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.
Highlights
Progress in the modern biomedicine is governed by successful development of novel materials effectively exploring nanostructural atomistic and sub-atomistic length scales
Under such analysis, the long-lived component is attributed to o-Ps annihilation in free-volume holes, the second component with intermediate lifetime τ2 is due to free positron annihilation in interfacial free volumes or other defect states in solid phase, and the shortest-lived component is ascribed to p-Ps selfannihilation overlapped with reduced positron annihilation from defect-free bulk states [1, 2]
Our previous results with some acrylic-type dental resin composite (DRC) [16] show that even under incomplete decomposition of positron annihilation lifetime (PAL) spectra because of some measuring instabilities, in part, in a vicinity of second component originated from free positron annihilation, the best goodness of PAL spectra reconstruction is achieved under constraint-free x3-fitting
Summary
Progress in the modern biomedicine is governed by successful development of novel materials effectively exploring nanostructural atomistic and sub-atomistic length scales. That is why high-informative characterization probes are needed to engineer such biomaterials suitable for advanced medical practice. One of the most promising probes is grounded on analytical space-time continuum determination for electron interaction with its antiparticle (positron), this instrumentation tool being termed as positron annihilation lifetime (PAL) spectroscopy [1,2,3]. The methodological possibilities of PAL technique will be analyzed and examined in application to light-cured acrylic-type dental resin composite (DRC) Charisma®
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