Perineau Fabien, Rosticher Céline, Rozes Laurence, Chanéac Corinne, Sanchez Clément, Constantin Doru, Dozov Ivan, Davidson Patrick, Rochas Cyrille
Sorbonne Universités, UPMC Université Paris 06, ‡CNRS, and §Collège de France, UMR 7574, Laboratoire de Chimie de la Matière Condensée de Paris, F-75005 Paris, France.
ACS Appl Mater Interfaces. 2014 Feb 12;6(3):1583-8. doi: 10.1021/am404313s. Epub 2014 Jan 28.
For many important applications, the performance of polymer-anisotropic particle nanocomposite materials strongly depends on the orientation of the nanoparticles. Using the very peculiar magnetic properties of goethite (α-FeOOH) nanorods, we produced goethite-poly(hydroxyethyl methacrylate) nanocomposites in which the alignment direction and the level of orientation of the nanorods could easily be tuned by simply adjusting the intensity of a magnetic field applied during polymerization. Because the particle volume fraction was kept low (1-5.5 vol %), we used the orientational order induced by the field in the isotropic phase rather than the spontaneous orientational order of the nematic phase. At the strongest field values (up to 1.5 T), the particles exhibit almost perfect antinematic alignment, as measured by optical birefringence and small-angle X-ray scattering. The results of these two techniques are in remarkably good agreement, validating the use of birefringence measurements for quantifying the degree of orientational order. We also demonstrate that the ordering induced by the field in the isotropic suspension is preserved in the final material after field removal. This work illustrates the interest, for such problems, of considering the field-induced alignment of anisotropic nanoparticles in the isotropic phase, an approach that is effective at low filler content, that avoids the need of controlling the nematic texture, and that allows tuning of the orientation level of the particles at will simply by adjusting the field intensity.
对于许多重要应用而言，聚合物-各向异性粒子纳米复合材料的性能强烈依赖于纳米粒子的取向。利用针铁矿（α-FeOOH）纳米棒非常独特的磁性，我们制备了针铁矿-聚（甲基丙烯酸羟乙酯）纳米复合材料，其中纳米棒的排列方向和取向程度可通过在聚合过程中简单调节施加磁场的强度轻松调整。由于粒子体积分数保持较低（1 - 5.5体积%），我们利用了磁场在各向同性相中诱导的取向有序，而非向列相的自发取向有序。在最强磁场值（高达1.5 T）下，通过光学双折射和小角X射线散射测量发现，粒子呈现出几乎完美的反平行排列。这两种技术的结果非常吻合，验证了使用双折射测量来量化取向有序程度的方法。我们还证明，在去除磁场后，各向同性悬浮液中由磁场诱导的有序排列在最终材料中得以保留。这项工作表明，对于此类问题，考虑各向异性纳米粒子在各向同性相中的磁场诱导排列是有意义的，这种方法在低填料含量时有效，避免了控制向列织构的需求，并且只需通过调节磁场强度就能随意调整粒子的取向程度。
