Structure peculiarities and optical properties of nanocomposite: 5CB liquid crystal–CTAB-modified montmorillonite clay

Abstract

The effects of the modification of natural layered montmorillonite (MMT) clay by cetyltrimethylammonium bromide (CTAB) cations on the structure and optical properties of the composite material based on this mineral (4.5%mass) and a nematic liquid crystal (LC), 4-pentyl-4'-cyanobiphenyl (5CB), have been investigated. As shown by small-angle X-ray diffraction and infrared (IR) spectroscopy experiments, this modification results in a significant expansion of the interplane spaces in the MMT nanoparticles and a considerable growth of their surface affinity to the 5CB molecules, which allows the LC molecules to penetrate into the MMT galleries and additionally expand these galleries. According to IR studies, this heterosystem possesses van der Waals interactions between its components on the phase separation boundary and, as a result, orientation alignment of the molecules in the near-surface layers occurs. These interactions specify the electro-optical properties of the composite. When an electric field is applied to a system, the light transmittance of the material increases due to the induced orientation of the LC dimers. This LC ordering remains even after the voltage is shut off, i.e. the system shows an electro-optical memory effect.

Keywords:

• LC-clay nanocomposites
• CTAB
• montmorillonite
• 5CB

Acknowledgements

This work was partially funded by the NAS of Ukraine under the Program ‘Nanophysics and Nanoelectronics’, project VC-138. The authors would like to thank Dr N. Lebovka and A. Tolochko for their help in these investigations.