Magnetic Sol-Gel Derived Poly(oxyethylene)- Siloxane Nanohybrids
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Magnetic Sol-Gel Derived Poly(oxyethylene)- Siloxane Nanohybrids.
V.S. Amaral, L.D. Carlos, N.J.O. Silva Departamento de Física and CICECO, Universidade de Aveiro, Aveiro, PORTUGAL V. de Zea Bermudez Departamento de Química, Univ. de Trás-os Montes e Alto Douro Vila Real, PORTUGAL K. Dahmouche, C.V. Santilli Instituto de Química/UNESP, Araraquara-SP, BRAZIL A.F. Craievich Instituto de Física/USP, Sao Paulo-SP, BRAZIL F. Palacio Instituto de Ciencia de Materiales de Aragón, CSIC - Univ. de Zaragoza, Zaragoza, SPAIN.
ABSTRACT The magnetic and structural properties of sol-gel derived organic/inorganic nanocomposites doped with Fe(II), Fe(III), Nd(III) and Eu (III) ions are discussed. These hybrids consist of poly(oxyethylene)-based chains grafted onto siloxane nanodomains by urea cross-linkages. Small angle X-ray scattering data show the presence of spatial correlations of siloxane domains embedded in the polymer matrix. The magnetic properties of rare-earth doped samples are determined by single ion crystal-field-splitted levels (Eu3+ J=0; Nd3+ J=9/2) and the small thermal irreversibility is mainly associated to structural effects. Fe2+-doped samples behave as simple paramagnet with residual antiferromagnetic interactions. Fe3+-doped hybrids are much more complex, with magnetic hysterisis, exchange anisotropy and thermal irreversibility at low temperatures. Néel temperatures increase up to 14K for the highest (~5.5%) Fe3+ mass concentration. INTRODUCTION
Organic-inorganic sol-gel derived hybrids constitute nowadays a versatile way to tailor multi-functional advanced materials for optics, electronics, mechanics and biology [1]. One of such materials (di-ureasils) are siloxane-based networks to which poly(oxyethylene)-based chains of variable length are grafted by urea cross-linkages, for which a stable and efficient white light emission has been demonstrated. The incorporation of lanthanides (such as Eu3+ and Nd3+ ) into the di-ureasils reaches a finer tuning of the emission color [2]. The local structure of the undoped and Eu3+-based nanocomposites was modeled recently using Small angle X-ray scattering (SAXS), photoluminescence, mid-infrared and differential scanning calorimetry data [3]. The undoped matrix can be described as groups of spatially correlated siloxane rich clusters, with gyration radius of 5±0.5Å (and average inter-distance of 40±2Å), embedded in the polymeric media. For the Eu3+-doped-nanocomposites the ion-first coordination shell varies drastically with the ion concentration. For compositions 400 ≥ n ≥ 20 in U(2000)nEu(CF3SO3)3, the ions interact mainly with the carbonyl-type oxygens of the urea cross-links located at the organic/inorganic Q6.22.1 Downloaded from https://www.cambridge.org/core. Columbia University Libraries, on 22 Aug 2017 at 20:39:51, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-726-Q6.22
interfaces. For lower n, all the available urea groups are saturated and the coordination at the polymer ether-o
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