Gas-phase silicon alkoxide reactivity vs. Na-alginate droplets for conjugation of alginate and sol-gel technologies

• Published in: Journal of sol-gel science and technology 2006, Vol.37 (1), p.69-77
• Main Authors: CARTURAN, Giovanni, CAMPOSTRINI, Renzo, TOGNANA, Lorenzo, BONINSEGNA, Sara, DAL TOSO, Roberto, DAL MONTE, Renzo
• Format: Article
• Language: English
• Subjects: Alginates; Alkoxides; Beads; Calcium; Chemistry; Colloidal gels. Colloidal sols; Colloidal state and disperse state; Conjugation; Droplets; Ejection; Ethanol; Exact sciences and technology; General and physical chemistry; Mass spectrometry; Mathematical analysis; Nozzles; Outflow; Rheological properties; Rheology; Scientific imaging; Silica gel; Silicon dioxide; Sol-gel processes; Spectroscopy; Vapor phases
• ISSN: 0928-0707; 1573-4846
• DOI: 10.1007/s10971-005-4205-9

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.