Low temperature phase transformations in 4-cyano-4'-pentylbiphenyl (5CB) filled by multiwalled carbon nanotubes

TL;DR

This study investigates how multiwalled carbon nanotubes affect low-temperature phase transformations in 5CB liquid crystal, revealing changes in crystallization processes, molecular conformation, and electrical conductivity in the composite material.

Contribution

It provides new insights into the influence of nanotubes on phase behavior and electrical properties of 5CB at low temperatures, combining calorimetry, photoluminescence, and conductivity measurements.

Findings

Identification of two crystallization processes at 229 K and 262 K.

Photoluminescence indicates conformational changes during crystallization.

Electrical conductivity anomalies suggest interfacial phase transformation effects.

Abstract

The effects of multiwalled carbon nanotubes (NTs) on low-temperature phase transformations in 5CB were studied by means of differential scanning calorimetry (DSC), low-temperature photoluminescence and measurements of electrical conductivity. The concentration of NTs was varied within 0-1% wt. The experimental data, obtained for pure 5CB by DSC and measurements of photoluminescence in the heating mode, evidenced the presence of two crystallization processes at T->229 K and T->262 K, which correspond to C1a->C1b, and C1b->C2 phase transformations. Increase of temperature T from 10 K to 229 K provoked the red shift of photoluminescence spectral band that was explained by flattening of 5CB molecule conformation. Moreover, the photoluminescence data allow to conclude that crystallisation at T=229 K results in conformation transition to non-planar 5CB structure characteristic to ideal crystal. The non-planar conformations were dominating in nematic phase, i.e., at T>297 K. Electrical conductivity data for NTs-5CB composites revealed supplementary anomaly inside the stable crystalline phase C2, identified earlier in the temperature range 229 K-296.8 K. It can reflect the influence of phase transformation of 5CB in interfacial layers on the transport of charge carriers between NTs.