School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany.
Soft Matter. 2017 Jul 14;13(26):4636-4643. doi: 10.1039/c7sm01029j. Epub 2017 Jun 22.
Dispersions of magnetic nanoparticles in a nematic liquid crystal were investigated as magnetic fields were applied in three different boundary condition geometries: (i) planar substrates and B⊥n, (ii) planar substrates and B‖n, and (iii) homeotropic substrates and B⊥n. Particle chaining is observed when a magnetic field is applied, with a periodicity perpendicular to the chains. Furthermore, linear chains are observed for the magnetic field applied perpendicular to the director, while zigzag chains are formed when the magnetic field direction is parallel to the director field. This is attributed to a change from a dipolar defect configuration around dispersed nanoparticles, to a quadrupolar one, i.e. the change from satellite to Saturn-ring defects. This effect is largely independent of the sample thickness. The dynamic development of the chain length, as well as their two-dimensional order parameter was studied in all cases. Chain lengths increased rapidly until saturation at approximately l = 30 μm after a time of about t = 10 s. Similarly, the chain order parameters increased until saturation between S = 0.8-0.9, independent of sample geometry.
在三种不同边界条件几何形状下（i）平行基底和 B⊥n、（ii）平行基底和 B‖n、（iii）垂直基底和 B⊥n 施加磁场时，研究了磁性纳米粒子在向列液晶中的分散。当施加磁场时，观察到粒子链，其周期性垂直于链。此外，当磁场垂直于指向矢施加时，观察到线性链，而当磁场方向平行于指向矢场时，形成锯齿链。这归因于从分散的纳米粒子周围的偶极缺陷构型到四极缺陷构型的变化，即从卫星缺陷到土星环缺陷的变化。这种效应在很大程度上与样品厚度无关。在所有情况下都研究了链长以及它们的二维有序参数的动态发展。在大约 10 秒的时间后，链长迅速增加，直到大约 l = 30 μm 时达到饱和。同样，链有序参数增加，直到在 S = 0.8-0.9 之间达到饱和，与样品几何形状无关。
