Nanocomposites and nanomaterials

5CB liquid crystal phase transitions in the nanocomposites 
with inorganic particles of different nature
T.V. Bezrodna1, V.V. Nesprava1, O.M. Roshchin1, M. Drozd2
1Photoactivity Department, Institute of Physics, Natl. Acad. of Sci. of Ukraine. Prospect Nauki, 46, Kiev-03028, Ukraine. 
E-mail: nesprava@iop.kiev.ua
2Institute of Low Temperature and Structure Research, PAS, 2 Okolna St.,
50-950 Wroclaw, Poland.

Investigations of heterogeneous systems based on liquid crystals (LC) filled with nanoparticles of different nature (organomodified alumosilicate montmorillonite (OM), carbon nanotubes (NT)) is one of the important fields in modern physics. In these composites, under the influence of inorganic particles, LC changes considerably its structure, optical, electro-optical and dielectric properties, etc. These materials can be used in the development of optoelectronic devices, scattering displays, information recording and storage equipments. 
This work is aimed to study effects of different inorganic fillers on phase transitions of 5CB LC in the composite materials. Clay mineral particles OM taken from three deposites (Askan (OMa), Pyzhevsk (OMp) and Cherkassy (OMc)) or carbon NT have been chosen as fillers. These clay minerals differ by their dopant contents and physico-chemical properties, in particular, by cation-exchange capacity. We have used multiwall carbon NT with their outer diameter of 12-20 nm, inner one of 1-3 nm, tens of microns long and a specific surface of 190 m2/g.
Initial 5CB substance possesses the crystal–nematic and nematic–isotropic liquid phase transitions at t=24.4 and 37.0C, correspondingly. Since large agglomerates of NT do not practically affect the 5CB bulk structure, DSC thermograms of the 5CB+NT composite are nearly the same as for the pure 5CB. Strong interphase interactions in the 5CB+OM system cause the formation of less ordered 5CB near-surface layers. Their presence lowers melting temperature of the stable crystal phase C2 (t=20.4C) and results in two endotherms at t=35.3 and 36.5C in the region of nematic–isotropic liquid transition in a case of OMa. The corresponding transition temperatures for the 5CB with OMp and OMc fillers are reduced to t=29.7 and 28.6C, respectively. The observed changes in 5CB phase transitions have been explained on the basis of structure and component interaction peculiarities, studied for these nanocomposites. The spectral properties of the mentioned systems, in particular, photoluminescence have been analyzed. 
The work was financed by NASU, Project 1.4.VC/188.