title: Free Volume Structure of Acrylic-Type Dental Nanocomposites Tested with Annihilating Positrons.
abstract: Positron annihilation spectroscopy in lifetime measuring mode exploring conventional fast-fast coincidence ORTEC system is employed to characterize free volume structure of commercially available acrylic-type dental restorative composite Charisma® (Heraeus Kulzer GmbH, Germany). The measured lifetime spectra for uncured and light-cured composites are reconstructed from unconstrained x3-term fitting and semi-empirical model exploring x3-x2-coupling decomposition algorithm. The governing channel of positron annihilation in the composites studied is ascribed to mixed positron-Ps trapping, where Ps decaying in the third component is caused entirely by input from free-volume holes in polymer matrix, while the second component is defined by free positron trapping in interfacial free-volume holes between filler nanoparticles and surrounded polymer matrix. Microstructure scenario of the photopolymerization shrinkage includes cross-linking of structural chains in polymer matrix followed by conversion of bound positron-electron (positronium) traps in positron-trapping interfacial free-volume voids in a vicinity of agglomerated filler nanoparticles.
authors.affiliation: Danylo Halytsky Lviv National Medical University, 69, Pekarska str., Lviv, 79010, Ukraine. boyko.olha@gmail.com.
authors.forename: Olha
authors.initials: O
authors.lastname: Shpotyuk
authors.affiliation: Opole University of Technology, 75, Ozimska str., 45370, Opole, Poland.
authors.forename: Adam
authors.initials: A
authors.lastname: Ingram
authors.affiliation: Jan Dlugosz University in Czestochowa, 13/15, Armii Krajowej str., 42200, Czestochowa, Poland.|Vlokh Institute of Physical Optics, 23, Dragomanov str., Lviv, 79005, Ukraine.
authors.forename: Oleh
authors.initials: O
authors.lastname: Shpotyuk
keywords: Dental resin composites; Light curing; Positron annihilation; Positronium; Trapping