# Divining the Shape of Nascent Polymer Crystal Nuclei

## TL;DR

This paper reveals that nascent polymer crystal nuclei are anisotropic and not spherical or cylindrical, emphasizing the importance of post-critical transitions and accurate modeling for understanding polymer crystallization.

## Contribution

It provides the first quantitative analysis showing the true anisotropic shape of polymer nuclei and highlights the need for new models to accurately predict nucleation.

## Key findings

- Polymer nuclei are anisotropic, not spherical or cylindrical.
- High symmetry geometries are thermodynamically unfavorable.
- Inaccurate nucleation models can cause large prediction errors.

## Abstract

We demonstrate that nascent polymer crystals (i.e., nuclei) are anisotropic entities, with neither spherical nor cylindrical geometry, in contrast to previous assumptions. In fact, cylindrical, spherical, and other high symmetry geometries are thermodynamically unfavorable. Moreover, post-critical transitions are necessary to achieve the lamellae that ultimately arise during the crystallization of semicrystalline polymers. We also highlight how inaccurate treatments of polymer nucleation can lead to substantial errors (e.g., orders of magnitude discrepancies in predicted nucleation rates). These insights are based on quantitative analysis of over four million crystal clusters from the crystallization of prototypical entangled polyethylene melts. New comprehensive bottom-up models are needed to capture polymer nucleation.