In Situ and Ex Situ Syntheses of Magnetic Liquid Crystalline Materials: A Comparison

Abstract

Magnetic hybrid liquid crystalline composites have been obtained either by thermal decomposition of a cobalt precursor in a solution containing a liquid crystal polymer or by dispersing preformed cobalt nanorods in a liquid crystal polymer matrix. The final materials are all mesomorphous and ferromagnetic. Their magnetic characteristics are compared as a function of the synthesis method.

Room‐Temperature, Strain‐Tunable Orientation of Magnetization in a Hybrid Ferromagnetic Co Nanorod–Liquid Crystalline Elastomer Nanocomposite

“…[12] We also proved the feasibility of the synthesis of aliquid crystalline network starting from ah ybrid magnetic liquid crystalline polymer. [13] We describe here the synthesis of new highly magnetic hybrid elastomer materials ( Figure 1): dispersion of preformed monodisperse cobalt nanorods into the liquid crystalline polymer,f ollowed by alignment and cross-linking in the presence of an external magnetic field. Thecritical step is the nanorod alignment within the elastomer, required to achieve the highest remnant/saturation magnetization ratio, and obtain as trong anisotropic ferromagnet.…”

“…[15] Thel iquid crystalline elastomer was synthesized by ah ydrosilylation [13,16] reaction at room temperature in at wo-step procedure.T he poly(methylhydrogenosiloxane) backbone was mixed with 0.9 silane equivalents of mesogens and the catalyst in am inimum quantity of toluene.Along aliphatic diene was then used to cross-link the remaining reactive silane functions;0.5 wt %nanorods were also added in this second step.T oo btain macroscopically oriented samples,a1T uniform magnetic field, produced by an electromagnet, was applied during cross-linking.B oth oriented and non-oriented, 1mmt hick samples were prepared for comparison.…”

Liquid Crystalline Polymers as Tools for the Formation of Nanohybrids

“…Vice versa, the elastic force acting on the NPs could orientate them and change the magnetic properties of the composite material with respect to the free NPs. These two approaches were followed by different teams (Song et al 2007;Riou et al 2012;Garcia-Marquez et al 2011;Haberl et al 2013a, b). The composite material homogeneity and the shape change amplitude are essential characteristics to be taken into account in the design of these materials.…”

“…The solid white arrow points to the (002) reflection due to the organization of the Co nanorods in rows within the bundles whereas the dashed arrows point to the (100) and (110) reflections of the hexagonal 2-dimensional lattice. The dotted white arrow points to the smectic reflection from the mesogens; (b) schematic representation of the nanorod bundles in the composite; (c) typical TEM picture of a magnetic liquid crystal composite (adapted with permission from Riou et al 2012) contained 7 %wt of ferrite NPs, but no information was given about the effective content of iron oxide.…”

“…As in the case of the LC polymer mentioned above, Riou et al used anisotropic ferromagnetic NPs (Riou et al 2012) in order to achieve a strong orientational coupling between magnetic nanoparticles and the liquid crystal medium and maximize the torque induced by the applied magnetic field on the medium. They described the synthesis of a LCE and showed the potential for this new kind of material.…”