resumo
Fourier transform mid-IR and Raman spectroscopies were extensively used to examine cation/polymer and cation/cross-link interactions, as well as hydrogen bonding, in Eu3+-doped sol-gel derived organic/inorganic materials (monourethanesils). The hybrid framework of these xerogels contains short methyl end capped polyether segments covalently bonded to a siliceous backbone through urethane groups. The cations were incorporated as europium triflate, Eu(CF3SO3)(3). Samples with compositions infinity > n greater than or equal to 10 (where n indicates the ratio of (OCH2CH2) moieties per lanthanide ion) were investigated. The spectral data obtained provided unequivocal evidence that the cations coordinate exclusively to the urethane carbonyl oxygen atoms in compounds with 400 greater than or equal to n greater than or equal to 50. The participation of the ether oxygen atoms of the polymer chains in the Eu3+ complexation process is initiated at n = 30. The presence of a crystalline phase was detected at n = 10. The variation of the glass transition temperature of the monourethanesils studied with salt concentration is in perfect agreement with these claims. The beginning of the Eu3+-polyether interaction is accompanied by a breakdown of the hydrogen bonded aggregates of the matrix, as confirmed by photoluminescence spectroscopy.
palavras-chave
ORGANICALLY MODIFIED SILICATES; SHORT POLYETHER CHAINS; FULL-COLOR PHOSPHORS; ALKALI-METAL SALTS; POLY(ETHYLENE OXIDE); POLYMER ELECTROLYTES; RAMAN-SPECTRA; SILICA/POLY(ETHYLENE OXIDE); SEGMENTED POLYURETHANE; INFRARED TEMPERATURE
categoria
Chemistry; Physics
autores
Bermudez, VD; Ostrovskii, D; Goncalves, MC; Carlos, LD; Ferreira, RAS; REis, L; Jacobsson, P
nossos autores
Luís Carlos
Professor Catedrático