Structure formation and its influence on thermodynamic and optical properties of montmorillonite organoclay–5CB liquid crystal nanocomposites

Abstract

Montmorillonite (MMT) clay modified with octadecylbenzyldimethylammonium chloride (OBDM), B2, and its composites with nematic liquid crystal (LC) 4‐pentyl‐4′‐cyanobiphenyl (5CB), 5CB–B2, with different concentration of the clay (3–8 wt %) were investigated by X‐ray diffraction, polarizing optical microscopy, differential scanning calorimetry, FTIR spectroscopy and atomic force microscopy. Modification of Na‐MMT with OBDM surfactant results in an increase of the chemical affinity of the clay for 5CB. This results in considerable increase of the basal spacings of the clay, giving a possibility for 5CB dimers to penetrate into the interlayer space. Better affinity of the clay for LC allows clay nanoparticles to disperse homogeneously in the LC, and affects thermodynamic and optical properties of the nanocomposites. For 5CB–B2 composites, the structure formation and the strength of the interface interactions were practically independent on B2 concentration. A comparison with 5CB–B3 composites (B3 is MMT modified with dioctadecyldimethylammonium chloride) revealed that the ability of the clay to form homogeneous structures in the LC and thermodynamic and optical properties of the composites are highly dependent on the chemical nature of the surfactant. Varying the type of the clay mineral modifier, it is possible to develop novel heterogeneous LC nanocomposites with desirable electro‐optical properties.

Keywords:

• LC–clay nanocomposites
• montmorillonite
• 5CB

Acknowledgements

This work was partially funded by the NAS of Ukraine under the Program “Nanophysics and nanoelectronics”, project VC‐138 and under the Program “Nanomaterials, Nanosystems and Nanotechnologies”, project 10/07‐n. The authors would like to thank Dr. Anton Hauser for his help with AFM measurements.