静电共组装超顺磁性纳米棒的生长机理
Growth mechanism of nanostructured superparamagnetic rods obtained by electrostatic co-assembly
摘要：
我们报告的纳米结构棒的生长制造的静电共组装氧化铁纳米粒子和聚合物之间。γ-Fe_2O_3和磁赤铁矿的粒径分别为6.7 nm和8.3 nm，多分散性较窄。共组装由i）聚合物和颗粒之间的静电相互作用和ii）外部施加的磁场的存在驱动。棒的特征在于大的各向异性因子，直径为200 nm，长度为1 - 100 μ m。在目前的工作中，我们提供了第一次作为离子强度和浓度的函数的棒的形态图。我们表明存在一个临界纳米粒子浓度和一个临界离子强度超过该杆不形成。在中间制度，只有曲折和分支的聚集体被检测到。在较高的浓度和较低的离子强度下，产生具有超顺磁性的线性和刚性棒。根据这些数据，提出了一种杆形成的机制。该机制分为两个步骤：球形颗粒团簇的形成和生长，以及由磁偶极相互作用引起的团簇的排列。就这些过程的动力学而言，团簇的生长和它们的排列伴随发生，导致颗粒或小团簇的连续增长，以及棒状结构的焊接。
英文摘要：
We report on the growth of nanostructured rods fabricated by electrostatic co-assembly between iron oxide nanoparticles and polymers. The nanoparticles put under scrutiny, γ-Fe2O3 or maghemite, have diameter of 6.7 nm and 8.3 nm and narrow polydispersity. The co-assembly is driven by i) the electrostatic interactions between the polymers and the particles, and by ii) the presence of an externally applied magnetic field. The rods are characterized by large anisotropy factors, with diameter 200 nm and length comprised between 1 and 100 μm. In the present work, we provide for the first time the morphology diagram for the rods as a function of ionic strength and concentration. We show the existence of a critical nanoparticle concentration and of a critical ionic strength beyond which the rods do not form. In the intermediate regimes, only tortuous and branched aggregates are detected. At higher concentrations and lower ionic strengths, linear and stiff rods with superparamagnetic properties are produced. Based on these data, a mechanism for the rod formation is proposed. The mechanism proceeds in two steps : the formation and growth of spherical clusters of particles, and the alignment of the clusters induced by the magnetic dipolar interactions. As far as the kinetics of these processes is concerned, the clusters growth and their alignment occur concomitantly, leading to a continuous accretion of particles or small clusters, and a welding of the rodlike structure.
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