Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States.
Langmuir. 2010 Nov 16;26(22):16890-900. doi: 10.1021/la103098q. Epub 2010 Oct 14.
A series of polyelectrolytes with controlled molecular weight, a narrow chain-length distribution, and systematic structural differences were synthesized using atom-transfer radical polymerization and investigated as stabilizers for magnetite nanoparticles in aqueous suspensions. Structural differences include the degree of polymerization, the chain architecture, and the identity of the charged functional unit. The synthesized polymers are sulfonated poly(2-hydroxyethyl methacrylate), a block copolymer of the former with poly(n-butyl methacrylate), poly(sodium styrene sulfonate), poly(sodium acrylate), and poly(sodium vinylphosphonate). The colloidal stability is assessed by measuring the fraction of particles, based on turbidity, that sediment after a period of time at increasing ionic strength. Sedimentation results are complimented by dynamic light scattering determinations of the hydrodynamic diameter of the particles that remain suspended. When adsorption and sedimentation are conducted at high pH, poly(sodium acrylate) and poly(sodium vinylphosphonate) yield the most stable suspensions because of their strong coordinative interactions with the iron oxide surface. At low pH, the polymers that retain pendant negative charges (each of the sulfonated polymers) yield high stable fractions at all ionic strengths investigated up to 100 mM (NaCl), whereas polyelectrolytes that become protonated with decreasing pH, poly(sodium acrylate) and poly(sodium vinylphosphonate), lose their stabilizing capacity even at low ionic strengths. The chain-length distribution profoundly alters a polymer's stabilization tendencies. Two poly(sodium acrylate) samples with the same number-average molecular weight but widely different chain-length distributions proved to have opposite tendencies, with the polydisperse sample being a good stabilizer and the low polydispersity one being a strong flocculant. This investigation provides guidelines for the design of polymeric stabilizers for magnetite nanoparticles according to the pH and ionic strength of the intended application.
采用原子转移自由基聚合方法合成了一系列具有受控分子量、窄链长分布和系统结构差异的聚电解质，并将其作为水悬浮液中磁铁矿纳米粒子的稳定剂进行了研究。结构差异包括聚合度、链结构和带电官能单元的身份。合成的聚合物是磺化聚（2-羟乙基甲基丙烯酸酯），它是前一种聚合物与聚（正丁基甲基丙烯酸酯）、聚（苯乙烯磺酸钠）、聚（丙烯酸钠）和聚（乙烯基膦酸钠）的嵌段共聚物。通过测量在增加离子强度后一段时间内基于浊度的颗粒沉淀分数来评估胶体稳定性。沉降结果通过动态光散射法测定悬浮颗粒的水动力直径来补充。当在高 pH 值下进行吸附和沉降时，由于与氧化铁表面的强配位相互作用，聚（丙烯酸钠）和聚（乙烯基膦酸钠）产生最稳定的悬浮液。在低 pH 值下，保留悬垂负电荷的聚合物（每种磺化聚合物）在所有研究的离子强度下（高达 100mM（NaCl））都产生高稳定分数，而随着 pH 值降低而质子化的聚电解质，聚（丙烯酸钠）和聚（乙烯基膦酸钠），即使在低离子强度下也会失去其稳定能力。链长分布极大地改变了聚合物的稳定倾向。具有相同数均分子量但链长分布差异很大的两种聚（丙烯酸钠）样品表现出相反的趋势，多分散样品是良好的稳定剂，低分散度样品是强絮凝剂。本研究根据预期应用的 pH 值和离子强度为磁铁矿纳米粒子设计聚合物稳定剂提供了指导。
