Gas-Phase Silicon Alkoxide Reactivity vs. Na-Alginate Droplets for Conjugation of Alginate and Sol-Gel Technologies |
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Authors: | Giovanni Carturan Renzo Campostrini Lorenzo Tognana Sara Boninsegna Roberto Dal Toso Renzo Dal Monte |
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Affiliation: | (1) Dipartimento di Ingegneria dei Materiali e Tecnologie Industriali, Università di Trento, Via Mesiano 77, Trento, 38050, Italy;(2) IRB srl, Via Lago di Tovel 7, Altavilla Vicentina, Vicenza, 36077, Italy |
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Abstract: | Solutions with Na-alginate concentrations ranging from 0.5 to 2.5% w/v are processed to prepare Ca-alginate beads using a nozzle ejector under constant He-flow. Beads were spherical in shape and their size distributions were determined; in all samples the average diameter fell in the 120–140 μm interval. Volumetric yields were found to be linearly dependent of the original Na-alginate load whereas the bead diameters were almost constant, according to a constant hindrance of Ca-alginate macromolecular units in the final Ca-alginate gel. The rheology of Na-alginate solutions was studied, with determination of intrinsic viscosity; experimental evidence of microsphere formation, even at the lowest Na-alginate concentrations, indicated that ejection processing changes the rheological parameters controlling bead formation in ordinary dropping processing. Gaseous silicon alkoxides – Si(OEt)4 and MeSi(OEt)3 – carried by a He flow were deposited on Na-alginate droplets during ejection. The process was studied by continuous mass spectrometry analysis before and after Na-alginate ejection during the 5-min treatment; in all cases results indicated a deposition yield of 58%. Traces of alcohol in the mass spectrometry analysis of the out-flow gas excluded instantaneous formation of sol-gel silica on the Na-alginate droplets during their residence in the gas phase. For various Na-alginate concentrations, ethanol released by silica gel formation is constant as well as the amount of deposited SiO2; a siliceous layer ranging from 0.08 to 0.17 μm thick on the surface of the Ca-alginate beads was calculated. |
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Keywords: | alginate silicon alkoxides beads |
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