Ourry Laurence, Toulemon Delphine, Ammar Souad, Mammeri Fayna
Université Paris Diderot, Sorbonne Paris Cité, CNRS UMR 7086 ITODYS, Case 7090, 5 rue Thomas Mann, Paris, France.
Beilstein J Nanotechnol. 2017 Feb 9;8:408-417. doi: 10.3762/bjnano.8.43. eCollection 2017.
Magnetic nanoparticles (NPs) must not only be well-defined in composition, shape and size to exhibit the desired properties (e.g., exchange-bias for thermal stability of the magnetization) but also judiciously functionalized to ensure their stability in air and their compatibility with a polymer matrix, in order to avoid aggregation which may seriously affect their physical properties. Dipolar interactions between NPs too close to each other favour a collective magnetic glass state with lower magnetization and coercivity because of inhomogeneous and frustrated macrospin cluster freezing. Consequently, tailoring chemically (through surface functionalization) and magnetically stable NPs for technological applications is of primary importance. In this work, well-characterized exchange-biased perfectly epitaxial Co Fe O@CoO core@shell NPs, which were isotropic in shape and of about 10 nm in diameter, were decorated by two different polymers, poly(methyl methacrylate) (PMMA) or polystyrene (PS), using radical-controlled polymerization under various processing conditions. We compared the influence of the synthesis parameters on the structural and microstructural properties of the resulting hybrid systems, with special emphasis on significantly reducing their mutual magnetic attraction. For this, we followed two routes: the first one consists of the direct grafting of bromopropionyl ester groups at the surface of the NPs, which were previously recovered and redispersed in a suitable solvent. The second route deals with an "all in solution" process, based on the decoration of NPs by oleic acid followed by ligand exchange with the desired bromopropionyl ester groups. We then built various assemblies of NPs directly on a substrate or suspended in PMMA. The alternative two-step strategy leads to better dispersed polymer-decorated magnetic particles, and the resulting nanohybrids can be considered as valuable building blocks for flexible, magnetic polymer-based devices.
磁性纳米粒子（NPs）不仅必须在组成、形状和尺寸上具有明确的定义，以展现出所需的特性（例如，用于磁化热稳定性的交换偏置），还必须经过明智的功能化处理，以确保其在空气中的稳定性以及与聚合物基体的兼容性，从而避免可能严重影响其物理性能的聚集现象。彼此距离过近的纳米粒子之间的偶极相互作用，由于不均匀且受阻的宏观自旋簇冻结，有利于形成具有较低磁化强度和矫顽力的集体磁玻璃态。因此，为技术应用量身定制化学性质（通过表面功能化）和磁稳定性良好的纳米粒子至关重要。在这项工作中，通过在各种加工条件下进行自由基控制聚合，用两种不同的聚合物聚甲基丙烯酸甲酯（PMMA）或聚苯乙烯（PS）对形状各向同性、直径约为10 nm且具有良好表征的交换偏置完美外延CoFeO@CoO核壳纳米粒子进行了修饰。我们比较了合成参数对所得杂化体系的结构和微观结构性质的影响，特别强调显著降低它们之间的相互磁吸引力。为此，我们采用了两条路线：第一条路线是在预先回收并重新分散在合适溶剂中的纳米粒子表面直接接枝溴丙酰酯基团。第二条路线涉及一种“全溶液法”，即先通过油酸对纳米粒子进行修饰，然后与所需的溴丙酰酯基团进行配体交换。然后，我们直接在基板上或悬浮在PMMA中构建了各种纳米粒子组件。这种两步替代策略可使聚合物修饰的磁性粒子分散得更好，所得的纳米杂化物可被视为用于柔性磁性聚合物基器件的有价值的构建块。
