Aggregation, percolation and phase transitions in nematic liquid crystal EBBA doped with carbon nanotubes

Abstract

Electrical conductivity, optical transmittance and microstructure of multiwalled carbon nanotubes (MWCNTs) dispersed in nematic liquid crystal 4-ethoxybenzylidene-4′-n-butylaniline (EBBA) were studied in the temperature range between 287 and 363 K. The concentration C of MWCNTs was varied within 0.01–1% wt. The percolation threshold with a noticeable increase in electrical conductivity (by many orders of magnitude) was observed in the vicinity of C ≈ 0.1% wt. The heating–cooling hysteretic behaviour of electrical conductivity and optical transmittance thermal pre-history effects were studied. These effects reflected strong agglomeration and rearrangement of nanotubes during the thermal incubation. The estimates show that transient behaviour during the thermal incubation can be caused by Brownian motion of MWCNTs. The solidification of MWCNT + EBBA composite in the nematic range extended by conditions of supercooling was also studied as a function of temperature using electrical conductivity measurements. The solidification lag-time dependence on supercooling temperature followed the classical heterogeneous nucleation law, with MWCNTs serving as centres of EBBA solidification.