considered as a ideal candidates for the experimental realization of equilibrium polymer crystals.