In this article we show how spherical nanoparticles (NPs) imposing planar anchoring can strongly impact the viscoelastic, dielectric, and electro-optical properties of a nematic liquid crystal when they are not aggregated. We also demonstrate that when the NPs are magnetic, most nematic properties are more impacted than when they are nonmagnetic. With magnetic NPs a molecular disorder is induced that decreases the nematic order parameter, this decrease impacting the values of elastic constants, viscosity, and response time. The impact on 5CB liquid crystal (LC) has been investigated with spherical nanoparticles (NPs) of identical size around 6 nm, magnetic ($\gamma {\mathrm{Fe}}_2{\mathrm{O}}_3$), and nonmagnetic (${\mathrm{CeO}}_2$) ones that are both surface functionalized by poly(aminopropylmethylsiloxane-b-dimethylsiloxane) (PAPMS-b-PDMS) block copolymer ligands to promote planar anchoring. In the presence of nonmagnetic NPs, despite an almost constant nematic order parameter, a significant decrease of elastic constants (25.4%), viscosity (22%), and response time (23%) is measured. It suggests a dilution effect for the intermolecular interactions in the presence of NPs. This hypothesis is supported by the observation of an enhanced decrease of the same nematic parameters in the presence of magnetic NPs that can be fully explained by the corresponding order parameter decrease. This finally leads to a remarkable decrease of the splay elastic constant by 51% in the presence of magnetic NPs. The decrease of the nematic order parameter by 18% in the presence of magnetic NPs demonstrates that the NP magnetic moments are only weakly coupled to the nematic director and consequently only induce a disorder in the composite system. A significant influence of the expected large LC structural modifications in the presence of magnetic NPs is, however, shown by a particularly large increase of the diffusion coefficient 43% and large decrease of the dielectric anisotropy (43%). We believe that the observed impact of NPs with planar anchoring on nematic properties could be extended to most spherical NPs if their aggregation can be avoided. In particular, the difference between magnetic and nonmagnetic NPs could be extended to ferroelectric and nonferroelectric NPs.

中文翻译：

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磁性和非磁性纳米粒子掺杂的5CB向列液晶的粘弹性和介电性能

在本文中，我们展示了施加平面锚固的球形纳米粒子（NP）如何在向列型液晶未聚集时强烈影响其向列型液晶的粘弹性，介电性质和电光性质。我们还证明，当NP具有磁性时，大多数向列性质比非NP受到的影响更大。使用磁性NP时，会引起分子混乱，从而降低了向列顺序参数，这种降低影响了弹性常数，粘度和响应时间。已使用尺寸约为6 nm的相同球形球形纳米颗粒（NP）研究了对5CB液晶（LC）的影响。$\gamma {铁}_2{\mathrm{Ø}}_3$）和非磁性（${\mathrm{首席执行官}}_2$）都被聚（氨基丙基甲基硅氧烷-b-二甲基硅氧烷）（PAPMS-b-PDMS）嵌段共聚物配体表面官能化以促进平面锚固的基团。在存在非磁性NP的情况下，尽管向列参数几乎恒定，但仍可测量到弹性常数（25.4％），粘度（22％）和响应时间（23％）的显着降低。这表明在NP存在下对分子间相互作用的稀释作用。通过在存在磁性NP的情况下观察到相同向列参数的增强增强，可以支持这一假设，这可以通过相应的阶数参数减小来完全解释。最终，在存在磁性NP的情况下，扩张弹性常数显着降低了51％。在存在磁性NP的情况下，向列顺序参数降低18％，这表明NP磁矩仅弱耦合到向列导向子，因此仅在复合系统中引起混乱。但是，在存在磁性NP的情况下，预期的较大LC结构修饰的重大影响通过扩散系数43％的特别大的增加和介电常数各向异性（43％）的大的减少来显示。我们认为，如果能够避免聚集，则具有平面锚固的NP对向列性质的影响可以扩展到大多数球形NP。特别地，磁性和非磁性NP之间的差异可以扩展到铁电和非铁电NP。