Structural and spatially resolved studies on the hardening of a commercial resin-modified glass-ionomer cement
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A commercial photopolymerizable resin-modified glass-ionomer (Fuji II LC) was studied using a variety of nuclear magnetic resonance (NMR) techniques. 1H and 19F stray-field imaging (STRAFI) enabled to follow the acid–base reaction kinetics in self-cured (SC) samples. Gelation and maturation processes with 25 min and 40 h average time constants, respectively, were distinguished. In self- & photo-cured (SPC) samples, two processes were also observed, which occurred with 2 s and 47 s average time constants. 1H, 27Al and 29Si magic angle spinning (MAS) NMR, 13C cross-polarization (CP)/MAS NMR and 27Al multiple quanta (MQ)MAS NMR spectroscopy were used to obtain structural information on the glass and cements that were either SC or SPC. The presence of methacrylate groups was identified in the solid component. Unreacted hydroxyl ethylmethacrylate (HEMA) was detected in self-cured cement. 27Al data showed that approximately 28% and 20% of Al is leached out from glass particles in SC and SPC samples, respectively. The upfield shift detected in 29Si MAS NMR spectra of the cements is consistent with a decrease in the number of Al species in the second coordination sphere of the silicon structures. Scanning electron microscopy (SEM) showed existence of 3D shrinkage of the cement matrix in photo-cured cements.
KeywordsNuclear Magnetic Resonance Nuclear Magnetic Resonance Spectrum HEMA Magic Angle Spin Glass Particle
RP gratefully acknowledge the Ph.D. research grant (BD/21572/99) from the Portuguese Foundation for Science and Technology. Part of this work was performed on the frame of the research project POCTI/33193/FCB/2000 (FCT/FEDER). GC Europe is acknowledged for kindly supplying Fuji II LC.
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