| Summary: | 碩士 === 國立中興大學 === 材料科學與工程學系所 === 101 === Abstract
A polymeric surfactant, hereafter termed Gallol-PEG, was synthesized and used as the dispersing agent in order to examine the dispersion and rheological behavior of titanium dioxide (TiO2) nanoparticles in water. The Gallol-PEG polymer was prepared from esterification reaction utilizing reagent-grade gallic acid (molecular weight Mw = 188.13 g‧mole-1) and poly(ethylene glycol) monomethyl ether (PEG-Me) at 130 °C in dry nitrogen atmosphere. The PEG-Me used had an averaged molecular weight of 750 g‧mole-1, and is hence also called Gallol-PEG 750. Preferential adsorption of the Gallol-PEG 750 molecules on the TiO2 particle surface was verified by zeta potential, particle-size distribution, and adsorption isotherm. The adsorption appeared to involve multiple layers. The suspension viscosity reached a low value when the surfactant concentration was at 2wt%, at which the Gallol-PEG molecules were considered to have covered all the surface available on the TiO2 particles. An optimal surfactant concentration was hence determined to be 2wt% of the solids. When compared to the surfactant prepared from PEG-ME of different molecular weights, tail chain engagement and particle bridging are more likely to occur as solids loading and tail length of the Gallol-PEG molecule are increased. The particles that gathered into denser flocs increased yield stress and led to a higher viscosity. Fractal dimension (Df) of Gallol PEG350, 550 and 750 was 2.1, 2.48 and 2.51, respectively. The suspension structure was hence of a reaction-limited cluster-cluster aggregation (RLCA), regardless of the different molecular weights used. With solids loading being 17.5%, the effective volume fractions (ϕeff) of Gallol-PEG 350, 550 and 750 were calculated to be 33%, 41% and 51%, respectively. When the solids loading increased, the yield stress and viscosity increased accordingly. The effective volume fraction (ϕeff) of Gallol-PEG was estimated to be 0.51, and the solid volume of which was less than that of the random close-packing construction with ϕm= 0.64. Theoretical calculation of potential energy between particles showed that steric hindrance provided the primarily interparticle repulsion, prevailing the Coulomb repulsion, when the Gallol-PEG polymer was used.
Keywords: Gallol-PEG, Surfactant, Dispersant, Rheology, Interparticle Potential, TiO2
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