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中文摘要: 以溴化苄为疏水改性剂，采用双分子亲核取代反应(SN2)制得苄基接枝海藻酸衍生物(BAD)。通过动态光散射技术，考察了在不同pH和离子强度下BAD对TiO2纳米粒水悬浮液分散稳定性的影响。并采用红外光谱和扫描电镜对BAD/TiO2纳米粒复合物的官能团和表面形貌进行了测试。结果表明，通过SN2反应成功地合成了具有胶体性能的BAD。BAD胶束的平均水动力学粒径(dH)大小为423.4 nm，Zeta电位值为-27.4 mV，表现出较好的胶体性能。在不同pH下，BAD的吸附可提高TiO2纳米粒的带电性，使其Zeta电位均低于-30 mV，而且其dH相比单一的TiO2纳米粒显著减小。在不同离子强度下，BAD可明显削弱反离子对TiO2纳米粒静电屏蔽作用的影响，使TiO2纳米粒的团聚行为大大降低，dH显著减小。BAD分子链不仅能够提高TiO2颗粒间的静电斥力，而且还能提供有效的空间位阻，提高TiO2纳米粒在不同pH和离子强度下的分散稳定性。红外和扫描电镜分析结果表明，BAD和TiO2纳米粒主要通过氢键作用来实现BAD在TiO2纳米颗粒上的吸附，从而提高TiO2纳米颗粒间的空间位阻作用使其稳定分散。
Abstract:Benzyl-grafted alginate derivative (BAD) was prepared by bimolecular nucleophilic substitution reaction (SN2) using benzyl bromide as a hydrophobic modifier. The effects of BAD on the dispersion stability of aqueous suspension of TiO2 nanoparticles at different pH and ionic strength were investigated by dynamic light scattering. Additionally, the functional groups and morphology of BAD/TiO2 nanoparticle composite were measured by Fourier transform infrared spectroscopy and scanning electron microscopy. The experimental results show that the colloidal BAD is successfully synthesized by SN2 reaction. The average hydrodynamic size (dH) of BAD micelles is 423.4 nm and the Zeta potential is -27.4 mV, which exhibits good colloidal properties. At different pH, the adsorption of BAD can enhance the chargeability of TiO2 nanoparticles, which makes their Zeta potential to be lower than -30 mV and their dH to be significantly lower than that of single TiO2 nanoparticles. At different ionic strength, BAD can obviously weaken the electrostatic shielding effect of counterions on TiO2 nanoparticles, which makes the agglomeration behavior of TiO2 nanoparticles to be greatly reduced and their dH to be significantly decreased. The molecular chain of BAD can not only enhance the electrostatic repulsion among TiO2 particles, but also provide effective steric hindrance, which improves the dispersion stability of TiO2 nanoparticles at different pH and ionic strength. The results of infrared spectroscopy and scanning electron microscopy indicate that the adsorption of BAD on TiO2 nanoparticles is achieved mainly through the hydrogen bonding between BAD and TiO2 nanoparticles, which has enhanced the steric hindrance among TiO2 nanoparticles and thus makes them dispersed stably.
keywords: bimolecular nucleophilic substitution reaction benzyl grafted alginate derivative dynamic light scattering TiO2 nanoparticle dispersion stability
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