| Abstract |
Phosphonium-based bolaamphiphiles have been found to stabilise silicic acid beyond its solubility limit (~150 ppm). Three bolaamphiphiles have been tested having a quaternary phosphonium group on each end, linked by a number of ethylene oxide (EO) units (5, 21, and 91, resulting in PEGP+-200,PEGP+-1000, and PEGP+-4000 dicationic bolaamphiphiles, respectively). Specifically, the ability of PEGP+-200, PEGP+-1000, and PEGP+-4000 to retard silicic acid condensation at circumneutral pH in aqueous supersaturated solutions was explored. The goal was to investigate the effect of P-based cationic molecules, EO chain length (and by inference the P-to-P spatial separation) on silicic acid stabilisation performance. PEGP+-200 showed no stabilisation ability in ‘‘long term’’ tests (i.e. 24, 48, 72 h). For PEGP+-1000, and PEGP+-4000, it was discovered that in ‘‘short-term’’ (0–8 h) and ‘‘long term’’ ( 24 h) studies the inhibitory activity is additive dosage-dependent, demonstrating that there is a clear increase in stabilisation ability upon PEGP+ dosage increase. Specifically, soluble silicic acid levels reach 420 ppm and 400 ppm after 24 h in the presence of 150 ppm PEGP+- 1000, or PEGP+-4000, respectively. Neutral PEG additives (PEG-200, PEG-1000, and PEG 4000) containing no phosphonium cations were also tested as a control. Although PEG-200 and PEG-1000 showed no silicic acid stabilisation effects, PEG-4000, surprisingly, was a strong stabiliser. In fact, the inhibitory efficiencies of PEGP+-4000 and PEG-4000 were virtually identical. These results present strong proof that the polyethylene chain beyond a certain length (n(EO)<21) strongly contributes to silicic acid stabilisation. Lastly, the effects of these boloamphiphiles on silica particle morphology were investigated by SEM. Spherical particles and their aggregates, irregularly shaped particles and porous structures, are obtained depending on the additive.
Also, in this research we used dendrimeric chemical additives which can act as inhibitors in colloid formation SiO2. Dendrimers that were tested as inhibitors in silicic acid polymerization contained attractive structural characteristics,sush as different generations (G1 and G2) and various surface groups (-NH2, -NHCH2CH2CH3and –OH). The level of inhibition activity of these dendrimers depends on the structural characteristics of each dendrimer such as generation number and identity of the surface groups.
|
Σταθεροποίηση διαλυτών μορφών πυριτικού οξέως με χρήση κατιοντικών πολυμερών και δενδριμερών
