SYNTHESIS AND PROPERTIES OF Li3PO4 NANOCRYSTALS AND TRANSPARENT BULK Li3PO4/PMMA

Oleic acid capped Li3PO4 nanocrystals were synthesized in high boiling coordinating solvent. After modifying Li3PO4 nanocrystals with amphiphilic polymer poly(ethylene glycol)-oleate (PEG-oleate),Li3PO4/PMMA nanocomposites were obtained by means of in situ photopolymerization method. The X-ray diffraction (XRD) pattern indicates a pure orthorhombic structure of Li3PO4 (JCPDS:25-1030)with a space group of Pmn 21 (31). The boarding peaks suggest that the size of Li3PO3 nanocrystals is about 10 nm, which is also demonstrated by TEM. The XRD pattern of the nanocomposites shows obvious peaks of Li3PO4, which confirm the existence of Li3PO4 nanocrystals in PMMA matrix. The TEM analysis of ultramicrotome cut of composite demonstrates that Li3PO4 nanocrystals are dispersed in the PMMA matrix with about 50 nm agglomerations, which contributes to the decrease of transparence of the nanocomposites. The FTIR spectroscopy of as synthesized Li3PO4 nanocrystals shows absorbance bands at 2920 and 2850 cm(-1), which are attributed to C H symmetric and asymmetric stretches respectively. The weak absorption at 2955 cm(-1) results from the asymmetric stretching of the terminal C-H, group of the alkyl chain. The spectrum indicates the presence of an adsorbed carboxylate group with symmetric and asymmetric modes around 1634 and 1466 cm(-1), respectively. The FTIR spectroscopy indicates the Li3PO4 nano crystals are well capped by oleic acid. The UV-Vis transmission spectra show the nanocomposites still maintain the transmittance of 75% even with 14.6 wt% Li3PO4 content. The thermogravimetric analysis (TGA) reveals the thermal stabilities of nanocomposites are significantly improved after incorporating the Li3PO4, as evidenced by a retardation of degradation initiation of 95 K. The improvement in the thermal property of Li3PO4/PMMA nanocomposites could be attributed to the increase of surface area and the interaction between the surface of Li3PO4 nanocrystals and the polymer chains. All the results indicate that the as prepared Li3PO4/PMMA nanocomposites are promising materials for thermal neutron detection.