Dynamics of Polymerization and Gelation in Epoxy Nanocomposites via X‑ray Photon Correlation Spectroscopy

• Published in: Macromolecules Vol. 54; no. 13; pp. 6575 - 6584
• Main Authors: Trigg, Edward B, Wiegart, Lutz, Fluerasu, Andrei, Koerner, Hilmar
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 13.07.2021
• Subjects: amines; epoxy; fluid dynamics; gelation; MATERIALS SCIENCE; nanocomposite; organic polymers; thermoset; viscosity; x-ray photon correlation spectroscopy
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.1c00727

The details of the curing process of epoxy resins are notoriously difficult to ascertain, hampering polymer matrix composite manufacturing. Here, the curing of a series of six epoxy resins containing dilute spherical nanoparticles was investigated via X-ray photon correlation spectroscopy (XPCS). The resin formulation was varied to achieve a range of crosslink densities and topologies. Prior to gelation, the viscosities obtained from XPCS agreed with bulk rheology. A clear dynamic transition was detected in all samples, where the q-scaling changes from approximately q 2.2 to q 1, indicating a transition from sub-diffusive to ballistic-like nanoparticle motion. For the samples with a high crosslink density, this change was abrupt and coincided with gelation, and there was no evidence of crosslink heterogeneity. Chain entanglement played a role in the transition for samples with lower crosslink density. This work reveals the potential of XPCS to deliver new quantitative insights into the curing process of thermosetting resins.