ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Positron annihilation spectroscopy as a tool for examining a microstructure in differently thick polymeric sample

Katarína Cifraničová, Dávid P. Královič, Ondrej Šauša, and Helena Švajdlenková

Department of Nuclear Chemistry, Faculty of Natural Science, Comenius University in Bratislava, Bratislava, Slovak Republic

E-mail: katarina.cifranicova@uniba.sk

Received: 3 October 2022  Accepted: 22 March 2023

Abstract:

The photopolymerization process of a liquid mixture of monomers (2 M) and photoinitiator (PI) takes place under specific and controllable conditions. UV light-induced photopolymerization of mixture leads to the reactions of a photoinitiator with a monomer to produce a polymer. The microstructural properties of the materials were measured by positron annihilation spectroscopy. The lifetime of orthopositronium (o-Ps) (τ_o–Ps) obtained from the complex annihilation time spectrum monitors the influence of various chemical and physical parameters on the change of local free volume. The structural changes of the mixture of two dimethacrylates (2 M) with a small amount of photoinitiator (PI) were investigated during periodically illumination of two differently thick samples by positron annihilation lifetime spectroscopy (PALS). Samples were cured for a specific time, when a constant lifetime of o-Ps reflecting free volume was reached. It was found that the 2 mm sample (2 M-2 mm) cross-links faster and reaches a more reduced local free volume in the structure compared to the 5 mm sample (2 M-5 mm). Moreover, the near-infrared (NIR) spectra and bulk density of both cured samples revealed the molecular and micro-structural relations for two different thick samples.

Keywords: Dimethacrylate; Orthopositronium lifetime; Photopolymerization; Free volume; NIR spectroscopy

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-023-02797-1

Chemical Papers 77 (12) 7277–7282 (2023)