# Homogeneous Crystal Nucleation of Poly(3-hydroxybutyrate): Kinetics, Stability, and Cluster-Size Distribution

## TL;DR

This study examines how poly(3-hydroxybutyrate) forms crystals at high cooling rates, revealing insights into the speed and stability of crystal nucleation.

## Contribution

The paper presents new findings on the high thermal stability and sharp size distribution truncation of homogeneous P3HB crystal nuclei.

## Key findings

- Homogeneous nuclei form fastest at around 40 °C, with an onset time of about 1 second.
- Homogeneous nuclei remain stable up to about 100 K above their formation temperature.
- Nuclei numbers sharply decrease beyond 100 K and fully dissolve at 120 K above formation temperature.

## Abstract

The kinetics of homogeneous
crystal nucleation in poly­(3-hydroxybutyrate)
(P3HB) near its glass transition temperature (T
g) was investigated using fast scanning calorimetry (FSC) combined
with Tammann’s two-stage crystal nuclei development method.
Crystallization on cooling is fully suppressed at rates of a few K/s,
while the formation of crystal nuclei is inhibited only at higher
rates, above around 100 K/s. The formation of homogeneous nuclei is
fastest at around 40 °C (approximately 30 K above T
g), with an onset time of their formation of about 1 s,
which is two orders of magnitude shorter than the crystallization
onset time. To evaluate their thermal stability, a modified Tammann
nucleation experiment involving a temperature spike before the growth
stage was employed. The number of homogeneous nuclei of supercritical
size at the growth temperature formed under the given conditions remained
nearly constant upon heating up to about 100 K above their formation
temperature. Beyond this limit, the number of surviving nuclei drastically
decreased, and complete dissolution was observed at about 120 K above
the temperature of their formation. Besides the finding of an exceptionally
high stability of homogeneous crystal nuclei of P3HB, the sharp disappearance
of the number of nuclei within a narrow temperature range of 10–15
K suggests a sharp truncation of the nuclei-size distribution for
larger nuclei.