Koch Karin, Kundt Matthias, Eremin Alexey, Nadasi Hajnalka, Schmidt Annette M
Universität zu Köln, Department Chemie, Institut für Physikalische Chemie, Luxemburger Str. 116, D-50939 Köln, Germany.
Otto-von-Guericke-Universität Magdeburg, Institut für Physik, Universitätsplatz 2, D-39016 Magdeburg, Germany.
Phys Chem Chem Phys. 2020 Jan 28;22(4):2087-2097. doi: 10.1039/c9cp06245a. Epub 2020 Jan 6.
Switching of liquid crystal phases is of enormous technological importance and enables digital displays, thermometers and sensors. As an alternative to electric fields or temperature, magnetic fields are an interesting trigger, as they are on the one hand versatile to design, and on the other hand, they are compatible with a bouquet of applications. An interesting option to enable the magnetic switchability of nematic phases is by doping them with functional magnetic nanoparticles, but it remains a challenge to achieve well-compatibilized and stable ferronematic phases. Here, we report a new approach for the experimental realization of finely dispersed MNPs and nematic LC by creation of a surface-coupled mesogen-functionalized polymer brush, and the determination of their corresponding magneto-optical response. For this purpose, CoFeO particles are equipped with a covalently attached polymeric shell carrying mesogenic groups and successfully dispersed in 4-pentyl-4'-cyanobiphenyl (5CB) to form a stable ferronematic phase at ambient concentration up to ∼1 vol%, as shown by DSC and Abbé refractometry. The magneto-optic response is detected in planar aligned LC cells. As compared to undoped 5CB, the hybrid system shows a significantly increased magnetic sensitivity, and the magneto-nematic surface anchoring is quantified by analysis of the magneto-nematic cross-correlation.
液晶相的转换具有巨大的技术重要性，并使数字显示器、温度计和传感器成为可能。作为电场或温度的替代方案，磁场是一种有趣的触发因素，因为它们一方面在设计上具有通用性，另一方面与一系列应用兼容。使向列相具有磁开关性的一个有趣选择是用功能性磁性纳米颗粒对其进行掺杂，但要实现良好相容且稳定的铁电液晶相仍然是一个挑战。在此，我们报告了一种通过创建表面耦合的介晶官能化聚合物刷来实验实现精细分散的磁性纳米颗粒（MNPs）和向列型液晶（LC）的新方法，以及对它们相应的磁光响应的测定。为此，CoFeO颗粒配备了带有介晶基团的共价连接的聚合物壳，并成功分散在4-戊基-4'-氰基联苯（5CB）中，在室温下浓度高达约1体积%时形成稳定的铁电液晶相，差示扫描量热法（DSC）和阿贝折射仪测量结果表明了这一点。在平面取向的液晶盒中检测磁光响应。与未掺杂的5CB相比，混合系统显示出显著提高的磁灵敏度，并且通过对磁向列交叉相关性的分析对磁向列表面锚定进行了量化。
